SWITCHYARD and GENERAL SIGNIFICANCE
Electrical vitality administration system ensures provide of vitality to each shopper always at rated voltage, frequency and specified waveform, at lowest value and minimal environmental degradation. The switchgear, safety and community automation are integral elements of the fashionable vitality administration system and nationwide economic system.
The fashionable Three-ph, 50 Hz, AC interconnected system has a number of typical 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 methods and related electrical hundreds. The vitality in electrical kind is equipped to varied shoppers positioned in huge geographical space, immediately, routinely, and safely with required high quality always. The service continuity and prime quality of energy provide have grow to be crucial.
For fulfilling the foresaid goal, a cutting-edge, scientifically and technologically superior SUBSTATION is required. Sub-Station is the load management middle 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 15.75 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 right down to voltage 6.6 KV which is used to run the main auxiliaries of the plant.
After step up, the 220 KV output from the generator transformer is fed to both of the 2 bus bars via relays and circuit breakers and these are related to varied feeders via varied equipments.
DIFFERENT TYES OF EQUIPMENTS USED IN SUB-STATIONS
1. BUS-BARS: –
Bus bar is a time period used for foremost 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 via the bus bars.
2. LIGHTENING ARRESTORS: –
These are equipments designed to guard insulators of energy strains and electrical installations from lightening surges by diverting the surge to earth and immediately restoring the circuit insulation to its regular power with respect to earth.
Three. CURRENT TRANSFORMERS: –
The primary goal of present transformer is to step down the present to a degree that the indicating and monitoring devices can learn. When rated present flows via its major winding, a present of almost 1 amp will seem in its secondary winding.
The first is so related that the present being passes via it and secondary winding is related to an ammeter. The CT steps down the present to the extent of the ammeter.
four. POTENTIAL TRANSFORMER: –
These are used to step do the voltage to a degree 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 degree on the identical frequency. Shunt reactor in EHV substations is to supply reactive energy compensation throughout low hundreds.
6. WAVE TRAP: –
Wave entice is used to stop excessive frequency alerts from getting 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 ability hundreds.
eight. ISOLATORS: –
One of many cardinal measures for guaranteeing full security in finishing up work on gear in electrical installations is to disconnect reliably the unit or the part on which the work is to be finished from all different dwell elements of the set up. To protect in opposition to errors, it’s essential that equipment, which makes a visual break within the circuit reminiscent of isolators, ought to do that.
Isolators would not have arc management gadgets subsequently can’t be used to interrupt currents at which the arc will likely be drawn throughout the contacts. The open arc in these could be very harmful, in that it’ll not solely harm the isolator or the gear surrounding it however will even trigger the flashover between the part in different phrases, it can end in quick circuit within the set up i.e. why isolators are used just for disconnecting elements 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 strains to earth. An auxiliary swap to supply interlock all the time accomplishes it.
10. CIRCUIT BREAKERS: –
Circuit breakers are mechanical gadgets designed to shut o open contact or electrical circuit below regular or irregular situations. CB is supplied with a strip coil immediately hooked up to relay or different means to function in irregular situations reminiscent of over energy and many others. In GNDTP three sorts of CB are used. SF6 CB is used to regulate 220 KV in switchyard.
VCB are used to regulate 6.6kv in switchgear & ABCB are used to regulate 415 KV in switchgear.
In sulphar puffer kind SF6 CB is full of SF6 fuel at single stress (4to6kgf/cm2). The stress and fuel movement required for arc extinction is obtained by piston motion.
In double stress kind 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
Three. Lightening impulse stand up to Voltage 1050V
four. Switching impulse stand up to voltage 1050V
5. Brief circuit breaking present 40KA
6. Brief circuit stand up to present And period 40KA Three sec
7. Line charging breaking present 125A
eight. Working sequence – First pole to clear issue 1.Three
9. Provide voltage 220 V dc
10. Auxiliary circuit provide voltage 240 V dc
11. Air stress 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 supply compensation to reactive a great deal of lagging energy issue.
Collection reactors are used to scale back the quick circuit present or beginning currents. Impartial grounding resistors are used to restrict the earth fault present.
Coupling capacitors are used to supply connection between excessive voltage line and energy line service gear.
Working Voltage 230 V
Rated present 2000 A
Minimal quick 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.zero M
Peak of tubular bus-bar of first degree above floor 6 m
Peak of tubular bus-bar of second degree above floor four m
Tubular aluminium bus bar AL ASTMB241 four”IPS (Worldwide pipe customary)
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, gear 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 many others. with protected step- Potential and contact potential.
2. Overhead earth wire shielding or lightning To guard the out of doors substation gear from lightning strokes.
Three. Illumination system (lightning) – For switchyards – Buildings – Roads, and many others. To supply illumination for vigilance, operation and upkeep.
four. Safety system – Safety relay panels – Management cables – Circuit breakers – CT’s, PT’s, and many others. To supply alarm or automated tripping of defective half from wholesome half and in addition to reduce harm to defective gear 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 entice – Coupling capacitor – PLCC panels For communications, telemetry, tele management energy line service safety, and many others.
eight. Fireplace combating system – Sensors, detection system – Water spray system – Fireplace safety management Panels To sense the prevalence of fireside by sensors and to provoke water energy spray, to disconnect energy provide to affected area to pin level location of fireside by indication in management room.
9. J Cooling water system – Coolers – Water tanks This technique 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 – Swap gear – Distribution system For supplying beginning energy, stand by energy for auxiliaries.
12. Phone system For inner and exterior Communication.
12. BUS BAR ARRANGEMENT IN SWITCHYARDS
There are a number of methods in witch the switchyard will be related within the electrical format of producing station, receiving station or a switchgear in a distribution system. The next features generally have an effect on the choice of the scheme:
1. Diploma of flexibility of operations desired.
2. Significance of load and native situations.
Three. Financial situations, availability, and value.
four. Technical situations.
5. Upkeep, security of personnel.
7. Provision of extension.
eight. Protecting zones.
DUPLICATE BUS BAR ARRANGEMENT
The duplicate bus bar system supplies extra flexibility, continuity of provide and permits periodic upkeep with out complete shut down. Within the occasion of fault o n one bus the opposite bus can be utilized.
Whereas transferring the ability to the reserve bus, the next steps could also be carried out:
1. Shut tie circuit breaker, i.e. bus coupler. The 2 buses are actually on the identical potential.
2. Shut isolators on reserve bus ranging from far finish.
Three. Open isolators o9n foremost 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 mounted and transferring contact. The transferring contacts will be drawn aside by the use of the working hyperlinks of the working mechanism. The working mechanism of the circuit breaker provides essential vitality for opening and shutting of contacts of the circuit breaker.
Relay is a tool by the use of which an electrical circuit (journey or alarm circuit) is managed (closed) by change within the different circuit. Relays are automated. The operate of relay in energy provide system is to acknowledge a begin out and to provoke the operation of CB or different gadgets to isolate the faulty components with minimal disturbance to the conventional energy provide system. The should function at required velocity and stability to stop the present and voltage to exceed their limits.
Just a few relays with their worldwide codes are talked about under:
S. NO. CODES TYPES
1. 27 Instantaneous below voltage relay
2. 99 Composite motor safety relay
Three. 64 Earth fault relay
four. 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
eight. 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 Verify 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 situations 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 transferring 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 methods. The present reaches last zero because the arc is extinguished.
The switchgear constitutes all elements or equipments of energy plant whose operate is to obtain and distribute electrical energy. It includes of the next:
· Assemblies of switching equipment
· Protecting and indicating metering gadgets
· Interconnecting bus bar methods and related equipment
Features of Switchgear: –
The features 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 gear so routinely disconnect defective half from the system.
· To interrupt effectively quick circuits with out giving rise to harmful situations.
The switchgear has the duty of transmitting the ability from the generator to the grid. Nevertheless plant additionally wants energy for its working. It’s necessary to not use greater than 10% of the ability developed by the plant. So that every one the auxiliaries and lightening system of the plant have to be designed in such a means 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 an identical 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 many others. is used for management provides as required for system management and safety gear.