1. Basic Transformer Protection Steve Rainwater Energy System Operations Trainer (LCRA)

2. The objective of this class is to provide the student with a general knowledge of the fundamentals of transformer protection

3. PUBLIC Enabling Objectives Identify the basic operational characteristics of an SMD dual-element power fuse Identify the requirements of R1-5 of NERC Standard PRC-001-1 System Protection Coordination Identify the principle of operation and application of transformer differential protection 3

4. PUBLIC Enabling Objectives continued Identify the principle of operation and application of transformer overload protection Identify the principle of operation and application of transformer sudden pressure protection 4

5. PUBLIC PRC-001-1 System Protection Coordination R1 each TO shall be familiar with the purpose and limitations of protective schemes applied in its area –Relay engineering databases –training –alarms 5

6. PUBLIC PRC-001-1 System Protection Coordination R2 Each TO shall notify reliability entities of relay or equipment failures: –R 2.2 If a relay failure reduces reliability, TO shall notify RC and any other affected TO’s as soon as possible 6

7. PUBLIC TOP-006-2 Monitoring System Conditions R3 Each TO shall provide appropriate technical information concerning protective relays to operating personnel –How does your shop meet this? 7

8. PUBLIC PRC-001-1 System Protection Coordination R4 Each TO shall coordinate protection systems with neighboring GO’s, TO’s, and BA’s. R5 TO shall coordinate changes in system or conditions that could require changes from others: –R5.2 each TO shall notify neighboring TO’s in advance of any changes that could require changes in neighboring protection systems 8

9. PUBLIC Zones of Protection The area of responsibility for any relay scheme is known as the “Zone of Protection” Zone of Protection is determined by the location of the CT’s. Zones of Protection are designed to overlap in order to provide redundancy 9

10. PUBLIC 69kV Bus BKR 3 BKR 2 BKR 4 R BKR 1 Tie BKR Protective Relay Zone In most cases a zone is identified by the location of the current transformers used in the protective scheme 138kV Bus 10

11. PUBLIC G G BUS LINE XFMR GEN / GSU FDR BKR BUS GEN / GSU BUS LINE BUS 11

12. PUBLIC Transformer Protection 12

13. PUBLIC 13 Although this looks bad, the protection in this case functioned as designed

14. PUBLIC Xfmr protection must mitigate: faults internal to the transformer tank (e.g., short on a winding) severe overloading (due to external factors) overheating overpressure 14

15. PUBLIC Transformer Protection Speed can make the difference between a repairable transformer and one that is a total loss Pressure transformer tanks have ruptured from internal faults resulting in oil spills or large fires from the burning insulating oil 15

16. PUBLIC Transformer Protection Types: Overcurrent relays Differential relays Fault pressure relays Fuses Gas detection 16

17. PUBLIC Overpressure Protection 17

18. PUBLIC Whenever corona, heating or arcing occurs inside the tank of a transformer gasses are formed Samples removed from the transformer insulating oil and nitrogen blanket are analyzed H2-insulation breaking down Acetylene-oil breaking down 18

19. PUBLIC High pressures are created instantly when a transformer internal fault occurs A protective device called a Fault Pressure Relay (FPR or 63 device) can detect this rapid pressure increase and initiate trip to the transformer protective devices 19

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21. PUBLIC Sudden Pressure Relay (FPR) Oil Level Wires to trip circuits Pressure Created by Sudden Gassing 21

22. PUBLIC + Trip Oil Nitrogen Gradual Pressure Increase Bellows (No Expansion) Transformer Tank Contacts Open Sudden Pressure Relay 22

23. PUBLIC + Trip Oil Nitrogen Rapid Pressure Increase Contacts Close Transformer Tank Fault Pressure Relay Bellows Expand 23

24. PUBLIC Lessons Learned – 63 Device Substation personnel call control center request permission to pull oil sample from power transformer –What picture does this conjure in your mind? 24

25. PUBLIC What really happened 25

26. PUBLIC Sudden pressure relays cannot protect against gradual increases in pressure as the bellows will equalize Another form of protection is required against slower-building pressure increases 26

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30. PUBLIC Overcurrent Protection

31. PUBLIC Dual Element SMD Power Fuse A. Stainless-steel drive spring - provides stored energy to drive arcing rod upward through arc-extinguishing medium during fuse operation. B. Solid-material arc-extinguishing medium. C. Silver-clad copper arcing rod. D. Filament-wound glass-epoxy tube. E. Fusible element — helically coiled silver or pretensioned nickel-chrome provide precise melting characteristics and no damage performance. 31

32. PUBLIC Dual Element SMD Power Fuse How it works –Overcurrent melts fusible element. The strain wire severs, initiating arcing. –Released force of drive spring accelerates arcing rod upward, causing rapid elongation of the arc in bore. Under high-fault conditions, heat from arc causes solid material in the large-diameter lower section (B) to undergo thermal reaction, generating gases and enlarging the bore diameter so that the arc energy is released with a mild exhaust. Under low-to-moderate-fault conditions, arc is extinguished in upper section of the arc-extinguishing chamber, where deionizing gases complete arc extinction. –upward travel of the arcing rod causes arcing rod to drive release tube upward, tripping latch mechanism and initiating drop-out of the fuse unit. 32

33. PUBLIC 33 Overcurrent (50/51) relays can be used to protect a transformer from severe overloading. The overcurrent relays can also function as backup protection for internal faults.

34. PUBLIC 24.9 kV Bus 1 138 kV Bus BKR 2 Secondary Lockout Relay 200/5 BKR 1 86T S 50/51 T Trips: BKR 1 & BKR 2 50 - Instantaneous O.C. Relay 51 – AC Time O.C. Relay A, B, C Ø 34

35. PUBLIC 35 Severe overloading of a transformer can result in rapid overheating of the windings, winding insulation and insulating oil. Damage from overheating can reduce the level of effectiveness of the insulation and insulating oil and could result in premature failure of the transformer.

36. PUBLIC 24.9 kV Bus 1 138 kV Bus BKR 1 BKR 2 Trips: BKR 1 & 2 51N 86T S Transformer Neutral Overcurrent Protection 36

37. PUBLIC Transformer Differential

38. PUBLIC  Usually deployed as primary protection  Advantages over 50/51 protection are:  speed –detection is faster, thus so is actuation,  selectivity- since zone of protection is more well-defined than 50/51, will not actuate for external faults 38

39. PUBLIC Primary Lockout Relay 24.9 kV Bus 1 138 kV Bus BKR 1 BKR 2 4000/5 200/5 86T P 87 T Differential Relay Trips: BKR 1 & BKR 2 A, B, C Ø 39

40. PUBLIC Differential protective relaying is commonly used as the primary protection for larger power transformers and auto transformers C2K Operate Coil BKR 40

41. PUBLIC 200/5 3A C2K 230-13.8kV 50MVA 3000/5 Operate Coil 120A 2000A *3.33 x 1.73 *5.7A 2.7A 3A 5.7A Transformer Differential Relaying 3A BKR 41

42. PUBLIC 25A 1000A *1.66 x 1.73 25 +2.9 = 27.9A 25A 2.9A *2.9A Operate Coil 200/5 C2K 230-13.8kV 50MVA 3000/5 BKR 25A 42

43. PUBLIC 24.9 kV Bus 1 138 kV Bus BKR 1 BKR 2 4000/5 200/5 Trips: BKR 1 & 2 Trips: BKR 1 & 2 86T S 86T P 50/51 T 87 T Differential Relay Primary Lockout Relay Secondary Lockout Relay 51N 86T S Trips: BKR 1 & 2 43

44. PUBLIC RCD- WHT 5E54 5E53 87T6P SEL387 67 6 Transformer_____ 161-115kV-13.8kV Tert. EGP 2000:5 1200:5 600:5 GTP 67 GP 87 51N 51H 63 0I No. 1 138 kv Bus 86T6 LOR Trip TC-2 52/5E53 52/5E54 Key RCD-WHT T.T XMTR Open 89/6E56 89_ 6E56 -2 86T6 2000:5 No. 2 138kv Bus _No. 6 Transformer_Protection____ Example of SEL 387 Solid State Relay Application 44

45. PUBLIC Over Temperature Protection

46. PUBLIC Overheating due to heavy normal loading of the transformer on hot still days can also be a problem Radiators cool the transformer oil and fans mounted on the radiators can be turned on as needed to increase the cooling 46

47. PUBLIC 47 Types of cooling  Convection  Forced air  Forced oil/air

48. PUBLIC Winding temperature devices (Hot Spot) can be used to monitor the combined heating effect of the load on the windings and transformer oil temperature. This device can be used to turn on the cooling fans in stages as needed, alarm the control center and can sometimes be used to send trip to deenergize the transformer. 48

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50. PUBLIC Winding Temperature CT Heating Element Oil Level Winding Temperature Gauge w/Cooling Fan, Alarm and Trip Contacts Wires to alarm and trip circuits 50

51. PUBLIC Oil Level Gauge with Alarms Pressure Relief Device (PRD) with Alarms Fault Pressure Relay (FPR) Low Oil Trip with Alarms Winding Temperature Gauge with Fan Control, Alarms & Trip Option Top Oil Temperature Gauge with Alarms 51

52. PUBLIC Underfrequency

53. PUBLIC Underfrequency Three steps –Step 1 @ 59.3 Hz (5%) –Step 2 @ 58.9 Hz (10%) –Step 3 @ 58.5 Hz (10%) 53

54. PUBLIC 24.9 kV Bus 1 138 kV Bus BKR 1 Trips: BKR 1 & 2 BKR 2 86T S 50/51 T 63 71Q 3 86/63 *Trip BKR 2 8190 LTC * Modern U.F. schemes will trip and restore individual feeder breakers as needed. 54

55. PUBLIC 55 References: Schweitzer Engineering Laboratories, SEL Application Guide, Applying the SEL321 Relay DCB Schemes Schweitzer Engineering Laboratories, SEL Application Guide, Applying the SEL321 Relay DCUB Schemes General Electric, Differential Voltage Relays GEH-1770E Fodero, Kenneth J., Introduction to Relay Communications, Dowty Control Technologies, 1990 Elmore, Walter A., Protective Relaying Theory and Applications,, ABB Power T&D, Marcel Dekker,1994. Blackburn, J. Lewis, Protective Relaying Principles and Applications, Marcel Dekker, 1987 Westinghouse Electric Corporation, Silent Sentinels, 1949 Rockefeller Jr, George D., Protective Relaying, International Textbook, 1964 General Electric, The Art of Protective Relaying, 1982

56. PUBLIC 56 Questions?