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GEK-26423
APPENDIX I
MINIMUM PERMISSIBLE REACH SETTING
FOR THE CEYG51A
The CEYG5IA relay will measure positive sequence impedance and, therefore, distance on the transmis
sion line accurately on three phase faults.
However, on single phase to ground faults, when zero sequence
current compensation is NOT used, its reach is foreshortened.
If zero sequence current compensation is
used, the only remaining variation in unit reach will be due to zero sequence mutual impedance with a
parallel line.
These factors will be evident from the following equations Ta and lb
The mho units of
the CEYG51A relay must not be compensated for the zero sequence mutual impedance due to a parallel line.
This is because reversal mutual in the parallel line could cause the who unit to operate incorrectly on
the protected line.
NO ZERO SEQUENCE CURRENT COMPENSATION
When zero sequence current compensation is NOT used, the effective impedance as seen by the relay on
the faulted phase for a single phase to ground fault at the far end of the line is:
z
+
(Z
0
'
-
Z
1
) C
0
ZI'
1
2C+C
I
o
a
Ia
where:
=
Positive sequence impedance of the protected line.
Z'
=
Zero sequence impedance of the protected line.
z
m
=
Total zero sequence mutual impedance between protected line and
parallel line.
I
"
=
Zero sequence current in the parallel line, taken as positive when the
0
current flow in the parallel line is in the same direction as the current
in the protected line.
'a'
=
Phase A current in the relay.
C
=
Positive sequence distribution constant I'/l.
C 0
=
Zero sequence distribution constant 10/10.
T
=
Tap setting in percent.
K
=
Design Constant
100 for the 1.0 ohm basic minimum tap
200 for the 2.0 ohm basic minimum tap
300 for the 3.0 ohm basic minimum tap
0
=
The aigle the fault current lags the fault voltage.
To insure that the relay on the faulted phase picks up for a fault at the remote bus, the maximum per
cent tap setting permissible is:
T
=
KCos (600_U)
(Z
0
'
-
z
1
) C
0
ZI"
1
lb
1.25
L
Z 1
+
2C ÷ C 0
+
Ta
I
17
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