WELDING TRANSFORMER CONTROL BY THE ELECTRONIC CONTROL OF LEAKAGE-FLUX

In this paper, the triac is used to control the welding transformer leakage reactances and thus the welding currents. This new method keeps the input and output currents and voltages in sinusoidal wave forms. The triac is connected across the terminals of a coil wound on a fixed limb magnetic shunt. A simple triggering circuit is used to control the current of the triac and thus the current of magnetic shunt coil. This leads to variation of welding transformer leakage flux, leakage reactances and thus a variation of welding current. The distortion due to the triac is only affecting the leakage flux of the welding transformer. The leakage flux is very small (compared with main flux) and most of it passes in the transformer window. Then, no harmonic pollution in the bus-bar or in the welding transformer. Thus, high operating efficiency is obtained. This new method can be used with single or three phase arc welding transformer. In this work, a three phase multi-operator welding transformer is experimentally checked with the new system. The recorded wave forms support the system advantages. Performance characteristics are experimentally measured and give adequate results.