Siemens 7UT51 Instruction Manual page 53

7UT51 v3
Internal Single Phase to Ground Fault with
Io-Elimination
Refer to Figure 4.8
Wye-Winding
Currents:
=
*
I 0
A
=
*
I 0
B
=
*
I 0
C
=
*
I 0
0
= ∠
* 0
I 1 0
N
Wye-Winding Currents after
I0-Elimination:
=
*
I
A , E lim
=
*
I
B , E lim
=
*
I
C , E lim
Delta-Winding Currents after I0-Elimination
and Phase-Shift Correction:
⎡ ⎤
*
I
⎡
... 1 .... 1
, 1 E lim
⎢ ⎥
⎢
1
=
*
⎢ ⎥
I
... 0 .... 1
⎢
, 2 E lim
3
⎢ ⎥
⎢
−
⎣ 1 .... 0
*
⎢ I ⎥
⎣ ⎦
, 3 E lim
Differential
Current:
= +
* * *
I I I
D , A A , E lim , 1 E lim
= +
* * *
I I I
D , B B , E lim , 2 E lim
= +
* * *
I I I
D , C C , E lim , 3 E lim
PRIM-2330C
Delta-Winding
Currents:
= ∠
* 0
I 1 0
1
=
*
I 0
2
=
*
I 0
3
= − = ∠
* * *
I I I 1 0
1 3
a
= − = ∠
* * *
I I I 1 180
b 2 1
= − =
* * *
I I I
0
c 3 2
− =
* *
I I 0
A 0
− =
* *
I I 0
B 0
− =
* *
I I 0
C 0
⎡
2 ∠
0
0
⎡ ⎤
*
⎤ I
... 0 ⎢ 3
a
⎢ ⎥
⎥
⎢
= 1 ∠
* 0
⎢ I ⎥
... 1 180
⎥
⎢
3
b
⎢ ⎥
⎥
⎢
*
... 1 ⎦
I
⎣ ⎦ 1 ∠
0
180
⎢
c
⎣
3
= 2 ∠
0
0
3
Trip !
with
= 1 ∠
0
180
3 reduced
sensitivity
= 1 ∠
0
180
3
Transformer Differential Protection (87T and 87HS)
0
0
Figure 4.8
⎤
⎥
⎥
⎥
⎥
⎥
⎦
I
I
A
1
A
I
B
I
2
B
I
C
I
3
C
I
N
Internal Single Phase to Ground
4
I
a
a
I
b
b
I
c
c
-
Fault
53