Protection of three=phase motor against asymmetrical faults - improves security of contact protection and prevents consequences of phase angle without dependence on circulating current

摘要

The motor is disconnected from the mains by a magnetic switch in a so-called AAC circuit subdivided into three sections. A signal convertor produces a DC voltage proportional to phase current of the motor. A difference indicator and amplifier serve as a responsive element for asymmetrical loading. A final amplifier acts as a contact relay. When the load exceeds 33 percent the circuit is brought into operation for 20 to 33 percent asymmetry. USE/ADVANTAGE - In conjunction with traditional motor protection, measures are effective against all asymmetrical faults, with active contact protection within 100 ms.