Calculation Of Settings - GE CEY51A Instructions Manual

GEl-1275
TABLE I
Basic Minimum Restraint Min. 3-phase Fault
Tap Setting Tap Setting
Current Requi red
0.2 ohms 25% 15.0 amps
0.2
50%
22.5
0.2 100% 30.0
0.375
25% 8.0
0.375 50% 12.0
0.375 100% 16.0
0.4 25% 7.5
0.4 50% 11.25
0.4
I
100% 15.0
0.75 25% 4.0
0.75 50% 6.0
0.75 100% 8.0
0.8 25% 3.75
0.8
50% 5.6
0.8
100% 7.5
1.5 25% 2.0
1.5 50% 3.0
1.5 100% 4.0
3.0 25% 1.0
3.0 50% 1.5
3.0 100% 2.0
6.0 25% 0.5
6.0 50% 0.75
6.0 100% 1.0
The CEY51A and its companion zone-packaged relays may be combined in many
different ways for use in different schemes, including straight distance protection,
directional-comparison carrier protection, permissive overreaching, permissive- and
direct-underreaching transferred tripping and many different back-up schemes.
Figure 3 illustrates the external connections to the CEY51A when used in conjunction
with a CEY52A, a CEB52A and an RPM21D for three-zone protection of a transmission
line against all multi-phase faults.
The section under CALCULATION OF SETTINGS provides a worked example for a
typical application of the CEY51A relay.
CALCULATION OF SETTINGS
Consider a 230 kV transmission line 50 miles long having a phase-to-neutral
impedance of:
Zprim
=
0.14 + jO.80 ohms per mile
4