Experimental methods for measuring the q-axis saturation characteristics of synchronous machines

The d-axis saturation characteristic of a synchronous machine can be measured easily by the conventional open-circuit test with the machine excited from its field winding. On the other hand, the q-axis saturation characteristic of a synchronous machine cannot be measured applying similar easy, simple methods and, so, these characteristics are usually not measured experimentally and are not available. Three possible experimental methods for determining the q-axis saturation characteristics of synchronous machines are presented. The merits and demerits of these experimental methods are discussed from the point of view of their complexity and their accuracy. Moreover, the various sources of errors in the determination of the q-axis saturation characteristic applying these methods are also reported.