ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F1 of 44
Transformer Protection in Transmission Networks
ABB
Transformer Protection
in
Transmission Networks

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F2 of 44
Transformer Protection in Transmission Networks
ABB
Power transformers in a power system
400 kV AC Transmission
130 kV Subtransmission
Distribution
MV
Generation
LV
M

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F3 of 44
Transformer Protection in Transmission Networks
ABB
Different vector group and neutral connections
Y d + z
YN d11 + zn
Y y
YN yn0 (d1)
Y d
YN d1
D y
D yn11

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F4 of 44
Transformer Protection in Transmission Networks
ABB
Different winding arrangements
2 windings
+ unloaded
tertiary
3 windings Autotransformer
+ tertiary
e.g. Yy 6 d1
e.g. YN Auto d1
2-winding transf.
+ Auxiliary
transformer
0

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F5 of 44
Transformer Protection in Transmission Networks
ABB
Possible Faults
Insulation breakdown
Short circuits phase-to-phase
Inter-turns
Ground faults
Overvoltage U> (overexcitation U/f>)
Overtemperature
Oil leakage or contamination
Oil level monitor
Reduced cooling

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F6 of 44
Transformer Protection in Transmission Networks
ABB
Possible Transformer Failures
Winding failures
Tap changer failures
Bushing failures
Core failures
Miscellaneous failures

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F7 of 44
Transformer Protection in Transmission Networks
ABB
Selective Protection of:
- two or
- three winding transformer
- autotransformer
- generator-transformer unit
Detection of:
- all-phase faults
- earth-faults at solidly or
low-impedance earthed systems
- interturn faults

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F8 of 44
Transformer Protection in Transmission Networks
ABB
Recommended Transformer Protection
Functions Rating
up to 2 MVA 2 - 5 MVA less 60 MVA over 60 MVA
Gas Detector
Relay (Buchholz)
Overload Protection
(Thermal or
temperature
monitoring relay)
Overcurrent
Protection
Differential
Protection
Ground Fault
Protection
Voltage Regulating
Relay
for exposed overvoltage
situations
Oil level monitor
Overexcitation

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F9 of 44
Transformer Protection in Transmission Networks
ABB
Transformer Protection Basic Versions
Transformer Protection Basic Versions
Type of Transformer Unit High-Voltage Side Medium-Voltage Side Low-Voltage Sid
Prot. Prot. 1 Prot. 2 Prot. 1 Prot. 2
(Main) (Back-up) (Main) (Back-up)
2-Winding (Star/Delta) Id I> + IN + TH + SBEF I>
Id REF I> + IN + TH + SBEF I>
2-Winding (Star/Stern) Id I> + IN + TH I> + IN + SBEF
Id REF I> + IN + TH REF I> + IN + SBEF
2-Winding (Star/Delta) + Earth.transf. Id I> + IN + TH I> + IN + SBEF
Id REF I> + IN + TH I> + IN + SBEF
3-Winding (Star/Star/Delta) Id I> + IN + TH I> + IN + SBEF I>
Id REF I> + IN + TH REF I> + IN + SBEF I>
3-Winding (Star/Star/Delta) + Earth.transf. Id I> + IN + TH I> + IN I> + IN + SBEF
Id REF I> + IN + TH REF I> + IN I> + IN + SBEF
2-Winding (Auto) Id + REF I> + IN + TH I> + IN
3-Winding (Auto) Id + REF I> + IN + TH I> + IN I>
Remark: The SBEF-Function (Stand-by EF Prot.) is only needed if earthing resistor is installed
Transformer Rating
S < 60 MVA S > 60 MVA

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F10 of 44
Transformer Protection in Transmission Networks
ABB
Transformer protection example (1)
Bu / LOL
OT / WT
I >
IN
TH
I
I >>
•
IN
IN
I >
REF

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F11 of 44
Transformer Protection in Transmission Networks
ABB
Transformer protection example (2)
- Differential prot. (87T)
- REF (87N)
- Overcurrent (51T)
- E/F protection (51N)
- Thermal overload prot. (49)
- Overvoltage prot. (59)
I> 51T υ 49
REF 87N I0 51N
87T
U> 59
B
87T

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F12 of 44
Transformer Protection in Transmission Networks
ABB
Transformer protection example (3)
I
Bu / LOL
OT / WT
I>
IN
TH
Id
I>
I>
I N

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F13 of 44
Transformer Protection in Transmission Networks
ABB
I
Bu / LOL
OT / WT
I >
IN
TH
Id
I >
IN
I >
REF
I >>
REF
Transformer protection example (4)

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F14 of 44
Transformer Protection in Transmission Networks
ABB
Differential protection (87T)
Features / requirements
• low impedance principle
• for two and three-winding
transformers
• non-linear current-dependant
tripping characteristic
• high stability during through-
fault and CT-saturation
• compensation for vector group
• compensation for current
amplitude (CT-ratio)
• inrush restraint
Causes
• phase faults in the
protection zone
effects
• high currents
• potential damage to
transformer winding
• expensive outage and
repair due to damage

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F15 of 44
Transformer Protection in Transmission Networks
ABB
Features
Differential Protection
includes:
• C.T. Ratio adaption
• Connection group adaption
• Back-up functions
• Large setting ranges

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F16 of 44
Transformer Protection in Transmission Networks
ABB
Differential protection (87T)
• Id= ¦I1+I2 ¦
• by external faults can due to
-ratio errors
-saturation
-losses in the transfomer
-tapchanger
a differential current can occur,
therefore a stabilized tripping
characteristic is needed
• Inrush can also provoke differential
current
87T Protection
zone

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F17 of 44
Transformer Protection in Transmission Networks
ABB
Differential protection (87T)
Features
• True measurement for three-wind.
transformer
– compares the greatest current the with
sum of the two others
• I-instantaneous independ. of inrush
• Inrush
– eval.ratio 2nd.harm to fundamental
– detection of largest phase current
– detection of energised transformer using
load current
• Adaptive characteristic (b-line)
Id/ IN
No Trip
Trip for
I1 / IN < b or
I2 / IN < b
Trip
v
g-high
g
b
Ih/ IN

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F18 of 44
Transformer Protection in Transmission Networks
ABB
Differential protection (87T)
AI 7,8,9
AI 1,2,3
A
D
DIFF A
D

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F19 of 44
Transformer Protection in Transmission Networks
ABB
Differential protection for 3 windings
AI 1,2,3
AI 7,8,9
A
D
DIFF
A
D
A
D
AI 4,5,6

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F20 of 44
Transformer Protection in Transmission Networks
ABB
Differential protection 87T
• CT's at the Aux. transformer
must have the same ratio as
the other two.
• Correction of the ratio with
Ref.-Value or a-Factor in the
protection function
G
87GT
10'000/ 5
30MVA
18/ 6 KV
800/ 5
300MVA
220/ 18 KV
300MVA
18 KV
10'000/ 5

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F21 of 44
Transformer Protection in Transmission Networks
ABB
Fault inside protected zone
I1 I2 ∆I
1
2
3
4
1 2 3 4 5 IH
cos α < 0
IH = 0
g

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F22 of 44
Transformer Protection in Transmission Networks
ABB
Fault outside protected zone
Low short circuit current
Load I < (1.5...3) * Irated
I1 I2
v=50%
∆I
4
cos α = 1
IH I1 I2 cos
= • • α
3
2
1
IH = I1 = I2 =
ILoad < (1.5...3)*Irated g
IH
1 2 3 4 5

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F23 of 44
Transformer Protection in Transmission Networks
ABB
Fault outside protected zone
High short circuit current
Isc
1
2
3
4
1 2 3 4 5 IH
∆I
v=50%
I1 I2
IH = I1 = I2
g
I > (1.5....3) * Irated
cos α = 1
v= infinite
IH I1 I2 cos
= • • α
b

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F24 of 44
Transformer Protection in Transmission Networks
ABB
Effect from different time constants

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F25 of 44
Transformer Protection in Transmission Networks
ABB
Operating characteristic of the RE..16 differential protection
v
g
1 2 3
b
Restraint
I
IN
Operation
Operation for
I1
IN
< b
or
I2
IN
< b
IH
IN
Protected unit
I 1 I 2
2)
-
1;
1
2
2
1
1
H
2
1
H
H
3
2
1
I
(I
α
I
-
I
I
I
;
I
of
greatest
I
:
where
0
α
cos
for
0
I
0
α
cos
for
α
cos
I
I
I
current
.Restraint
..........
..........
I
current
Operating
....
I
I
I
I
∠
=
∆
=
=
<
=
≥
⋅
⋅
=
+
+
=
∆

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F26 of 44
Transformer Protection in Transmission Networks
ABB
Vector group adoption for Yd5 transformer

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F27 of 44
Transformer Protection in Transmission Networks
ABB
Protection example of a Yd11 Transformer with a Zig-Zag grouding
on low voltage side within the protected zone
Set Yz11 connection group

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F28 of 44
Transformer Protection in Transmission Networks
ABB
Transformer with a Zig-Zag grouding on low voltage side
within the protected zone (conventional solution)

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F29 of 44
Transformer Protection in Transmission Networks
ABB
Restricted earth-fault protection (REF)
AI
Trip
REF
Id
REF
Id Trip
• Used at direct and low
impedance earthing
• Clears internal EFs
instantaneously
• Unaffected by inrush current
and external fault

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F30 of 44
Transformer Protection in Transmission Networks
ABB
<<<
200/1A
<<<
>
Yd1
10MVA
66/33kV
100/1A
<
>
<
<
>
<
<
>
R
IE=3IO
S
<<<
<<<
<<<
l >
T
>
>
1/0,33 A
200/1A
>
<<<
REF
<
<
<<
R

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F31 of 44
Transformer Protection in Transmission Networks
ABB
High-impedance restricted earthfault protection REF
All CT‘s have identical ratios
REF

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F32 of 44
Transformer Protection in Transmission Networks
ABB
Thermal overload protection
Rise of temperature
τ
0,63
Time

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F33 of 44
Transformer Protection in Transmission Networks
ABB
Overexcitation protection
t
Definite
V/Hz inverse
V/Hz

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F34 of 44
Transformer Protection in Transmission Networks
ABB
Requirements for overcurrent protection
Fast operation for primary short circuit
Non operation for inrush
Discrimination with other overcurrent
protection
Non operation at short or long term overload
Back up protection for network faults,
outside the transformer

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F35 of 44
Transformer Protection in Transmission Networks
ABB
Application, typical HV bay
Transformer protection
R
E
C
Control unit
Autoreclosure*
Busbar protection
OFF 1
ON
OFF 2
* ev. separate unit

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F36 of 44
Transformer Protection in Transmission Networks
ABB
Protection function structure
Ir12 = 0,80 A
Ir22 = 0,98 A
110 V
√3
Ur22 = 110/√3 V
30 MVA
145 kV
11 kV
Ir1 = 120 A
Ir2 = 1575 A
1600 / 1 A
150 / 1 A
11 kV
√3
150 / 1 A IrN12 = 0,80 A
A/D
conv.
BI
DIFF
TOC
REF
etc.
NOV
Trip
logic
Trip
F
i
l
t
e
r
i
n
g
>1

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F37 of 44
Transformer Protection in Transmission Networks
ABB
Main functions
• Compact design including:
• Basic SW functions and transformer protection functions:
- Differential protection
- Overcurrent protection
(Definite time or inverse functions)
- Thermal overload
- Overvoltage protection
- Metering U I f P Q
- Distance protection
- Overexcitation U/f
- FUPLA
- Logic functions,
delay & counter
- Disturbance Recording
- Check functions (I, U)

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F38 of 44
Transformer Protection in Transmission Networks
ABB
Main Features
- No interposing CT's
- Standard wiring diagram
- Inputs for external functions (Buchholz, temperature sensors) available
- Programmable indication of tripping and signalling
- Indication of measuring values
- Continuous self-monitoring
- Modular SW protection functions
- 4 serial interfaces:
* one front for local commmunication (PC)
* one rear for remote communication SPA or VDEW6
* two others (spare)
- Member of the 316*4-family and part of PYRAMID
- Fits into ABB solution

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F39 of 44
Transformer Protection in Transmission Networks
ABB
Transformer Protection Options
• I> back up
• Sensitive earth fault I0>
for not grounded windings
• Restricted earth fault
(High impedance principle)
• Thermal overload
• U>, U<
• Distance Protection
2W only
2W only
2W only
2W only

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F40 of 44
Transformer Protection in Transmission Networks
ABB
Additional Logic
Additional Logic
A
A
Monitoring
Monitoring
Communication
Communication
Power Supply
Power Supply
Protection Functions
Protection Functions
Additional Logic
Additional Logic
B
Monitoring
Monitoring
Communication
Communication
Power Supply
Power Supply
Protection Functions
Protection Functions
INTERBAY BUS
COMMUNICATION
Station A
B8 B9
C1
T1 T2
B1 B2
B3 B4 B5 B6 C7
C2
B7
DEC 3000 AXP
Alpha
1252 123 123 123 123 123 123 123 123 123 123 123 123 123
123 123
SCS/ SMS
Q1
Q53
Q51
Q2
Q0
Q9
G
Redundancy

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F41 of 44
Transformer Protection in Transmission Networks
ABB
Redundancy example
Transformer protection
A
B
Transformer protection
R
E
C
R
E
C

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F42 of 44
Transformer Protection in Transmission Networks
ABB
Signal data flow
etc.
Trip
MUX
1 DiffGen on
2 Current on
3 BinInp 2 off
COM
I>
U<
etc.
A/D
S
H
DSP
COM
SCS/
SMS
Analog to
digital
conversion
A/I
MMI Numerical
signal
processing
Binary
signal
processing
B/I
B/O

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F43 of 44
Transformer Protection in Transmission Networks
ABB
∼
∼
∼
A/I B/O
∼
∼
∼
Binary
output
isolation
Algorithm and Logic
processor
Digital
filter
Amplifier
Low pass
filter
Shunt
Analog
input
isolation
4
7
2
3
0
0 ms 0 ms 3 ms 5 ms 12 ms 21 ms 25 ms
Z<
I >
I
etc
FUPLA
etc
9
A/D
S
H
Typical tripping time
MUX

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F44 of 44
Transformer Protection in Transmission Networks
ABB
Advantages
• Self monitoring
• Long term stability
• Event recorder
• Self documentation
• Number of CT cores reduced
• User designed performance
• Selectable protection functions
• Facility for communication to SMS/SCS