| 摘要 |
1527032 Protective arrangements for welding apparatus I BAUMGARTNER [trading as WKS SCHWEISSTECHNIK WILLY KALNBACH] 6 Jan 1976 [10 Jan 1975] 00335/76 Heading H2H A circuit for supplying high currents to a load connected to terminals X, Y comprises a transformer S-TO having a primary winding P connected in series with a choke Dr, reverseparallel thyristors T1, T2 connected across the choke and a control circuit SG for shifting the phase of the thyristor firing pulses when the output of the transformer secondary winding S is short circuited. The load may be a welding apparatus the electrodes of which are connected to the terminals X, Y. A mains supply is connected to terminals AS, SB and to terminals A, B of the control circuit. If the electrodes are short circuited, the fall in the welding voltage below a limit value determined by Zener diodes Z2, Z3 prevents a supply of power to a transformer TO2. A transistor T is non-conductive so that a capacitor C1 charges via resistors R7, R8 and a potentiometer POT. When the capacitor voltage reaches a predetermined value, a unijunction transistor PUT is switched on and the capacitor discharges through a transformer Z-TO which supplies firing pulses to the thyristors. In view of the resistor R8 the firing points of the thyristors are retarded so that the choke Dr prevents excessive current flowing through the transformer. During normal welding operations the transistor T is conductive and shorts out the resistor R8 so that the firing point of the thyristors and therefore the welding current is determined by the potentiometer setting. A temperature responsive switch TS short circuits the supply to the control circuit in the event of an excessive temperature. The load may alternatively be a motor or a rectifier station. |
