Electrical noise generated by thyristor control

The possible sources of the electrical noise generated by thyristor circuits is discussed, and the results of an investigation to determine the relative importance of the noise sources are presented. The influence of cycle-to-cycle variations in the a.c. supply-voltage amplitude and period is considered in detail. It is established that the most significant effect which produces noise at the higher frequencies is the random variation in the timing of the a.c. supply-mains period, not the thyristor itself. However, the noise from this source is associated with the harmonics in the waveform and would not be produced without thyristor switching.