ABB REG650 Technical Manual page 87

1MRK 502 034-UEN -
Technical Manual
é ù é
-
IDL 1 _ NS 2 1
ê ú ê
1
×
= -
IDL 2 _ NS 1 2
ê ú ê
3
ê ú ê
ë û ë
- -
IDL 3 _ NS 1 1
1
EQUATION1247 V1 EN
where:
1. is Negative Sequence Differential Currents
2. is Negative Sequence current contribution from W1 side
3. is Negative Sequence current contribution from W2 side
and where:
IDL1_NS is the negative sequence differential current in phase L1 (in
W1 side primary amperes)
IDL2_NS is the negative sequence differential current in phase L2 (in
W1 side primary amperes)
IDL3_NS is the negative sequence differential current in phase L3 (in
W1 side primary amperes)
INS_W1 is negative sequence current on W1 side in primary
amperes (phase L1 reference)
INS_W2 is negative sequence current on W1 side in primary
amperes (phase L1 reference)
Ur_W1 is transformer rated phase-to-phase voltage on W1 side
(setting parameter)
Ur_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 the symmetrical three phase
current system on each transformer side (that is, negative sequence currents in
every phase will always have the same magnitude and be phase displaced for 120
electrical degrees from each other), it is only necessary to calculate the first
negative sequence differential current that is, IDL1_NS.
As marked in equation 23, the first term on the right hand side of the equation,
represents the total contribution of the negative sequence current from W1 side
compensated for eventual power transformer phase shift. The second term on the
right hand side of the equation, represents the total contribution of the negative
sequence current from W2 side compensated for eventual power transformer phase
ù é ù
-
1 INS W _ 1
ú ê ú
Ur W _
×
- × +
1 a INS W _ 1
ú ê ú
Ur W _
ú ê ú
2 ×
û ë û
2 a INS W _ 1
2
1 3
j
2 2
Section 5
Differential protection
é ù é
-
1 0 1
ê ú ê
2 1
× × ×
-
1 1 0 a INS W
ê ú ê
1
3
ê ú ê
2
ë û ë
-
0 1 1 a
3
(Equation 24)
ù
INS W _ 2
ú
×
_ 2
ú
ú
×
û
INS W _ 2
(Equation 23)
81