Thermal Plants

SWITCHYARD and GENERAL SIGNIFICANCE

Thermal Plants
Thermal Plants

Electrical vitality administration system ensures provide of vitality to each shopper always at rated voltage, frequency and specified waveform, at lowest price and minimal environmental degradation. The switchgear, safety and community automation are integral components of the fashionable vitality administration system and nationwide financial system.

The trendy 3-ph, 50 Hz, AC interconnected system has a number of traditional and non-conventional energy crops, EHV AC and HVDC Transmission system, Again to Again HVDC coupling stations, HV Transmission community, substations, MV and LV Distribution programs and related electrical hundreds. The vitality in electrical kind is equipped to varied customers positioned in huge geographical space, immediately, mechanically, and safely with required high quality always. The service continuity and prime quality of energy provide have grow to be crucial.

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For fulfilling the foresaid function, a state-of-the-art, scientifically and technologically superior SUBSTATION is required. Sub-Station is the load management heart of the thermal plant the place energy at rated voltage, frequency and waveform is exported/imported as per necessities.

The substation at GHTP Lehra Mohabat has just one 220 KV switchyard. There are two output items every having a capability of 210 MW. The producing voltage is proscribed to fifteen.75 KV and this voltage as stepped up by two-generator transformer 15.75/220 KV manufactured by BHEL. Part of 15.75 KV provide is fed to unit auxiliary transformer, which is stepped all the way down to voltage 6.6 KV which is used to run the foremost auxiliaries of the plant.

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After step up, the 220 KV output from the generator transformer is fed to both of the 2 bus bars by relays and circuit breakers and these are related to varied feeders by varied equipments.
DIFFERENT TYES OF EQUIPMENTS USED IN SUB-STATIONS

1. BUS-BARS: –

Bus bar is a time period used for major bar of conductor carrying an electrical present to which many connections could also be made. These are primarily handy technique of connecting switches and different equipments into varied preparations.

At GNDTP there are two 220 KV bus bars. These are fabricated from aluminium and all of the incoming and outgoing provides are related by the bus bars.

2. LIGHTENING ARRESTORS: –

These are equipments designed to guard insulators of energy traces and electrical installations from lightening surges by diverting the surge to earth and immediately restoring the circuit insulation to its regular energy with respect to earth.

3. CURRENT TRANSFORMERS: –

The primary function of present transformer is to step down the present to a stage that the indicating and monitoring devices can learn. When rated present flows by its main winding, a present of almost 1 amp will seem in its secondary winding.

The first is so related that the present being passes by it and secondary winding is related to an ammeter. The CT steps down the present to the extent of the ammeter.

4. POTENTIAL TRANSFORMER: –

These are used to step do the voltage to a stage that the potential coils of indicating and monitoring devices can learn. These are additionally used to feed the potential coils of relays. The first winding is related to the voltage being measured and the secondary winding to a voltmeter. The PT steps down the voltage to the extent of the voltmeter.

5. POWER TRANSFORMER: –

These are used to step up down the voltage from one a.c voltage to a different a.c voltage stage on the similar frequency. Shunt reactor in EHV substations is to offer reactive energy compensation throughout low hundreds.

6. WAVE TRAP: –

Wave lure is used to forestall excessive frequency alerts from coming into different zones.

7. INDICATING AND METERING INSTRUMENTS: –

Ammeters, voltmeters, watt meters, KWH meters, KVAR meters are put in in sub-station to look at over the currents flowing within the circuit and the voltages and the facility hundreds.

8. ISOLATORS: –

One of many cardinal measures for making certain full security in finishing up work on tools in electrical installations is to disconnect reliably the unit or the part on which the work is to be carried out from all different dwell components of the set up. To protect in opposition to errors, it’s obligatory that equipment, which makes a visual break within the circuit resembling isolators, ought to do that.

Isolators would not have arc management units subsequently can’t be used to interrupt currents at which the arc might be drawn throughout the contacts. The open arc in these could be very harmful, in that it’ll not solely injury the isolator or the tools surrounding it however will even trigger the flashover between the part in different phrases, it’s going to lead to brief circuit within the set up i.e. why isolators are used just for disconnecting components after de-energizing them by opening their respective circuits by use of their circuit breakers.

9. EARTHING SWITCHES: –

Earthing swap is used to discharge the voltage on lifeless traces to earth. An auxiliary swap to offer interlock all the time accomplishes it.

10. CIRCUIT BREAKERS: –

Circuit breakers are mechanical units designed to shut o open contact or electrical circuit underneath regular or irregular circumstances. CB is supplied with a strip coil instantly connected to relay or different means to function in irregular circumstances resembling over energy and so on. In GNDTP three forms of CB are used. SF6 CB is used to manage 220 KV in switchyard.
VCB are used to manage 6.6kv in switchgear & ABCB are used to manage 415 KV in switchgear.

In sulphar puffer sort SF6 CB is crammed with SF6 fuel at single strain (4to6kgf/cm2). The strain and fuel movement required for arc extinction is obtained by piston motion.

In double strain sort SF6 CB the fuel from high-pressure system is launched to into low-pressure system over the arc throughout the arc quenching course of.

SPECIFICATIONS OF CB TYPE ELF-SL4-1

S. NO. SPECIFICATIONS RATINGS

1. Voltage 245KV

2. Regular present 3150 A

3. Lightening impulse face up to Voltage 1050V

4. Switching impulse face up to voltage 1050V

5. Quick circuit breaking present 40KA

6. Quick circuit face up to present And period 40KA 3 sec

7. Line charging breaking present 125A

8. Working sequence – First pole to clear issue 1.3

9. Provide voltage 220 V dc

10. Auxiliary circuit provide voltage 240 V dc

11. Air strain 20.5 bar

12. Frequency 50 HZ

13. Mass 3800 kg

14. Rated present 1600 A

11. VARIOUS OTHER EQUIPMENTS

Shunt capacitors are used to offer compensation to reactive a great deal of lagging energy issue.

Sequence reactors are used to scale back the brief circuit present or beginning currents. Impartial grounding resistors are used to restrict the earth fault present.

Coupling capacitors are used to offer connection between excessive voltage line and energy line service tools.

Working Voltage 230 V
Rated present 2000 A
Minimal brief circuit present in bus bars 40 KV
Minimal part to part clearance 2.5 M
Variety of horizontal ranges of tubular bus bar/versatile bus bars 2.0 M
Top of tubular bus-bar of first stage above floor 6 m
Top of tubular bus-bar of second stage above floor 4 m
Tubular aluminium bus bar AL ASTMB241 4″IPS (Worldwide pipe commonplace)

VARIOUS SUBSYSTEMS IN SUBSTATIONS AND THEIR FUNCTION

S.NO. SYSTEM FUNCTION

1. Substation Earthing (Grounding) System – Earth mat – Earthing spikes – Earthing risers To supply an earth mat for connecting impartial factors, tools physique, help constructions to earth. For security of personnel and for enabling earth fault safety. To supply the for discharging the earth currents neutrals, faults, surge arrestors over-head shielding wires and so on. with secure step- Potential and contact potential.

2. Overhead earth wire shielding or lightning To guard the out of doors substation tools from lightning strokes.

3. Illumination system (lightning) – For switchyards – Buildings – Roads, and so on. To supply illumination for vigilance, operation and upkeep.

4. Safety system – Safety relay panels – Management cables – Circuit breakers – CT’s, PT’s, and so on. To supply alarm or computerized tripping of defective half from wholesome half and likewise to attenuate injury to defective tools and related system.

5. Management cabling For protecting circuits, management circuits, metering circuits.

6. Energy cables To supply provide path to varied auxiliary equipments and machines.

7. PLCC system energy line service present system – Line lure – Coupling capacitor – PLCC panels For communications, telemetry, tele management energy line service safety, and so on.

8. Fireplace combating system – Sensors, detection system – Water spray system – Fireplace safety management Panels To sense the incidence of fireplace by sensors and to provoke water energy spray, to disconnect energy provide to affected area to pin level location of fireplace by indication in management room.

9. J Cooling water system – Coolers – Water tanks This method is required for cooling the valves in HVDC substation.

10. DC batteries units and battery chargers Auxiliary low voltage DC provide.

11. Auxiliary stand by energy System – Diesel generator units – Change gear – Distribution system For supplying beginning energy, stand by energy for auxiliaries.

12. Phone system For inside and exterior Communication.

12. BUS BAR ARRANGEMENT IN SWITCHYARDS

There are a number of methods in witch the switchyard may be related within the electrical format of producing station, receiving station or a switchgear in a distribution system. The next features basically have an effect on the choice of the scheme:

1. Diploma of flexibility of operations desired.

2. Significance of load and native circumstances.

3. Financial circumstances, availability, and value.

4. Technical circumstances.

5. Upkeep, security of personnel.

6. Simplicity.

7. Provision of extension.

8. Protecting zones.

DUPLICATE BUS BAR ARRANGEMENT

The duplicate bus bar system gives further flexibility, continuity of provide and permits periodic upkeep with out whole shut down. Within the occasion of fault o n one bus the opposite bus can be utilized.

Whereas transferring the facility to the reserve bus, the next steps could also be carried out:

1. Shut tie circuit breaker, i.e. bus coupler. The 2 buses at the moment are on the similar potential.
2. Shut isolators on reserve bus ranging from far finish.
3. Open isolators o9n major bus ranging from far finish.

Every pole of the circuit breaker includes a number of interrupts or arc extinguishing chambers. The interrupts are mounted on help insulators. The interrupts enclose a set of fastened and shifting contact. The shifting contacts may be drawn aside via the working hyperlinks of the working mechanism. The working mechanism of the circuit breaker provides obligatory vitality for opening and shutting of contacts of the circuit breaker.

13. RELAYS

Relay is a tool via which an electrical circuit (journey or alarm circuit) is managed (closed) by change within the different circuit. Relays are computerized. The perform of relay in energy provide system is to acknowledge a begin out and to provoke the operation of CB or different units to isolate the faulty components with minimal disturbance to the conventional energy provide system. The should function at required pace and stability to forestall the present and voltage to exceed their limits.

A number of relays with their worldwide codes are talked about under:

S. NO. CODES TYPES

1. 27 Instantaneous underneath voltage relay

2. 99 Composite motor safety relay

3. 64 Earth fault relay

4. 87M Differential relay for motors

5. 50N Earth fault relays with occasions for time delayed operation

6. 95 Fuse failure relay

7. 80 Auxiliary provide for DC supervision

8. 80B DC provide management supervision

9. 80A Relay for mains

10. 500/L Triple pole over present particular time period

11. 98 Journey circuit supervision relay

12. 87 Triple pole circulating present

13. 63 Auxiliary relay for transformer fault indication

14. 33B Auxiliary relay for cease

15. 25 Test synchronizing relay

16. 52SC Instantaneous excessive set over present relay

17. 2B Static time delay relay

18. 51RYB Single pole (IDMTL) Inverse particular Minimal time over present relay.

THE FAULT CLEARING PROCESS

Throughout irregular or defective circumstances the relays sense the fault and shut the journey circuit of the circuit breaker.

Because the relay contact shut, the journey circuit is closed and the working mechanism of the CB opens and an arc is drawn between them. The arc is extinguished at some pure present zero of a.c. wave.

o Fault Happens: – Because the fault happens the fault impedance being low, the currents improve and the relay get actuated. The shifting a part of the relay strikes due to the rise within the working torque. The relay takes a while to shut its contacts.

o Relay contacts shut, the journey CB closes and journey coil is energized.

o The working mechanism begins working for the opening operations. The CB contacts separate.

o Arc is drawn between the breaker contacts. The arc extinguished within the CB by appropriate strategies. The present reaches closing zero because the arc is extinguished.

SWITCHGEAR

The switchgear constitutes all components or equipments of energy plant whose perform is to obtain and distribute electrical energy. It includes of the next:

· Assemblies of switching equipment

· Protecting and indicating metering units

· Interconnecting bus bar programs and related equipment

Features of Switchgear: –

The capabilities carried out by switchgear are listed under: –

· To facilitate redistribution of load, inspection and upkeep of system.
· To localize the results of faults by operation of protecting tools so mechanically disconnect defective half from the system.
· To interrupt effectively brief circuits with out giving rise to harmful circumstances.

The switchgear has the accountability of transmitting the facility from the generator to the grid. Nonetheless plant additionally wants energy for its working. It’s obligatory to not use greater than 10% of the facility developed by the plant. So that each one the auxiliaries and lightening system of the plant should be designed in such a method that there consumption is within the restrict.

There are two bus bars positioned in ducts, which provide energy to the switchgear and are fed by two station transformers ST-I and ST-II. The ranking of those similar bus bars is 6.6 KV, 3150 Amps, 50 Hz. These are referred to as C-I and C-II station buses respectively. The fabric of conductor is Aluminium. C-I station bus feeds US-IA & US-2A buses and C-II feeds US-IB & US-2B buses. C-I & C-II buses are additionally interlinked. These unit service buses feed the completely different sorts of load.

The auxiliary voltage for the ac provide system is 6.6 KV and 415 V. 6.6 KV provide system is supplied with excessive resistance grounded impartial with provision of alarm/ journey. 415V auxiliary provide system has solidly/excessive resistance earthed impartial. All the electrical motors of 150 KW ranking or under are rated at 415 V and motors above 160 KW are rated at 6.6 KV.

GENERAL ELECTRICAL SUPPLIES IN THE PLANT

Electrical Auxiliary System

· AC Auxiliary provide system

· DC provide system

AC auxiliary provide system is used to feed all of the AC auxiliaries put in within the plant.

The DC provide system which consists of 220 V DC, 110 V DC,
+/- 24 V DC, 48 V DC and so on. is used for management provides as required for system management and safety tools.