G. Ziegler. Digital Differential Protection
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G. Ziegler, 10/2005 page 150
Differential Protection Symposium
Belo HorizonteNovember 2005
E
R
F
R
Uh
I
⋅
=
F
n
n
FK
I
U
U
hI
w
wh
I ⋅
⋅
⋅=⋅
⋅
=
3
1
2
1
2
E
R
R
U
n
U
n
U
h
K
I ⋅⋅⋅=
1
2
3
1
2
Source: P.M. Anderson: Power System Protection, McGraw-Hill and IEEE Press (Book)
h⋅U
R
R
E
U
R
I
F
I
K
Infeedside
Short-circuited winding part h in %
Max
I
I
50
0
20
40
60
80
100
100
%
I
F
I
K
Transformer winding to earth fault
Resistance or reactance earthed neutral
G. Ziegler, 10/2005 page 151
Differential Protection Symposium
Belo HorizonteNovember 2005
I
P
x In
I
F
, I
K
x In
Short-circuited winding part h in %
I
F
I
K
Transformer winding short-circuit
Source: Protective Relays, Application Guide, GEC AlstomT&D, 1995
100
80
60
40
20
0
5101520
25
2
4
6
8
10
I
F
I
K
G. Ziegler, 10/2005 page 152
Differential Protection Symposium
Belo HorizonteNovember 2005
I>
∆ I
E
I
0
*
I
0
**
I
N
I
R
I
S
I
T
Restricted earth fault protection of relay 7UT6
Polarised earth current
differential protection
0
20
40
60
80100
120
140
160
180
200
220
240
260 280
300
320
340
2
1.6
1.2
0.8
0.4
0
3.14
*)*/I*(I
0
0
00
e
**I
*I
ϕ
⋅
+
1
Blocking
Tripping
K0= 4
K0= 2
K0= 1.4
K0= 1
ϕ
G. Ziegler, 10/2005 page 153
Differential Protection Symposium
Belo HorizonteNovember 2005
Restricted earth fault protection 87N (7UT6)
Application aspects
n Increased sensitivity with earth faults near winding neutral
Preferably used in case of resistance or reactance neutral earthing
n Sensitive to turns short-circuit
n I0 / IN amplitude and angle comparison
n 2nd harmonic stabilised
n Can protect a separate shunt reactor or neutral earthingtransformer in
addition to the two winding transformer differential protection
n Not applicable with autotransformers! (as only one stabilising input at transformer
terminal side, --high impedance principle to be used in this case.
G. Ziegler, 10/2005 page 154
Differential Protection Symposium
Belo HorizonteNovember 2005
∆I
E
>
I
N
I
r
I
s
I
t
∆I
E
>
I
R
I
S
I
T
Z
E
Transformer HI-earth fault protection
G. Ziegler, 10/2005 page 155
Differential Protection Symposium
Belo HorizonteNovember 2005
I
r
I
s
I
t
87
I
R
I
S
I
T
87 87
HI differential protection of an autotransformer
G. Ziegler, 10/2005 page 156
Differential Protection Symposium
Belo HorizonteNovember 2005
I
N
I
r
I
s
I
t
∆I>
I
R
I
S
I
T
HI earth fault protection of an autotransformer
G. Ziegler, 10/2005 page 157
Differential Protection Symposium
Belo HorizonteNovember 2005
Transformer tank protection 64T: Principle
Insulated
I
E
>
G. Ziegler, 10/2005 page 158
Differential Protection Symposium
Belo HorizonteNovember 2005
Transformer protection, Relay design
7UT612: for protection objects with 2 ends (1/3 x 19’’case 7XP20)
7UT613:for protection objects with 3 ends (1/2 x 19’’case 7XP20)
7UT633:for protection objects with 3 ends (1/1 x 19’’case 7XP20)
7UT635: for protection objects with 5 ends (1/1 x 19’’case 7XP20)
7UT6 differential protection
for
•Transformers
•Generators
•Motors
•Busbars
G. Ziegler, 10/2005 page 159
Differential Protection Symposium
Belo HorizonteNovember 2005
7UT6
Integrated protection functions
FunctionANSI No.
Differential87T
Earth differential87 N
Phase overcurrent, 50/51
Neutral overcurrentI
N
>, t50N/51N
Ground overcurrent(I
E
, t)50G/51G
Unbalanced current I
2
>, t46
Thermal overload IEC 60255-849
Therm. OL IEC 60354 (hot spot)49
FunctionANSI No.
OverfluxingV/Hz24
Breaker failure50BF
Temperature monitoring38
Hand reset trip86
Trip circuit supervision74TC
Binary inputs for tripping commands