Utilization of harmonics for self-excitation of a synchronous generator by placing an auxiliary winding in the rotor

Abstract

This study is concerned with a new excitation system in which a voltage is induced by the flux density harmonics of the air-gap in an auxiliary rotor winding supplying the field winding through a rectifier. The system is brushless and self-regulated. The applicability of various harmonics for producing the excitation current is studied; it has been shown that the field current component proportional to the resulting air-gap flux can only be obtained by means of permeance variations due to irregularities of the stator air-gap face. The field current component proportional to the load current can be produced by harmonics due to the stator winding distribution. Experimental studies were made with a generator of 3 kVA size, in which the first slot harmonic was utilized to create the excitation current. The generator has characteristics similar to those of conventional compounded synchronous generators. The measurements show that the method presented for calculating the terminal voltage gives a satisfactory result in practice.