03_Prot.transmission_Trafo.pdf

ABB Power Automation Ltd
T2314 / trafoprot_a.ppt / F1 of 44
Transformer Protection in Transmission Networks
ABB
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
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
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
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
Possible Transformer Failures
Winding failures
Tap changer failures
Bushing failures
Core failures
Miscellaneous failures

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
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
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
Transformer protection example (1)
Bu / LOL
OT / WT
I >
IN
TH
I
I >>
•
IN
IN
I >
REF

ABB
- 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
I
Bu / LOL
OT / WT
I>
IN
TH
Id
I>
I>
I N

ABB
I
Bu / LOL
OT / WT
I >
IN
TH
Id
I >
IN
I >
REF
I >>
REF

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
Features
Differential Protection
includes:
• C.T. Ratio adaption
• Connection group adaption
• Back-up functions
• Large setting ranges

ABB
• 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
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
AI 7,8,9
AI 1,2,3
A
D
DIFF A
D

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
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
Fault inside protected zone
I1 I2 ∆I
1
2
3
4
1 2 3 4 5 IH
cos α < 0
IH = 0
g

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
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
Effect from different time constants

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
Vector group adoption for Yd5 transformer

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
Transformer with a Zig-Zag grouding on low voltage side
within the protected zone (conventional solution)

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
<<<
200/1A
<<<
>
Yd1
10MVA
66/33kV
100/1A
<
>
<
<
>
<
<
>
R
IE=3IO
S
<<<
<<<
<<<
l >
T
>
>
1/0,33 A
200/1A
>
<<<
REF
<
<
<<
R

ABB
High-impedance restricted earthfault protection REF
All CT‘s have identical ratios
REF

ABB
Thermal overload protection
Rise of temperature
τ
0,63
Time

ABB
Overexcitation protection
t
Definite
V/Hz inverse
V/Hz

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
Application, typical HV bay
Transformer protection
R
E
C
Control unit
Autoreclosure*
Busbar protection
OFF 1
ON
OFF 2
* ev. separate unit

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
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
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
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
Additional Logic
Additional Logic
A
A
Monitoring
Monitoring
Communication
Communication
Power Supply
Power Supply
Protection Functions
Additional Logic
Additional Logic
B
Monitoring
Monitoring
Communication
Communication
Power Supply
Power Supply
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
Redundancy example
A
B
R
E
C
R
E
C

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
∼
∼
∼
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
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

03_Prot.transmission_Trafo.pdf

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03_Prot.transmission_Trafo.pdf