Voltage changes produced by single-phase loads

THE PROBLEM of determining the voltage change produced by a single-phase load has become one of considerable importance to the utility engineer. One of the principal reasons for this situation is the application of single-phase resistance welding to many new processes. The usual type of single-phase resistance welder requires for its operation large intermittent values of kilovolt-amperes at a low power factor. This type of load will, of course, produce voltage fluctuations on the power system adjacent to the welder. If these variations are severe enough, they may cause objectionable lighting flicker to other customers served from the same portion of the power system. The usual range of permissible voltage variation is from 0.5 to 1.5 volts on a 120-volt base. The actual value is dependent upon the type of welder load — whether cyclic or noncyclic — and if cyclic, upon the frequency of the load application.