SWITCHYARD EQUIPMENTS, SWITCHING SCHMES & LAYOUTS

EHV SWITCHYARD EQUIPMENTS, SWITCHING

SCHMES & LAYOUTS

Switchyard Type

Conventional Air Insulated Type. Gas Insulated type. Outdoor Gas Insulated type.

Selection of Bus Switching Scheme

PRE-REQUISITES

1)System security2)Operational flexibility3)Simplicity of protection arrangements4)Ability to limit short circuit levels (ease

of sectionalizing)5)Maintenance – Its effect on system security 6)Ease of extension7)Total land area8)cost

DESIGN GUIDELINES CONTD…

OPTIONS/ALTERNATIVES

1)Single sectionalised bus2)Main and transfer bus3)Sectionalised Main bus with transfer bus4)Sectionalised double main and transfer bus5)Double Bus Scheme6)Ring bus7)One and a half breaker8)Double bus, double breaker

CONTD…

DESIGN PRACTICES/PHYLOSOPHY

1) Consideration in Selection of Bus Switching Scheme

2) Comparison of Schemes a) Sectionalized main bus with transfer bus

(Scheme-I)

b) Sectionalized double main and transfer bus (Scheme-II)

c) One and a half breaker (Scheme- III)

DISCUSSIONS OF SCHEMES

SCHEME 1

Main and Transfer Bus Scheme

SCHEMES CONTD…

SCHEME 2

Sectionalised Double Main and Transfer Bus Scheme

SCHEMES CONTD…

SCHEME 3

One and Half Breaker Bus Scheme

System Security (Reliability

i) feeder fault

ii) Bus fault

iii) Redundancy in design

Main & Transfer

i) require operation of one breakerii) supply would be interrupted until all the feeders are transferred to the healthy busiii) No alternate path (Offline redundancy available)

Double Main & Transfer

i) require operation of

one breaker

ii) supply would be interrupted until all the feeders are transferred to the healthy busiii) No alternate path (Offline redundancy available)

One & Half Breaker

i)require operation of two breakersii) continuity of supply is maintained because each circuit gets fed through two pathsiii) Alternate path is available(Online redundancy available)

Operational Flexibility:

Simplicity of Protection Arrangements

Ability to limit Short Circuit Levels (Ease of Sectionalizing)

Switching operation to take out the breaker from the bay more extensive

Protection arrangement involves AC & DC switching .

Sectionalising of bus bars or introduction of reactors in buses with a view to limit short circuit level is adoptable.

Switching operation to take out the breaker from the bay more extensive

Protection arrangement involves AC & DC switching & bus differential protection is complicated as it involves CT switching.


A breaker can be taken out of service without the need for additional switching

Protection arrangement is simplified as no AC & DC switching involve and Bus differential protection is simple.


Ease of extension

Total land area

Cost

Switchyard shall be suitable for future extension without loss of feeders. This scheme is flexible for such future additions

This scheme occupy more or less the same land area as of the other two schemes.

one breaker per feeder is required



one breaker per feeder is required



Three breaker per 2 feeder is required

Switchyard layout

Objective: Substation layout consists essentially in

arranging a number of switchgear components in an orderly pattern governed by their function and rules of spatial separation as described in electrical single line diagram.

Pre-requisites: 1) single line diagram 2) general layout plan of power plant 3) orientation of line evacuation 4) control room building

LAYOUT CONTD…

Options / Alternatives The layout will vary for the

following:1) Switching schemes 2) Type of insulation - Air

Insulated/Gas Insulated.

LAYOUT CONTD…

Design Philosophy / Practice

1) Space around the switchyard 2) Switchyard location 3) Switchyard fencing.

4) Clearance. i) phase to earth clearance

ii) phase to phase clearance iii) section clearance iv) ground clearance

TABLE I: INSULATION LEVELS & CLEARANCE REQUIREMENTS AT DIFFERENT VOLTAGE LEVELS

NOMINAL SYSTEM VOLTAGEKV

INSULATION LEVELS HIGHEST SYSTEM VOLTAGE KV

MINIMUM CLEARANCE GROUND CLEARANCE(MM)

SECTIONAL CLEARANCE (MM)

HEIGHT OF SUPPORTS (mm)LIGHTNING

IMPULSE LEVEL(kVp)

SWITCHING SURGE LEVEL(kVp)

POWER FREQUENCY IMPULSE LEVEL(kVrms)

BETWEEN PHASE AND EARTH(MM)

BETWEEN PHASES(MM)

3366

132220400765

170325650

105014252100

----

10501550

70140275460630830

3672.5145245420800

320630

1300210035006400

320630

1300210040009400

37004000460055008000

--

28003000350043006500

10300

250025002500250025002500

Clearance contd…

5) Equipment spacinga) Ease of maintenance/removal of

equipment.b) Equipment foundation & their

cable trenches. c) Distance between LA and

equipment based on the protection reach of LA.

d) The spacings are generally kept in order to achieve various

clearances specified at Table-I.

Clearance contd…

6) Bus bars: The bus bars of 400 kV switchyard are generally made up 4 “IPS

aluminum tube or Quad Moose rated for 3000 A”. The bus bars of 220/132kV switchyard are generally made up of 3

“IPS aluminum tube or quad/ twin moose conductor”. Bus bars are placed at right angles to the feeders for tapping the power.

7) Equipment Interconnection

8) Spacer spans and locations

9) Connection Level

10) Land & Road Layout

11) Sequence and mounting of line traps

Clearance contd….

12) Control Room Layout

13) Lighting System

14) Cabling Philosophy

15) Gravel Filling

16) Earthing System

17) Lightning Protection System

EVOLVING A SUBSTATION LAYOUT

LAYING OUT A SUBSTATION INVOLVES STEP-BY-STEP PROCEDURE. MOST IMPORTANT POINTS TO BE CONSIDERED ARE BRIEFLY DESCRIBED BELOW:

THE IMPORTANT ELECTRICAL PARAMETERS ARE ESTABLISHED BY THE SYSTEM DESIGN. THE MAIN PARAMETERS ARE:

1) THE VOLTAGE AND BASIC INSULATION LEVEL OR SWITCHING SURGE LEVEL., THE SITE AND

CLIMATIC CONDITIONS, THE METHOD OF CIRCUIT CONNECTION, AND SWITCHING OVER-VOLTAGE CONDITIONS.

2) THE BUS BAR SYSTEM DIAGRAM, THE NUMBER OF CIRCUITS AND THEIR PURPOSE I.E. THE CONTROL OF GENERATORS, TRANSFORMERS, FEEDERS, ETC.

THE DIAGRAM SHOULD INCLUDE DETAILS OF EXTENSIONS AND FUTURE CONVERSION TO A DIFFERENT BUS BAR SYSTEM, IF INTENDED.


1) THE CONTINUOUS CURRENT RATING OF THE BUS BARS AND CIRCUITS.

2) THE SHORT CIRCUIT RATING OF BUS BARS AND EQUIPMENTS.

3) PARTICULARS OF REACTORS, NEUTRAL EARTHING EQUIPMENT AND REACTING, Interconnecting Transformers REQUIRED.

4) METHOD OF CONNECTION OF CIRCUITS, WHETHER BY OVERHEAD LINES OR BY CABLES.

5) DETAILS OF LIGHTNING PROTECTION EQUIPMENT.

6) DETAILS OF PROTECTIVE EQUIPMENT, DETERMINING THE INSTRUMENT TRANSFORMERS REQUIREMENTS, CARRIER CURRENT EQUIPMENT ETC.


THE EXTENT TO WHICH CIRCUIT AND BUSBAR OUTAGES FOR MAINTENANCE WILL BE POSSIBLE.

SOME PARAMETERS WHICH INFLUENCE THE FORM OF THE LAYOUT ARE DETERMINED BY THE LOCAL CONDITIONS. THESE ARE:

1) THE AVAILABLE LAND AREA, SITE AND CLIMATE CONDITIONS, PLANNING AUTHORITY REQUIREMENTS AND AESTHETIC CONSIDERATIONS DETERMINE THE TYPE OF SUBSTATION.

2) THE DIRECTION OF OVERHEAD LINE ENTIRES POSITION AVAILABLE FOR TERMINAL TOWERS, LOCATION OF TRANSFORMERS AND REACTORS, ETC.

3) THE AVAILABILITY OF MATERIALS AND THE TRANSPORT AND ACCESS FACILITIES.

4) THE CAPABILITY AND SKILL OF THE MAINTENANCE STAFF DETERMINES THE IMPORTANCE OF CLARITY OF LAYOUT AND SIMPLICITY OF MAINTENANCE ZONING.

PREPARATION OF BASIC LAYOUT

WHILE MEETING ALL THE NEEDS ESTABLISHED THE FOLLOWING IDEALS SHOULD BE AIMED AT IN MAKING THE BASIC CIRCUIT LAYOUT.

MINIMUM GROUND AREA

MINIMUM QUANTITIES OF CONDUCTOR, JOINTS AND STRUCTURE

MINIMUM NUMBER OF INDEPENDENT INSULATORS, ESPECIALLY IN THE BUS BAR ZONE.

AFTER HAVING DETERMINED THE ELECTRICAL CLEARANCE BE USED A ROUGH CIRCUIT LAYOUT IS MADE. SEVERAL POSSIBLE ALTERNATIVES ARE PREPARED FROM WHICH THE MOST SUITABLE ONE WILL BE SELECTED. SOME VARIATION IS NEEDED, TO MEET THE REQUIREMENTS OF DIFFERENT TYPES OF CIRCUIT.

IT IS ALSO NECESSARY TO CALCULATE SHORT CIRCUIT AND ATMOSPHERIC FORCES TO DETERMINE THE STRESSES IN CONDUCTORS, INSULATORS AND STRUCTURES. THESE HELD IN DECIDING THE MOST OPTIMUM DIMENSIONS.

PURPOSE OF EARTHING

THE OBJECT OF EARTHING IS TO MAINTAIN A LOW POTENTIAL ON ANY OBJECT.

THE PURPOSE OF A EARTHING SYSTEM IN A SUBSTATION AREA IS TO LIMIT THE POTENTIAL GRADIENT WITHIN AND IMMEDIATELY OUTSIDE THE AREA IS A VALUE, SAFE FOR THE WORKING PERSONNEL. SAFETY IS TO BE ENSURED UNDER NORMAL AS WELL AS ABNORMAL OPERATING CONDITION.

REQUIREMENTS OF A GOOD EARTHING SYSTEM

FOLLOWING BASIC REQUIREMENTS ARE TO BE SATISFIED SO AS TO ENSURE A PROPER AND SOUND EARTHING SYSTEM.

1) THE EARTH RESISTANCE FOR THE SWITCHYARD AREA SHOULD BE LOWER THAN A CERTAIN LIMITING VALUE “RA” IN ORDER TO ENSURE THAT A SAFE POTENTIAL GRADIENT IS MAINTAINED IN THE SWITCHYARD AREA AND PROTECTIVE RELAY EQUIPMENT OPERATE SATISFACTORILY. FOR MAJOR SWITCHYARDS AND SUBSTATIONS IN INDIA, THIS LIMITING VALUE OF EARTH RESISTANCE (RA) IS TAKEN TO BE LESS THAN 0.5 OHM.

2) THE GROUNDING CONDUCTOR MATERIAL SHOULD BE CAPABLE OF CARRYING THE MAXIMUM EARTH FAULT CURRENT WITHOUT-OVERHEATING AND MECHANICAL DAMAGE. THE MAXIMUM FAULT LEVEL IN THE 400 KV SYSTEM HAS BEEN ESTIMATED TO BE 40 KA AND THIS VALUE OF FAULT CURRENT TO USED IS THE DESIGN OF EARTH MAT FOR THE 400 KV SUBSTATION.

REQUIREMENTS OF A GOOD EARTHING SYSTEM

ALL METALLIC OBJECTS WHICH DO NOT CARRY CURRENT AND INSTALLED THE SUBSTATION SUCH AS STRUCTURES, PARTS OF ELECTRICAL EQUIPMENTS, FENCES, ARMOURING AND SHEATHS OF THE LOW VOLTAGE POWER AND CONTROL CABLES SHOULD BE CONNECTED TO THE EARTHING ELECTRODE SYSTEM.

. THE DESIGN OF THE GROUND CONDUCTOR SHOULD

TAKE CARE OF THE EFFECT OF CORROSION FOR THE TOTAL LIFE SPAN OF THE PLANT.

Switchyard Equipments.

Circuit Breaker. Disconnectors (Isolators) Current Transformers. Capacitor Voltage Transformers

(CVT). Lightning Arrestors. Post Insulators. Wave Traps

General Parameters

Dielectric Parameters .(IEC 694)- Power Frequency Voltage.- Lightning Impulse Voltage.- Switching Impulse Voltage.- Corona Extinction Voltage.- RIV Level.

General Parameters (Contd.)

Rated Current. Short Time Current. Creepage Distance.

400kV Equipmentsa. Rated voltage 420 kV b. Rated frequency 50 Hz c. Rated short time withstand

current capacity 40 kA rms for one (1) second

d. Insulation levels for 420kV Circuit breakers and Disconnecting Switches

e. i) Rated one minute power Frequency withstand voltage

a) 520 kV rms between live terminals and earth.

b) 610 kV rms across isolating distance.

ii) Rated lightning impulse withstand voltage

a) +/- 1425 kVp between live terminals and earth.

b) +/- 1425 kVp impulse on one terminal and 240 kVp power frequency of opposite polarity on other terminal (across isolating distance).

iii) Rated switching impulse withstand voltage

a) +/- 1050 kVp between live terminals and earth.

b) +/- 900 kVp impulse on one terminal and 345 kVp power frequency of opposite polarity on other terminal (across isolating distance).

f. Max. Radio interference voltage at 266kVrms

1000 micro volts for frequency between 0.5 Mhz and 2.0 Mhz for all equipment. However, for insulator strings the measurement would be at 305 kV .

g. Corona extinction voltage Not less than 320 kV rms

Circuit Breakers Type (IEC: 62271-100)

MOCB. ABCB. SF6

Rated operating duty cycle- O-0.3 sec-CO-3 min.-CO

Operating mechanism Total Break Time Pre Insertion Resistor –( 300-450Ώ)

Disconnectors

HCB Type. Double Break Type. Pantograph type. Vertical Break type. Provision of Earth Switches. Motor / manual operated. Gang operated/Single pole type.

Current Transformer ( IEC 60044, IS 2705)

Dead tank/Live tank type. Bar Primary type. Ring Type. No. of Cores. Ratio. Accuracy. rated primary current Rated burden for metering Knee Point voltage

Capacitor Voltage Transformer (IEC 60044, IS 3156)

Capacitance. Voltage Ratio. No. Of Cores. Accuracy. Output Burden Rated Secondary Voltage

Lightning Arrestor ( IEC 60099)

Gap Type / Gapless Type. Voltage Rating. Energy Capability. Monitoring. Location. Nominal Discharge Current.

Post Insulators

Voltage Rating. Cantilever Strength. Fixing Details.

Wave Trap (IEC 60353)

Rated Inductance(0.5/1.0 mH). Rated current. Band Width. Coupling (Phase to Phase).

SWITCHYARD AUXILIARY SYSTEMS

CONTROL ROOM HVAC FOR CONTROL ROOM A RELIABLE 415V AC SUPPLY ( LT SWGR) 220 V & 48 V DC SUPPLY( BATTERY &

BATTERY CHARGER) POWER & CONTROL CABLE LIGHTING ( Yard lighting & indoor lighting of

control room) Other items-Clamps, connectors , Insulator strings ,

BMK etc.

192

69 ~10%400kV GIS

275kV GIS

Trfr 1 Trfr 2 Trfr 3 Trfr 4 SVC Trfrs

400kV AIS

275kV AIS

COMPARASON BETWEEN AIS AND GIS SUBSTATIONFOOTPRINT FOR HECTOR

INDOOR GIS

OUTDOOR GIS - SEISMIC AREAS

ConductorPhase Spacing

PHASE SPACING

OVERHEAD STRUNG BUSBARS

9,81.mi

fs

SAG DUE TO CONDUCTOR

fs = 9,81.mi.Lc2 8.T

fs = maximum conductor sag (m)

mi = mass of conductor (kg/m)

Lc = conductor span length (m) T = tension per conductor (N)

T

Lc

LOW PROFILE SUPPORTED TUBULAR BUSBAR SUBSTATIONS

TUBE SAG EXCESSIVE INCORRECTLY SELECTED

TYPICAL TUBULAR BB BUS SECTION BAY

MMM

Attraction Repulsion

CANTILEVER FORCES DUE TO FAULT CURRENTCOMBINATION SUPPORT STRUCTURE FOR 3 PHASES

F S

TUBE

TUBULAR BUSBAR EXPANSION CLAMP

TRANSFORMER FIRE AT MINERVA

Upgradation of transmission voltage from 400kV AC to 765kV AC.

Presently the highest AC Transmission voltage is 400kV only. NTPC is fully geared up for implementing next AC voltage of 765kV.

Advantages: Step up from generation voltage to 765kV. High Capacity Transmission to the order of 2500MW per line

with lower right of way requirement. 765kV Transmission system is techno economically better

option whenever power transmission system requires multi point tapping at various location for catering the load requirement of high growth area.

765kV system offers low transmission losses, resulting in higher utilisation of generating capacity and optimises the resource required for capacity addition.

765kV Major Parameters

Highest system voltage : 800 kV rms Lightning Impulse voltage : 2100 kVp

Switching impulse voltage : 1550 kVp Power frequency withstand : 830kV(rms) for 1 min. (rms) : Max. fault level (1 sec.) : 40 kA Minimum creepage distance : 20000 mm Max. Radio Interference Voltage : 2500 micro volts. level at 508kV (rms). Corona extinction voltage : 508kV (rms minimum) Phase to earth clearance : 4900 mm Conductor to

Structure : 6400 mm Rod to

Structure Phase to phase clearance : 7600 mm Conductor to

Conductor : 9400 mm Rod to Conductor Section clearance : 10300 mm Average electric field at 1.8 m from ground 10kV/m Average magnetic field 500 micro tesla

((((

ADOPTION OF CONTROLLED SWITCHING OF TRANSFORMER AND REACTORS.

Switching of transformer, shunt reactors, capacitors and uncharged overhead lines is normally a 'three-phase' process, where all three phases are switched simultaneously. The actual circuit closing or opening instant is left up to chance. This results in high inrush currents or switching surges causing undue repercussions to switchgear equipment and networks system. For overcoming this the switching in and out is done at desired point on wave so that the overvoltages are reduced.

765KV CIRCUIT BREAKER

765KV DISCONNECTOR WITH 1E/S

THANK YOU!

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SWITCHYARD EQUIPMENTS, SWITCHING SCHMES & LAYOUTS