GE 845 Instruction Manual page 203

CHAPTER 4: SETPOINTS
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Magnitude compensation for winding 2 currents:
M = (CT .V )/ (CT
W2 W2 W2
factor for Winding 2 currents
Winding 2 currents = (M
To check that the measured currents from both windings will sum-up to zero after applying
magnitude compensation, one can perform the following simple calculations:
Phase Shift Compensation
From the transformer example, the phase reference winding is winding 2 (i.e.,w
phase compensation angle for each winding is then calculated as follows (Rotation =
"ABC"):
φ
[1] = -30°– 0° = -30° = 30° lag
comp
φ
[2] = -30° – (–30°) = 0°
comp
The non-reference Wye winding will be rotated by -30° degrees to be in-phase and match
the currents from the Delta winding.
Per figure: Two-winding transformer connections for phase compensation angle of 30 lag,
the relay will use the following phase and zero-sequence compensation equations:
Winding 1 (Wye – grounded neutral):
p
I [w]= (1/√3)I [w] - (1/√3)I
A A
p
I [w]= (1/√3)I [w] - (1/√3)I
B B
p
I [w]= (1/√3)I [w] - (1/√3)I
C C
Winding 2 (Delta):
p
I [w] = I [w]
A A
p
I [w] = I [w]
B B
p
I [w]= I [w]
C C
The complete compensated winding 1 and winding 2 currents would be as follows:
The differential and restraint currents would be as follows:
Differential currents:
Id = 0 x CT
A
Id = 0 x CT
B
Id = 0 x CT
C
Restraint currents:
Ir = 0.209 x CT
A
Ir = 0.209 x CT
B
Ir = 0.209 x CT
C
.V ) = (1500*4.16)/(500*13.8) = 0.9043, -magnitude comp.
W1 W1
* I (W ))/CT = (0.9043*347)/1500 = 0.209 x CT
W2 load 2 W2
[w]
C
[w]
A
[w]
B
SYSTEM
W2
= 2). The
f
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