Siemens 7UT51

7UT51 v3
Transformer Differential Protection (87T and 87HS)
4
PRIM-2330C 53
Internal Single Phase to Ground Fault with
Io-Elimination
Refer to Figure 4.8
Figure 4.8
Internal Single Phase to Ground
-
Fault
Wye-Winding
Currents:
Delta-Winding
Currents:
0*
*
0
*
*
*
01
0
0
0
0
∠=
=
=
=
=
N
C
B
A
I
I
I
I
I
0
1801
01
0
0
01
*
2
*
3
*
0*
1
*
2
*
0*
3
*
1
*
*
3
*
2
0*
1
=−=
∠=−=
∠=−=
=
=
∠=
III
III
III
I
I
I
c
b
a
Wye-Winding Currents after
I0-Elimination:
0
0
0
*
0
**
lim,
*
0
**
lim,
*
0
**
lim,
=−=
=−=
=−=
III
III
III
CEC
BEB
AEA
Delta-Winding Currents after I0-Elimination
and Phase-Shift Correction:
⎥
⎥
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎢
⎢
⎣
⎡
∠
∠
∠
=
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
−
=
⎥
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎢
⎣
⎡
0
0
0
*
*
*
*
lim,3
*
lim,2
*
lim,1
180
3
1
180
3
1
0
3
2
1...0....1
1...1....0...
0...1....1...
3
1
c
b
a
E
E
E
I
I
I
I
I
I
Differential
Current:
0*
lim,3
*
lim,
*
,
0*
lim,2
*
lim,
*
,
0*
lim,1
*
lim,
*
,
180
3
1
180
3
1
0
3
2
∠=+=
∠=+=
∠=+=
EECCD
EEBBD
EEAAD
III
III
III
Trip !
with
reduced
sensitivity
I
A
I
B
I
C
I
1
I
a
I
2
I
3
I
b
I
c
a
b
c
A
B
C
I
N
Sourc e