AC circuit breaker test unit - has auxiliary voltage source coupled to FET control device

摘要

A test circuit is provided to determine the release current for an a.c. supply system circuit breaker which is intended to release at a current between two specified values. The circuit includes a programming device (20) incorporating a capacitor (21) to store a voltage from an auxiliary voltage source (24). The capacitor is connected in series with a resistor (22) and the common point is coupled to the control electrode of an FET (19). The on resistance of the FET makes a potential divider with a resistor (18) and is connected to the second input of an amplifier (13) having a high amplification factor. The voltage divider (18, 19) is connected across a bridge rectifier (6) connected to the A.C. system. Feedback devices are provided to generate a current if the breaker voltage rises above its upper limit without the cut-out operating.