The use of line current as a condition monitoring tool for three phase induction motors

Many researchers have worked on the problem of detecting rotor faults in induction machines while the machine is still in operation. The methods proposed have been varied, including the measurement of rotor speed to look for the fault indicating speed ripple, the measurement of vibration at the machine stator housing and the measurement of axial fluxes. The main problem concerning these monitoring methods is that they are essentially invasive, requiring transducers to be fitted in or around the machine with the obvious interruption to operation. For the above reasons, line current has become the favoured parameter for the purpose of detecting rotor faults in squirrel cage induction motors. Line current can be monitored noninvasively via clip-on current transducers hence no interruption to the machine operation is required, and the system can be made versatile and portable. Recent work has seen the development of the technique to monitoring the current of the motor while under transient conditions during start-up. As discussed below this can, under certain conditions, offer distinct advantages over steady-state monitoring