Solving SCR line voltage notching: to solve 3-phase voltage notching problems, use a 3% impedance reactor

摘要

When silicon-controlled rectifiers (SCRs) are used in electrical controls, we frequently experience line voltage distortion in the form of "notches" in the waveform The types of equipment that frequently use SCR control schemes (and thus experience notching) include DC motor speed controls and induction heating equipment. Line notches are an irregularity in the voltage waveform that appear as a notch (see Fig. 1). They're typically present in the waveform during SCR commutation or when someone turns a one-phase SCR off and the next one on. During this small amount of time, we actually experience a short circuit between the two phases. This results in the current going high and the voltage going low. In the most severe cases, the notch touches the zero voltage axis. This typically causes the most problems.