Page 268 - Offshore Electrical Engineering Manual
P. 268
Overcurrent Relay Setting 255
FIGURE 4.7.2
Overcurrent discrimination flowchart.
OVERCURRENT RELAY SETTING
RELAY F: RANGE 10%–200%, CT RATIO 1500/1
From the load flow study:
Standing load = 50 kW + j20 kVA r ≈ 71 A
Motor load (2 motors) = 96 kW + j40 kVA r
Motor load (1 motor) = 96/2 + j40/2 = 52 kVA = 68 A
Motor starting current ≈ 6 × 68 A = 408 A
Therefore the maximum load including motor starting, assuming that the currents
are in phase, is
71 + 68 + 408 = 547 A
