ABB Relion Technical Manual page 108

Section 6
Differential protection
102
é ù é -
IDNS _ A 2 1
ê ú 1 ê
= × -
IDNS B _ 1 2
ê ú ê
3
ê ú ê
- -
IDNS C _ 1 1 2
ë û ë
1
EQUATION1560 V1 EN
where:
1. is the Negative Sequence Differential Current per phase
2. is Negative Sequence current contribution from the W1 side
3. is the Negative Sequence current contribution from the W2 side
and where:
IDNS_A is the negative sequence differential current in phase A (in
W1 side primary amperes)
IDNS_B is the negative sequence differential current in phase B (in
W1 side primary amperes)
IDNS_C is the negative sequence differential current in phase C (in
W1 side primary amperes)
INS_W1 is the negative sequence current on the W1 side in primary
amperes (phase A reference)
INS_W2 is the negative sequence current on the W1 side in primary
amperes (phase A reference)
Vn_W1 is the transformer rated phase-to-phase voltage on the W1
side (setting parameter)
Vn_W2 is transformer rated phase-to-phase voltage on W2 side
(setting parameter)
a is the complex operator for sequence quantities, for example,
o
= × = - + ×
j 120
a e
EQUATION1248 V1 EN
Because the negative sequence currents always form a symmetrical three phase system
(negative sequence currents in every phase will always have the same magnitude and a
120 degrees phase rotation compared to each other), it is only necessary to calculate the
first negative sequence differential current that is, IDNS_A. This value is then reported as
IDNSMAG.
é ù
- ù
1 INS W _ 1
ê ú
ú Vn W _
- × × +
1 a INS W _ 1
ê ú
ú
Vn W _ 1
ê ú
ú
û 2
×
ë a INS W _ 1 û
2
1 3
j
2 2
1MRK 502 048-UUS A
é
é - ù
1 0 1 INS W _
ê
2 1 ê ú
× × - × ×
1 1 0 a INS W
ê
ê ú
3
ê
ê ú
-
0 1 1
ë û 2
×
ë a INS W
3
(Equation 24)
Technical manual
ù
2
ú
_ 2
ú
ú
_ 2 û
(Equation 23)