Woodward MRM4, Manual

Page: 265 / 460

Protective Elements
The Start to Run transition is based on the setting » TRN Criteria« , which has four transition behaviors for the
User to select:
•
TRN T - Transition to RUN after time setting TRNT only. Current is ignored.
•
TRN C - Transition when starting current drops below the setting only. If the time set in TRNT
expires before the current transition, the motor trips.
•
TRN T or C - Transition on time or current, whichever comes first.
•
TRN T and C - Transition on time and current. Both must occur, and the current must drop below the
setting before the time delay expires. If the timer expires before the current falls below
the set transition level, the motor trips.
If there is no transition trip, the protective device relay declares a successful transition to »RUN« cycle and the
corresponding transition signal(s) (current or time, or both, depending on the settings and motor current) is set.
The transition signal(s) is the part of the global output list, which can be assigned to any module input or relay
output. If it is assigned to a relay output, it can control a reduced-voltage starter, switching to full running
voltage.
Even if the transition control output contact is not used, the transition function can provide clear indications of the
actual state of the motor (»START« versus »RUN«) on the front panel display and via data communications. A
good way to do this is to use the settings of TRN Criteria = TRN T or C and TRNC = 130% of » Ib« (FLA). Modify
the latter, if needed, to lie at a transition value between the starting current and post-start maximum load current.
Set the transition timer well beyond the normal start time to avoid a transition trip.
Start Delays
The parameters for the Start Delays have to be set within menu [Protection Para\MStart\Start Delay Timer]
When the protective device declares a »START«, all start timers of the enabled functions begin to time. Each of
these timers blocks the respective function until the set delay expires. These start timers are affected by
transitions - they run for the set time, which may be less than or greater than the time of transition. These start
delay timers include:
•
IOC (Instantaneous overcurrent start delay);
•
GOC (Ground fault start delay);
•
UnderLoad (Underload trip and alarm start delay);
•
IUnbalance (Current unbalance trip and alarm start delay);
•
JAM (Jam trip and alarm start delay); and
•
Generic1 to Generic5 (Generic start delay).
Note that the generic start delays are not tied to anything, and they can be used to block anything at the User’s
choice.
Motor Start Blocked
A Motor Start can be blocked by certain events, if any of the following conditions are noted - motor starts limit,
starting frequency, thermal and mechanical constraints. The User may choose to use the states to block the
motor from starting or use it as an alarm or indication.
EN MRM4 01/11 Page 265