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TWI Industrial Member Report Summary 107/1980
By M Murch and W Lucas
Background
The potential of square wave AC power sources for reducing the open circuit voltage requirements of manual metal arc welding has been investigated for rutile, cellulosic and basic flux-covered electrodes. The characteristic reignition behaviour of these electrodes was defined from oscillograms of circuit current and voltage at the instant of arc reignition, for both sine wave and square wave alternating current supplies. When operated at not greater than 80Vrms open circuit, which has been recommended by CENELEC as the maximum permitted no-load voltage on AC eqaipment, the magnitude and distribution of the reignition voltages and the mean time to reignite the arc, showed quite clearly that the square wave AC waveform facilitated arc reignition. Furthermore, on polarity reversal, the voltage demanded by the arc for reignition through zero was instantaneously available, even at reduced no-load voltage levels, to the extent that basic flux-covered electrodes could be operated at an open circuit as low as 4OVrms without impairing arc
stability.