Experiment on motor’s starting rush current

An experiment on the 3-phase 200V rating motor (0.2 to 30kW) was performed to understand the coordination of the Class E motor’s starting rush current and MCCB instantaneous tripping range.

Using the circuit shown in Fig. 4. 28, MCCB was switched during the direct-ON starting, and the magnetic contactor was switched for inching and plugging. Based on the oscillograph, the starting rush current flowed for approx. 1/2 cycle and then immediately attenuated to the correct starting current.

These experiments were carried out without controlling the closing phase, and the size of the rush current when starting varies because the size of the residual voltage in the motor winding during inching and plugging vary.