A short circuit condition occurs when the insulation between the phase conductors fails and the load current level exceeds the normal locked rotor current levels that a motor would draw during start-up. The fault level of the motor feeder supply determines the current level during a short circuit and can be as high as 15 to 50 times the motor full load current value.
A short circuit fault is a system level fault, which means that it will compromise the stability of the entire network and result in total power loss of the healthy drive and shut down the entire process. The MCCB is a maintenance specific item that can still appear to be functional but may not be, and will result in a catastrophic failure on the next fault clearance.
NewElec’s MA motor protection relay is able to protect against thermal overloads, locked rotor and running stall or jam protection. The MA also protects against short circuit faults and automatically takes care of trip co-ordination so that the main contactor is not used to disrupt high energy faults.
Additional MA features include real time and date stamping recorded by the relay for the last four trips, a recording utility of actual RMS loads, thermal conditioning, mains phase voltage, line voltage, as well as the status of digital inputs and output contacts. The user has the possibility of expanding the unit for fieldbus communications via Profibus DP, Modbus RTU and Canbus protocols.
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