Problems on high failure incidence of induction motors and protection

This paper discusses results of investigations done at Combine Electric Motor Workshop - C.E.M. The need for the work arose from the unusually high failure incidence on one of the coal/ore haulage locomotives braking system, namely the 22 kW squirrel cage compressor induction motor for the hydraulic sub-system. Specific causes of the high failure incidences on the subsystem are explored and a PLC based motor protection scheme proposed. The protection scheme is three layered as opposed to the single layer i.e. current overload installed on the locomotive in question. The new scheme provides for voltage unbalance, thermal, current overload and leaks detection motor start/trip interlocks. Projected cost benefits and Implications on availability are significant when viewed in the context that it takes six coupled locomotives to haul the required economic tonnage using 200 wagons.