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GEK-26423
Basic
Rated
3-4, 5-6, or 7-8 Circuit
9-10 Circuit
Ohms
Freq.
I
X
2
1
R
X
Z
1
-
3D
60
5
0.070
0.040
0.080
5
0.210
0.120
0.240
0.5
-
15
60
5
0.007
0.005
0.008
5
0.021
0.013
0.024
1
-
30
50
5
0.058
0.033
0.067
5
0.175
0.100
0.200
NOTE:
Above data is for the mho units set on their maximum ohmic reach taps.
The burden
for the lower reach tap settings will be less than the tabulated burdens.
CALCULATION OF SETTINGS
In applying the relay to a particular line and system, the limitations outlined under APPLICATION fre
quently do not materialize.
Therefore, it is recommended that the initial calculations of 1 and 2 below
be followed to determine what final calculations may be necessary and how the relay may be applied.
1.
Determimimme if zero sequence current compensation is required. This will depend upon on evaluation of
the necessary rnho unit tap settings and the relation of the resulting mho characteristic with the
line power loadings and power swings.
See Appendix I, equations 'b and I.
2.
Determine if there is a limitation in the application for incorrect operation on faults behind the
relay terminal.
a.
When zero sequence current compensation is
t.{Qi
used:
if
Co is equal to or less than C, no
further evaluation need be made.
See Appendix II, equations ha, hib and tIc.
b.
When zero sequence current compensation is used: if (3K
+
1) Co is equal to or less than C,
no further evaluation need be made.
See Appendix III, equations lIla, hlIb and Ihic.
c.
If neither a nor b above is applicable, evaluate the equations of either Appendix II or III to
determine if it is necessary to use the zero sequence directional overcurrent supervising re
lay, Type CFPH16A.
The following calculations are made as an example of determining the actual tap settings to be used.
Consider the protected line to be between breakers A and B
on
the portion of a system shown in Fig. 5.
Assume the following characteristics:
Z 1
=
24.0
/790
primary ohms
=
72.0
/750
primary ohms
14.4 /75° primary ohms
CT Ratio
600/5
PT Ratio
1200/1
Secondary Ohms
=
CT Ratio
x Primary Ohms
PT Ratio
21
=
2.4
/79°
=
0.47
+
j2.36 secondary ohms
Z
0
'
=
7.2 /75°
=
1.9
+
j6.95 secondary ohms
Zom
1.4 /75°
=
0.36
+
jI.35 secondary ohms
Checking Appendix I first to establish the maximum tap setting that would still permit the CEYG5IA at
breaker A to detect a single phase to ground fault (F2) at the remote bus, Equation lb should be used.
The burdens imposed on the current transformers by the current circuits are given below:
7
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