Why 400Hz Used For Brushless Excitation System

In the brushless excitation system, the excitation generator's (called exciter) field is stationary and armature is rotating. The AC is produced in the excitation generator's armature and it is then converted to DC (for the field supply of the main generator) using the rectifiers which are fixed to the rotating shaft. With the use of high frequency of the exciter output, the frequency of the ripple of DC is also high, which helps effective filtering of the ripple with the high inductive nature of the field coil of the main generator with the use of filtering capacitors across the rectifiers. Thus, the good quality of DC is produced and passes through the field for the excitation of the main generator.

So, the use of high frequency of exciter output voltage is used to create the good quality of DC for the main generator's excitation.

-MS