BE1-51/27R - Installation
4-17
Table 4-1. Three-Phase Fault Currents, -A @ 11 kV
Current Type
Out of Service
Fault Location
Downstream
Generator
Transient
T2
1
7256
776
Steady-State
T2
1
5961
129
Transient
-
2
7256
776
Transient
T2
2
1552
776
Steady-State
T2
2
258
129
Transient
-
3
713
713
Steady-State
-
3
127
127
Coordination With Feeder Relay 51 for Fault 1
Multiples of pickup in the 51 relay at transient level are:
7256
800
5
×6
7256
960
7.6
Relay 51 time at 7.6 multiples (from B6 curves) @ 08 time dial: 0.31 seconds.
Set 51/27 relay pickup:
1.75×3700
11×1.73
340 A Primary
340
(
300
5
)
5.7 A Secondary
Set 51/27 relay time to provide 0.3 seconds coordinating interval: 0.31 plus 0.3
0.61 seconds at 776 A
51/27 relay voltage = 0, so pickup = 0.25 × 5.7
1.4 A (84 A Primary)
51/27 multiples:
776
1.4 ×
300
5
9.2
51/27 time dial (from B6 curve @ 9.2 multiple and 0.61 seconds): 23.
Multiples of pickup in the 51 relay at steady state level are:
5961
800
5
×6
6.2
51/27 time at 6.2 multiples: 0.36 seconds.
51/27 multiples at 129 A:
129
1.4 ×
300
5
1.5
51/27 time at 1.5 multiples: 9.0 seconds.