They're introduced to help avoid motor stator insulation failure which is said to account for two-thirds of medium voltage motor failures worldwide.
MSIM detects motor insulation degradation then provides early warnings of motor failure. Its predictive capability helps reduce economic impact of motor replacement and repair: It assesses motor condition without taking a motor offline or shutting down a process.
MSIM technology enables continuous and direct measurement of stator winding capacitive and resistive leakage currents. It relies on High Sensitivity Current Transformer to measure the very small leakage current in milliamp range in the presence of hundreds of amps.
It also uses High Voltage Sensors with interface modules along with motor stator temperature RTDs or thermocouples as inputs to the system.