Low loss switching system for AC mains supplied LV relay - has short circuit arrangement based around thyristor that protects against change in range switch setting

摘要

The relay winding, together with a bias capacitor (C1), forms a voltage divider when the main switch (S) is open such that, with minimum a.c. voltage (AC), a response voltage is ensured. Between the switch and filtering capacitor (C2), a short circuit arrangement,-consisting of a thyristor (THYR), resistors (R1-R4) and a transistor-is installed. If a sudden increase in the voltage supply occurs the circuit responds independently of the switch and protects coupled equipment. ADVANTAGE - Protects against unacceptable change in voltage range switch.