Falcon Products Lightning Arrestor Connection
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SWITCHYARD and GENERAL SIGNIFICANCE Electrical energy management system ensures supply of energy to each buyer at all times at ranked voltage, frequency and specified waveform, at lowest cost and minimum environmental degradation. The switchgear, shelter and network automation are integral constituents of the progressed energy management system and national economy. The progressed 3-ph, 50 Hz, AC interconnected scheme has assorted established and non-conventional power plants, EHV AC and HVDC Transmission system, Back to Back HVDC coupling stations, HV Transmission network, substations, MV and LV Distribution systems and connected electrical loads. The energy in electrical form is supplied to respective buyers located in immense geographical area, instantly, automatically, and safely with required quality at all times. The service continuity and high quality of power supply have become very important. For fulfilling the foresaid purpose, a state of the art, scientifically and technologically progressed SUBSTATION is required. Sub-Station is the load control center of the thermal plant where power at ranked voltage, frequency and waveform is exported/imported as per requirements. The substation at GHTP Lehra Mohabat has only one 220 KV switchyard. There are two output units each having a capacity of 210 MW. The generating voltage is fixed to 15.75 KV and this voltage as stepped up by two-generator transformer 15.75/220 KV fictitious by BHEL. A share of 15.75 KV supply is fed to unit auxiliary transformer, which is stepped down to voltage 6.6 KV which is applied to run the major auxiliaries of the plant. After step up, the 220 KV output from the generator transformer is fed to either of the two bus bars through relays and circuit breakers and these are connected to respective feeders through respective equipments. 1. BUS-BARS: - Bus bar is a term employed for main bar of conductor carrying an electric current to which numerous connections may be made. These are principally commodious means of connecting switches and other equipments into respective arrangements. At GNDTP there are two 220 KV bus bars. These are made of aluminium and all the incoming and outgoing furnishes are connected through the bus bars. 2. LIGHTENING ARRESTORS: - These are equipments designed to protect insulators of power lines and electrical installations from lightening surges by diverting the surge to world and instantaneously restoring the circuit insulation to it is normal strength with respect to earth. 3. CURRENT TRANSFORMERS: - The main aim of current transformer is to step down the current to a level that the indicating and monitoring instruments may read. When ranked current flows through it is indispensable winding, a current of closely 1 amp will appear in it is secondary winding. The indispensable is so connected that the current being passes through it and secondary winding is connected to an ammeter. The CT steps down the current to the level of the ammeter. 4. POTENTIAL TRANSFORMER: - These are used to step do the voltage to a level that the potential coils of indicating and monitoring instruments may read. These are likewise employed to feed the potential coils of relays. The essential winding is connected to the voltage being measured and the secondary winding to a voltmeter. The PT steps down the voltage to the level of the voltmeter. 5. POWER TRANSFORMER: - These are applied to step up down the voltage from one a.c voltage to another a.c voltage level at the same frequency. Shunt reactor in EHV substations is to provide reactive power compensation for the duration of low loads. 6. WAVE TRAP: - Wave trap is used to prevent high frequency signals from entering other zones. 7. INDICATING AND METERING INSTRUMENTS: - Ammeters, voltmeters, watt meters, KWH meters, KVAR meters are installed in sub-station to watch over the currents flowing in the circuit and the voltages and the power loads. 8. ISOLATORS: - One of the cardinal measures for ensuring full safety in carrying out work on instrumentation in electrical installations is to disconnect reliably the unit or the section on which the work is to be done from all other live elements of the installation. To guard versus mistakes, it is necessary that apparatus, which makes a visible break in the circuit such as isolators, ought to do this. Isolators do not have arc control appliances consequently can not be used to interrupt currents at which the arc will be drawn all over the contacts. The open arc in these is very dangerous, in that it will not only harm the isolator or the instrumentation surrounding it but will also cause the flashover amidst the phase in other words, it will result in short circuit in the installation i.e. why isolators are employed only for disconnecting parts after de-energizing them by opening their respective circuits by use of their circuit breakers. 9. EARTHING SWITCHES: - Earthing switch is used to discharge the voltage on dead lines to earth. An auxiliary switch to provide interlock always accomplishes it. 10. CIRCUIT BREAKERS: - Circuit breakers are mechanical appliances designed to close o open contact or electrical circuit underneath normal or unnatural conditions. CB is equipped with a strip coil directly attached to relay or other means to operate in unnatural conditions such as over power etc. In GNDTP three types of CB are used. SF6 CB is employed to control 220 KV in switchyard. In sulphar puffer type SF6 CB is filled with SF6 gas at single pressure (4to6kgf/cm2). The pressure and gas flow required for arc extinction is received by piston action. In double pressure type SF6 CB the gas from high-pressure scheme is freed to into low-pressure system over the arc for the duration of the arc quenching process. SPECIFICATIONS OF CB TYPE ELF-SL4-1 S. NO. SPECIFICATIONS RATINGS 1. Voltage 245KV 2. Normal current 3150 A 3. Lightening momentum withstand Voltage 1050V 4. Switching instinctive withstand voltage 1050V 5. Short circuit breaking current 40KA 6. Short circuit withstand current And duration 40KA 3 sec 7. Line charging breaking current 125A 8. Operating sequence – First pole to clear factor 1.3 9. Supply voltage 220 V dc 10. Auxiliary circuit supply voltage 240 V dc 11. Air pressure 20.5 bar 12. Frequency 50 HZ 13. Mass 3800 kg 14. Rated current 1600 A 11. VARIOUS OTHER EQUIPMENTS Shunt capacitors are applied to provide compensation to reactive loads of lagging power factor. Series reactors are used to reduce the short circuit current or starting currents. Neutral grounding resistors are applied to limit the world fault current. Coupling capacitors are employed to provide connection amid high voltage line and power line carrier equipment. Operating Voltage 230 V VARIOUS SUBSYSTEMS IN SUBSTATIONS AND THEIR FUNCTION S.NO. SYSTEM FUNCTION 1. Substation Earthing (Grounding) System – Earth mat – Earthing spikes – Earthing risers To provide an world mat for connecting neutral points, instrumentation body, support structures to earth. For safety of personnel and for enabling world fault protection. To provide the for discharging the world currents neutrals, faults, surge arrestors over-head shielding wires etc. with safe step- Potential and touch potential. 2. Overhead world wire shielding or lightning To protect the outdoor substation instrumentation from lightning strokes. 3. Illumination scheme (lightning) – For switchyards – Buildings – Roads, etc. To provide illumination for vigilance, operation and maintenance. 4. Protection system – Protection relay panels – Control cables – Circuit breakers – CT’s, PT’s, etc. To provide alarm or automatic tripping of faulty share from healthful portion and likewise to minimize harm to faulty instrumentation and affiliated system. 5. Control cabling For protective circuits, control circuits, metering circuits. 6. Power cables To provide supply path to respective auxiliary equipments and machines. 7. PLCC system power line carrier current scheme – Line trap – Coupling capacitor – PLCC panels For communications, telemetry, tele control power line carrier protection, etc. 8. Fire fighting scheme – Sensors, detection system – Water spray system – Fire shelter control Panels To sense the occurrence of fire by sensors and to initiate water power spray, to disconnect power supply to affected region to pin point emplacement of fire by indication in control room. 9. J Cooling water system – Coolers – Water tanks This system is required for cooling the valves in HVDC substation. 10. DC batteries sets and battery chargers Auxiliary low voltage DC supply. 11. Auxiliary stand by power System – Diesel generator sets – Switch gear – Distribution system For supplying starting power, stand by power for auxiliaries. 12. Telephone system For internal and external Communication. 12. BUS BAR ARRANGEMENT IN SWITCHYARDS There are assorted ways in witch the switchyard may be connected in the electrical layout of generating station, receiving station or a switchgear in a distribution system. The following distinct features in frequent affect the selection of the scheme: 1. Degree of flexibleness of operations desired. 2. Importance of load and local conditions. 3. Economic conditions, availability, and cost. 4. Technical conditions. 5. Maintenance, safety of personnel. 6. Simplicity. 7. Provision of extension. 8. Protective zones. DUPLICATE BUS BAR ARRANGEMENT The duplicate bus bar system provides further and added flexibility, continuity of supply and permits periodic maintenance without total shut down. In the event of fault o n one bus the other bus may be used. While transferring the power to the reserve bus, the following steps may be performed: 1. Close tie circuit breaker, i.e. bus coupler. The two buses are now at the same potential. Each pole of the circuit breaker comprises one or more interrupts or arc extinguishing chambers. The interrupts are mounted on aid insulators. The interrupts enclose a set of fixed and moving contact. The moving contacts may be drawn detached by means of the operating links of the operating mechanism. The operating mechanism of the circuit breaker gives necessary energy for opening and closing of contacts of the circuit breaker. 13. RELAYS Relay is a device by means of which an electric circuit (trip or alarm circuit) is controlled (closed) by alter in the other circuit. Relays are automatic. The function of relay in power supply scheme is to recognize a start out out and to initiate the operation of CB or other gimmicks to isolate the defective parts with minimum disturbance to the normal power supply system. The will have to operate at required speed and stability to prevent the current and voltage to exceed their limits. A few relays with their international codes are noted below: S. NO. CODES TYPES 1. 27 Instantaneous underneath voltage relay 2. 99 Composite motor shelter relay 3. 64 Earth fault relay 4. 87M Differential relay for motors 5. 50N Earth fault relays with times for time delayed operation 6. 95 Fuse failure relay 7. 80 Auxiliary supply for DC supervision 8. 80B DC supply control supervision 9. 80A Relay for mains 10. 500/L Triple pole over current definitive term 11. 98 Trip circuit supervision relay 12. 87 Triple pole circulating current 13. 63 Auxiliary relay for transformer fault indication 14. 33B Auxiliary relay for stop 15. 25 Check synchronizing relay 16. 52SC Instantaneous high set over current relay 17. 2B Static time delay relay 18. 51RYB Single pole (IDMTL) Inverse definitive Minimum time over current relay. THE FAULT CLEARING PROCESS During unnatural or faulty conditions the relays sense the fault and close the trip circuit of the circuit breaker. As the relay contact close, the trip circuit is closed and the operating mechanism of the CB opens and an arc is drawn among them. The arc is extinguished at galore natural current zero of a.c. wave. o Fault Occurs: – As the fault occurs the fault impedance being low, the currents increase and the relay get actuated. The moving percentage of the relay moves because of the increase in the operating torque. The relay takes a good deal of time to close it is contacts. o Relay contacts close, the trip CB closes and trip coil is energized. o The operating mechanism starts operating for the opening operations. The CB contacts separate. o Arc is drawn amidst the breaker contacts. The arc extinguished in the CB by suitable techniques. The current reaches final zero as the arc is extinguished. SWITCHGEAR The switchgear constitutes all elements or equipments of power plant whose function is to receive and disseminate electric power. It comprises of the following: · Assemblies of switching apparatus · Protective and indicating metering devices · Interconnecting bus bar systems and applicable accessories Functions of Switchgear: - The functions performed by switchgear are listed below: - · To facilitate redistribution of load, inspection and maintenance of system. The switchgear has the obligation of transmitting the power from the generator to the grid. However plant likewise needs power for it is working. It is mandatory not to use more than 10% of the power invented by the plant. So that all the auxiliaries and lightening scheme of the plant will have to be designed in such a way that there consumption is in the limit. There are two bus bars placed in ducts, which supply power to the switchgear and are fed by two station transformers ST-I and ST-II. The rating of these identical bus bars is 6.6 KV, 3150 Amps, 50 Hz. These are known as C-I and C-II station buses respectively. The material 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 also interlinked. These unit service buses feed the dissimilar kinds of load. The auxiliary voltage for the ac supply scheme is 6.6 KV and 415 V. 6.6 KV supply scheme is provided with high resistance grounded neutral with provision of alarm/ trip. 415V auxiliary supply scheme has solidly/high resistance earthed neutral. All the electric motors of 150 KW rating or beneath are ranked 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 supply system · DC supply system AC auxiliary supply scheme is applied to feed all the AC auxiliaries installed in the plant. The DC supply scheme which comprises of 220 V DC, 110 V DC, |
Kindle vs. Nook (updated 1/2/2011)