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?