Fault sensing system for 3 phase inverter and asynchronous motor

摘要

A fault sensing system for a 3 phase inverter (2) supplying an asynchronous motor (3) employs differences between the actual line currents measured by the current transformers (11) and their expected values as an indication of fault observable at the terminal (25). The difference is amplified (26) to result in a control voltage signal of amplitude subject to a limiter circuit (27) which enters a saturable region registered by the detector (32) when the difference exceeds a reference value. A comparator (30) determines whether a preset (31) current difference threshold has been exceeded and if confirmed together with the above saturation condition an AND gate output signals a control abnormality.