Switchgears and its basics in power plant.pptx

switchgear basics

1. Switchgears PMI Revision 01 1

2. SWITCH PMI Revision 01 2 A switch is simply a means of opening or closing the current path in an electric circuit. There is no special opening condition for short circuit or other fault. It is operated manually.

3. SWITCHGEAR PMI Revision 01 3 It is the generic term including the entire range of switching devices and their combination with associated control, measuring, protecting, and regulating equipment.

4. FUNCTIONS OF SWITCHGEAR PMI Revision 01 4 Carrying the normal load current o r breaking the no r mal load Making current Cle a ring sensing the fault current devices like CT, (for w h ich PT, and various relays are employed)

5. P ARTS OF SWITCHGEAR PMI Revision 01 5 Switching device Power circuit Control circuit Measurement and display Protection

6. Switching devices : Circuit breakers / contactors Isolators Earthing switch Control Circuit : service / test /isolated position selectors Tripping and closing circuit Spring charging, anti pumping arrangement Supply monitoring , space heaters , indications Measurement : Ammeter, voltmeter, energy meter Protection : Relays, CT, PT, PMI Revision 01 6

7. SW I TCHGEAR V ari o u s s y mb ol s : Isolator / Disconnecting switch Circuit Breaker Earthing switch Lighten i ng Arrestor CT PT Ammeter Voltmeter V PMI Revision 01 7 A

8. COMPONENTS OF SWITCHGEAR PMI Revision 01 8 Circuit Breaker Current Transformer (CT) Potential Transformer (PT) Protective Relays Measuring Instruments

9. CIRCUIT BREAKER PMI Revision 01 9 The circuit breaker is a piece of equipment which can do any one of the following tasks: Makes or breaks a circuit either manually or by remote control under normal conditions Breaks a circuit automatically under fault conditions Makes a circuit either manually or by remote control under fault conditions

10. CIRCUIT BREAKER PMI Revision 01 10 A circuit breaker is a switching i.e. current interrupting or making device in switchgear.

11. Supply from source Equipment RELAY Bat t ery PMI Revision 01 11 Trip Coil of Breaker CB CT Basic relay circuit scheme

12. COMPONENTS OF SWITCHGEAR PMI Revision 01 12 Switches Fuses Surge Arresters Isolators Miniature Circuit Breakers (MCB)

13. SWITCHGEAR REQUIREMENTS PMI Revision 01 13 There are several voltage levels and fault situations between the generating stations to the final load points. Hence vary switchgear requirements may depending upon following factors: Location Ratings Local Needs

14. SWITCHGEARS VOLTAGE LEVELS PMI Revision 01 14 Vide ANSI C84.1-1989 (Voltage ratings for electric power systems and equipment) Low Voltage: 120V to 600V Medium Voltage: 2400V to 69000V High Voltage: 115KV to 230KV Extra High Voltage: 345KV to 785KV Ultra High Voltage: 1100KV ANSI: American National Standards Institute

15. Switchgear classification PMI Revision 01 15 By the current rating. By interrupting rating (maximum short circuit current that the device can safely interrupt) Circuit breakers can open and close on fault currents Load-break/Load-make switches can switch normal system load currents Isolators may only be operated while the circuit is dead, or the load current is very small. By voltage class: Low voltage Medium voltage High voltage By insulating medium: Air Gas (SF6 or mixtures) Oil Vacuum

16. Switchgear classification PMI Revision 01 16 By construction type: Indoor (further classified by IP (Ingress Protection) class or NEMA enclosure type) Outdoor Industrial Utility Draw-out elements (removable without many tools) Fixed elements (bolted fasteners) Metal-enclosed Metal-clad Metal enclose & Metal clad Arc-resistant

17. Switchgear classification PMI Revision 01 17 By interrupting device: Fuses Air Blast Circuit Breaker Minimum Oil Circuit Breaker Oil Circuit Breaker Vacuum Circuit Breaker Gas (SF6) Circuit breaker

18. Switchgear classification PMI Revision 01 18 By operating method: Manually-operated Motor-operated Solenoid/stored energy operated By type of current: Alternating current Direct current By application: Transmission system Distribution.

19. Metal enclosed switchgear Switchgear surrounded by a metal case or housing which is earthed. PMI Revision 01 19

20. Metal Clad switchgear PMI Revision 01 20 Metal enclosed switchgear in which Circuit breakers are usually withdrawable type Mechanism to move between connected and disconnected positions components are arranged in separate compartments with metal enclosures intended to be earthed. Primary circuits are completely enclosed by metal barriers Automatic shutters that covers primary circuit when removable component is disconnected.

21. Metal Clad switchgear PMI Revision 01 21

22. L V COM P A RTM E NT CT AND CABLE COMPARTMENT BREAKER COMPARTMENT BUSBAR COMPARTMENT TYPICAL AIR INSULATED ME T AL ENCLOSED S WITC H GEAR 22 PMI Revision 01

23. CHAMBERS IN SWITCHGEAR HT CHAMBER LT CHAMBER Breaker Chamber Busbar Chamber CT/PT Chamber Instrument Chamber (Relay/meters/switches etc.) PMI Revision 01 23

24. Shutters PMI Revision 01 24

25. Indoor and Outdoor circuit breakers PMI Revision 01 25

26. Outdoor pole mounted circuit breakers PMI Revision 01 26

27. POLE MOUNTED AUTO RECLOSER PMI Revision 01 27

28. Purpose of circuit breakers PMI Revision 01 28 The important characteristics from a protection point of view are: The speed with which the main current is opened after a tripping impulse is received. The capacity of the circuit that the main contacts are capable of interrupting.

29. Total fault clearing time PMI Revision 01 29

30. Events/Timings during fault clearing process Fault clearing Time R el a y t i me Circuit breaker Time Instant Of F ault Closure of Trip Circuit Final arc Extinction Circuit breaker Time Closure of Trip Circuit = + = = to to R el a y t i me PMI Revision 01 30

31. Main Parts of a Circuit Breaker : Fixed Contact Movable Contact Operating Mechanism Arc extinguishing medium PMI Revision 01 31

32. Arc When short-circuit occurs, fault current flows, corresponding to the network parameters. The breaker trips and the current is interrupted at the next natural current zero. The network reacts by transient oscillations, which gives rise to the transient recovery voltage (TRV) across the circuit breaker main contacts. All breaking principles involve the separation of contacts, which initially are bridged by a hot, highly conductive arcing column. PMI Revision 01 32

33. Arc PMI Revision 01 33 After interruption at current zero, the arcing zone has to be cooled to such an extent that the TRV is overcome and it cannot cause a voltage breakdown across the open gap. Three critical phases are distinguished during arc interruption, each characterized by its own physical processes and interaction between system and breaker.

34. High current phase PMI Revision 01 34 This consists of highly conductive plasma at a very high temperature. Proper contact design prevents the existence of metal vapour in the critical arc region.

35. Thermal phase PMI Revision 01 35 Before current zero, the diameter of the plasma column decreases very rapidly. This thermal phase is characterized by a race between the cooling of the rest of the plasma and the reheating caused by the rapidly rising voltage. Due to the temperature and velocity difference between the cool, relatively slow axial flow of the surrounding gas and the rapid flow in the hot plasma core, vigorous turbulence occurs downstream of the throat, resulting in effective cooling of the arc.

36. Dielectric phase PMI Revision 01 36 After successful thermal interruption, the hot plasma is replaced by a residual column of hot, but no longer electrically conducting medium. However, due to marginal ion-conductivity, local distortion of the electrical field distribution is caused by the TRV appearing across the open brea k.

37. Behaviour under fault conditions 37

38. Fault clearing process PMI Revision 01 38 During any Fault….. Fault impedance will be low, so fault current will increase and relay senses this increase in current. Relay contacts closes and sends trip signal to circuit breaker and the trip coil of the circuit breaker will get energized. Operating mechanism of the circuit breaker will operate and separate the contacts. Arc will be initiated between the contacts and it is extinguished by suitable methods.

39. Arcing phenomenon PMI Revision 01 39 - When a fault occurs, heavy current flows through the contacts of the circuit breaker before they are opened by the protective system. At the instant when the contacts begin to separate, the contact area decreases rapidly and current density (I/A) increases and hence rise in temperature. -The heat produced is sufficient to ionise the medium between the contacts. This ionised medium acts as conductor and an arc is struck between the contacts. The potential difference between the contacts is very small and is sufficient to maintain the arc. The cu r rent flow depends upon the Arc r e si stan c e .

40. Restriking Voltage –After the arc has been extinguished, the voltage across the breaker terminals does not normalize instantaneously but it oscillates The transient voltage which appears across the breaker contacts at the instant of arc being extinguished. Rate of Rise of Re-striking Voltage (RRRV) The RRRV is the slope of the re-striking voltage transient measured in volts per microsecond. Recovery Voltage –Power frequency voltage which appears across the breaker contacts after the arc is finally extinguished and transient oscillations die out. PMI Revision 01 40 Few definitions

41. Breaking Capacity Max fault current at which a CB is capable of breaking a circuit. Making Capacity Max current a CB can withstand if it closing on existing Short circuit. Short-time Rating. This is the maximum time (usually specified as 3 sec or 1 sec) for which the switch will carry, without damage, the full fault current before that current is broken. PMI Revision 01 41 Few definitions

42.  Various t ypes of C Bs Miniature CB Air Break CB (iii)Oil CB SF6 CB Vacuum CB Bulk Oil CB PMI Revision 01 42 Minimum Oil CB

43. TY P E M E D I UM R A NGE Air-break C.B. Tank-type oil C.B. Minimum oil C.B. Air-Blast C.B. SF 6 C.B Vacuum C.B. Air Dielectric oil Dielectric oil Compressed air(20-30)kgf/cm 2 SF 6 gas vacuum L.V. up to 1000v Up to 33kv 36kv 132kv to 400kv 6.6 to 760kv 6.6 kv,11kv,33kv TYPES OF CIRCUIT BREAKERS PMI Revision 01 43

44. Air Break C B 44

45. Air Break CB PMI Revision 01 45

46. Air Blast CB : PMI Revision 01 46

47. ABCB- Principle of arc quenching 47 PMI Revision 01

48. Current Interruption in Oil PMI Revision 01 48 When an arc is drawn in oil the contacting oil surfaces are rapidly vaporized due to the high temperature of the arc, the vaporized gas then forms a gas bubble, which totally surrounds the arc. Arc energy decomposes oil into 70% hydrogen, 22% acetylene, 5% methane and 3% ethylene. Arc is in a bubble of gas surrounded by oil.

49. Current Interruption in Oil PMI Revision 01 49

50. Bulk Oil CB

51.  Minimum Oil CB PMI Rev

52. Oil Circuit Breaker: Advantages PMI Revision 01 52 Ability of cool oil to flow into the space after current zero and arc goes out Cooling surface presented by oil Absorption of energy by decomposition of oil Action of oil as an insulator results into more compact design of switchgear.

53. Oil Circuit Breaker:Disdvantages PMI Revision 01 53 However, oil can be degraded by small quantities of water and by carbon deposits that are the result of the carbonization of the oil. Arc produced in the oil is inflammable MOCB is not suitable for frequent operation Maintenance (oil changing and purifying). Not suitable for capacitor switching.

54. SF6 Circuit Breaker PMI Revision 01 54 Sulfur Hexafluoride (SF6) is an excellent gaseous dielectric for high voltage power applications. The combined electrical, physical, chemical and thermal properties offer many advantages when used in power switchgears. Some of the outstanding properties of SF6 making it desirable to use in power applications are: V High dielectric strength V Unique arc-quenching ability V Excellent thermal stability V Good thermal conductivity

55. Inert gas with very high dielectric strength. Also this gas recovers its dielectric strength very rapidly following a period of arcing. Colour less and odour less. Non-toxic and non- inflammable. Sf6 is blown axially to the arc, hence it removes the heat by axial convection and radial dissipation. As result the arc dia reduces and comes to zero at current zero. The decomposition products of arcing are not explosive hence no chance of fire. PMI Revision 01 55 Advantage of SF6

56. SF 6 CB : Op mechanism Interrupter Support Op rod Linkage Terminals Filters PMI Revision 01 Puffer cylinder Nozzle Fixed position Fixed contact Moving contact Gas inlet

57. SF 6 CB PMI Revision 01 57

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59. Main and Arcing Contacts PMI Revision 01 59

60. Advantages of SF6 breakers PMI Revision 01 60 Low level of current chopping and no excessive switching over voltage. No multiple re-ignition, no explosion because of SF6 is inert gas Minimum contact erosion due to inert gas and half cycle of arc. Well suited for switching of transformers and reactors Well suited for capacitor bank switching.

61.  Vacuum CB : P

62. VACUUM CIRCUIT BREAKER The sealed vacuum interrupter used in VCBs is a completely welded construction and dose not allow any conventional opening which detiorates over a period of time. The small volume of fixed and moving contacts and the vacuum inside the tube ensures that there is no danger due to explosion or failure. PMI Revision 01 62

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66. OPE R A TING M E C H A N ISM PMI Revision 01 66

67. Used up to 66 KV. Vacuum is of the range of 10ˉ6 to 10ˉ8 torr. Vacuum is highly dielectric, so arc can ’ t persists. Separation of contacts causes the release of metal vapour from the contacts, the density of vapour depends on the fault current. At current zero the vapour emission will tends to zero and the density will becomes zero and dielectric strength will build up and restriking will be prevented. No emission to atmosphere, hence pollution free. Non- explosive and silent operation. Compact size. PMI Revision 01 67 Advantage of vacuum CB

68. Disadv a ntag e s PMI Revision 01 68 * High initial cost. * Surge suppressors (R or RC combination) are to be connected at load side for limiting switching over-voltage while switching low pf loads.

69. MOVING PORTION (Mechanism cover removed) PMI Revision 01 69

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72. MECHANISM AND ITS OPERATION : GEAR BOX M O T O R CLOSING COIL TR I PPING COIL MECH A NISM SHAFT CLOSING SPRING LIMIT SW I TCH TRIPP I NG SPRING PMI Revision 01 72

73. Comparison of insulating methods for CBs PMI Revision 01 73

74. THANK YOU 74 PMI Revision 01