Using A Ground Or Neutral Current Ct - Siemens 7UT51 Instruction Manual

4
Transformer Differential Protection (87T and 87HS)
Internal Single Phase to Ground Fault with
Io-Correction
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-Correction:
=
* *
I I
,
A Corr A
=
* *
I I
B , Corr B
=
* *
I I
C , Corr C
Delta-Winding Currents after I0-Elimination
and Phase-Shift Correction:
⎡ ⎤
*
I
⎡
... 1 ....
, 1 E lim
⎢ ⎥
⎢
1
=
*
⎢ ⎥
I ... 0 ....
⎢
, 2 E lim
3
⎢ ⎥
⎢
−
⎣ 1 ....
*
⎢ ⎥
I
⎣ ⎦
, 3 E lim
=
* *
I I
, ,
D A A Corr
Differential
=
* *
I I
, ,
D B B Corr
Current:
=
* *
I I
, ,
D C C Corr
54
Delta-Winding
Currents:
= ∠
* 0
I 1 0
1
=
*
I 0
2
=
*
I
0
3
= − = ∠
* * *
I I I 1
a 1 3
= − = ∠
* * *
I I I 1 180
b 2 1
= − =
* * *
I I I 0
c 3 2
1 1
+ = ∠
* 0
I 0
N
3 3
1 1
+ = ∠
* 0
I 0
N
3 3
1 1
+ = ∠
* 0
I 0
N
3 3
⎡
2 ∠
0
0
⎡ ⎤
*
⎤ I
⎢ 3
1 ... 0
a
⎢ ⎥
⎥
⎢
= ∠
1
*
⎢ ⎥
1 ... 1 I 180
⎥
⎢
3
b
⎢ ⎥
⎥
⎢
0 ... 1 ⎦ *
I
⎣ ⎦ 1 ∠
180
c ⎢
⎣
3
+ =
*
I 1
Trip !
, 1 lim
E
with
+ =
*
I 0
, 2 lim
E
maximum
+ =
*
sensitivity
I 0
, 3 lim
E
4.3.7
If the protection application includes measuring one or
two ground currents (or neutral currents), relay model
7UT513 must be used. If the relay is ordered with the
optional tank-leakage protection, one of the relay's two
ground-current inputs measures the absolute ground
current. If instead the relay was ordered with the
ground-differential protection option, both
ground-current inputs measure the ground current as
a multiple of the rated nominal current of the reference
0
winding of the protected transformer, I
0
7806 and 7807 tell the relay how the corresponding
0
ground current input is to be used.
7806 STAR
7807 STAR
What is connected to each ground
Option
NO
ASSIGNMENT
SIDE 1
SIDE 2
SIDE 3 / V. OBJ
⎤
⎥
⎥
0
⎥
⎥
0
⎥
⎦
Using a Ground or Neutral
Current CT
-
POINT A (7UT513 only)
-
POINT B (7UT513 with 87N option only)
-
current input of the relay.
Description
No CT is connected to this
-
ground current input (default).
A CT monitoring the ground or neutral
current of Winding 1 of the protected
transformer.
A CT monitoring the ground or neutral
current of winding 2 of the protected
transformer.
A CT monitoring the ground or neutral
current of winding 3 of the principal
protected transformer, or the ground or
neutral current of a separate, additional
protected device (see Chapter 11).
7UT51 v3
. Addresses
n
PRIM-2330C