The vast majority of three-phase motor starters are simple devices using contactors that connect and disconnect all phases of a three-phase power supply to a motor at substantially the same time. This simultaneous application of the three-phase supply results in high peak surge currents and torque pulsations which place undue, and potentially destructive, stresses on the power distribution network, motor, and driven load. These surge currents are additional to the normal in-rush currents and can damage the electrical contacts used in the starter contactor and reduce the life of the starter. In order to avoid nuisance trips because of the higher peak currents caused by these surge currents, it is common practice to set higher trip levels on circuit breakers in the power distribution network than those needed to support the nominal load. This reduces the breaker's ability to minimize damage in the event of a fault condition. While alternative approaches to starting motors (such as motor drives and electronic soft starters) exist that reduce or eliminate these negative attributes, these alternatives are typically larger, more expensive, more complex to install and configure, and have shorter useful lives than electro-mechanical starters.
USPTO Backgrounds
USPTO Backgrounds