Woodward MRM4, Manual

Page: 264 / 460

Protective Elements
The Start Control Module drawing shows an example of how the protective device reacts to a normal operating-
cycle current profile. Initially, the motor is stopped and the current is zero. As long as the protective device is
not in a »trip« state, it permits contactor energization by closing its trip contact in series with the contactor. The
contactor is energized by the operator or process control system through a normal two-wire or three-wire motor
control scheme, external to the protective device. The protective device declares a motor start when it senses a
motor current that exceeds 30% of the » Ib« (FLA) setting. Meanwhile, the transition timer » TRNT« begins to
run. The protective device also monitors the large starting current, noting when the current falls below the
transition level » TRNC« .
Page 264 EN MRM4 01/11
Run Start Start Stop
TRN I
t1 t2 t3 t4 t5 t6
Current
T1
T3
T1 : Stop Cycle
t4 – t3 : Start Cycle if TRNC is select
t6 – t3 : Start Cycle if TRNT is select
TRN TIME
TRN T or I
TRN T and I
TRN Criteria
I > 0,3 *Ib (FLA)
TRN I
t
T2=TRN TIME