Protection of the electric motor from open-phase mode. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network
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The open-phase motor protection device responds to interruptions in the voltage supply to the three-phase motor of any of the three phases.
The scheme of the improved device is shown in the figure. By pressing the SB1 button, voltage is applied to the coil of the KM1 magnetic starter, which includes the Ml electric motor. Reliable operation of the starter when powered by its coil, designed for 380 V AC voltage, with a smaller amplitude pulsating voltage is ensured by a significant constant component of the latter.
Simultaneously with the actuation of the starter, the voltage is supplied to the anode and the control electrode of the trinistor VS1. Now the capacitor C1 is recharged through a periodically opening trinistor, the voltage on it remains sufficient to keep the KM1 starter in the triggered state. In the event of a power failure in any of the phases, the trinistor stops opening, the capacitor quickly discharges and the starter disconnects the motor from the network.
Author: V. Yakovlev, Shostka, Sumy region, Ukraine; Publication: radioradar.net
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