4.37
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
current). However, the minimum acceptable value of 50REF1P must meet the
following two criteria.
1. 50REF1P must be greater than any natural residual current
imbalance caused by load conditions.
2. 50REF1P must be greater than a minimum value determined by
the relationship of the CTRn (where n is N, X, or Y) values
used in the REF function.
You must set the threshold setting, 50REF1P, at the greater of the two criteria
values. See sample calculations in REF Current Pickup Level.
Polarizing Quantity
Figure 4.20 shows the effect of the X_CUR_IN setting on the polarizing quantity.
(I
NOM
= Nominal Current of n CTs, n = X, Y, N)
Figure 4.20
Effect of X_CUR_IN Setting on Polarizing Current
Calculation of the residual current for X and Y CTs is as follows:
IGn = IAn + IBn + ICn (n = X, Y)
X_CUR_IN = NEUT
I
POL
= IGY • CTRY / (CTRN • I
YNOM
)
I
OP
= IN / I
NNOM
Delta-Wye Transformer
100 MVA
13.8 kV 138 kV
Neutral N-CT
CTRN = 150:5
Y-CTs
CTRY = 500:5
IGY
IN
X_CUR_IN = NEUT
I
POL
= IGY • CTRY / (CTRN • I
YNOM
)
I
OP
= IN / I
NNOM
Generator
IN
Y-CTs
Neutral CT
IGY
X_CUR_IN = TERM
I
POL
= –IGX • CTRX / (CTRN • I
XNOM
)
I
OP
= IN / I
NNOM
Generator
X-CTs
Neutral CT
IGX
X-CTs
IN
Summary of Contents for SEL-700G Series
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