Brushless and current-compounded frequency-convertor exciter

The paper describes a frequency-convertor AC exciter for use with a synchronous generator to produce a unit which is brushless, self-excited and current compounded. The stator contains a shunt winding fed from the output voltage of the generator and a series winding carrying the output current. These two windings are arranged so that the excitation current supplied to the generator from the rotor winding of the exciter, via a rotating rectifier, increases with both an increasing load current and a decreasing load power factor. The paper presents a detailed consideration of the new exciter, which shows that it possesses all the characteristics found in the familiar static current-compounded arrangement. An optimal design investigation demonstrates a conflict between the requirement for a minimum drift in the generator terminal voltage due to changes in temperature and the need to minimise the VA loading that the exciter imposes on the generator. It is shown, however, that the use of capacitors in series with the shunt winding will go a long way towards eliminating this problem. Consideration is also given in the paper to a suggested development of the frequency-convertor exciter, aimed at the production of a variable-speed but constant-frequency generating unit.