Measurement of inductance coefficients of saturated synchronous machines

In order to employ a coupled-circuit approach for the accurate prediction of the performance of a synchronous machine, it is necessary to know the winding-inductance variations with the machine currents. The paper describes simple techniques by which these variations can be determined in terms of a resultant direct-axis or equivalent field current, and which thereby enable the complete nonlinear inductance matrix of the machine to be specified in these terms. Some of the inductance variations are derived by correct interpretation of results obtained from conventional ballistic techniques. The remainder are associated with the inaccessible damper windings, and these are derived from the results of a proposed new set of tests. The techniques described were used to obtain the parameters of a 15 kVA alternator, and the results obtained are presented in the paper.