Starting current limiter for single phase circuits - consists of time delayed relay in associated DC circuit

摘要

A limiting resistor (10) in one line is bridged by a contact (11) of a time delayed relay (12). The delay time is fixed by the resistor/capacitor network (17, 18) across the relay coil which is supplied with dc from a thyristor (15) connected to the mains. The thyristor gating is provided from a current transformer (14) in one mains lead. When the appliance is switched on the current is resistance limited. THe thyristor operates and charges the RC circuit (17, 18) through the smoothing capacitor (16). When the voltage on the large capacitor (18) reaches the appropriate value the relay coil picks up and the relay contacts (11) short circuit the limiting resistor (10). Operation thereafter is normal.