Resistance-Welding Transients

This paper discusses quantitatively the effect of indiscriminate (random phase-angle) switching in the primary of a resistance welder. The current and power transients occurring because of ``off-angle'' switching are investigated through oscillographic records of transients in loads built up to simulate actual welder-head loads as nearly as possible. In the switching of loads of either high or low power factor and those with or without iron at high-flux densities, the power transients were found to be damped to unimportant values within the time of a very few cycles after the instant of switching. In spot and projection welding, the first few cycles may be extremely important, however, determining the quality of weld even though the total time of the weld period is much greater. This investigation is limited to 60-cycle frequency and to welding periods of two cycles or more.