Rectifier Considerations in the Design of Salient Pole Synchronous Machines

A review is made of existing methods for calculating the transient field current during three phase and single phase line to line terminal short circuits, since this current determines the ratings of rectifiers in the field supply. An equation, of improved accuracy is given for the three phase fault. Measurements and calculations are shown for laminated and solid pole machines. It is shown that the latter construction gives sufficiently different field currents and decrements to affect rectifier ratings but the new equation can be empirically modified to account for this. A method is given for calculating the inverse voltage of rectifiers during the fault when a rotating exciter is employed. The effect of thyristor waveforms upon bearing currents and frame to ground potential is demonstrated by calculations and measurements.