14/1/98
Page 27
Issue H
Guide to settings
In order to ensure full protection to the equipment, a co-ordination study must be made that takes
account of all possible faults or conditions that may occur, this usually takes the form of ensuring
that all of the tripping characteristic of the MPR3E5, is between all the possible starting
characteristics, and the full thermal withstand of the machine, for both hot & cold conditions.
In the absence of the above information, it is usual to set the overload pick-up at 105%, Is at the FLC
of the machine, low set ( I> ) OFF, hot/cold ratio at 50% with the high set ( I>> ) set OFF for fuse
contactors, and at 8x FLC, tI>> at 0.0, for circuit breakers.
In order to determine a suitable value for t6x, the start time of the machine must be obtained. A
setting for t6x may then be selected as follows,
For Direct On Line starters, t6x
≅
1.1 x start time.
For Star-Delta starters, t6x
≅
0.35 x start time
These are a guide only, and are unlikely to enable a hot start of the machine.
Co-ordination With Short Circuit Protective Device.
It is important that the relay parameter settings, trip relay matrix settings and characteristics should
be carefully co-ordinated with that of the Short Circuit Protective Device for all fault conditions.
This is especially important in the case of a fused contactor starter where it is necessary to ensure
that the contactor can never attempt to break a fault current in excess of its rating. For this purpose a
setting parameter is provided to inhibit all fault protection trips above a range 4 to 12 x In current.
NOTE THAT THE THERMAL OVERLOAD PROTECTION FUNCTION IS ALWAYS
ENABLED IRRESPECTIVE OF THE INHIBIT SETTING.
