2 2
1_ 2 1 1 _ 1 1 0 1 _ 2
1 _ 2 1
2 _ 1 2 1 _ 1 1 1 0 _ 2
3 _ 1
3
3 _ 1 1 2 _ 1 0 1 1 _ 2
IDL NS INS W INS W
Ur W
IDL NS a INS W a INS W
Ur W
IDL NS a INS W a INS W
- - -
= - - × + - ×
- - -
× × × × ×
× ×
é ù é ù é ù é ù é ù
ê ú ê ú ê ú ê ú ê ú
ê ú ê ú ê ú ê ú ê ú
ê ú ê ú ê ú ê ú ê ú
ë û ë û ë û ë û ë û
EQUATION1247 V1 EN (Equation 23)
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:
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 the negative sequence current on the W1 side in primary
amperes (phase L1 reference)
INS_W2 is the negative sequence current on the W1 side in primary
amperes (phase L1 reference)
Ur_W1 is the transformer rated phase-to-phase voltage on the 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,
120
1 3
2 2
j
a e j
×
= = - + ×
o
EQUATION1248 V1 EN (Equation 24)
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,
IDL1_NS. This value is then reported as IDNSMAG.
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 the 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
Section 6 1MRK 502 048-UEN A
Differential protection
96
Technical manual
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