Current motor starting methods: Advantages, disadvantages

摘要

During direction line (DOL) starting and stopping, low- and medium-voltage motors experience starting currents of up to eight times the nominal current and high acceleration rate or torque. These characteristics cause voltage dips in the network as well as mechanical wear and in some cases destruction of equipment, such as gearing, couplings, shafts, belts, or fragile parts or products. One of the most common problems during motor starting and stopping is the so-called water hammer in pipelines, caused by sudden reduction of flow rate when the pump abruptly stops. Although the motor-pump combination is hardly under any mechanical stress, this is not the case for the valves and the pipeline. A repair of such equipment is very time-consuming and costly.