Phase loss or overvoltage protector for motor - has signal fed to comparator via Zener network and driving cut=off relay in motor supply

摘要

The electric motor protector provides an interruption of the motor supply in the event of overvoltage or loss of a phase. The protection circuit uses three transformers as current-voltage converters their primary windings being in series with the motor supply lines. The secondary winding outputs are rectified in a Graetz bridge and smoothed in an LC network (3, C2). This common output is fed across a potentiometer (R2, P, R3) and provides a signal in the case of overvoltage to a comparator (A2) via a Zener network (A4, Z5, Z6), the comparator output driving a cut-out relay (Rx) in the motor supply. In the absence of a phase a further comparator (A3) fed from a potentiometer (R10, R11) across the transistor regulated (T1, T2) supply drives a further comparator (A1) and the final relay driving comparator (A2).