Diagnostic system for on-line detection of rotor faults in induction motor drives

The paper presents an on-line condition monitoring and diagnostic system for induction motor drives. It enables detection of many different faults, which may arise during the lifetime of the motor, although special attention was devoted to identify broken rotor bars at an early stage of the fault propagation. The method is based on the analysis of stator current frequency spectrum, which can be measured without disturbing normal motor operation, therefore it is completely non-invasive and easy to implement in industrial environments. The presented diagnostic system is being applied on 17 high-voltage motors (range of power 1000 ÷ 6400 kW) in two thermal power plants to increase operational reliability of induction motors and to reduce costs of their maintenance. Concepts of hardware and software configurations are explained in details as well as some of the numerous monitoring results during the last five-years period. The paper also discusses two examples of a timely and efficient detection of rotor electric asymmetry due to cracked end-ring segments of induction motors, which exhibited no obvious problems during operation.