Comparison of protection requirements in IE2-, IE3-, and IE4-class motors

In this paper, an overview of the main motor features influencing the protection devices settings is presented, pointing out key differences between three-phase direct-on-line motors of different efficiency classes. The results of experimental tests and simulations are presented and discussed in the scope of the motor protection against overload, short-circuit, current unbalance and locked-rotor conditions, for 7.5-kW, 4-pole, IE2- and IE3-class squirrel-cage induction motors and for IE4-class line-start permanent-magnet motors, offering important data related to their electrical and thermal behavior. Two commercial digital thermal-magnetic motor protection devices, whose thermal models were in most cases designed for IE1- and IE2-class motors, are evaluated in terms of operation effectiveness in the tested motors. This work is important for industry due to the significant penetration of IE3-class induction motors, as well as to the recent introduction in the market of IE4-class induction motors and line-start permanent magnet motors.