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33/11 KV TRANSMISSION LINE
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- 3. INDEX • Introduction • Classifiedof substation • Single line diagram • Lighting arrester • Capacitor voltage transformer(CVT) • Current transformer • Potential transformer • Circuit breaker
- 4. INDEX • Relay • Bus •Transformer • Working • Control panel • Battery • Isolator
- 5. INTRODUCTION • The present-dayelectrical power system is A.C. i.e. electric power is generated, transmitted and distributed in the form of alternating current. • It is delivered to the consumers through a large network of transmission and distribution. • At many places in the line of the power system, it may be desirable and necessary to change some characteristic (e.g. voltage, A.C. to D.C., frequency, Power factor etc.) of electric supply.
- 6. • This isaccomplished by suitable apparatus called sub-station. For example, generation voltage (11KV or 6.6KV) at the power station is stepped up to high voltage (say132KV or 220KV) for transmission of electric power. • The assembly of apparatus (e.g. transformer etc.) used for this purpose is the sub-station. • Similarly, near the consumer’s localities, the voltage may have to be stepped down to utilization level. • This job is again accomplished by a suitable apparatus called ‘substation’.
- 7. TYPE OF SUBSTATION Thereare several ways of classifying sub-stations. However, the two most important way is used to make substation. According To The Requirements:- A sub-station may be called upon to change voltage level or improve power factor or convert A.C. power into D.C. power etc. According to the service requirement, sub-stations may be classified into: 1. Transformer sub-stations 2. Switching sub-stations 3. Converting sub-stations 4. Industrial sub-stations
- 8. According To TheConstructional Features • A sub-station has many components (e.g. circuit breakers, switches, fuses, instruments etc.) which must be housed properly to ensure continuous and reliable service. According to constructional features, the sub-stations are classified as 1.Indoor sub-station 2.Outdoor sub-station 3.Underground sub-station
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- 10. LIGHTENING ARRESTOR • Lighteningarresters are the instruments that are used in the incoming feeders so that to prevent the high voltage entering the main station. This high voltage is very dangerous to the instruments used in the substation. Even the instruments are very costly, so to prevent any damage lightening arresters are used. The lightening arresters do not let the lightening to fall on the station. If some lightening occurs the arrestors pull the lightening and ground it to the earth. In any substation the main important is of protection which is firstly done by these lightening arrestors. The lightening arresters are grounded to the earth so that it can pull the lightening to the ground.
- 11. FIGURE OF L.A (i)Surge Diverter (ii)Characteristics of The Non Linear Resister Lightning Arrester
- 12. WORKING OF L.A. •Under normal operation, the lightning arrester is off the line i.e. it conducts no current to earth or the gap is non-conducting. • On the occurrence of over voltage, the air insulation across the gap breaks down and an arc is formed providing a low resistance path for the surge to the ground. In this way, the excess charge on the line due to the surge is harmlessly conducted through the arrester to the ground instead of being sent back over the line. • It is worthwhile to mention the function of non-linear resistor in the operation of arrester. As the gap sparks over due to over voltage, the arc would be a short circuit on the power system and may cause power-follow current in the arrester. Since the characteristic of the resistor is to offer low resistance to high voltage (or current), it gives the effect of short circuit. After the surge is over, the resistor offers high resistance to make the gap non conducting.
- 13. CPPACITOR VOLTAGE TRANSFORMER •A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra high voltage signals and provide low voltage signals either for measurement or to operate a protective relay. • These are high pass Filters (carrier frequency 50KHZ to 500 KHZ) pass carrier frequency to carrier panels and power frequency parameters to switch yard. • In its most basic form the device consists of three parts: two capacitors across which the voltage signal is split, an inductive element used to tune the device and a transformer used to isolate and further step down the voltage.
- 14. FIGURE OF C.V.T CircuitDiagram of C.V.T Capacitor Voltage Transformer
- 15. WORKING OF C.V.T •The device has at least four terminals, a high-voltage terminal for connection to the high voltage signal, a ground terminal and at least one set of secondary terminals for connection to the instrumentation or protective relay. CVTs are typically single-phase devices used for measuring voltages in excess of one hundred KV where the use of voltage transformers would be uneconomical. In practice the first capacitor, C1, is often replaced by a stack of capacitors connected in series. This results in a large voltage drop across the stack of capacitors, that replaced the first capacitor and a comparatively small voltage drop across the second capacitor, C2, and hence the secondary terminals.
- 16. WAP TRAP • Wavetrap is an instrument using for trapping of the wave. • The function of this wave trap is that it traps the unwanted waves. Its shape is like a drum. • It is connected to the main incoming feeder so that it can trap the waves which may be dangerous to the instruments in the substation. • Generally it is used to exclude unwanted frequency components, such as noise or other interference, of a wave.
- 17. • Line trapalso is known as Wave trap. • What it does is trapping the high frequency communication signals sent on the line from the remote substation and diverting them . • The telecom/ tele protection panel in the substation control room through coupling capacitor.
- 18. CURRENT TRANSFORMER • Currenttransformer is a current measuring device used to measure the currents in high voltage lines directly by stepping down the currents to measurable values by means of electromagnetic circuit.
- 19. WORKING PRINCIPLE OFC.T • The basic principle induced in designing of current transformers is- • Primary ampere turns = Secondary ampere turns • Ip Np = Is Ns • Where, Ip - Primary current • Np – Primary Winding Turns • Is - Secondary Current; Ns – Secondary Winding Turn • Ampere turns plays very important role in designing current transformers. • Current transformers must be connected in series only. • Current transformer has less no of turns in primary and more no of turns in secondary. • The secondary current is directly proportional to primary current.
- 20. POTENTIAL TRANSFORMER • Aninstrument transformer in which the secondary voltage. • in normal conditions of use ,it is substantially proportional to the primary voltage and differs in phase from it by an angle. • which is approximately zero for an appropriate direction of the connections.
- 21. WORKING OF P.T •The basic principle involved in the designing of Voltage Transformer is- • Voltage Ratio = Turns Ratio • VP / VS = NP / NS • Thus NS VP = NP VS • As heavy primary voltages will be reduced to low secondary voltages. • it will have more turns in the primary & less turns in the secondary. • It must always be connected in parallel only. • Even if we connect it directly from high voltage to earth, it is not going to be a short circuit as its primary winding has very high resistance. Its core is a set of assembled laminations.
- 22. FIGURE OF P.T PotentialTransformer Line Diagram of VT.
- 23. CIRCUIT BREAKER • Thecircuit breakers are used to break the circuit if any fault occurs in any of the instrument. • These circuit breaker breaks for a fault which can damage other instrument in the station. • For any unwanted fault over the station we need to break the line current. • This is only done automatically by the circuit breaker.
- 24. CIRCUIT BREAKER TYPE Thepresent trend is up to 33KV, VCBs are preferred and beyond 33KV, SF6 gas circuit breakers are preferred. There are mainly two types of circuit breakers used for any substations. They are (a) SF6 circuit breakers, (b) Vacuum circuit breakers.
- 25. SF6 CIRCUIT BREAKER •Sulphur hexafluoride (SF6) is an inert, heavy gas having good dielectric and arc extinguishing properties. • The dielectric strength of the gas increases with pressure and is more than the dielectric strength of oil at 3 kg/cm2. • SF6 is now being widely used in electrical • equipment like high voltage metal enclosed cables; high voltage metal clad switchgear, capacitors, circuit breakers, current transformers, bushings, etc. • The gas is liquefied at certain low temperature, liquidification temperature increases with the pressure.
- 26. PROPERTY OF SF6 Someof the properties of SF6 are, • Very high dielectric strength • High thermal and chemical inertia • Superior arc extinguishing • capability • Low decomposition by arcing
- 27. BUS • The busis a line in which the incoming feeders come into and get into the instruments for further step up or step down. • The first bus is used for putting the incoming feeders in la • single line. • There may be double line in the bus so that if any fault occurs in the one the other can still have the current and the supply will not stop. • The two lines in the bus are separated by a little distance by a conductor having a connector between them. • This is so that one can work at a time and the other works only if the first is having any fault.
- 28. TRANSFORMER • Transformers comein a range of sizes from a thumbnail-sized coupling transformer. • hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. • All operate with the same basic principles, although the range of designs is wide. • While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. • Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical .
- 29. BASIC PRINCIPLE OFTRANSFORMER • The transformer is based on two principles: • firstly, that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). • Changing the current in the primary coil changes the magnetic flux that is developed. • The changing magnetic flux induces a voltage in the secondary coil.
- 30. Induction law which statesthat, where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and Φ equals the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic field strength and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary.
- 31. CAPACITOR BANK ATTACHEDTO THE BUS • The capacitor banks are • used across the bus so that the • voltage does not get down till at • the require place. • A capacitor bank is used in the • outgoing bus so that it can • maintain the • voltage level same in the • outgoing feeder.
- 32. Capacitor Control IsUsually Done To Achieve The Following Goals • Reduce losses due to reactive load current. • Reduce KVA demand, decrease customer energy consumption. • Improve voltage profile, and increase • revenue. • Indirectly capacitor control also results in longer equipment lifetimes because of reduced equipment stresses.
- 33. TRANSFORMER PROTECTION • StationTransformer: HG Fuse protection on HV side and fuse protection on LV side and Vent pipe. • Power transformers up to 7.5MVA: • HV side: O/L & Directional E/L protection with highest element in O/L relays. • LV side: O/L & E/L protection Buchholz Relay OLTC Buchholz Relay • Power transformers from 8.0MVA and above: HV side O/L & Directional E/L • protection with high set element in O/L relays. LV side O/L & E/L • protection: differential protection Buchholz Relay OLTC Buchholz Relay OTI, WTI • and PRV. • Power transformers from 31.5MVA and above: Over flux protection & LV WTI in addition to protection.
- 34. FEEDER PROTECTION • 33KVfeeders: Non directional O/L & E/L protection with highest and IDMT characteristics. • 132KV feeders: Main protection: Distance protection. Back up protection: Directional • O/L & E/L protection. • 220KV feeders: Main-1 protection: Distance protection Main-2protection: Distance protection, LBB protection, pole discrepancy Relay.
- 35. isolator • Isolator isa mechanical switch which isolates a part of circuit from system as when required. Electrical isolators separate a part of the system from rest for safe maintenance works.
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