Chapter 7

THUNAG MINI HYDRO PROJECT 400KW

1

Developer:- Tek Singh Rathore

CHAPTER-VII

ELECTRICAL & MECHANICAL

DESIGN M

General

Thunag MHEP utilizes the flow of Debla nallah tributary of Beas river and is located in

Distt-Mandi of Himachal Pradesh. A net head of 118.56m has been utilized which generates

400 KW of power at surface power house.

The salient features of Thunag MHEP are as under:-

* Net head : 118.56 m

* Installed Capacity : 400 KW

* Number and size of units: : 400KW ( one unit)

* Type of power house : Surface

* Design discharge of plant : 0.40 cumecs

* Turbine type : Horizontal Francis

* Speed of turbine : 500rpm

* Generation voltage : 0.415KV

* Transmission voltage : 11KV

* Step-Up Transformer : 600KVA

7.1 POWER HOUSE

In a Mini hydropower scheme the role of the powerhouse is to protect the electromechanical

equipment that convert the potential energy of water into electricity. The number, type and

power of the turbo-generators, their configuration, the scheme head and the geomorphology

of the site determine the shape and size of the building.


2


In Thunag MHEP, the surface of power house will have a generating unit of 400KW along

with all auxiliary facilities such as cooling water/potable water supply system, fire protection

system, compressed air supply, oil system, ventilation and air conditioning system etc.

The control room, LT room, battery room, offices, cable spreading area will be

accommodated in different floors adjacent and parallel to the machine hall, the service bay

shall be located at one end of the machine hall. The generator transformer will be located in

the switchyard located up stream of the machine hall and will be connected to generating

units through 11KV bus ducts.

MEDIUM AND HIGH HEAD SCHEME

In medium and high head schemes, powerhouses are more conventional with an entrance for

the penstock and a tailrace. Although not usual, this kind of powerhouse can be underground.


3


The following equipment will be displayed in the powerhouse:

• Inlet gate or valve

• Turbine

• Speed increaser (if needed)

• Generator

• Control system

• Condenser, switchgear

• Protection systems

• DC emergency supply

• Power and current transformers

7.2 TURBINE

Particulars of Hydro Turbine

S.N. Technical Particulars Specifications/Parameters

1. Type of Turbine/Shaft orientation Horizontal Francis

2. No. of unit 1

3. Output

a. Rated output at rated net head 400 Kw

b. Max. Output at rated net head 480 Kw

4. Efficiency 90%

5. Speed

a. Rated speed in r.p.m. 500 rpm

b. Maximum runaway speed in r.p.m. 900 rpm

c. Direction of rotation when viewed from

generator end/top.

Clockwise


4


General

The maximum gross head is 124.81 m. Total head losses in the penstock corresponding to

design discharge of 0.40 Cumecs mainly comprises of frictional losses. Net head works out

to 118.56. Alternatives of installing single unit of appropriate capacity have been examined.

The provision of one units appear advantageous and has been proposed. Therefore, one

number turbines are proposed to fulfill the following design requirements

A mini hydropower scheme converts hydro potential energy into mechanical energy and

then to electrical energy. Energy is power delivered in unit time.

Output power = P

Turbine output power (kW) = ȠT × ȠG x Q× g ×H

Where: ȠT - Efficiency of turbine (90 %)

ȠG-Efficiency of generator (95%)

g - Gravity (9.81 m2/s)

H net - Net head available at the turbine (118.56 m)

Q - Water volume enters into turbine per second (0.40 m3/s)

Turbine output power (kW) = 0.90x0.95x0.40x9.81x118.56

=397.87KW, say 0.40MW

Therefore, out power of unit = 400 = 400 kW

Specific speed

It is the speed in revolution per minute at which the given turbine would rotate, if reduced

homologically in size so that it would develop unit power under unit head at full gate.

Low specific speeds are associated with high heads and high specific speed is

associated with low heads. The selection of a high specific speed for a given head will

result in a smaller turbine and generator with saving in capital cost. However the turbine

will have to be placed lower for which the cost may offset the saving.

Also at high specific speed lower efficiency is expected.


5


Specific speed is given by the formula.

n√P

Ns = -------------

H (5/4)

Where:

Ns = Specific speed in r.p.m

η = Speed of turbine in r.p.m

P = output power of turbine in KW

H = Net head in meter

A set of curves showing specific speed versus head of Francis, propeller, and Francis

turbines are shown in Fig. given below. Curves for cavitation coefficient σ for francis and

Kaplan turbines are also shown in the same figure.

Assuming Francis Turbine

n = 375

Ns = (375x√400)/118.565/4

= 19.17


n = 500

Ns = (500x√400)/118.565/4

= 25.56


n = 750

Ns = (750x√400)/118.565/4

= 38.34



6


n = 1000

Ns = (1000x√400)/118.565/4

= 51.12


7


The ranges of specific speed for various types of turbines are given below:

Type of runner Specific speed (Ns)

(i)Impulse Francis/Turgo = 12-70

(ii)Cross flow = 20-80

(iii)Reaction Francis = 80-400

(iv)Propeller and Kaplan = 340-1000

On the basis of above data we can considered Francis turbine for this project. Due to

small capacity of the unit it would be economical and beneficial to install Francis Turbine

with speed of 500rpm and specific speed is 25.56rpm, at Thunag MHEP, as higher the

speed of turbine lesser will be the cost of Generator.

One number of horizontal Francis turbines each 400 KW 90% of efficiency was used in

order to increase the part flow efficiency, increase reliability and easiness in overhauling

the turbines without shutdown the plant.

Effective head was same for both units. But flow was shared equally and subsequently

output power was divided equally.

7.2 Generator

Particulars of GENERATOR

Sl. No. Description.

1. Type. Synchronous

2. Rated output in kw 400 kW

3. Continuous Over Load Capacity. 10%

4. Power Factor. 0.85

5. Shaft orientation. Horizontal

6. Speed.

a. Rated Speed. 500 RPM.

b. Runaway Speed. 900 RPM.


8


(i) Type of Generator

Generators transform mechanical energy into electrical energy. Although most early

hydroelectric systems were of the direct current variety to match early commercial

electrical systems. Now days only three-phase alternating current generators are used in

normal practice.

• Synchronous generators: They are equipped with a DC electric or permanent magnet

excitation system (rotating or static) associated with a voltage regulator to control the

output voltage before the generator is connected to the grid. They supply the reactive

energy required by the power system when the generator is connected to the grid.

Synchronous generators can run isolated from the grid and produce power since

excitation is not grid-dependent .

(ii) Class of insulation

Present practice is to specify class F insulation system for the stator and rotor winding

with class B temperature rise over the ambient. Ambient temperature rise should be

determined carefully from the temperature of the cooling water etc.

Accordingly maximum temperature for the insulation class under site conditions should

be specified.

a) Stator:

Class F insulation level and Class B temperature rises are recommended.

b) Rotor:

The insulation level should normally be Class-F and temperature raises Class-B.

(iv) Type of cooling

Losses in a generator appear as heat which is dissipated through radiation and ventilation.

The generator rotor is normally constructed to function as an axial flow blower, or is

equipped with fan blades, to circulate air through the windings. Small-generators up to 5

MW may be partially enclosed, and heated generator air is discharged into the generator

hall, or ducted to the outside.

Adequate ventilation of the generator hall preferably thermostatically should be provided

in this case.


9


Water to air coolers normally is provided for all modern hydro generators rated greater

than 5MW. The coolers are situated around the outside periphery of the stator core.

Normally, generators should be furnished with one cooler than the number required for

operation at rated MVA. This allows one cooler to be removed for maintenance without

affecting the unit output.

(v) Generator inertia

The moment of Inertia of the generator together with the moment of inertia of the turbine

shall be such that the maximum momentary speed rise under Governor Control on full

load rejection shall not exceed 45% of rated speed for the grid connected generator as

station power is supplied from main generator and adverse effect of this speed rise on

motor driven station auxiliaries is not desirable. Additional flywheel required shall be

built in the rotor. Separate flywheel shall not be permitted.

(vi) Starting method

The starting method used in Thunag MHEP should be in Manual and Auto both mode.

7.3 Generator-transformer connections

The power shall be generated at 0.415 kv which is economical voltage for generators in

the capacity range 0.5-2.5MW and also in view of transportation weight limitation. Unit

system layout of the generating unit shall be adopted at the power station. The generating

units will be connected through 0.415/11kv step up transformers to the outdoor 11 kv bus

bar. The electrical scheme proposed for the power station and the switch yard is shown in

the single line diagram.

7.4 Transformer

The generator step up and auxiliary power supply transformers shall be installed in the

switchyard of the power station. The detail of transformers is given below:

Generator step up

Transformer

Station auxiliary

suppply Transformer


10


Voltage ratio 0.415/11 kv 11/0.415 kv

Rated capacity 600 KVA 75KVA

No of transformers 1 1

Voltage range ±10% ±10%

Cooling type ONAN ONAN

Rated Frequency 50 Hz 50 Hz

Frequency variation ± 3% ± 3%

7.5 Switchyard equipment

Switchyard consists following equipments:-

(a) 11 KV circuit Breaker

(b) 11 KV C/R Panel

(c) 11 KV Isolator without Earth switch

(d) 11 KV CTs

(e) 11 KV/110V PTs

(f) 11KV LAs

(g) 11 KV Isolator with Earth switch

7.6 Single line scheme

Single line scheme is shown in the SLD Drawing.


11


7.7 Control & protection equipment

Controls of Switchgear Panel,Protection Panel & Power

Transformer

1

TG control,Relay,Metering cum PLC based Governor

panel

ANSI Protection

21 Under Impedance relay

24 Over fluxing relay

27/59 Voltage protection relay

32 Reverse power relay

37 Under power relay

40 Field failure relay

46 Negative sequence relay

49 Thermal overload protection

50/27 Unintentional energisation of standstill

50V/51V Voltage controlled over current

51BF Breaker failure relay

60FL VT fuse failure

64S Stator earth fault relay

81 Under frequency relay

87G Generator differential relay

86B Electrical Action Shutdown

86C Control Action Shutdown

86E Emergency Action Shutdown


12


2

1.1 KV Breaker panel

ANSI Protection

86 Master Trip relay

94 Trip circuit supervision relay

64B Bus Earth fault relay

3

Transformer cum Line Relay metering and protection

panel

ANSI Protection

67 Directional overcurrent relay

67N Directional Earthfault relay

27 Undervoltage rerlay

59 Overvoltage relay

64REF Resticted Earth fault relay

86L Master Trip relay for Line

87T Transformer Differential relay

4

Line Relay metering cum protection panel(Receiving

End)

ANSI Protection

67 Directional overcurrent relay

67N Directional Earthfault relay

27 Undervoltage rerlay

59 Overvoltage relay

86L Master Trip relay for Line


13


5

LTAC panel(415V)

ANSI Protection

50 Overcurrent relay

51N Earth fault relay

6

Power Transformer Accessories

ANSI Protection

WTI Winding Temperature Indicator

OTI Oil Temperature Indicator

BZ Bucholz relay

MOG Magnetic oil level gauge

(A) GOVERNORS

Governing system shall be complete with actuator unit comprising of speed response

element, restoring mechanism having adjustable temporary and permanent drop setting, load

limiting device and speed level control. The oil pressure system will comprise of sump tank

and an oil pressure oil tank and one electrically operated governor oil pumps, one with

normal running and other acting as stand by unit shall be provided.

Governor shall be suitable for selected turbines. In the event of any abnormal operation,

generator will be isolated from main line and turbine will be stopped by closing inlet/gate

valve. Over current and earth fault protection are provided on H.T switch gear and

transformers, against voltage surges lightening arrestor will be provided. All electrical

equipment in the power house and switch yard area will be protected, grounded and rubber

mats will be used wherever necessary in order to protect the workers from electric shock.

All electrical equipment in power house and switch yard area will be properly insulated


14


wherever necessary in order to protect the workers from electric shock, noncurrent carrying

parts of all equipment will be connected to earth net.

(B) ELECTRICAL MASTER CONNECTIONS AND CONTROL

Electrical master connections are composed of generators, transformers, circuit breakers,

current and voltage transformers, including conductor between them for generation,

transmission and distribution of electrical energy. Electrical master connections are

proposed to fulfill the following essential requirements:-

(i) To ensure quality and reliable supply of electrical energy as per the requirement of power

grid and consumers.

(ii) To achieve economy and low investment on Maintenance and Operation.

(iii) To ensure reliability and flexibility in operation.

(iv) To ensure convenience in maintenance.

A central control panel will be provided from where all functions of the generating units,

transformers and lines etc. will be controlled.

The generators manufacturer shall be asked to supply all equipment and devices for control

instrumentation and safety relating to the generators. These together with equipment

supplied by the turbine manufacturer shall constitute a complete and coordinated set of

instruments, control and safety devices for the control of these units during normal running

and in an emergency.

The AVR shall control the voltage within the limits specified. The AVR shall have a

provision for operation in both power factor and voltage control mode. The AVR shall

also have a manual channel supplied independently of the auto channel and proper follow

up to facilitate the switching between auto and manual channels. The AVR shall have

provision for quadrate droop compensation for stable operation. The control/indication

and power handling components though housed in the same cabinet shall be suitably

isolated.

The AVR shall also have following features:-

- Under/Over Excitation protection.


15


- Maximum/Minimum excitation limiters.

- Grid paralleling features.

(C) EMERGENCY CONTROL AND PROTECTION

Emergency control shall be provided to protect the equipment and auxiliary system during

emergency. Control board and H.T. gear panel will be provided for each turbine generator

set so that all functions of machine are monitored and controlled. The 110V DC supply will

be provided for emergency lights, indicators and control equipment.

Over voltage, restricted earth fault, over speed, over current, under voltage and speed action

equipment shall be provided for turbine and generators. Suitable circuits shall be provided

for abnormal conditions such as increase in bearing temperature, low oil pressure etc. A

protection scheme with automatic control circuit shall be provided to stop the turbine in the

event of power supply failure or any other fault by operating emergency solenoid of power

pack. It is proposed to provide:-

Control switch, indicating meters and position indicator lamps on the control panel.

Protective relays for machine control and alarm units etc. on the units control board.

Control and relays for the power circuit are provided on the separate gear cubical which also

houses the incoming and outgoing LT bus.

Suitable provision for all the electrical equipment in power house and switch yard etc. to

provide full protection to equipment and working persons in the event of short circuiting

and other faults.

Generator Protection and Metering

a) LAVT Panel

The lightening arrestor and the voltage transformer panel shall be located near the

generator and shall house the surge arrestor and PT with necessary fuses etc.


16


b) NGC

The neutral grounding cubicle shall have leads from all the three winding and shall house

the protection CTs for differential protection, neutral forming link and earthing resistor,

CT for stator earth fault protection.

c) Protections

Following protections shall be provided for the Turbine generator set in Generator

Control panel.

- Generator differential protection.

- Voltage restrained over current relay.

- Earth fault relay.

- O/V and U/V relay.

- Phase unbalance relay.

- Over speed relay and switch.

- Stator Temperature Detector.

- Field failure/Diode Failure relays.

Following indicating and logging meters too shall be provided.

- Current for all the three phases.

- Voltmeter with selector switch.

- KW meter with Kwh logging.

- Pf meter.

- Unit running hour meter.


17


Electrical Auxiliaries and Equipments:-

Power plant controls and monitoring system shall have microprocessor based controls

comprising controls for unit control, switching equipment and auxiliaries. The system

shall also have provision for data logging periodical report generation and alarm and

annunciation. The control and monitoring equipment shall also have provision for remote

control and remote alarm and annunciation.

7.8 Auxiliary Mechanical services

(i) HOT Crane

It is proposed to install a 10 tonne capacity HOT crane with auxiliary hooks of 5 tonns

designed to travel the full length of the power house. The capacity of the HOT crane has

been selected on the basis of preliminary assessment of rotor weight including the lifting

arrangement.

(ii) Ventilation & air conditioning

The powerhouse shall be provided with ventilation and air conditioning as required to

maintain the work areas, powerhouse at the selected temperature and humidity levels would

be provided for control room and offices. The temperature and humidity levels would be

selected to suit the requirement of equipment and plant staff.

(iii) Fire protection

Fire protection system complete with CO2 cylinders, ring headers, discharge nozzles shall

be provided. This system shall be complete with manual operation facility to release

carbon dioxide.

(iv) Water Cooling

A pumping system would be provided to supply adequate quantity of water from the tail race

channel for cooling of the turbine and generator bearings generator air coolers and selected

plant services.


18


7.9 Electrical services

(i) A.C.auxiliary services

3 phase,11kv/415v delta/star 75KVA capacity step down transformer will used for station

lighting and heating load for power house, staff ,illumination for road and switch yard.

Emergency lights on important places will be operated by D.C.battery provided in the

power house. 50 KVA diesel generator set will also be provided for illumination in power

house, staff, street lights & switch yard during shut down of machine.

(ii) D.C. auxiliary service

Float and boost type 110 Volts,200AH battery charger and tabular battery will be

provided for feeding power to indication lamps, protection relay ,initial impulse to the

self excitation system by means of field flashing and to operate few emergency light.

(iii) Cables

H.T. cables shall be used. Heat shrink type cable termination shall be provided for H.T.

cable connecting generator to generation transformer, neutral grounding end.

(iv) SWITCH YARD

In designing Switchyard layout, the need for simple features, closeness to power house,

equipment specifications according to Indian standards, ease of operation have been kept in

view. Fencing will be provided for security reasons.

0.415KV high voltage cable laid in underground trenches will connect the feeder’s panel

with the step up transformer. Step up transformer with normal protection such as restricted

earth fault, differential etc. as per manual with circuit breakers will be provided for

disconnection of the transformers and control of the outgoing line taking off from the power

station. Lightening arrestor will be provided to protect lines and transformer from the surges.

The required rating of CT (current transformer) and PT (potential transformer) is provided

in the switchyard.


19


(v)TRANSMISSION LINES

General

It is proposed to evacuate the power from switchyard of Thunag MHEP to substation at

Thunag through the 11kv single circuit line near about 2.0km long.

Power Evacuation

It is proposed that the electricity shall be generated at 0.415kV and evacuated at 11 kV switchyard.

One step up transformer, 0.415kv/11kv for each machine shall be provided switchyard near the

power house. The switch yard shall be 11kv outdoor type.

Documents

Chapter 7