GB210254A - Improvements in or relating to electric arc welding and apparatus therefor - Google Patents

Abstract

210,254. Davies, W. Langdon-, and Soames, A. Jan. 1, 1923. Systems depending on use of static transformers.-An alternating current arc welding system is provided with an automatic safety device tending to reduce the voltage when the arc is broken, in combination with a supplementary safety de vice which cuts off the current in the event of the main safety device failing to operate. In the system shown in Fig. 1 there is a working voltage source A and a low safety voltage source B, these sources constituting the secondaries of transformers whose primaries A<1>, B<1> are connected in parallel across the supply mains C. When the welding circuit is made, the coil F is energized by the secondarv B and the switch G moves over to close contacts H<1>, H<2>. The welding current is then fed from the secondary A. If, when welding is stopped, the switch G fails to return to its original position, the contact breaker K, arranged across the arc, breaks the circuit from the secondary A. In the system shown in Fig. 2, there is a working voltage secondary L and a low voltage secondary M, the primary M<1> of the latter being connected in parallel with the secondary L. A switch T operates to increase and decrease the voltage when starting and stopping the welding operation. The supplementary safety device U is fitted so as to break the circuit of the primary L, if the switch T fails to act.