Siemens 7UT51

4
Transformer Differential Protection (87T and 87HS)
7UT51 v3
52 PRIM-2330C
Figure 4.7
External Phase to Ground Fault
External Single Phase to Ground Fault,
Io
-
Correction
Refer to Figure 4.7
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
Source
0*
0*
0
*
*
0*
01
180
3
1
0
0
1801
∠=
∠=
=
=
∠=
N
C
B
A
I
I
I
I
I
Wye-Winding
Currents:
Delta-Winding
Currents:
⎥
⎥
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎢
⎢
⎣
⎡
∠
∠
∠
=
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
−
=
⎥
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎢
⎣
⎡
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
No Trip !
Differential
Current:
Wye-Winding Currents after
I0-Correction:
Delta-Winding Currents after I0-Elimination
and Phase-Shift Correction:
0
0
0
*
lim,3
*
,
*
,
*
lim,2
*
,
*
,
*
lim,1
*
,
*
,
=+=
=+=
=+=
ECorrCCD
ECorrBBD
ECorrAAD
III
III
III
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
0***
,
0***
,
0***
,
0
3
1
3
1
0
3
1
3
1
180
3
2
3
1
∠=+=
∠=+=
∠=+=
NCCorrC
NBCorrB
NACorrA
III
III
III