Switching circuit allows LV AC vacuum switch to switch DC load - using relay to control thyristor in series with capacitor across vacuum switch

摘要

The switching circuit allows LV AC vacuum switches to be used for switching DC loads. The vacuum switch (2) is connected in series with the load (1) across the d.c. supply and is shunted by the series combination of a capacitor (3) and thyristor (5). (The thyristor is connected across the supply via a ballast resistor (4)). The thyristor is controlled by a pulse derived from the vacuum switch's opening. These pulses are obtained with the aid of a relay (7, 8) operated by the vacuum switch and with its contact connected to the gate of the thyristor. (The thyristor may be replaced by other forms of switch).