Transformer Protection 2

TRANSFORMER PROTECTION

Presented by:

Romulo A. AmoguisElectrical Engineer


Participants• Electrical Engineers• Protection Engineers• Test & Commissioning Engineers• Power System Engineers• Utility Engineers• Electrical Technicians


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.


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.


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.


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 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.


87

220kV

50/51ABC-N

50/51ABC-N

132kV

51G

24

TYPICAL TRANSFORMER PROTECTION (Electrical)

59

87G51G

87G

51G


220kV

132kV

TYPICAL TRANSFORMER PROTECTION (Electromechanical)

63

26

49

69


Circulating current principle (87)

NORMAL CONDITION

Protected equipment

R

Ip Is

I1 I2

a

b c

de

f g

h

j

I diff. =I1-I2=0I1 I2

CT-1 CT-2



EXTERNAL FAULT

Protected equipment

R

FaultIp Is

I1 I2

a

b c

de

f g

h

j

I diff. =I1-I2=0I1 I2

CT-1 CT-2

I1=I2



INTERNAL FAULT

R

Fault

Ip Is

I1I2

Protected equipment

I diff= I1+I2 ≠ 0

I1 I2

Fault

CT-1

CT-2


Circulating current principle (87REF)

NORMAL CONDITION

C

B

A

Stab. Res

R

Ia

Ib

Ic

I1 =Ia’ +Ib’ + Ic’ =0

I1 IN = 0I2=0

IR=0

Ia’

Ib’

Ic’

CT-1

CT-2



INTERNAL FAULT

A

B

C

Stab. Res

R

IA=IF

IB=0

IC=0

I1IN I2

I1

Ia’=IF

Ib’=0

Ic’ = 0

I1 › I2

Ik

I2

A

B

C

CT-1

CT-2

Idiff=I1-I2 ≠0



EXTERNAL FAULT

A

B

C

Fault

Ia=0

Ib=0

Ic = IF

IN

R

I1

I2I1=I2 (No Trip)

IG

I2I1I1=I2Idiff = I1-I2= 0

CT-1

CT-2

A

B

C


Overcurrent principle (50/51ABC-N)

INTERNAL PHASE-PHASE FAULT

IA=IF

IB=-IAA

B

C

CT

Ia Ib

A B C N

IC = 0

50/51

A

B

C


Overcurrent principle (50/51ABC-N)

EXTERNAL PHASE-GROUND FAULT

IA

IB

IC

CT

IaIn

ABCN50/51

A

B

C

IA=IF

IN

IB=0

IC=0

A

B

C


Buchholz Relay (INCIPIENT FAULT)

Alarm circuit

Trip circuit

Main Tank

Conservator tank

Buchholz Relay

Upper float

Lower float

Alarm circuit

GAS


Buchholz Relay (OIL LEAKS)

Alarm circuit

Trip circuit

Main Tank

Conservator tank

Buchholz Relay

Upper float

Lower float

Alarm circuit

OIL

Flap

OIL


Buchholz Relay (SEVERE FAULT)

Alarm circuit

Trip circuit

Main Tank

Conservator tank

Buchholz Relay

Upper float

Lower float

Alarm circuit

OIL

Flap

The EndTHANK

YOU….Any questions?

Documents

Transformer Protection 2