PROJECT REPORT

ON

Study of electrical system in power plant

SUBMITTED BY:

VANYA GUPTA

SUMMER TRAINEE B.TECH THIRD YEAR

ELECTRICAL AND ELECTRONICS ENGG

GURU TEGH BAHADUR INSTITUTE OF TECHNOLOGY

CERTIFICATE

We would like to express my appreciation to Ms. VANYA GUPTA (Summer Trainee) for her enthusiasm and dedication to her quality of work during the Project Work. This report has presented a comprehensive STUDY of ELECTRICAL SYSTEM in POWER PLANT. We wish her all the success in future.

P K GAUTAM RAJIV NIRMAN Manager DGM PEM Electrical PEM Electrical

ACKNOWLEDGEMENT

I hereby take this opportune moment to express our deep sense of gratitude to our Department Head Mr. K.K KHURANA (AGM-Electrical) for his unstinted support and

encouragement I express my heartfelt thanks to Mr. RAJIV NIRMAN (DGM) for being a source of guidance and inspiration during this period. His wonderful style of mentoring has surely made our training period a great learning experience. I would also like to give my due concern to Mr.PK GAUTAM (MANAGER), who have supported me in the completion of my project. The close cooperation from Ms. MANDVI GUPTA (Senior Engineer) & Mr. RAM KUMAR YADAV (Engineer) for their technical guidance and encouragement which has been of great help in carrying out the project work. I express my sincere thanks to all the members of electrical department for their friendly and helpful attitude. Finally, I wish to thank my parents for their continuous undivided support and encouragement, which inspired me to go my own way. Without them it would not be possible to complete this project.

Vanya gupta

Date: Summer Trainee

B.Tech (3rd year)

GTBIT

Table of Contents

Abstract

Sr.no TOPIC PAGE NO.

1. INTRODUCTION TO BHEL

2. INTRODUCTION TO PEM

3. OVERVIEW OF ELECTRICAL SYSTEM

4. M.V SWITCH GEARS

5. RATING OF BREAKERS IN HT

6. L.V SWITCHGEARS

7. RATING OF BREAKERS IN LT

8. PROTECTION OF L.V SWITCHGEARS

9. SWITCHGEAR COMPONENTS

10. BREAKER CONTROL FROM DCS ONLY

11. COMMUNICATION SYSTEM

12. GENERATOR CONTROL

13. GENERAL OVERVIEW OF SUE3000 HIGH SPEED

TRANSFER DEVICE

14. OVERVIEW OF ETAP

The purpose of this report is to give a brief idea about what has been done in the training to facilitate the evaluation process of learning and gaining knowledge on electrical system. This report comprises various activities constituting training.

In first section, overview of BHEL & PEM has been given. In the next section, Switchgear in general and High & Low Voltage Switchgear in particular are described. And the last section enlists the various routine tasks and special assignments handled by me.

On the whole, this report gives a clear picture about my two months training

period in BHEL.

bhel- an overview

BHEL is the largest engineering and manufacturing enterprise in INDIA in the energy related /

infrastructure sector today. BHEL was established more then 50 years ago ushering in the

indigenous Heavy Electrical Equipment Industry in India, a dream which has been more then

realized with a well –recognized track record performance.

BHEL caters to core sector of the Indian economy viz., Power Generation and Transmission,

Industry, Transportation, Renewable Energy, Defense, etc. The wide network of BHEL’s 14

manufacturing divisions, 4 power sector regional centers, 8 service centers , 15 regional offices

and a large number of projects sites spread all over INDIA and abroad enable the company to

promptly serve its customers and provide them with suitable product, systems and services –

efficiently and at competitive prices.

Power generation

Power generation sector comprises thermal, gas, hydro, and nuclear power plant business. As of

31.3.2006, BHEL supplied sets account for 76,741 MW or nearly 65% of the total installed

capacity of 1, 18,561 MW in the country, as against nil till 1969-70. The Company has proven

expertise in the plant performance Improvement through renovation , modernization and

updating of a variety of power plant equipment , besides specialized know –how of residual life

assessment, health diagnostics and life extension plants.

Industries

BHEL manufactures and supplies major capital equipments and systems like captive power

plants , centrifugal compressors , drive turbines , industrial boilers and auxiliaries , waste heat

recovery boilers , gas turbines , pumps heat exchangers , electric machines , valves , heavy

casting and forgings , electrostatic precipitators , ID/FD fans , seamless pipes etc. to a number of

industries other than power utilities like metallurgical, mining , cement, paper , fertilizers ,

refineries and petro- chemicals etc. BHEL has also emerged as a major supplier of controls and

instrumentation system, especially distributed digital control systems for various power plants

and industries.

Transportation

Most of the trains in Indian Railways, whether electrical or diesel powered are equipped with

BHEL’s traction propulsion system and controls. India’s first underground metro at Kolkata

runs on drives and controls supplied by BHEL. BHEL is geared up for turnkey execution of

electrical trolley bus systems, light rail systems and metro systems.

Renewable energy

BHEL has been manufacturing and supplying arrange of renewable energy systems and

products. It includes Solar Energy systems namely, PV modules, PV power plants, solar

lanterns, street lightning, solar pumps and solar water heating systems. A large number of small

hydro power stations have been completed. New areas like Wind power generation etc. are also

being explored for entry.

Transmission

BHEL supplies a wide range of products and systems for transmission and distribution

applications. The product manufactured by BHEL include power transformer , instrument

transformer , dry type transformer shunt reactor , capacitors , vacuum and SF6 switchgear, gas

insulated switchgear s, ceramic insulator etc.

Technology up gradation, research& development

To remain competitive and meet customer’s expectation, BHEL lays great emphasis on the

continuous up gradation of products and related technologies besides development of new

products. The company has upgraded its products to contemporary levels through continuous in-

house efforts as well as through acquisition of new technologies from leading engineering

organizations of the world.

The company is also engaged in research in futuristic areas like fuel cells for distributed,

environment friendly power generation, clean coal technology applications, super conductivity

application in transformer, motor etc., and nano technology applications for insulators and

membrane filters.

Health , safety and environment management

Harmony between man and environment is the essence of healthy life and growth. Therefore,

maintenance of ecological balance and a pristine environment is of utmost importance to BHEL.

Environment protection continues to be a key area of activity in BHEL along with the growth of

the company.

BHEL is committed to be an environment friendly company in all its area of activities, products,

and services, providing a safe and healthy working environment to all its stakeholders. In fact,

this aspect has become an integral part of the company’s business performance.

INTRODUCTION TO PEM

FUNCTIONAL STRUCTURE

HEAD

PEM

HEAD

PROCUREMENT

HEAD (s)

PROJECT

COORDINATIO

&COMMERCIAL

HEAD

QUALITY, LRP, IT &

VENDOR

DEVELOPMENT

PROJECTS PRODUCT GROUPS

ELECTRICAL

SYSTEMS

HEAD (s)

PROPOSALS

HEAD (s)

ENGINEERING

HEAD

HUMAN

RESOURCES

MECHANICAL

SYSTEMS

ENGINEERING HEAD

FINANCE

MECHANICAL

PIPING AND

LAYOUT HEAD

VIGILANCE

MECANICAL

AUXILIARIES

CIVIL

CONTROL &

INSTRUMENTATION

CCP ENGG.

pem-

At the core of the core

PEM coordinates with all the agencies involved in the setting up of the

power plant and smoothly integrates all the requirements of

manufacturing, fabricate, erection, commissioning, operations and

maintenance, right at the engineering and design stage.

PROJECT ENGINEERING

MANAGEMENT

CUSTOMER CONSULTANT NATIONAL

BOIDES

PROJECT/SITE

MANGEMENT

QUALITY/

INSPECTION

AGENCIES

BALANCE OF PLANT

VENDORS

BHEL

MFG.UNITS

CONTRACTING

AGENCIES

Strengths

Capability to handle projects on turnkey/ EPC basis

Wide range of engineering capabilities

Capability to design to national and international codes and

standards- BS, Din, ASME, API, IBR, EJMA, IEC, VDE, IEEE

Varied experience with national and international consultants

Pool of experienced human resources

Experience of over 200 coal based and gas based power stations,

up to 500 MW unit rating

Over 500 qualified and registered vendors/ sub contractors

Engineering and Design Office with adequate modeling, analysis

and design software

Infrastructure of servers, engineering workstations, LAN, high

band width external connectivity for e-mail, internet and data

transfer

Variety of Plants handled Coal-based thermal power plants

Gas- based power plants (Open Cycle/Co-generation/ Combined

Cycle)

Nuclear power plants (Conventional cycle)

Diesel generating station

Non-conventional energy sources (solar, IGCC etc)

range of capabilities Concept stage Feasibility Studies

Detailed Project Reports

Bid preparation Proposal Engineering

Technical Guarantees

Project engineering Basic Design

System Design

Station Engineering

Development Techno-Economic Studies

Plant Optimization

Technology up-gradation / absorption

Contracts management Project Engineering Coordination

Procurement support Engineering &Procurement of Balance of Plant System

Engineering support To site Erection and commissioning support

Trouble shooting

Renovation, modernization& repowering of power plant electrical systems System design for auxiliary system, Dc system, emergency power, black start power. Power &auxiliary transformers

MV &LV motors

Generator main connections

Generator circuit breaker

MV switchgear

MV &LV bus ducts

LV switchgear/ motor control centers/distribution boards

Control and protection for generator/ transformer

Computer control & instrumentation cables

Dc supply (batteries, chargers, distribution boards)

Lighting

Earthing & lightning protection

Plant communication

Electrical equipment layout

Cabling

Electrical laboratory equipment

Overview of Electrical System

Diagram of a typical coal-fired thermal power station

Typical diagram of a coal-fired thermal power station

1. Cooling tower 10. Steam Control

valve 19. Superheater

2. Cooling water pump 11. High pressure

steam turbine

20. Forced draught

(draft) fan

3.transmission line

(3-phase) 12. Deaerator 21. Reheater

4. Step-up transformer

(3-phase) 13.Feedwater heater

22. Combustion air

intake

5. Electrical generator

(3-phase) 14. Coal conveyor 23. Economiser

6. Low pressure steam

turbine 15. Coal hopper 24. Air preheater

7. Condensate pump 16. Coal pulverizer 25. Precipitator

8. Surface condenser 17. Boiler steam

drum

26. Induced draught

(draft) fan

9.Intermediate pressure

steam turbine

18. Bottom ash

hopper 27. Flue gas stack

ELECTRICAL SYSTEM & EQUIPMENT

The electrical system is designed and engineered to provide a high

degree of reliability, operational flexibility and personnel safety. The

electrical equipment generally conform to Indian Standards and Indian

Electricity Rules.

Various electrical equipment are designed for an ambient temperature of

50 deg C.

ELECTRICAL SYSTEM DESCRIPTION

The Electrical System is shown in `Electrical Single Line Diagram for

Auxiliary Power Distribution' Drg. No. PE-DG-E29-565-E001.

In INDIA, Two Main & Transfer Bus Scheme is more popular although One and a Half

Breaker Scheme is also being adopted.

Plant layouts of 220 kV&400 kV.

1.Two main & transfer bus scheme

a. This scheme is shown in figure-1. In this scheme under normal conditions

incoming & outgoing circuits are normally connected to the main buses in such a

way that due to a bus fault outage of al feeders connected to the faulty bus does

not affect the stability of the system.

b. However, under bus fault conditions, the feeders connected to the faulty bus get

tripped and there is an interruption in the supply.

c. The supply can be restored by transferring all the feeders to the healthy bus,

since both the buses are designed to handle the entire load of the substation.

d. The faulty bus can thus be maintained and brought back in service after

rectification of the fault

e. The planned maintenance of a circuit breaker of any feeder can be carried out

by transferring its load to the bus transfer breaker to transfer bus

f. This is done without interruption of the load.

g. The control and protection signal of the particular feeder circuit are transferred to

the transfer bus breaker.

h. In this scheme, maintenance of one breaker in the substation can be done at a

time.

2.One and a half breaker scheme a. This scheme has been used in a very few substation in INDIA but is very popular

in the U.S.A

b. This basically employs three breaker for two feeders as shown in figure-2.

c. In this scheme for a bus fault all the breakers connected to the faulty bus get

tripped, but interruption in the supply does not occur since power flow is

maintained though the other bus.

d. Maintenance of one breaker out of three used for two feeders can be done at

any time.

e. More breakers can be maintained at time when both the buses healthy , but

under bus fault condition one feeder is lost if necessary on any braker.

3.Techno-economic analysis

a. Both the scheme have to be analyzed further and their merit and demerits

compared in detail before selecting it for use in the thermal power stations.

System Security

a. FAULT CLEARANCE

It is preferable to trip one breaker for any feeder fault..As such Scheme-1 is better in this respect since two breakers will be required to trip in case of one and half breaker scheme.

The number of feeders lost for a bus bar fault should be as few as

possible.

For scheme-1 there is an interruption till all the affected feeders are

transferred to the health bus.

In scheme-2 continuity of supply is maintained.

b. STUCK BREAKER

This condition Leads to tripping of all the feeders connected to the

particular bus section in case of Scheme-2:

An adjacent feeder trips if the stuck breaker is the middle

breaker

No other feeder is affected if the stuck breaker is the bus side

breaker, even though all the other breakers connected to that

bus also get tripped.

c. REDUNDANCY

In scheme-2 each circuit is fed by two parallel paths i.e. there is

active redundancy or stand-by facilities permanently connected to

the system whereas in Scheme-1 passive redundancy which can be

switched on when required and limited to only one feeder of a

particular bus section at a time is available.

Operational flexibility

a. In Scheme-1, only one breaker is to be operated for switching in or out a feeder.

Secondly, for taking out breaker maintenance, the transfer path through transfer

bus has to be established.

b. In Scheme-2, two breakers are to be operated for bringing a circuit in or taking it

out but for maintenance of a breaker no additional operation is necessary.

Simplicity of protection & control scheme

a. In Scheme-1, the CT‟s have to be switched into the relevant zone of bus bar

protection though the auxiliary contacts of the isolators, which are weak points &

create problems.

b. Secondly, the transfer from main breaker to bypass breaker needs transfer of

closing controls from main breaker to bypass breaker needs transfer of closing

controls from synchronizing and transfer of tripping controls from protection

schemes.

c. In thermal power stations where generator circuit breakers are controlled from

the control desk in the power station the controls of by-pass breaker also need

duplication on the control desk.

d. In Scheme-2, no such provisions are necessary and hence can be considered

more reliable in this respect.

Sectionalizing of buses

a. Both the schemes are capable of being sectionized so as to minimize the

number of circuits affected or the amount of generation lost in the event of a bus

bar fault.

b. Normally outage due to any bus fault shall be limited to the single largest size of

generator connected in the system.

c. However ,detailed system analysis only can determine the exact extent of

sectionalizing to be adopted to maintain system stability.

Maintenance facilities BREAKER MAINTENACE

Both schemes under consideration allow a breaker to be taken out

for planned maintenance without interruption of supply.

The switching sequences, the switching sequence is simple,

comprising tripping of the concerned breaker and opening of the

associated isolators.

For Two Main and Transfer Bus scheme, in addition, the transfer

path has to be established.

ISOLATOR MAITENANCE

In the INDIAN context, isolator maintenance has also to be given

consideration.

Line isolator maintenance needs shutdown of the particular circuit in

both schemes.

For maintenance of bus side isolator in Two Main and Transfer Bus

Scheme there is no interruption in the feeder but the establishing the

transfer path and switching-off the normal breaker.

For One and Half Breaker scheme, there is no loss of feeder but all

the breakers of a particular bus need tripping.

Ease of extension

Both the schemes are capable of being extended.

If future extensions are planned in the initial stages itself, an isolator

in the bus bar run can avoid shutdown when extension is being

carried out.

Land area

In INDIA, generally, availability of land area is not restricted and

hence not a major factor.

However, space reduction due to selection of a particular scheme

can be used for other purposes in the power station.

The area requirement for 220 kV and 400kV switchyards, based on

8 circuits has been worked out and a comparison is given in table -1

It can be seen that area required for scheme-2 is about half in case

of 400 kV and 22okV when compared with scheme-1

Maximum is derived when circuits are arranged back to back to form

a pair.

This arrangement is possible in large generating stations.

Initial cost

Comparisons of cost of typical 8 circuit 220 kV and 400kV substations

for scheme and the scheme 2 is indicated. In this comparison cost of

major equipment, switchyard materials and steel are included. The cost

of civil works and land have not been included since it will vary from

place to place. The cost of cabling and protection equipment has also

not been included.

From this comparison it can be observed that the initial cost of

scheme-2 is about 9% less than the cost of scheme-1 in case

of400kV and 6.75 less in case of 220kV. Since the area requirement

of scheme 2 is less than the scheme -1, the cost of cable trenches,

roads, gravel spreading, illumination equipment, etc, will be less for

scheme -2.

Therefore we can safely assume that the cost for scheme-2 will be les than scheme-1.

Conclusion

The techno-economic analysis done above indicates that one and a half breaker scheme is more favorably placed technically as well as economically when compared to the two main Bus and transfer Bus scheme. As such it is expected that utilities will make more and more use of this scheme in future power stations.

Generator Main Connections System

Typical Coal Fired Power Plant Steam Generator

Each generator is connected to its generator transformer by means of isolated

phase bus ducts. Tap-offs are provided on phase bus ducts for connection to

surge protection & voltage transformer (SP&VT) cubicle and unit transformer

(UT). Isolated bus ducts are also used to form delta connection for low voltage

side of three nos. single phase generator transformers forming the three phase

bank. Generator transformers are sized to evacuate rated MVA of generator.

AC Auxiliary System

Medium Voltage System

Two level medium voltage system, i.e. 11kV and 3.3kV is envisaged. Motors of

rating above 1500 kW are connected to the 11kV switchboards while

motors of rating above 160kW and upto 1500kW are connected to 3.3kV

switchboards. Auxiliary Transformers for power distribution at 3.3kV and

415V levels are also connected to 11kV switchboards.

The total unit and station auxiliaries electrical power is derived through two nos.

Unit Transformers (UTs) (1 No. UT for each unit) and two nos. Station

transformers (STs).

Each UT is connected to 2 nos. 11 kV unit switchboards and sized to meet the

requirement of loads connected to 11kV unit buses corresponding to unit MCR

operation.

Each ST is connected to 2 nos.11kV station switchboards. Each ST is sized to

meet higher of the MVA requirements for the following conditions:

A. One UT not available condition:

The loads served by one fully loaded UT, plus one motor driven BFP load,

plus half of the total station loads.

B. One ST not available condition:

Total station loads, plus one motor driven BFP load, plus all loads of one

unit operating under HP-LP bypass mode.

A tie connection is provided to each unit switchboard from station switchboard.

Fast auto changeover facility is provided from UT switchboard to the

interconnected ST switchboard following the tripping of unit transformer feeder.

Slow auto changeover facility is provided between the interconnected station

switchboards. This will ensure quick restoration of power supply to unit & station

auxiliaries in the event of failure of one of the incoming supplies to 11 kV

switchboards. Further, planned change over facility is also provided between 11

kV interconnected buses.

3.3kV voltage Unit distribution system is envisaged. Unit Auxiliary Transformers

[UAT] are connected to 11kV unit switchboard to step down power to 3.3kV

voltage. For each unit, 3.3kV unit auxiliary switchboard is provided with one UAT

connected to each section.

3.3kV Coal Handling Plant Switchboard & 3.3kV Ash handling Switchboard are

also provided, as required. Each section of these boards is fed from a

step-down auxiliary transformer connected to 11kV Station Switchboard.

3.3kV switchboards are equipped with auto changeover and planned

changeover facilities.

Low Voltage System

415V power is derived from 11kV/433V LV service transformers connected to

the various 11kV switchboards as shown in the 'Electrical Single Line Diagram

for Auxiliary Power Distribution‟. Dry type LV service transformers are

envisaged for Unit PCC and Station PCC in the main power house for indoor

installation. For ESP and other auxiliary plants, mineral oil filled service

transformers are envisaged. The service transformers are rated as per the

power requirement of the associated loads. Power Control Centers (PCCs),

Motor Control Centers (MCCs) and Power-cum-Motor Control Centers (PMCCs)

are provided as shown in the drawing to feed auxiliary loads and services of unit

and station. Incoming supplies to PCCs & PMCCs are duplicated with auto

changeover facility to ensure reliability of distribution supplies.

Motors rated 160 kW and below are connected to 415V system.

Standby Supply System

One number emergency diesel generator set is provided for each unit for safe

shut down of the generating units under normal AC supply failure. The

diesel generator is started automatically from auto-mains failure (AMF)

panel in the event of normal supply failure. A standby DG set common for

both the units is also provided.

DC System

220V DC system is envisaged for unit DC loads such as switchgear, protection,

emergency lighting, DC drives etc. For electronic control & instrumentation,

DC system, as required, is envisaged as part of C&I package.

System Grounding

Grounding philosophy envisaged for the power supply system in the plant is as

follows:

a) Each generator neutral is high resistance grounded by means of neutral

grounding transformer with secondary loading resistor.

b) HV side neutral of generator transformer is solidly grounded.

c) Neutrals of 11kV side of each UT & ST are low resistance grounded, utilising

a grounding resistor and limiting the earth fault current to 300A.

d) 3.3kV system is low resistance grounded at neutrals of 3.3kV side of each

UT, utilising a grounding resistor and limiting the earth fault current to 300A.

e) 415V system is solidly grounded at the 415V neutral of all LV service

transformers. 3 phase, 4 wire system is envisaged for 415V power supply

distribution.

f) 220V DC System is ungrounded.

TURBO GENERATOR

GENERATOR BUSDUCT AND ASSOCIATED EQUIPMENT

Generators are connected by means of isolated phase busduct (IPB) of continuous type between generator line terminals and LV side of generator transformer. Isolated bus ducts are used to form delta connection for low voltage side of three nos. single phase generator transformers forming the three phase bank

Busduct on neutral side is of IPB continuous design up to the star

formation point from where a single neutral duct runs to the neutral

grounding cubicle. An adopter chamber is provided at the generator

terminals to facilitate connections to line and neutral side busducts.

Material for conductor and enclosure is aluminium alloy. Busduct is

supplied in length upto 6-7 meters. It is further reinforced with aluminium

channel rings at intervals, which are also used for enclosure and insulator

mounting. Sealed openings are provided in the busduct run near insulator

for inspection and maintenance. The three phase enclosures are

interconnected effectively at the ends to permit flow of current. Different

sections of each phase are generally connected together by aluminium

make up pieces at site.

Main busduct is sized to carry generator output current at rated

continuous MVA capacity at minimum permissible voltage of 95%. The

bus duct rating chosen is 19,000A. The delta run busduct is rated at

11,000A. One-minute power frequency withstand voltage and standard

impulse withstand voltage for the busduct is as per IS: 8084.

Tap off busducts are provided from main busduct for connection to:

- Unit transformer;

- Surge protection & voltage transformer (SP&VT) cubicle.

The busduct is natural cooled.

The busduct is complete with various current transformers for metering,

protection and voltage regulation. Other fittings like inspection covers,

rubber bellows, expansion joints, insulators, shunt, seal-off bushings, wall

frame assembly etc. are provided along with support structure, as required.

Rubber bellows are provided at busduct terminations and in the run of bus

duct if route length is more than 30 to 35 meter. To take care of machine

vibrations, alignment and expansion / contraction due to temperature

variations. Further, it insulates the termination equipment connected to

bus duct and thus does not let the bus enclosure currents to flow in the

connecting equipment.

Copper flexible are provided at bus duct terminations i.e. at Generator

end, Generator transformer end, Surge Protection & Voltage Transformer

Cubicle, NG Cubicle and other connecting equipment end. Aluminum

flexibles are provided in the run of bus duct to take care of alignment,

variation in bus bar lengths due to temperature variations.

Epoxy Seal off bushings are provided at Power house wall and at

Generator termination end.

Air pressurization system is envisaged for the bus duct. Air for this

purpose is taken from Station Air system and suitably regulated to the

required pressure [25 – 40 mm of water column] for the bus duct.

The busduct is designed to meet the air tightness and water tightness

requirement specified in IS: 8084.

SP&VT cubicle houses voltage transformers for metering, protection and

voltage regulation, lightning arresters and surge capacitors. Lightning

arresters for generator protection are of station class type. Protective

surge capacitors are non-inflammable synthetic liquid impregnated type,

provided with built-in discharge resistors.

Generator neutral grounding equipment comprises a single phase, dry

type, neutral grounding transformer of rating based on 5 minute duty

cycle. The transformer secondary is loaded with a grounding resistor of

grid type rated for 5 minutes.

TRANSFORMERS

Power Transformers

Power transformers [generator transformers (GT), unit transformers (UT) and

station transformers (ST), unit auxiliary transformers (UAT)] are mineral oil filled,

outdoor design type. The transformers generally conform to IS: 2026.

A] Generator Transformers:

Generator Transformer comprises a bank of three numbers single phase OFAF

cooled transformers. One no. spare single phase generator transformer is also

envisaged, common for the plant. No load voltage ratio of single phase GT is

21 / 420/√3 kV.

The windings of the transformer are of paper insulated electrolytic grade copper

conductor. The core of the transformer is of CRGO steel. The terminal

arrangement of transformer is through OIP bushing on HV side and through

Porcelain bushing on LV & Neutral side. The transformer is fitted with Off-circuit

Tap Changer suitable for ±5% voltage variation of HV [in steps of 2.5%].

The transformer is envisaged to be dispatched under dismantled condition by

ROAD under gas filled condition with additional gas cylinder provided on

transformer tank to cater for the transport period. Transformer oil is envisaged to

be supplied separately (directly to site), to be filled in transformer during erection

stage.

B] Unit Transformers and Station Transformers:

Unit Transformer of no load voltage ratio of 21 / 11.5kV and Station Transformer of no

load voltage ratio of 400 / 11.5 / 11.5kV are envisaged.

UT and ST are of CORE type construction. It has three limbed core made of CRGO

(Cold rolled grain oriented) steel. Each limb accommodates set of winding for one

phase. Windings are HELICAL/DISC type made of electrolytic copper. The core and

winding assembly is kept in a tank made of Commercial grade mild steel.

On load tap changer (OLTC) is provided for tap changing purpose. For OLTC, local

manual/electric/remote type of control mechanism has been provided. The cooling

control is affected from cooler control cubicle mounted on transformer tank. The cooling

control is done automatically as per WTI and OTI settings.

The fittings and accessories for each UT and ST are:

1) Conservator (air cell type).

2) Magnetic type oil gauge with low oil level alarm.

3) Silica gel breather.

4) Buchholz relay with alarm and trip contacts with one shut off valve

on conservator side.

5) Pressure relief.

6) Pocket on tank cover for thermometer.

7) Oil temperature indicator with maximum pointer and two sets of

contacts.

8) Winding temperature indicator with maximum pointer and two sets

of contacts.(ONAN & OFWF) and 4 sets of contacts (for ONAN/

OFAF and ONAN/ONAF). Repeater dial of winding temperature

indicator for remote indication.

9) VALVES:

a) Oil valve between cooler and main tank.

b) Drain valve

c) 2Nos. filter valves on diagonally opposite corners-size

50mm.

d) 2Nos. sampling valve at top and bottom of main tank.

11) 2Nos. earthling terminals.

12) Rating and diagram plate.

13) Jacking pads.

14) Lifting lugs.

15) Haulage lugs.

16) Cover lifting lugs.

17) Bi-directional flanged rollers with locking and bolting device.

18) Tank mounted weather-proof marshalling box for housing control

equipment and terminal connect.

19) Air release device.

20) Wiring up to marshalling box with PVC SWA PVC copper cables

660/1100 volts grade.

21) COOLING ACCESSORIES [ONAN/ONAF cooling]:

a) Requisite number of radiators with shut-off Valves.

b) Fans.

C] Unit Auxiliary Transformers:

UAT is envisaged with a no load voltage ratio of 11 / 3.5kV.

UAT is of CORE type construction. It has three limbed core made of CRGO

(Cold rolled grain oriented) steel. Each limb accommodates set of winding

for one phase. Windings are HELICAL/DISC type made of electrolytic

copper. The core and winding assembly is kept in a tank made of

Commercial grade mild steel.

Off-circuit tap changer is provided for tap changing purpose. UAT is ONAN

cooled and provided with standard fittings and accessories, generally in

line with those listed for UT above.

LV Service Transformers

Dry type and oil filled service transformers are provided to feed various

auxiliaries of the plant. Dry type LV service transformers are envisaged for

Unit PCC and Station PCC in the main powerhouse for indoor installation.

For ESP and other auxiliary plants, mineral oil filled service transformers

are envisaged. 2x100% rated transformers are connected to each PCC /

PMCC. A margin of 10% is considered while selecting the capacity of these

service transformers.

A] Dry Type Service Transformers:

In case of dry type transformers, the High Voltage & Low Voltage windings

of the transformer are made up of copper conductors that are completely

encapsulated and cast in moulds under vacuum using liquid epoxy resin.

The insulation system of Fibre Glass – Epoxy Resin gives uniform

encapsulation possessing highest electrical and mechanical properties. HV

and LV windings of each phase are cast separately into individual solid

robust cylindrical coils. The insulation system corresponds to Class „F‟ as

per Indian Standards.

The iron core is made from laminations of cold rolled grain oriented non-

aging silicone steel sheets. The limbs and yokes are of circular structure.

The core is coated with resin as a protective coating against corrosion. HV

and LV coils of each phase are placed in each limb of the core. The core is

clamped tightly by galvanized steel channels.

The transformer (Core-Coil Assembly) is mounted on roller base with plain

bi-directional rollers. Transformer is provided with protective enclosure

made up of HRC steel sheet of protection class IP-23. The control wiring is

terminated on the terminal blocks inside the junction box fitted on

enclosure.

Transformer is provided with following fittings and accessories:

1) For variation of transformation ratio, off circuit tap changer is

provided on HV side. Changing of taps can be done by changing

the tapping links on all the three phases manually.

2) R & D Plate

3) Earthing terminals with lugs

4) Lifting angles

5) Junction Box with wiring

6) Limit Switch

7) Anti Vibration Pad

For thermal protection, temperature monitoring is done by RTD PT-100 sensors

embedded in the coils. These sensors feed signals to temperature scanner

unit for continuous monitoring of winding temperature. The temperature

scanner is provided with auxiliary relays – one for alarm and one for trip.

B] Oil Filled Service Transformers:

Constructional aspects and fittings and accessories for oil filled service

transformers in general are in conformance to `CBIP Manual on

Transformers‟.

MEDIUM VOLTAGE SWITCHGEAR

Following medium voltage Switchboards are provided:

- 4 Nos. 11kV unit switchboards to feed 11kV unit loads

- 4 Nos. 11kV station switchboards to feed 11KV station loads

- 2 Nos. 3.3kV unit auxiliary switchboards to feed 3.3kV motor loads

- 1 No. 3.3kV Coal Handling switchboard

- 1 No. 3.3kV Ash Handling switchboard [if, required]

The switchboards envisaged are of type-tested design. Breakers of

identical rating and design are interchangeable. The switchboards are

provided with "Service/Test/Isolated" position facility for draw out circuit

breakers. The switchboards are complete with standard fittings &

accessories like current transformers, voltage transformers, measuring

instruments, protective/auxiliary/tripping relays, control & selector

switches, indicating lamps, space heaters etc. Interposing relays are

provided for interface with C&I system,

Wherever required. One no. earthing truck for cable end earthing and one

no earthing truck for bus earthing is provided. Earthing trucks are solid

link type.

For motors for Coal Handling Plant, vacuum contactors may be provided

as an alternative to circuit breakers.

Protections envisaged in MV switchgear are as follows:

MV Bus protection

- Time graded over-current protection for all incoming and bus sectionalising

circuits.

- Time graded earth-fault protection for all incoming and bus sectionalising

circuits.

MV motor protection

- Thermal overload protection.

- Instantaneous high set over-current for short-circuit protection

- Instantaneous earth fault protection

- Unbalance current protection

- Locked rotor protection

- Under voltage protection with time delayed tripping under sustained under

voltage

Service transformer protection

- Time graded over-current protection.

- Low voltage winding earth-fault protection

- Buchholz, winding and oil temperature alarm and trip for oil filled transformer

- Winding temperature alarm and trip for dry type transformer.

MEDIUM VOLTAGE SEGREGATED PHASE BUSDUCT

11kV Segregated phase busducts (SPBs) are provided to connect UT and

ST to the respective 11kV Unit and Station Switchboards and also for the

interconnecting ties for these switchboards. 3.3kV SPBs are provided to

connect UATs to the respective sections of 3.3kV Unit Auxilary

Switchboards.

SPB has aluminium conductor and is suitable for indoor/outdoor duty with

natural cooling. Aluminium conductor is supported on epoxy insulators

inside the busduct enclosure. The bus duct enclosure is made of

aluminium alloy sheet. Insulating barriers of 2 mm thick Aluminium sheet

provide complete phase segregation inside the enclosure. The Aluminium

sheet is welded on a framework made up of aluminium angles. Bolted

type inspection covers provide access to the conductor joints and

insulators.

Neoprene bonded cork gaskets are provided between the inspection

covers and the enclosures in order to achieve

fully weather proof duct and airtight construction. The adjacent

enclosures are connected together by means of bolted type flange-to-flange

joints.

Busduct is complete with accessories like rubber bellows, flexibles, seal

off bushings. Space heaters are provided to maintain IR value inside the

bus duct.

Busduct is generally supported from ground in outdoor areas and from

ceiling in indoor areas.

Manual & automatic transfer of loads

The station switchgear shall be provided with manual line changeover

scheme for planned changeover of supply from one incomer to

another and vice versa.

Automatic fast changeover scheme for changeover supply from one

source to another in the event of supply from one source failure from

upstream end shall be provided. Changeover shall be locked if

incomer has tripped due to bus fault.

The closure of the unit supply breaker shall be supervised by a

synchro-check relay permanently connected to nad energized by the

secondary voltages of the unit bus P.T.s. if fast auto change over fails

for whatever reason, an automatic “slow”transfer shall be initiated.

The fast changeover scheme shall be such that the running motors

are not tripped or there is only allowable inrush current due to motor

re-acceleration.

The FBTS should have following transfer modes:

i. FAST TRANSFER

The bus voltage and incoming source voltage should be monitored on

a continuous basis for magnitude and phase angle to ensure that

transfer operation is carried out under conditions conducive to fast bus

transfer as per high speed sync-check supervision.

ii. IN PHASE TRANSFER

The breaker power contacts shall close when the decaying and

drifting bus voltage synchronises with the incoming source voltage

within acceptable voltage and frequency parameters.

The Bus transfer system shall continuously process the bus voltage

and the drifting phase angle dynamics to determine in real-time the

exact moment of sending a command to the breaker-closing coil to

achieve the above.

iii. SLOW TRANSFER

The breaker power contacts shall close when the falling bus voltage

shall reach an acceptable safe value. The auxiliary drives are

selectively tripped simultaneously to limit the transformer inrush

current.

iv. MOMENTARY PARALLELING TRANSFER

This is a “ Make before break “ transfer for a very short duration of the

order of few cycles where, under supervision of the bus voltage and

incoming source voltage for magnitude and phase angle, the new

source breaker is closed before opening the old source breaker.

Normally not recommended for unplanned transfers and auto/

protective transfers from the system safety considerations.

RATINGS OF BREAKERS USED IN THE HT SWITCHGEAR 1. Vacuum circuit breaker (JYOTI) Rated frequency: 50Hz

Rated voltage: 7.2 kV

Rated current: 1250A

Ins. Level: Imp. 75 kVp

PF 28KV

Rated breaking current: 44KA

Rated making current: 110-peak kA

Supply voltage closing: 220DC

Rated short time current: 44KA 3s

Wt. Of breaker: 100Kg

2. Minimum oil circuit breaker (KILOSKAR) Rated frequency: 50Hz

Rated voltage: 6.6 kV

Rated current: 1250A

Breaking capacity: 34.7 kA symmetrical

34.7 kA Asymmetrical

60 MVA symmetrical

Supply voltage closing: 220DC

3. Minimum oil circuit breaker (JYOTI) Rated frequency: 50Hz

Rated voltage: 11/6.6 kV

Rated current: 630A

Impulse sec: 65 kA peak

STC (1sec): 40 kA

Breaking capacity: 350/280 kA symmetrical

55 kA Asymmetrical

360 MVA symmetrical

Supply voltage closing: 220DC

4. SF6 circuit breaker (KILOSKAR) Rated frequency: 50Hz

Rated voltage: 6.6 kV

Rated current: 1600A

Tripping coil: 220V DC

Spring charge motor: 220V DC

5. SF6 circuit breaker (VOLTAS) Rated frequency: 50Hz

Rated voltage: 6.6 kV

Rated current: 1600A

Tripping coil: 220V DC

Spring charge motor: 220V DC

6. Air Blast circuit breaker (VOLTAS) Rated frequency: 50Hz

Rated voltage: 6.6 kV

Rated current: 680A

Tripping coil: 220V DC

Spring charge motor: 220V DC

7. Air Blast circuit breaker (USA comp.) Rated frequency: 50Hz

Rated voltage: 25 kV

Rated current: 2500A

Symmetrical MVA 6.9-8.25: 600 KV

Rated symmetrical SC current: 42000 A

Asymmetrical rated factor: 1.2

Tripping coil: 220V DC

PPRROOTTEECCTTIIOONN AANNDD RREELLAAYYSS UUSSEEDD IINN 66..66 KKVV SSWWIITTCCHHGGEEAARR 1. Instantaneous overcurrent relays for short circuit protection

2. Inverse time ground detection relay for zero sequence voltage protection.

3. Under voltage protection.

RATINGS OF OVER CURRENT RELAYS

1. FOR FEEDER AND UNIT BUSES

CT ratio: 600/5A

RMA: 18A

RT: 0.5 sec

2. FOR STATION BUSES

CT ratio: 2000/5/1A

RMA: 15A

RT: 1.5 sec

3. FOR RESERVE SUPPLY

CT ratio: 1000/5/1A

RMA: 14A

RT: 1.0 sec

4. FOR COOLING TOWERS

CT ratio: 400/5/1A

RMA: 16A

RT: 1.0 sec

5. FOR XMERS (SAY TRANSFORMER NO. 1(630 KVA))

CT ratio: 100/5/1A

RMA: 14A

RT: 0.5 sec

Rest Xmers have almost similar relay ratings

A. Metering & protection

Adequate protection/metering shall be provided for the switchgear panels. Location of relays in the switchgears shall be at convenient height, such that it

can be surfed by standing at ground. All relays except for LBB ,PT fuse failure shall be numerical with RS232/RS485

port. Separate meters shall be provided for each of the feeders mentioned below, if

same is not available in the numerical relays. Relay setting software for setting all the numerical relays in 6.6 kV switchgear

and generator protection panels shall be loaded in a dedicated operator station in the main control room. All numerical relays shall be time synchronized with the GPS master clock.

On failure of any of the numerical relay contact shall be generated, which shall provide the annunciation to the DCS.

All the protective relays, except for auxiliary relays shall have- remote/local reset facility, and shall be suitable for efficient and reliable operation of the protective schemes.

A combination of electro mechanical and numerical communicable type relays for main protections is not acceptable.

The bidder shall include in his bid a list of installation where the relays offered are in trouble free operation for last two years.

The minimum protections or metering shall be provided required for various typical feeders shall include, but not be limited to the following:

1. Incomers

PROTECTIONS METERING

Composite numerical feeder protection relay

All the metering of the electrical parameters shall be through the Power monitors.

Under Voltage relay

Local breaker backup protection

Fuse failure relay

2. TIE breakers

PROTECTIONS METERING

Composite motor protection relay

All the metering of the electrical parameters shall be through numerical relay

Local breaker back up protection

3. Bus PT Feeders

PROTECTIONS METERING

Under voltage protection Voltmeter with selector switch

Fuse failure protection Voltage transducers-3 Nos,

4. Motor feeders

PROTECTIONS METERING

Composite motor protection relay (99)

All the metering shall be through the composite motor protection relays only.

Differential protection for motor feeders (rated 1000kW or above)

Local Breaker backup protection

Time delayed under voltage trip

5. Service Transformer feeders

PROTECTIONS METERING

Composite numerical transformer protection relay

All the metering shall be through the composite motor protection relays only.

Local Breaker back-up protection

Winding temperature and Buccholtz protection

The switchgears shall be designed to offer adequate level of safety to

operating/ maintenance personnel. Means shall be provided to prevent access to the live part to avoid accidents during service as well as maintenance period. A detailed instruction plate suitable for wall mounting shall be provided for each switchgear/MCC room describing various safe operating procedure/ safety precautions for safe operation and maintenance of the switchgear.

TESTS

All relevant routine and acceptance tests shall be conducted as per applicable standards and typical type test certificates of identical switchgear shall be submitted.

Minimum electrical system requirements in respect of control, monitoring, measurements, annunciation, and synchronization are indicated.

Sl.No. DESCRIPTION UNITS VALUES/REQUIREMENTS

6.6kV SWITCHGEAR

1 Switchboard Cubicles and Bus bar ratings

a) Nominal system voltage, phases and frequency

V,ph,Hz 6600/3/50

b) System neutral earthing Non- effectively earthed

c) Maximum system voltage V 7200

d) One minute power frequency withstand voltage

kV(rms) 20

e) 1.2/50 microsecond impulse withstand voltage

kV(peak) 60

f) Maximum temperature of bus bars, droppers, connectors and contacts at continuous current rating under site ref.ambient temperature

0C 90

g) Material of bus bars Aluminum

h) Material of bus bar insulation

Heat shrinkable PVC sleeve. Removable bus bar joints with

shrouds of 7.2kV insulation

i) Bus bar support insulator 7.2kV

j) Bus- bar joints/connection Silver faced

k) Bus bar rating By bidder

l) Short circuit current rating and duration RMS 40kA for 3 sec.

m) Momentary withstand current PEAK 100 kA

2 Switchboard Constructional details

a. Thickness of sheet steel enclosures, doors and covers

mm Cold rolled

b. Thickness of gland plate for 1 core cable mm 3.0,Non- magnetic material

c. Degree of protection VT/relay compartments- IP52 Other compartments-IP42 Air conditioned area-IP31

LOW VOLTAGE SWITCHGEAR SCOPE

If we talk in simple language switchgear is one which makes or breaks on electric circuit.

This definition straight away does not attract much curiosity nor does it show any linking of the enormous consideration required in designing switchgear.

Numerous problems encountered in errection, testing and commissioning of the switchgear and various precaution are to be taken in operation and maintenance of the switchgear.

This report describes the various types of switchgear and their usage.

Low voltage switchgear comprises of 415V Power Control Centers (PCCs),

415V Motor Control Centers (MCCs), 415V Power cum Motor Control Centers

(PMCCs), 415V/240V AC Distribution Board (ACDBs) and Local Control

Centres (LCCs). PCCs & PMCCs are for Auxiliary Power Distribution. Low

voltage switchgear conforms generally to Indian Standard IS: 13947.

General Constructional Features All frames and load bearing members are fabricated using mild steel

structural sections or pressed and shaped cold rolled sheet steel of

thickness not less than 2 mm. Frame is enclosed in cold rolled sheet steel

of thickness not less than 1.6mm. Doors and covers are also of cold rolled

sheet steel of thickness not less than 1.6mm. Stiffners are provided

wherever necessary.

All switchboards/ panels are dust and vermin proof. All cutouts have synthetic

rubber gaskets.

All switchboards, MCCs and DBs have following distinct vertical sections:

1 Completely enclosed busbar compartment for horizontal and vertical

busbars.

2 Completely enclosed switchgear compartments, one for each breaker, motor

starter or switchfuse unit.

3 Compartment, alley or cable box for power and control cables.

4 Compartment for relays and other control devices associated with a circuit

breaker, wherever necessary.

MCCs and DBs are divided into vertical sections. Each vertical section is

provided with adequately sized cable alley covering entire height. In case

cable alleys are not provided for DBs, segregated cable boxes with

complete shrouding for individual feeders are provided at the rear for

direct termination of cables in each individual feeder.

Busbars are of high conductivity aluminium alloy. Minimum air clearance in

air between phases and phase-earth is 25mm. For all other components,

the clearances is at least 10mm. Wherever above is not possible except for

horizontal and vertical busbars, insulation is provided by sleeving or

barriers. In case of DCDBs/fuse boards, the busbar system is insulated or

physically segregated with barriers to prevent interpole short circuit.

Busbars insulators are of track-resistant, high strength, non-hygroscopic,

non-combustible type and suitable to withstand stresses due to over-

voltages and short circuit current.

All non-current carrying metal work of boards/panels is effectively bonded

to earth bus of galvanized steel, extending throughout the

switchboard/MCC/DB. Positive earthing is maintained for all positions of

chassis and breaker frame.

The maximum temperature rise of the horizontal and vertical busbars and

main bus link including all power drawout contacts when carrying 90% of

the rated current along the full run is 55deg.C with silver plated joints and

40deg.C with all other types of joints over an ambient of 50deg.C.

415V Power Control Centers (PCCs)

The switchboards are single front draw out type and compartmentalized to

accommodate circuit breakers in single tier or double tier. The switchboard

has a short circuit rating of 50kA rms for 1 sec. All switchboards up to 1600A

rating conform to DOP IP: 52, while the switchboards rated above 1600A are

provided with louvers and conform to DOP IP: 42. The outgoing feeders rated

630A and above are provided with ACBs. Switch fuse units are provided for

rating up to 400A. The circuit breakers are triple pole, air break, horizontally

draw out type having 'test/service/isolated' positions. The circuit breakers are

electrically operated having motor wound, spring charged stored energy

mechanism. The control voltage of circuit breakers is 220V DC.

Metering, protection and control equipment like ammeter, voltmeter, relays,

control and selector switch etc. are housed in the switchboard. Interlocks, auto

changeover between incomers and bus coupler breaker are provided as per

requirement. Feeder protections comprising over current and earth fault relays

are provided. Alternatively, circuit breakers may have built–in releases for the

same purpose. Breaker controlled starters for motors are generally connected

directly to PCC and provided with short circuit, overload and earth-fault

protection. Interposing relays for interface with C&I systems are provided,

wherever required. Cable gladding and termination arrangement is envisaged

at the rear side of the ACB panels.

415V Motor Control Centers (MCCs)

Required numbers of motor control centres are provided for the power

plant and these are located near the respective loads/plants.

Motor control centres are drawout type, double front, with degree of protection IP:52.

MCCs rated above 400A have air-circuit breakers as incomers. For

ratings up to 400A, load switches are provided. Outgoing supply feeders

of rating 400A and below are equipped with switch fuse units. MCCs fed

by circuit breakers have a short circuit rating of 50kA rms for 1 sec.

whereas MCCs fed by switch fuse units have a short circuit rating of 50kA

for 0.2 secs.

Motors rated upto125kW are provided with bi-metallic relays for thermal

overload protection and HRC fuses for short circuit protection. Motors

rated above125kW (upto160kW) are provided with locked rotor protection

in addition to above. Motor starters are direct-on-line type.

Motor starter schemes have provision for 240V supply for space heating

for motors rated above 30kW.

Interposing relays for interface with C&I system are provided, wherever

required.

Two common control transformers of ratio 415/110V and adequate rating

(one on each section of MCC) are provided in each motor control centre

for the purpose of control supply to all starters in that MCC. Each section

of MCC is provided with bus voltage module comprising of fuse and

voltmeter with selector switch. An ammeter is provided for motors rated

above 30 kW. For drives requiring ammeter on remote control

equipment, transducer is provided in the MCC.

415V Power cum Motor Control Centers (PMCC)

For load centres where the associated loads/plant are located in the vicinity of

the auxiliary transformer, power control centres and motor control centres are

made common to form a PMCC having features described above for PCC and

MCC and are in double front execution.

AC Distribution Boards (ACDBs)

AC distribution boards are provided for three phase and single phase power

distribution. The DBs are fixed type and floor mounted. Switchfuse outlets are

provided, as required.

Local Control Stations & Local Starters

Local control stations are provided near the unidirectional motors for emergency `stop'. These local control stations conform to degree of protection of IP: 54 for indoor and IP: 55 for outdoor.

Local push button stations have metal enclosure of die cast aluminium or

rolled sheet steel of 1.6mm thickness.

Local starters may be provided for exhaust fans, sump pumps etc., as per

requirements of the layout.

LV Busduct

Metal enclosed, natural air cooled, non-segregated phase busducts

(NSPBs) are provided for Interconnection between LV Service

transformers and LV switchgear.

The busduct has aluminium conductor and is suitable for indoor/outdoor

duty with natural cooling.

Conductors and inside surface of enclosures are treated with mat black

paint for efficient heat dissipation.

Bimetallic connectors are provided in case equipment terminals and

material of bus conductor are different.

Bolted and flexible joints for conductor and enclosure are provided at all

equipment terminations.

Busduct is generally supported from ground in outdoor areas and from

ceiling in indoor areas.

SECONDARY WIRING AND TERMINALS

a. All internal wiring for connections to remote equipment shall run to terminal boards. Spare auxiliary switches, contacts or relay contacts shall also be wired up to terminal board as per schemes. Wires shall not be jointed or teed-off between terminal points.

b. Wiring shall be made by 1100-volt grade seven strands PVC insulated copper wire

having a cross-sectional area of not less than 1.5 sq.mm. All connections from CT leads upto instruments, relays, terminal board shall be made by copper wires of minimum 2.5 sq.mm size. The cables shall be tested for flammability test as per applicable standards and shall also withstand service temperature without deterioration.

c. All wiring shall be made with the Colour Codes specified below:

a) 3 phase AC Connections Phase 1 (R) Red Phase 2 (Y) Yellow Phase 3 (B) Blue

b) 1 phase AC Connections Phase Red Neutral Black

c) DC Connections

Positive Red Negative Blue Neutral Black

d) Earth Connection Green

NOTE: 1. Colour of outer sheath of AC and DC wiring shall be grey. However for

DC control wiring, white colour of outer sheath is also acceptable.

2. Where the single-phase conductors are associated with the 3-phase system from which they are derived, the phase conductor shall use the same colour as that phase from which it is derived.

d. Where wiring is subjected to movement, flexible wires having not less than 40

strands, with a minimum cross-sectional area of 2.5 sq. mm. of conductors, shall be used.

e. Wiring shall be run mostly clear of all metal parts in insulated cleats & shall be

properly routed, neatly bunched. However, PVC wire holders and channels shall be preferred for running of wiring.

f. Where wiring passes from one compartment to another, the aperture shall be

„Bushed‟ to prevent damage of wires against sheet metal edges. Bushes may comprise of good quality rubber grommets.

g. Intermodule bus wires shall be kept separate from all other wiring. AC or DC

terminations shall be grouped function-wise as far as possible and labels of the function shall be affixed.

h. Every wire end for interpanel termination shall be fitted with numbered ferrules of

white or yellow colour having glossy finish with identification number engraved in black. Ferrules shall be made of moisture and oil resisting insulating material. Ferrules shall be of interlocked type or tight fitting type. Ferrules shall be so fitted that they will not get detached, when the wire is removed from the terminal.

i. System of marking of wiring shall be as per applicable standard.

j. All wires used internally shall have crimped on tinned copper lugs for terminations.

k. Terminal boards shall be either of stud or pressure screw or insertion type.

l. Insulating barriers of adequate height shall be provided between adjacent pairs of

terminals unless the terminal board moulding inherently provides a barrier between pair of terminals.

m. Transparent front covers shall be provided if the terminals are not finger proof.

Terminals shall have marking for terminal identification.

n. Terminal boards shall have separate terminals for incoming and outgoing wires with not more than two wires connected to any one terminal. Terminal boards shall have separate terminals for incoming and outgoing

wires with not more than two wires connected to any one terminal. o. Terminal boards shall be mounted vertically at the side of the cubicle or in the

horizontal rows and properly spaced to have clean wiring arrangement, adequate access for putting ferrules, making terminations etc.

p. It shall be possible to read the ferrule numbers when the wiring is complete. Where terminals may be live when the equipment is isolated from the main supply, these shall be clearly marked on the panel.

q. Spare terminals to the extent of twenty percent of the used terminals shall be

provided for each module. CONTROLS, INDICATIONS & ALARMS a. The controls, indications and alarms shall be provided as per enclosed schemes.

b. The location of control for switchgear shall be either the control room, local to the

equipment controlled, on the switchgear or in any combination of these as per typical schemes enclosed with Section-C. Control-Selector-Switch shall be provided accordingly.

c. All switchgear comprising of withdrawable units shall have test feature, where

specified in Data Sheet A, for operation check-up purposes. This will allow manual and/or electrical closing and tripping of switchgear with power connection disconnected both at the bus and circuit ends. In the TEST position, all incoming & outgoing remote electrical controls and interlocks shall not cause the switchgear equipment to be operated manually or otherwise.

d. Means for simulation testing shall be provided, where called for in Data Sheet A.

e. Circuit breaker control switches shall be operated in clockwise direction for closing

the circuit breaker and anti-clockwise for opening (tripping) and shall automatically return to the neutral (mid-position).

f. The alarm bell in alarm circuits shall be suitable for the duty imposed on it by the

ringing cycle as per scheme.

SWITCHGEAR MAIN ASSEMBLIES

AIR CIRCUIT BREAKERS

General Requirements

a. Circuit breaker units shall be of air-break, metal enclosed horizontal withdraw able type having short circuit ratings.

b. Moving portion of each circuit breaker unit shall consist of 3 or 4 poles, with

common operating mechanism, primary and secondary disconnecting (isolating) devices, auxiliary switches, mechanical position indicator and necessary wiring all mounted on a robust steel frame work.

c. Primary and secondary disconnecting devices shall be robust, reliable, fully

self-isolating and self-aligning. These shall comprise of silver plated copper

contacts. It is preferred to have a design with the secondary disconnecting devices located on the side of the circuit breaker.

d. All the secondary disconnecting devices shall make both in SERVICE & TEST

position of the circuit breakers, unless specified for programmable type functions and called for in Data Sheet A.

e. Secondary disconnecting device comprising of single multiway plug & socket is

also acceptable provided the interlocking requirements as specified in clause 4.1.6 are fulfilled.

f. Circuit breakers of same current rating shall be fully inter changeable with one

another. The design shall prevent circuit breakers from being taken into TEST and SERVICE positions of fixed housing of breakers of different ratings. The arrangement shall be such as to prevent damage to isolating contacts.

g. Positively driven auxiliary switches shall be provided for indication, control &

interlocking. These shall comprise of a minimum 6NO + 6NC contacts in addition to those required for internal use. These shall be wired up to the secondary isolating devices. Where the specified number of auxiliary contacts is not available, the same shall be derived through suitable contact multiplication.

h. It shall be possible to draw in or out the breaker to SERVICE, TEST &

ISOLATED position without opening the cubicle door. It shall be possible to close the door even when circuit breaker is drawn out to ISOLATED or TEST position, thus preventing entry of vermin & dust.

i. It shall be possible to manually charge the closing spring and close/trip the breaker without opening door. Access to the device affecting these shall be possible even with compartment door closed.

j. The circuit breaker shall be provided with the following set of positively driven

mechanical position indicators available on the door front.

Breaker ON/OFF Breaker SERVICE/TEST/ISOLATED Breaker closing spring CHARGED/DISCHARGED

The mechanism shall be such that failure of auxiliary spring shall not prevent tripping and also not cause tripping of closed circuit breaker.

Operating Mechanism

a. The operating mechanism shall be strong, positive & fast in operation.

b. The circuit breaker mechanism shall preferably be of motor wound charged spring assisted & of trip free design i.e. the trip command always predominating closing command. Where required, manually operated circuit breakers provided with manual spring charged stored energy closing mechanism shall be offered.

c. Circuit breaker operation shall be independent of the motor, which shall be

solely for the charging of the spring. d. Motor wound charged spring mechanism shall be provided with electrical

release coil.

e. The mechanism shall preferably be such that:

If the circuit breaker is open and the springs charged, the circuit breaker can be closed & tripped.

If the circuit breaker is closed and the springs charged, there shall be

sufficient energy to trip, close & then trip.

f. Circuit breaker operating mechanism shall be fitted with an electrical shunt trip coil in addition to mechanically operated hand-tripping device. The electrical tripping and closing devices shall be suitable for operating from Electrical (AC/DC) supplies as specified under Data Sheet A. The devices shall operate satisfactorily at their rated operating temperature over the following range of voltage variation:

Spring charging motor 85 to 110% Closing release coil 85 to 110% Shunt trip coil 70 to 110%

g. All operating coils for use in DC supply shall be connected such that failure of

insulation to earth does not cause the coil to be energised.

h. Tripping & closing circuits shall be provided with fuse or miniature circuit breaker in each pole on each unit and shall be independent of each other and all other circuits.

i. Locking facilities shall be provided to prevent the closing of circuit breaker

when it is open and from being manually tripped when it is closed. In case it is not possible to provide locking facility to prevent manual tripping suitable shroud or flap shall be provided on the manual trip actuator to prevent its inadvertent operation.

j. Provision shall be made to ensure that when manual-operating mechanism for

maintenance purpose is being used, it shall not be possible to electrically close the breaker.

k. All circuit breakers shall incorporate, preferably, both mechanical & electrical anti-pumping features.

l. Limit switches for sensing the circuit breaker position in SERVICE/TEST

position & closing spring CHARGED/DISCHARGED shall be provided. Isolating Devices

a. All circuit breakers shall be connected to their associated bus bars and cables

through isolating power contacts of an approved design which shall be arranged for operation while main circuit is live but no current is passing.

b. The design shall be such that it is impossible for the isolating contacts to be

opened by force due to current in the primary circuit and shall be inter-locked with the circuit breaker so that it is impossible to make or break current with the isolating contact.

c. When isolation is effected by the withdrawal of the circuit breaker, provision

shall be made for positively locating the circuit breaker in the SERVICE, TEST and ISOLATED position. Stops shall be provided to prevent over-travel beyond isolated position and each position shall be clearly indicated.

d. Isolating devices shall incorporate self-aligning contacts, the fixed contacts of

which shall be such that access can readily be obtained for maintenance purposes.

Shutters

a. Shutters shall be provided to completely shroud all the fixed isolating contacts of

the circuit breaker both on bus bar & circuit sides.

b. Shutters shall be opened and closed automatically by the movement of the circuit breaker carriage and shall prevent access to the fixed isolating contacts when the circuit breaker is withdrawn.

c. Painted labels shall be provided to indicate whether the shutters are bus bar

shutters or cable shutters.

d. The shutter for fixed isolating contacts connected to bus bars and cables shall have means for temporarily fixing the shutters in an open position to facilitate inspection or testing.

e. The arrangement of shutters shall be such that normal movement of circuit

breaker is not affected.

Contacts and Arc Shields

a. Circuit breaker shall be of single break type. The fixed and moving contact system shall be suitable for easy dismantling and replacement.

b. Circuit breakers shall be provided with an arc control device for each pole, a set

of fixed and moving contacts with an arc shield between poles.

c. Arc control devices shall be so placed that any emission shall not cause break down or damage to insulation.

Interlocking and Locking Facilities

a. Mechanical interlocking devices shall be provided to prevent maloperation of the circuit breakers. The list given below comprises the minimum of circuit breaker maloperations that shall be prevented by the use of mechanical interlocking devices.

The circuit breaker being withdrawn from or inserted into the primary

isolating contacts when the circuit breaker is closed & the plug for secondary disconnection where provided is not fully engaged.

The closing of the circuit breaker unless correctly located in the

SERVICE, ISOLATED or TEST position.

The circuit breaker being closed in the SERVICE position without completing the auxiliary circuits via the secondary isolating devices, where self-aligning secondary isolating contacts have not been provided.

The breaker cubicle door being opened unless the breaker is in the

OFF (or ISOLATED) condition.

Closing of circuit breaker in SERVICE position & door open.

Removal of the plug for secondary disconnection when the breaker is in SERVICE position and is ON.

Locking Facilities Shall Include The Following:

a. Circuit breaker control switch in the neutral position.

b. Mechanical trip on circuit breakers (so as to prevent manual trip). Also refer to clause no.4.1.2.9.

c. Access flaps for operating or withdrawing of circuit breakers.

Circuit Breaker with Releases

a. The circuit breaker, where specified in Data Sheet A, shall have built-in releases for overload, short circuit, earth fault & under voltage protection depending upon the functional requirements.

b. The short circuit protection employing electromagnetic and overload protection

through thermal bimetallic element shall be fed through individual current transformers fitted on each pole of the circuit breaker. However for solid-state protection release, common current transformer for short circuit & overload protection is acceptable.

c. The releases shall act on a common trip bar to trip the circuit breaker.

d. The releases shall be housed such as to make them tamper proof but at the

same time easily accessible for carrying out the desired settings.

e. Setting for the overload release shall be through a graduated scale and a fine pointer accessible and visible from the front of the breaker.

f. The short circuit release and under voltage release and earth fault release shall

have a clock work timer to delay the tripping and these shall be visible and accessible from front to enable easy adjustments.

g. Facility for testing of all type of release by means of secondary injection shall be

provided.

h. Means for remote indication of the release operation shall be provided, if specified in the schemes. This shall be preferably separate for each type of release fitted.

i. Solid State Protection

Air circuit breakers may, alternatively, be fitted with composite solid-state

protection system comprising of over current, or over current and earth fault protection.

The performance of the solid-state protection should have been verified

under short circuit conditions.

The protection shall be one, which is independent of temperature variations. The protection unit shall not need any external supply for its operation.

The overload protection unit shall have inverse time current

characteristics.

Other common requirements shall be as specified above for electromagnetic releases.

j. A combination of releases or protections for a given circuit breaker feeder type.

VIII Operating Conditions

a. Breakers controlling motors shall operate satisfactorily under the following conditions:

Direct-on-line starting of induction motors rated above 160 kW with a

locked rotor current of seven times the rated current and starting time up to 30 seconds.

Breaking no load, full load and locked rotor current of induction motors as

stated above. IX CONTACTOR STARTER UNITS

a. All motors upto and including 160 kW shall be controlled by Direct-on-line

contactor starters, a combination of following: Isolating device;

Contactor as main means of starting and stopping of motor;

A short circuit protective device (SCPD);

Thermal overload protection with built in single phasing prevention feature;

Locked rotor protection, if specified in Data Sheet A.

b. Hardware to achieve any given type of function shall be as per enclosed

schemes.

c. Withdraw able contactor starter units shall be provided with means for mechanically indicating the SERVICE and other positions of trolley.

d. The starter units shall carry designation labels in terms of module type codes,

signifying the function of the unit. Labels indicating these shall be affixed on fixed and withdraw able portion of the unit.

e. The units shall be designed to ensure safety of operating personnel.

f. Interlocks shall be provided to ensure that the unit access door can only be

opened when the associated isolating device is open. Defeat interlock facility shall be provided.

g. The selection of rating of power component and the coordination with protective

devices shall be done based on motor rating and characteristics. The type of co-ordination required shall be as specified in Data Sheet A in accordance with applicable standard.

h. Components of the contactor starter units shall meet the stipulations under

clause 5.0.

SWITCH FUSE UNITS

a. These units shall preferably comprise of switches having integral fuses, called

composite units. Alternatively, combination units of separate switch and fuse may also be acceptable.

b. These units shall be provided for general purpose i.e. incoming or outgoing units

on switchgear.

c. The units shall be of the air break air insulated type, and designed to ensure safety to operating personnel.

d. Composite units shall have integral fuses. The design shall ensure that the

moving contact is not live when switch is open i.e. in OFF position, so as to facilitate removal of fuse.

e. The switch shall be capable of breaking 3 times the normal rated current at 0.3

power factor and 110% rated voltage, and making and carrying the system prospective fault current, but limited in magnitude and duration by the cut off characteristics of the largest HRC fuse link that may be fitted to that unit.

f. The fixed contact shall be so shrouded that maintenance of the unit can be

carried out in safety with the bus bars live.

g. Where one isolating switch is used as the incoming device, the incoming side fixed contacts shall be shrouded to ensure that maintenance can be carried out with the remote fuse and switch closed.

h. Other common requirements viz. interlocking with access door, interphase

barriers, defeat interlock etc. shall be as stipulated elsewhere.

i. Composite units may also be provided as components in other main assemblies.

j. Composite switch-fuse or the combination of switch and fuse shall meet the requirements of its components specified in clause 5.0.

MOULDED CASE CIRCUIT BREAKERS

a. Moulded case circuit breakers (MCCBs) shall be provided when called for in

Data Sheet A for use in lieu of switch fuse for the motor controls.

b. MCCBs in AC circuits shall be of triple pole construction arranged for simultaneous three-pole manual closing and opening and for automatic instantaneous tripping on short circuit.

c. Power closing device for remote operation may be provided, if indicated in Data

Sheet A.

d. Operating mechanism shall be quick make, quick break and trip free type.

e. The ON, OFF & TRIP positions of the MCCB shall be clearly indicated so as to be visible to the operator when mounted as in service. Front of board operating handle shall be provided.

f. MCCBs shall be capable of withstanding the thermal stresses caused by

overloads and locked rotor currents/ starting currents of associated motor, and the mechanical stress caused by the peak short circuit current of value associated with the switchgear rating.

g. The instantaneous short circuit release shall be so chosen as to operate at a

current in excess of the peak motor in-rush current and a range of settings shall be provided for the purchaser‟s selection.

h. MCCB terminals shall be shrouded and designed to receive cable lugs for cable

sizes relevant to circuit ratings.

i. Overload inverse time release and other releases shall be provided as specified in Data Sheet A / BOM /Schemes.

j. MCCB by itself may be provided as component in other main assemblies.

RATINGS OF CIRCUIT BREAKERS: 1. AIR BLAST CIRCUIT BREAKER (BHEL)

Volts: 220 kV Amperes: 1200A

Breaking capacity: Symmetrical 26.31 kA Equivalent 10000 MVA Asymmetrical 32.1 kA Making capacity: Peak 67.1 kA Short circuit time: 3 sec. 26.3 kA Closing coil voltage: 220V DC Tripping coil voltage: 220V DC

Working pressure: Max. 28.1 kg/cm2-g

Min. 26.0 kg/cm2-g Lockout pressure: 21.1 kg/cm2-g

2. AIR BLAST CIRCUIT BREAKER (ABB) Volts: 245 kV Amperes: 1200A Breaking capacity: Symmetrical 31.5 kA

Asymmetrical 38.4 kA Short circuit time: 3 sec. 31.5 kA Closing coil voltage: 220V DC Tripping coil voltage: 220V DC RIL at 50 Hz: 480 kV

VI impulse: 1.2/50 s 1050 kV per sec. U switching impulse: first pole to clear 1.3 Mass: 1830 Kg Working pressure: Max. 27.31 kg/cm2-g

3. AIR BLAST CIRCUIT BREAKER (BHEL) Volts: 245 kV Amperes: 2000A Short circuit time: 3 sec. 26.3 kA Closing coil voltage: 220V DC Tripping coil voltage: 220V DC Working gas pressure: 6.1 kg/cm2-g at 200c Rated frequency and voltage for auxiliary: 415AC 50Hz Total weight of gas: 3900 Kg Rated operating scheme: O-0.3sec-CO-3 min.-CO Rated lightening impulse withstands voltage: 1050 kVp Rated short circuit breaking current: 40 kA Rated operating pressure: 15 kg/cm2-g First pole to clear factor: 1.3 Rated duration of short circuit current: 40 kA for 3 sec Rated line charging breaking current: 125 A

Gas weight: 21 kg

PPRROOTTEECCTTIIOONN AANNDD RREELLAAYYSS UUSSEEDD IINN 441155//224400VV SSWWIITTCCHHGGEEAARR

1. Earth fault relay for earth protection.

2. Under voltage and no voltage relays for under voltage protection

1. UNDER VOLTAGE RELAY English Electric type VAGM22 connected through potential transformer pick up when bus voltage goes down by 50%

2. NO VOLTAGE RELAY

English Electric type VAG11 picks up and trips incoming main supply breaker when bus voltage goes down by 25%

3. EARHT FAULT RELAY CDG 14 has been connected through CT in the secondary neutral of all auxiliary transformers and trips 6.6 kV breaker in case earth fault in 415V switchgear bus

Sl.No Description Units Values/Requirements

400V Switchgear/MCC

1 Switchboard & Bus bars

1.1 Rated voltage, phases & frequency

V/P/Hz 400, 3, 50, 3 wire

1.2 System neutral earthing Solidly earthed 1.3 One minute power frequency

voltage withstand

1.3.1 Power circuits V 2500

1.3.2 Control circuits V 1500

1.3.3 Auxiliary circuits V 2000

1.4 Reference ambient air temperature

oC 50

1.5 Material of bus bars Aluminium

1.6 Maximum temperature of bus bars contacts, droppers at site reference ambient of 50

0C

oC

105

1.7 Short circuit withstand

1.7.1 Short time current (1 sec) RMS 50kA for 1 sec.

1.7.2 Momentary current Peak 125kA

1.8 Switchboard /MCC construction

Switchboard/MCC

1.8.1 Fully draw out Yes

1.8.2 Double front/ single front Single front

1.8.3 Cable entry (Power & Control) Bottom

1.8.4 Modular construction Yes

1.9 Degree of protection for as per IS:2147

IP 52

1.10 Thickness of sheet steel Frame Door Cover

1.10.1 Cold rolled mm 2.5 1.6 1.6

1.10.2 Gland plate thickness mm 3

1.11 Clearances in air for live parts

1.11.1 Phase to Phase mm 25.4

1.11.2 Phase to earth mm 19.4

1.11.3 All other compartments mm 10

1.12 Plain shade RAL7032

2 Contactors & O/L relay

2.1 Utilization category for contactors

AC3 for non-reversible &AC4 for reversible

2.2 Contactor rated duty Uninterrupted

2.3 Reset feature for thermal O/L relay

Hand

2.4 Starter type DOL

3.0 Circuit Breakers

3.1 Circuit breaker type Air Break, three pole with shunt trip

3.2 Rated operated duty B-3min-MB-3min-MB

3.3 Type of operating mechanism Motor wound spring charged

3.4 Short circuit rating 50kA for 1 sec

3.5 Control voltge for spring charging motor and tripping &closing

V/DC 220V +10% & -15%

3.6 Emergency manual operation required in addition to electrical operating devices

3.6.1 For spring charging &closing Required

3.6.2 For tripping Required

3.6.3 Anti-pumping feature Required

4 CTs and VTs

4.1 Short time withstand current and duration for Ct

50kA for 1 sec

4.1.1 Breaker controlled Based on breaker short circuit current rating and duration

4.1.2 Switchfuse controlled To match with fuse withsatnd

4.2 Overvoltage withstand capacity for VT

4.2.1 Continuous pu 1.2

4.2.2 30 seconds pu 1.9

5 Meters Digital

5.1 Class of accuracy 0.5 for energy meters and 1.0 for others.

6 Applicable standards

6.1 Switchboard general requirements IS :4237

6.2 AC circuit breakers IS:13118

6.3 Factory built assemblies of switchborad and control gear for voltages upto & including 1000V AC &1200V DC

IS:8623

6.4 Air break switches IS:4064 & IEC 60947-3

6.5 Miniature circuit breakers IS:8828

6.6 HRC catridge fuses IS:9924

6.7 D type fuses IS:8187

6.8 Contactors IS:29259

6.9 Starters IS:8544

6.10 Control switches/ push buttons and maintenance of switchboard

IS:6875

6.11 Code of practice for phosphating iron and steel

IS:6005

6.12 Wrought aluminium & aluminium alloys for electrical purposes

IS:5082

6.13 Control transformer for switchboard and control gear for voltages not exceeding 1000V AC

IS:12021

7 Technical requirements Table for 400V AC Distribution Boards/ Control Panels

7.1 Location/ mounting Indoor/floor mounted

7.2 Current rating Max. expected load current +20%margin

SWITCHGEAR COMPONENTS

ISOLATING SWITCH

a. All switches shall have visible ON/OFF position indication and shall be pad lockable in any (ON/OFF) position.

b. The switch shall be capable of making on to the system prospective symmetrical

fault current but limited in magnitude and duration by the cut off characteristics of largest HRC fuse link appropriate to the unit.

c. It shall not be possible to gain access to inside the unit unless the isolating

switch is in OFF position.

d. All isolating switches shall have 1 NO + 1 NC auxiliary contacts. Otherwise multiply where required as per schemes.

e. The switches shall be suitable for independent manual operation from the front

of the switchboard without opening the door.

f. The switch contacts shall be of silver alloy or silver plated copper and springs of non-corrosive material.

g. Interphase barriers shall be provided to prevent possibilities of phase-to-phase

fault in the switch. The switch shall also be shrouded from all sides to prevent access to live parts on the switch after opening the unit door. The barriers and shrouding shall extend upto the height of switch to fully enclose both the bus and the load side terminals of the device. The arrangement shall permit easy maintenance.

h. When used in combination with fuse and contactor; Switch shall be of quick make, quick break type to electrically isolate the starter

from the incoming supply. The device shall also interrupt the control supply. Switch shall be capable of disconnecting the load from the bus bars in case the

contactor has welded in and is carrying the stalled rotor current as high as 8 times full load current at a power factor of 0.3.

CONTACTORS

a. Contactors shall be of the air break type fitted with arc shields.

b. The operating coil shall be suitable for satisfactory operation in the range of

85% - 110% of nominal voltage specified under the Data Sheet A. The coil shall be tropicalized having insulation not less than class „E‟.

c. Butt contacts of the rolling self-cleaning type shall be utilized and all portions

likely to suffer from arcing shall be easily removable.

d. The contactor shall be capable of closing onto system prospective symmetrical fault current, as specified under Data Sheet A, backed up by the largest HRC fuse appropriate to the rating of the contactor. This capability shall be backed up by test results or calculations based on comparison of let-through energies.

e. Electrically independent auxiliary contacts not less than 2NO + 2NC for remote

interlocking and indication shall be fitted to individual contactor.

f. Main contacts of contactor shall be silver faced copper.

g. All springs shall be made out of a corrosion proof material.

h. Type of coordination with other devices shall be as per Data Sheet A. HIGH RUPTURING CAPACITY (HRC) FUSES

a. The fuse serving as the short-circuit protective device in contactor-starter or isolating fuse-switch units shall be of HRC cartridge, current limiting and plug-in/bolted non-deteriorating type.

b. The fuses carriers shall be easily withdraw able for replacement of fuse.

Insulated fuse pullers shall be provided where fuses are not mounted in insulating carriers to remove and replace fuses in live conditions.

c. Live terminals of fuse bases shall be shrouded to prevent contact with personnel

where fuse links are not mounted in carriers and are directly plugged into the fuse base. Interphase barriers extending throughout the length of the fuse base shall be provided to prevent interphase short circuit. They shall be shrouded from all sides to prevent accidental contact.

d. Fuse carriers and bases shall be of good quality moulded insulating material.

Porcelain fuse bases and carriers will not be accepted.

e. The rating and characteristics of fuse links shall be chosen appropriately for short circuit protection of circuits downstream, while fulfilling the following:

Remaining inoperative for transient conditions viz. starting in-rush current

of a motor downstream;

(b) Matching the thermal withstand characteristics of contactor and thermal overload device to the extent required as per type of coordination.

Condition (b) above is applicable where appropriate.

THERMAL OVERLOAD PROTECTION

a. All contactor starter for motor shall be provided with ambient temperature compensated thermal overload relay, closely matching the thermal withstand characteristics of motor and affording full protection under all conditions of loading.

b. Relay shall either have a pair of 1NO + 1NC contact or a set of change over

contacts.

c. The relay shall be hand reset type.

d. Attention shall be paid to the selection of proper overload relay for motors driving high inertia equipment and having long starting time. Relay shall have calibrated dial for site adjustment as per full load current of motor.

e. Current transformers where used for feeding the thermal over load relays shall

be exclusive for this purpose.

f. The resetting of the relay subsequent to its operation shall be possible without opening the compartment doors.

g. The setting range of relay chosen shall preferably be 80% - 120% of full load

current of corresponding motor, to allow for adjustment at site.

h. Thermal overload relays shall provide built in single phasing protection upto a minimum of 50% of motor full load current, unless separate single phasing protection is asked for. SINGLE PHASING PREVENTER

a. Unidirectional motors, shall have separate means of protection against single

phasing and unbalanced voltage.

b. Single phasing protection shall be of current monitoring type based on the principle of negative phase sequence current detection.

c. The relay to achieve the protection shall be provided with either a set of change

over contacts or a pair of 1 NO + 1 NC contacts.

d. The relay shall be hand reset type.

e. The relay shall be stable under such transient conditions as may occur on the system.

f. The relay shall provide effective protection under all conditions of loading.

g. The relay shall be inoperative during starting conditions with heavy inrush of

each motor.

h. It shall be possible to reset the relay after its operation without opening the compartment door.

INSTRUMENTS AND METERS

a. Meters to be fixed in the switchboard shall be panel mounted, flush type and

suitable for rear terminal connection.

b. Meters and instruments shall be enclosed in dust proof; moisture resistant black finished cases and shall be suitable for tropical use. Instruments shall be suitable for operation from the secondary windings of CTs and VTs.

c. All instruments shall be calibrated to enable direct reading of primary quantities.

Instruments shall be adjusted and calibrated at manufacturer‟s works and shall have means of calibration, checking and zero adjustment at site.

d. All the divisions and the quantity to be measured shall be clearly marked.

Instruments shall conform to applicable standard and shall have class 2 accuracy having black numerals and lettering on white anti- parallax dial with knife-edge pointer. Indicating instruments may be of moving iron type or taut band.

e. Ammeter, voltmeter and wattmeter shall have scale range 150% of the rated

circuit value. In motor circuits, the ammeter shall have suppressed scale to indicate eight times full load current. The ammeter shall have accuracy clause 2.5 for the suppressed scale.

f. Instruments having metallic cases shall be fitted with earthing terminals

PROTECTIVE AND AUXILIARY RELAYS

a. For proper protection of equipment, relays shall be provided on the various circuits. Relays shall have dust-tight, moisture-proof enclosure and shall be flush mounted type. Relay case shall be painted with dull black or eggshell black enamel and with back connected terminals. Metal cases and frames of relay shall be earthed.

b. All protection relays shall be of withdrawable type with built-in testing facilities,

with provision for inspection, maintenance and replacement. Where built-in test facility is not provided for a particular relay, separate suitable test block shall be provided on the panel for this purpose.

c. Relays shall have silver to silver contacts with wiping action and shall be capable

of making and carrying maximum currents of the associated circuit. Relay contacts shall be capable of breaking such current unless provision is made for breaking such currents elsewhere in the circuit. Contact of the relay shall be capable of repeated operation without deterioration.

d. Relays, which are connected to complete either the tripping circuits of circuit

breaker or the operation, coil of the tripping relay shall be fitted with an externally operated hand reset type mechanical flag indicator. Each indicator shall be

provided with inscription to identify the nature of faults. Indicator shall be capable of being reset by hand without opening the relay case.

e. Relay performance shall not alter due to mechanical shock or vibration or

external magnetic field, which may be present at the place of mounting.

f. Marking for the colour of the phase on which the relay is to be used shall be provided on the front.

g. Protective relays which initiate tripping shall not have less than two independent

pairs of contacts.

h. Current coils of relays shall be rated for the secondary current of the associated CT.

i. D.C. relays used for tripping shall operate even when the supply voltage is

reduced to 50% of rated voltage.

j. To minimize the effect of electrolysis, D.C. operating coils shall be so connected in the circuit such that they are not connected to the positive pole of the battery supply except through contacts which are normally open.

k. The relay ranges and actual settings shall be properly coordinated to achieve

adequate discrimination between various electrical equipment in the distribution system and at the same time ensure adequate safety to equipment protected.

l. Generally, the over current and earth fault protection shall have inverse time characteristics m. Invariably, breaker controlled motor feeders shall be provided with

Instantaneous over current protection.

Thermal overload protection.

Instantaneous earth fault protection.

Negative phase-sequence and unbalanced protection.

Stalling protection.

All these may be available as a composite relay.

CURRENT TRANSFORMERS (CT)

a. CTs shall be air insulated having insulation class E or better, cast resin type and shall be capable to withstand the thermal and mechanical stresses resulting from maximum short circuit and momentary current rating of the switchgear.

b. CTs for air circuit breakers shall be mounted on the fixed portion of the

switchgear (except CTs for built in release system) and remote from the bus bar.

c. CT primary current shall be as near as possible to, but not less than the full load thermal rating of the associated circuit. CT secondary shall have either 1Amp or 5Amp rating and polarity shall be marked in a suitable manner. The ratings shall be adequate to cater for the burden of connected instruments and relays, lead resistance and VA burden of remote instruments.

d. Protection CTs shall have an accuracy limit factor greater or equal to 10 and

accuracy class of 5P.

e. Measuring CTs shall have accuracy class 1.0 and instrument security factor of not more than 5.

f. Unused CT terminals must be short circuited at the terminal block.

g. Separate cores of CT shall be used for protection and metering.

h. CTs shall be of bar primary/ wound primary type capable of carrying the rated

primary current. VOLTAGE, CONTROL & HEATING TRANSFORMERS

a. Voltage transformers (VT) and control transformers (for contactor operation)

shall be dry, cast resin type comprising of single-phase units. They shall have their primary windings protected by current limiting fuses with interrupting capacity corresponding to that of the switchgear.

b. VT and control transformers secondary windings shall be earthed at the switchgear through link, which can be removed for insulation testing. The earthing shall be in conformity with the schemes enclosed.

c. Transformers shall have secondary voltages as per Data Sheet A.

d. All Bus VTs for protection/ metering shall have voltage rating of

(Nominal System Voltage / 3) / (110 / 3)

so that secondary voltage shall be 110 volts phase to phase when the secondary winding is star connected. The accuracy class of protection/metering VTs shall be 1.0. VTs shall have an output rating adequate to cater to the burden connected to them.

e. Control transformers used for motor contactor operation shall have output rating

adequate for proper and satisfactory operation of all the contactors fitted to the switchboard at the maximum secondary transient current with the minimum voltages prevailing on the bus.

f. Separate control transformer shall be provided for individual motor starter unit if

indicated in.

g. Winding heating transformer shall be provided as per the requirements indicated in Data Sheet A, if motor winding heating is envisaged and the same is mentioned in Data Sheet A.

CONTROL AND SELECTOR SWITCHES

a. The rating and other features of the switches shall be suitable for the application for the control and selector switch. The number of position and the number of contacts or ways required for each switch shall be as indicated.

b. Control and selector switches shall be stay put or spring return to neutral type,

provided with properly designated escutcheon plates clearly marked to show operating position.

c. The switches shall be suitable for semi-flush mounting with the front plate and

operating handle projecting out. All connection to the switches shall be from the back.

d. Circuit breaker control switches shall be arranged to operate in an anti-clock

wise direction when tripping.

e. Ammeter selector switches shall have make before break contacts.

f. The arrangement for front mounting of these devices shall be such as to make them reasonably dust free so as not to interfere with normal operation.

ELECTRICAL CONTROL SYSTEM

For electrical system [OTHER THAN MOTOR FEEDERS] of main plant, two types of controls systems are envisaged:

- CRT Control System [DDCMIS based]

- Hardwired Control System [Electrical Control Board]

Motor control is part of Process Control.

1. CRT Control System [DDCMIS based]

Following controls are envisaged in this system:

(a) Closing of 11kV Breakers of outgoing transformer feeders & outgoing

feeders to other Switchboards from 11kV Unit & Station Switchboards [non

synchronising];

(b) Closing of all 415V Breakers of main plant & ESP [PCC O/G] [non

synchronising];

(c) Dead bus closing of all Breakers of 11kV Unit & Station Switchboards

[requiring synchronising];

(d) Dead bus closing of all Breakers of 3.3kV Unit Auxiliary Switchboards

[requiring synchronising];

(e) Dead bus closing of 415V Breakers of main plant & ESP [PCC & MCC I/C,

B/C];

(f) Tripping of GT EHV Breaker, 11kV Breakers of Unit & Station

Switchboards, 3.3kV Breakers of Unit Auxiliary Switchboards, 415V

Breakers of main plant & ESP [All PCC Breakers, MCC I/C, B/C];

(g) Trip Selection for planned changeover for 11kV Unit & Station

Switchboards, 3.3kV Unit Auxiliary Switchboards & 415V switchgear of

main plant & ESP;

(h) Exciter Field Breaker Close/Trip;

(i) Excitation System Channel selection;

(j) Excitation Lower/Raise Control;

(k) Excitation on/off;

(l) Emergency DG Start/Stop control;

(m) Emergency DG speed & voltage Lower/Raise control;

(n) UT OLTC Lower/Raise control;

(o) Station Transformer OLTC Lower/Raise control.

[Circuit Breaker Controls for Motor feeders are part of Process control system].

Synchronising is not envisaged from CRT control system.

In addition to above controls, facilities for status indication & mimic

diagrams of electrical system, alarm annunciations, metering of required

electrical parameters for generator & electrical distribution system are

also envisaged.

All interlocks for permissive closing, inter-tripping, synchronising, and

changeover functions are realized in DDCMIS. For permissive closing

conditions related to circuit breaker healthiness, hardwired contacts

available in Circuit Breaker are directly used.

Protection trip is effected directly from hardwired trip relay contacts.

2. Electrical Control Board [ECB]

ECB is a hardwired control board provided for each unit & the associated station

system. This board is located in UCR and envisaged for following functions:

(a) Mimic Diagram for Generator, 11kV Unit Switchboard, 11kV Station

Switchboard, 3.3kV Unit Auxiliary Switchboard, 415V Unit PCC, 415V Station

PCC & 415V Emergency switchboard;

(b) Metering for Generator circuit;

(c) Metering of important electrical parameters of 11kV Unit Switchboard, 11kV

station Switchboard, 3.3kV Unit Auxiliary Switchboard, 415V Unit PCC, 415V

Station PCC & 415V Emergency switchboard;

(d) Generator Excitation system metering, control & indication;

(e) Breaker off/on/auto trip indication for circuit breakers forming part of mimic;

(f) Emergency DG metering, start/stop, speed & voltage control;

(g) Manual with check synchronism facility for:

- GT EHV Breaker;

- 11kV Breakers of 11kV Unit & Station Switchboards and 3.3kV Unit

Auxiliary Switchboard requiring synchronising;

- 415V Breakers of Unit PCC, Station PCC & Emergency Switchboard

requiring synchronising.

The facilities include common check synchronising relay, synchronising

meters, synchroscope & indicating lamps. Synchronising selector & control

switches are also envisaged. All logic/interlocking for this purpose is built in

DDCMIS.

(h) Auto synchronising for Generator [Auto Synchroniser is part of ATRS];

(i) Dead bus closing of 11kV Unit & Station Switchboard Breakers, 3.3kV Unit

Auxiliary Switchboard, 415V Breakers of Unit PCC, Station PCC &

Emergency Switchboard [requiring synchronising];

(j) Closing of transformer outgoing & tie outgoing feeders from 11kV Unit &

Station Switchboards;

(k) Tripping of all breakers forming part of the mimic [for which

synchronising/closing facility is provided on ECB].

(l) Alarm Annunciation facia windows [for common alarms and troubles].

The operation philosophy for control of circuit breakers from ECB is given below:

i) The breaker to be controlled is selected by means of an illuminated push-

button.

ii) This activates common circuit breaker control switch, common synchronising

mode selector switch and common trip selector switch and associated LEDs

as applicable.

iii) The selected circuit breaker is controlled now through common circuit

breaker control switch.

iv) Resetting of Circuit breaker selector push button, common circuit breaker

control switch, common synchronising mode selector switch, common trip

selector switch and associated LEDs as applicable is done by means of a

common control reset push button.

Logic/interlocking to achieve above operations is suitably built in DDCMIS.

Theoretical explanation for Circuit Breakers controlled from DCS only This is a logical explanation for circuit breakers controlled from DCS. DCS is the abbreviated form for Distributed Control System. We have taken the case of control of outgoing feeders from 6.6 kv Unit Switchboard as shown in the diagram. The control diagram shows the (i) Closing of O/G FDR CB. (ii) Tripping of O/G FDR CB. With reference to the Simplified One Line Diagram and the table given along with Control Logic for O/G FDR :

1) I/C CB: 1CB011 and 1CB13.

2) B/C CB: 1CB012.

Condition for which O/G CB has to be closed:

i) When either of the I/C CB is closed(OR gate is used).

ii) The O/G CB itself is open.

iii) We give the instruction as CB CLOSE ( * ).

iv) The CB is chosen B<CB TAG>.

If all the above conditions are satisfied (as the instructions are sent through an AND gate) , then only a time pulse of 0.50 sec. is sent to the switch-gear to close the O/G CB. Condition for which O/G CB has to be tripped:

i) When the O/G CB is closed.

ii) When both of the I/C CB are open.

For the first condition, we give three instruction as shown in the logic control diagram : CB TRIP (*) as an insturtion to trip, B<CB TAG> to select, The state of the O/G CB(i.e closed). If the three clauses are satisfied, then it is passed through a current transformer. For the second condition, we take the following considerations as given in the logic control diagram : O/G CB is closed. Both the I/C CB are open. If the above clauses are satisfied, then it is passed through a potential transformer. If either of the above two conditions are satisfied( as passed through an OR gate), a pulse is sent from the DCS to the switch-gear to trip the O/G CB.

BATTERY, CHARGERS, DISTRIBUTION BOARDS AND STARTER PANELS

220V DC system is provided for unit and station DC loads like switchgear,

protection, emergency lighting, DC drives etc.

1. 220V DC Battery and Battery chargers

For each unit, the 220V system comprises of two sets of batteries with an

associated float-cum-boost charger for each battery.

220V batteries are sized to meet respective DC loads following an

emergency for a duty cycle of thirty (30) minutes. Each battery is rated to

cater for 100% loads. A 10% design margin is considered in battery

capacity. Suitable ageing factors and electrolyte temperature correction

factors are also considered.

In float mode, each battery charger is capable of meeting continuous

normal DC power requirement and trickle charging the connected battery.

For boost mode, the battery charger is sized to recharge the fully

discharged battery to its normal capacity in a period of about 10 hours. A

design margin of 10% is considered in selecting rating of the charger in the

respective modes.

The batteries are stationary, lead-acid type. The batteries are complete

with connectors & other accessories and supported on racks.

The chargers are of static type, comprising of silicon-controlled rectifiers

connected in three phase, full wave, full controlled bridge circuit. The

charger is provided with auto and manual voltage regulation. The charger

panels have a degree of protection of IP: 42.

Following protections are provided for the batteries and the battery chargers:

Fuse/MCCB for short circuit protection of battery.

Earth fault protection.

Current limiting, DC under voltage & over-voltage and AC

under voltage protection for charger.

2. 220V DC Distribution Board (DCDB)

A 220V DC Distribution Board is envisaged for feeding DC loads of each

unit and associated station equipment.

220V DCDB is indoor, metal enclosed, modular construction, fixed

execution, floor-mounted type. Two nos. feeders of adequate rating are

taken from battery/charger for the incomers of this board. The degree of

protection of these panels is IP: 52. Switchfuse units are considered for

outgoing and incoming feeders. Bus-sectionaliser is provided.

The general constructional features of 220V DCDB are similar to those

described under LV Switchgear, as applicable for distribution boards (DBs)

The diagram below shows the LT switchgear connections and

feeders for UNIT 5 BTPS.

Communication systems The audio communication systems in a thermal power station, play a very important role in coordinating power station, play a very important role in coordinating the activities of various departments and efficient operations, management control. Communication systems are of following type:-

Public Address System (PA). Public Automatic Branch Exchange (PABX) Rural Automatic Exchange (RAX). Radio Paging.

Public Address System

Every station has the facility for carrying out simultaneous communication in paging and private modes independently. On the paging mode, communication is heard over all the loudspeakers of all the stations and this is used to locate plant personnel and also to convey message of general nature. On the private mode, conservation is carried over the telephone handsets and this is used actual conservation, exchange of information and issue specific instruction. Public Automatic Exchange Provides intercommunication facility using telephone sets located at various locations of the power station. This system can also be hooked up to a nearby P&T exchange and any telephone connected to PABX can provide connection with any other phone belonging to the P&T exchange. Rural Automatic Exchange

This system cannot be connected with any P&T exchange. Accordingly, approval of post and telegraph department is not required in its installation and RAX works independently. Radio Paging System

Radio paging system is used in power stations for communication between persons apart within a range of appropriately 1 KM radius.

Generator control

1. The control, monitoring, measurement, annunciation, synchronising and

sequential event logging for each generator and its subsystem shall be provided

on the DCS.

2. Generator And Auxiliary Power Supply System Control &Monitoring

I. Provision in the plant control system shall be made for the starting, bringing

rated voltage and speed, initiation of synchronising, operation, annunciation and

monitoring, alarm, data logging, recording and sequential event recording for

generator and its excitation system from the DCS. The minimum requirements of

the measurements are indicated in the Main One Line diagram

II. One no. Of synchronising panel/trolley shall be provided through which the

synchronising of all the GCB &breakers in 220 kV switchyard can be

synchronised by plugging the control cable into socket provided on each Control

panel of the respective breaker. This synchronising trolley shall have all the

necessary equipments &meters for carrying out the manual synchronisation. The

Raise/Lower commands for carrying out the manual synchronisation. The

Raise/Lower commands for the same also be done through the trolley itself.

Apart from this the Auto synchronising facility shall be made available to auto

synchronise the above breakers through DCS.

III. The interlocks for the auxiliary power supply system shall be hard wired

interlocks.

3. Control and monitoring in DCS

I. Control, monitoring, measurement, annunciation, synchronising of complete

electrical system supplied under this contract shall be possible from plant DCS

system. In case of failure of any OS, it shall be possible to carry out the

necessary operation from one of the healthy OS. Synchronising, essential

controls, metering and annunciation shall also be available from the Respective

control panels for the lines.

4. DCS System

Minimum functional requirement of plant DCS systemin respect of electrical

system shall be as below:

a. Controls

Control of all the Incomers, bus ties of all the electrical switchboards except

outgoing fedres from main Lightning Distribution Board, DCDB &UPS DB,

shall be carried out from the DCS. It shall also have the facility to carry out

the live changeovers at all the switchboards at 6.6kV&400 V. Remote

position, service position, breaker health, permissive for interlock set shall

be considered as input to the DCS system.

Synchronising gear shall be housed in the respective switchboards.

All transformers with OLTC shall have provision for control viz. Issuing

raise/lower command to OLTC from plant DCS system

Control of generator excitation and governor system shall be possible from

plant DCS including mode selection and set point control for various

parameters viz. MW,MVAR&P.F. controls

Selector switch for the operation of equipment shall be at respective control

panel.

Initiation of auto synchroniser.

DG start, voltage Raise/Lower, speed Raise/Lower, DG breaker closing

shall be possible from DCS. Local/Remote and Auto/Manual selection will

be done at DG set control panel. Selector switch for the operation of

equipment shall be at respective control panel. All the necessary controls

required for synchronising the DG set &stopping of DG set after resumption

of Normal power shall be included in the DCS.

b. MONITORING

i. Indication-status of GCB, other breakers(ON, OFF, service, test) position of

Local/Remote selector switches, spring charged indication etc.,

ii. Abnormal conditions to be considered for alarm inputs to DCS are:

HV System (generator CB,6.6kV and 220kV breaker)

Operation of each of Generator protection, motor protection, TRIP

circuit unhealthy of each equipment, protection of unhealthy of each

equipment, VT circuit unhealthy of each of VT, signals generated in

Transformer MB about abnormal operating conditions of Transformer,

LBB operation of each breaker, DC supply failure of each

protection/control scheme as appropriate, Successful/Unsuccessful

changeover of 6.6kV supplies.GT and UAT condition shall be

monitored from DCS.

LV System (400)

Breaker auto trip, individual protective relay operation trip relay failure,

DC supply failure, bus under voltage, VT fuse failure, Trip circuit

unhealthy. Successful / Unsuccessful changeover of 400kV supplies.

Generator, Unit Auxiliary &Service Transformers

All alarm and trip conditions of generator transformers, unit auxiliary

transformers and service transformers. Monitoring of winding &of all

temperatures &pressure parameters related to Generator.

DC System

DC earth fault, DC under voltage, group faults in case of DC boards,

and normal operating parameters of the DC system etc.,

UPS System

All normal & abnormal conditions of UPS system in details

Battery Charger

Group trouble alarm for chargers with details as available from

equipment.

Excitation System and Generator

Each of protection relay and trip conditions, abnormal conditions in

excitation system and generator.

DG Set

DG operating parameters, alarm and trip conditions.

Alarm for the running hours of 30kW &above motors shall be

generated after achieving predefined set points.

Monitoring of the complete electrical system during the normal

operation.

Temperatures of all the>=100KW motors.

All the energy parameters of the lines, generator &auxiliary

consumption shall be taken from the ABT compliant energy meters

through communication

iii. Single line diagram showing Voltage, frequency, MW and MVAR flows,

breaker and isolator positions shall be available on DCS. More than one

frame can be used if all the details cannot be represented on single frame.

I. Event logging shall be provided for all manual operations and relay operations

as detailed below:

(a) Status of each breaker of all equipment being controlled, isolators and earth

switches.

(b) Close and open commands

(c) Selector switch positions.

(d) Each protective relay, trip relay, alarm relay operation. Event logging for each

phase shall be provided wherever applicable (e.g. 3-poles of line circuit breaker,

distance relay output contacts, generator protections, fuse fail alarm, etc.)

(e) Event logger shall be a part of the DCS with first up feature. It shall have a time

resolution of 1ms.

(f) Trip contacts of the complete electrical installation/equipments in the station viz.

Battery charger, UPS Generator, all transformer, electrical switchboards etc. Are

to be included.

II. Trending of parameters during disturbance shall be with resolution of 0.5/1.9

sec., and at 15 minutes during normal operation. The change from normal mode

to disturbance mode shall be through threshold/gradient settings provided in the

system for analog quantities and external binary signals obtained from selected

protective relays. Capturing of momentarily values of all these parameters shall

also be possible triggered either by a protective relay or by a manual keyboard

command.

5. Synchronising

Generator (Manual and through auto synchroniser).

Synchronising facility shall be provided for the generator through auto

synchroniser in auto mode and with the help of double voltmeter, double

frequency meter, and synchroscope and check synchronising relay permissive

condition in the manual mode.

6.6kV Incomer &tie circuit breakers shall have facility for fast and slow auto

changeover/manual synchronising and dead bus closing.

400V switch board /MCC incomer and bus coupler breakers shall have facility for

dead bus auto changeover/ manual live transfer.

Synchronizing facility with check feature has been provided for all 220KV breakers.

Whenever a breaker is proposed to be closed, its synchronizing switch should be

unlocked and synchronizing check relay by pass switch is in circuit position. It is

ensured that voltage and frequency of the incoming and running supplies are nearly

same, and the red „out of synchronism lamp is not continuously on. After the breaker

has been closed, its synchronizing switch should be returned to off position and

locked.

Synchronizing check relay SKE prevents closing of a breaker when incoming

and running supplies are out of synchronism. This relay has to be

bypassed when closing a breaker one side of, which is dead.

One (!) set of synchronising equipment consisting of double voltmeter, double

frequency meter, synchroscope, check synchronising relay, synchronising lamps,

synchroniser with lockable only in „Off‟ position, etc., shall be provided for each of

the following

Generator

Breaker associated with Emergency DG synchronising.

6. The functional requirement indicated above is minimum.

LINE FAULT DETECTORS

Y3

EARTH FAULT DETECTORS 64

ZONE

TIMING 2

EARTH FAULT REACTANCE UNITS X2

RANGE

EXTENSION 2X2X

DETECTOR AUXILIARIES

Y3X

7. The time critical controls and interlocks shall be hard wired system only

.

8. The control/selector switches and meters shall be of miniaturised.

9. Meter-ABT complain Tri-vector meters of accuracy class shall be 0.2s for lines,

UAT and generator metering.

10. Transducers

I. The contractor shall provided all the transducers for electrical system either in

respective switchgear/control panels. All the transducers shall be self-powered.

II. The transducers shall comply with the requirements specified for transducers in

electrical section.

11. Interposing Relays

I. The interposing relays required for the switchgear/equipment being supplied

under this contract shall be located in respective modules of switchgear/ relay

panels.

II. The coupling relays shall be rated for 0.5 Amp breaking at 220 V DC and 6 Amp

make and continuous current at 220 V Dc.

III. Interposing relays used for 220 kV circuit breaker closing shall be adequately

rated for the making current.

HIGH SPEED PROTECTION THROUGH THE SUE 3000 HIGH

TRANSFER DEVICE

General

Voltage decreases or complete supply interruptions represent the most

important and critical problems for the quality of energy supply today.

It is especially true that voltage disturbances with electronic control systems

and other sensitive installations can lead to complete loss of production and

long stoppage time.

The SUE 3000 High Speed Transfer Device guarantees an optimum

safeguarding of energy supply.

The device ensures the continued supply to the consumer through

automatic transferring to a stand by feeder and protects the subsidiary

process from expensive stoppage time.

Furthermore, through the possibility of manually-initiated transfers- for

targeted clearings, for example- the operation of the installation is

considerably simplified.

The SUE 3000 High Speed Transfer Device can be implemented

everywhere where a disturbance of the electrical supply would lead to a

breakdown in production, which would lead as a result to costs.

Auxiliary installations serving power stations, as for example

Steam power stations

Gas turbine power stations

Combined cycle power stations

Nuclear power stations

Environmental technology installations

Flue gas purification

Refuse incineration installations

Voltage supply to continuous industrial processes

Chemical plants

Industrial facilities with high degrees of automation

Fiber manufacturing

Petrochemical processes

In order to realize a permanent availability, the load is supplied

from at least two synchronized feeders which are independent from one another

and which are supplied with High Speed Transfer Devices.

In doing so, the High Speed Transfer Device has the task of ensuring

uninterrupted continues operation of the connected devices in case of a

power supply break down, taking into account different physical factors,

through the most rapid possible transfer to a different feeder kept stand-by.

Corresponding, to its multifaceted areas o f application,

The SUE 3000 is set up for different switchgear arrangement.

Switchgear configuration with two

circuit breakers

i. This arrangement is often used in auxiliary installations serving thermal power

plant stations.

ii. One of the two power supplies normally feeds the bus bar.

iii. One of the two is switched on, the other is switched off.

iv. A coupled operation of both power supplies is not intended, and due to

reasons of rating (short circuit withstand), it is often also not permissible.

v. If an error leads to a disturbance of the feeder currently in operation, the

transfer device switches the load over to the second feeder in the shortest

possible time.

vi. Following successful transfer, the bus bar is then supplied further by the

second feeder.

vii. Once the main feeder is again in operation, a manually initiated transfer back

can take place and the normal status can be restored once again.

viii. The high speed transfer device SUE 3000 is designed completely symmetrical,

so that a protection-initiated transfer can be executed from either of the

feeders, in case for example two feeders with equal status are present.

ARRANGEMENT WITH TWO FEEDERS AND ONE

BUSBAR COUPLING

i. With this configuration, the load is divided between two bus bar sections due to

reasons of redundancy.

ii. The coupling circuit-breaker usually remains open.

iii. Both feeders are in operation.

iv. In case of disturbance of one feeder, these follow a transfer from the circuit

breaker of the disturbed feeder to the coupling circuit breaker.

v. The circuit breaker which had previously been the feeder is opened and the

bus bar coupling is closed.

vi. After that, both bus bar sections are supplied by one feeder.

vii. Once the disturbed is again available, a manually-initiated transfer back can be

executed in order to restore normal status once again.

Prerequisites for the optimum utilization of the Sue 3000

In order to ensure optimal utilization of the SUE 3000, the following prerequisites should be fulfilled:

Existence of at least two synchronous feeders, which are independent of one another during normal operation. Circuit breaker with short operating time

Switchgear assembly/ load suitable for network transfers

Fast protective relays for initiation of the High Speed Transfer Device In case of disturbance leading to the breakdown of the distribution voltage, an

interruption is avoided through the automatic intervention of the High Speed

Transfer Device.

Transfers can continue to be manually triggered, depending on operation.

The enhancement of the installation availability leads to considerable cost savings

and to a short- term amortization of the investment.

Even just one single successful transfer, who ensures the continued operation of an

installation, prevents stoppage time and saves on expensive re-initialization

processes, can mean a complete amortization of the investment costs for the High

Speed Transfer Device.

Mode of operation

A significant task of the SUE 3000 is to ensure that when there is an initiation, a

minimum short transient time is achieved, the transient effects of which represent

no danger to the connected users during the transfer.

For this purpose, the SUE 3000 is equipped with a fast processing logic as well

as a high- precision analogue signal processing.

The device compares, on a permanent basis, the voltage of the busbar with the

voltage of the stand-by feeder. The following synchronicity criteria are generated

from out of the monitoring of the voltage amplitudes as well as the difference of

the frequency and of the phase angle:

Ø < Ømax Phase Angle

The phase angle is determined between the voltage of the bus-bar and that of the

stand-by feeder. The limit values for building the synchronicity criteria can be adjusted

individually for leading and aging busbars. A typical setting value is 200.

∆f < ∆fmax frequency difference The system determines the frequency difference between bus bar voltage and the voltage of the stand-by feeder. In view of the transfer process, the frequency difference provided permits indications of the running down behavior of the connected consumers (e.g. of medium- voltage motors) as well as their dynamic loads. The usual factory setting is 1HZ

U

Stand-by > U

Min1 stand-by feeder voltage

The monitoring of the voltage level of the stand-by feeder is an important criterion relevant the transfer: The SUE 3000 is only then ready for transfer when an intact stand-by feeder is available. UMin1 is set at the factory to 80% UNominal

UBusbar

> UMin2

Busbar voltage The value of the bus bar voltage plays an important role in the selection of the transfer mode: In case the bus bar lies below a present value (U –usually set to 70% UNominal ), no fast transfer is carried out.

Permanent determination of the network conditions An exceptionally important characteristics of the SUE 3000 High Speed Transfer Device is that the synchronicity criteria named are continuously available, e.g. that they are computed on-line by the SUE 3000. For that reason, in case of an initiation, the transfer mode which comes under consideration is already determined and can be immediately initiated. This means that the probability of a fast transfer is considerably enhanced. Systems which wait for the instant of initiation to initiate the determination of the network status have no opportunity, when one considers the physical givens, to perform a fast transfer with minimum interruption time.

This fact clearly distinguishes the high speed transfer device sue 300 from competing concepts. The high speed transfer device is ready for operation only when both circuit breakers to be actuated are definitely to be found in different switching statuses (plausibility monitoring) and also in operating position. Transfer modes

Decisive for the kind of transfer carried out are the network relationships in the instant of initiation of the High Speed Transfer Device. Here the corresponding optimum transfer mode is selected, taking the physical interrelationships into consideration. Four different transfer modes are available in detail:

Fast Transfer

Transfer at the 1st phase coincidence

Residual voltage transfer Time –operated transfer The fast transfer is the optimum transfer mode for ensuring in case of fault that only a minimum interruption of the voltage supply occurs. Should it be that the network status does not permit this mode, and then less rapid transfer modes are selected. Figure5.1 shows the typical decay characteristics (voltage and frequency) of a disconnected bus bar and the possible closing moments.

The transfer modes are explained in brief below:

Fast Transfer

The execution of fast transfers is the most preferred and most important

functional principle of the SUE 3000

A fast transfer takes place when the both the main and the stand-by feeder are

within specified limit values at the moment of initiation, e.g. that slip and phase

angle are limited between the networks and the stand-by voltage lies above a

minimum value.

Here the open and close commands to the circuit breaker from the High Speed

Transfer Device are issued as a rule synchronously.

The current-free transfer time occurring in this case for the users is exclusively

dependent upon the difference between the operating time for closing and

opening the circuit concerned.

Because these usually fall within the range of a few milliseconds with modern

circuit breakers, one can assume an uninterrupted further operation of the

installation.

An exemplary oscillogram of a fast transfer with a current transfer time (dead

time) of appropriately 20 ms.

1. Bus bar voltage 2. Current feeder 1 3. Current feeder2 4. Trip time 5. Dead time

Note Fast transfer condition/synch. Condition

Line Voltage > Set Value (min 85%) & Max 110%

Bus Voltage > Set Value (Min 80%)

Phase Angle diff. Between Unit Bus 1CA & 1CB volt.<Set Value (Max

20o)

Phase Diff. Between Unit I/C -1 & 1CA Volt. <Set Value

(Min 200) Slow transfer condition

Fast Transfer Has Failed

Bus Voltage <Set Value (Max 20%)

I/C -1 & B/C OFF For B/C Close, B/C OFF For I/C-1 Close.

Under Normal Working Condition I/C-1 and I/C-2 ON And B/C Off.

Similar Logic Shall Be Applicable For I/C-2 Also.

Transfer at the 1st phase coincidence The transfer at the 1st phase is executed when there are no synchronized

conditions present at the moment of initiation, so that no fast transfer can be

carried out, due to physical reasons.

First, the previous feeder will be opened without delay.

Afterwards, the connected users are without power supply and run down in

accordance with their specific characteristics curves.

For the connection of the stand-by feeder, a variety of points in time are possible

at which an adherence to physical limit values is ensured.

For the transfer at the 1st phase coincidence, the open command is issued

immediately and the connection of the stand-by network takes place in the first

minimum of the difference of stand-by and bus bar voltage (UStand-by –UBusbar)

Connection window (dependent upon breaker closing

time and d /dt)

UStand-by Stand-by feeder voltage UBusbar Busbar voltage

Angle between UStand-by and UBusbar

d /dt Angle speed between UStand-by and UBusbar (resulting from ∆f) The High Speed Transfer Device determines the course of the difference voltage

and the point in time of the 1st phase coincidence through anticipatory

computation.

In order to compensate for the installation-specific processing time (system

response time, circuit breaker operating time), the close command is issued

accordingly before the actual first minimum of the difference voltage occurs

within a previously- defined connection window.

The conditions prevailing with a transfer at the 1st phase coincidence are

presented in the vector diagram.

The busbar voltage vector in the first minimum of the difference voltage has

moved around against the fixed stand-by voltage and the angle has become

zero.

The difference voltage resulting at the moment of transfer is thereby exclusively

determined by the residual voltage value of the bus bar.

The synchronized connection makes possible a transfer time which is

exceptionally protective of the process while still being at the same time of

minimum duration.

Summary

A very important characteristic of the SUE 3000 high speed transfer Device is that the selection of the transfer mode carried out takes place dynamically in connection with respective current network relationships.

If one starts from the premises of networks which are usually synchronized, then fast transfers as a general rule will be carried out.

The principle they, embody of the simultaneous issuing of commands makes it possible to have short transfer time with nearly uninterrupted continued supply of the switch-over process.

In cases of mechanical failure in the circuit breaker to be switched off, a short-term coupling occurs between the two (synchronized) feeders, which is however detected by the SUE 3000 and automatically cancelled again, in order to avoid a impermissible coupling of the networks

If the networks are not synchronized at the point of time of the initiation,

then no fast transfer takes place. The current-free interlude time that then arise are different, depending on the installation involved, whereby the load to be switched over determines the run-down behavior of the bus-bar voltage and with it the transfer duration.

The various transfer types can be selectively activated or deactivated, in a

way dependent on the orientation. Thus it is ensured that, in accordance with the special requirements, the optimum transfer concept can be released for the overall installation.

COMPARISION AMONG VARIOUS PROJECTS

SNO. PROJECT NAME

PIPAVAV,GUJARAT (292)

HAZIRA,GUJARAT (293)

PRAGATI-III,DELHI (314)

OTPC,TRIPURA (319)

1 RATING 2*350MW 350MW 1500MW 726.6MW

2 NO of Modules

2 1 2 2

3 GENERATROR

(i) GTG 232MW at 50 degree C ,15.75kV ,pf=0.85

321.9MW at 50 degree C ,15.75kV, pf=0.85

2*186.7MW at 50 degree C, 16.5kV , pf=0.85

242.6MW at 40 degree C , 15.75kV,pf=.85

No.OF GTG'S 1 per module 1 per module 2 per module 1 per module

(ii) STG 129.5MW at 50 degree C ,15.75kV, pf=0.85

129.5MW at 50 degree C, 15.75kV, pf=0.85

239.8MW at 50 degree C, 16.5kV,pf=0.85

124.6MW at 40 degree C, 15.75kV,pf=0.85

No.OF STG'S 1 per module 1 per module 1 per module 1 per module

4 GENERATOR TRANSFOMER

(i) GTG-GT 273MVA at 50 degree C , 230/15.75kV

163/218/273MVA at 50 degree C ,420/16.75kV

220.6MVA at 50 degree C , 420/16.5kV

242.6MVA at 40 degree C , 420/15.75kV

(ii) STG-GT 153MVA at 50 degree C, 230/15.75kV

-------- 292.4MVA at 50 degree C , 420/16.5kV

146.9MVA at 40 degree C , 420/15.75kV

5 UAT 40/20MVA , 5.75kV/6.9kV

12.8/16MVA , 15.75/6.9kV

-------- 16MVA , 15.75/6.9kV

6 SAT ---------- --------- 3.15MVA,16.5/6.9kV ----------

7 ST --------- --------- -------- 25MVA , 132/6.9kV

8 NGT 50kVA , 15.75/.24kV

50kVA , 15.75/0.24 kV

75kVA , 16.5/0.24 Kv

50kVA , 15.75/.24 kV

9 EMERGENCY DIESEL GENERATOR

2.5MW , 6.6kV,3W, pf=0.8

625kVA , 415V , pf=0.85

1250kVA , 415kV 625kVA , 415V

No. Of DIESEL GENERATOR

2 1 3 2

10 GCB SCHEME REQUIRED

YES YES YES NO