TRANSFORMER PROTECTION Presented by: Romulo A. Amoguis Electrical Engineer TRANSFORMER PROTECTION Participants • • • • • • Electrical Engineers Protection Engineers Test & Commissioning Engineers Power System Engineers Utility Engineers Electrical Technicians TRANSFORMER PROTECTION Objective • To appreciate the importance of protective relays in protecting the transformer. • To be able to understand the basic principle of operation and function of protection relays installed in the power transformer. • To gain knowledge of power transformer protection. TRANSFORMER PROTECTION Introduction Transformers are a critical and expensive component of the power system. Due to long lead time for repair and replacement of transformers, a major goal of transformer protection is limiting the damage to a faulted transformer. The comprehensive transformer protection provided by multiple function protective relays is appropriate for critical transformers of all applications. TRANSFORMER PROTECTION The type of protection for the transformers varies depending on the application and importance of the transformer. Transformers are protected primarily against faults and overloads. The type of protection used should minimize the time of disconnection for faults within the transformer and to reduce the risk of catastrophic failure to simplify eventual repair. TRANSFORMER PROTECTION Any extended operation of the transformer under abnormal condition such as faults or overloads compromises the life of the transformer, which means adequate protection should be provided for quicker isolation of the transformer under such condition. TRANSFORMER PROTECTION Transformer Failures • Winding failures due to short circuit (turn- turn faults, phase-phase faults, phase-ground and open winding) • Core Faults (Core insulation failure, shorted laminations) • Terminal failures (open leads, loose connections and short circuits) • OLTC failures ( mechanical, electrical, short circuit and overheating) • Abnormal operating conditions (overfluxing, overloading and overvoltage) • External fault. TRANSFORMER PROTECTION TYPICAL TRANSFORMER PROTECTION (Electrical) 87 51G 50/51ABC-N 59 24 50/51ABC-N 132kV 220kV 87G 51G 87G 51G TRANSFORMER PROTECTION TYPICAL TRANSFORMER PROTECTION (Electromechanical) 63 49 26 132kV 220kV 69 TRANSFORMER PROTECTION Circulating current principle (87) Ip CT-1 a f I1 CT-2 Protected equipment e g d I1 R b j I2 h I2 I diff. Is =I1-I2=0 c NORMAL CONDITION TRANSFORMER PROTECTION Circulating current principle (87) Ip CT-1 a f I1 Protected equipment e g d I1 b CT-2 R h j I2 I2 I1=I2 I diff. =I1-I2=0 c EXTERNAL FAULT Is Fault TRANSFORMER PROTECTION Circulating current principle (87) Ip CT-1 Protected equipment CT-2 Is Fault Fault I2 I1 I I1 R diff= I1+I2 I2 INTERNAL FAULT ≠0 TRANSFORMER PROTECTION Circulating current principle (87REF) Ia CT-1 C Ia’ Ib B Ic Ib’ A Ic’ I2=0 I1 I1 =Ia’ +Ib’ + Ic’ =0 IR=0 Stab. Res IN = 0 CT-2 R NORMAL CONDITION TRANSFORMER PROTECTION Circulating current principle (87REF) IA=IF CT-1 A A IB=0 Ik Ia’=IF B B IC=0 Ib’=0 C C Ic’ = 0 I1 CT-2 Stab. Res I2 I1 Idiff=I1-I2 ≠0 R I2 IN I1 › I 2 INTERNAL FAULT TRANSFORMER PROTECTION Circulating current principle (87REF) CT-1 Ia=0 A A Ib=0 B B Ic = IF C C Fault I1 IG I1=I2 (No Trip) IN I1 R I2 I2 EXTERNAL FAULT CT-2 I1=I2 Idiff = I1-I2= 0 TRANSFORMER PROTECTION Overcurrent principle (50/51ABC-N) CT IA=IF A A B B C C IB=-IA IC = 0 Ia Ib 50/51 A B C N INTERNAL PHASE-PHASE FAULT TRANSFORMER PROTECTION Overcurrent principle (50/51ABC-N) A IA=IF CT IA A IB B B C IB=0 IC C IN IC=0 In 50/51 N Ia C EXTERNAL PHASE-GROUND FAULT B A TRANSFORMER PROTECTION Buchholz Relay (INCIPIENT FAULT) Buchholz Relay Alarm circuit Upper float Conservator tank Lower float GAS Main Tank Trip circuit TRANSFORMER PROTECTION Buchholz Relay (OIL LEAKS) Buchholz Relay Alarm circuit OIL Upper float Flap Conservator tank Lower float OIL Main Tank Trip circuit TRANSFORMER PROTECTION Buchholz Relay (SEVERE FAULT) Buchholz Relay Alarm circuit Upper float Flap Conservator tank Lower float OIL Main Tank Trip circuit The End THANK YOU….Any questions?