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Arc-Spark Source Unit Changes

Volume 12, Number 4 (Aug. 1958) Page 129-130

Owen, Louis E.

In commercial d.c. arc power supplies using a motor-driven variable reactor; it is not possible to predict accurately the excitation current before the arc is started. To permit pre-arc setting of the current, a circuit (Figure 1) is in use which temporarily shorts the d.c. so that its level can be adjusted. The circuit requires two relays which are energized by a single switch. One relay pulls in fast and drops out slowly; the other pulls in slowly and drops out fast. The fast-in, slow-out relay R1 is used to disconnect the normal output and timing circuits and to short the d.c. output internally. The slow-in, fast-out relay R2 connects the primary input power to the rectifier circuit. The relays can be time-delay types using hydraulic or pneumatic principles for delay, or they can be fed through RC networks as shown in Figure 1.