Cyclic Load Motor Applications

Input currents of a motor driving  cyclic  load  can vary between very low

to above the maximum allowable current during a load cycle. Variation in

current magnitude results in motor heating and cooling depending on the

heat and cooling time constants. Thermal overload protection response

is made adaptive to the cyclic load based on the cooling time constants.

In addition, to provide more accurate overload thermal model response

to cyclic load, the input currents to the thermal model are averaged over

the settable duty cycle interval. With a reciprocating load application, the

number of cycles to average can be determined from current waveform

capture using the Oscillography/Datalogger features in the 869 motor

protection relay.