Measurement of the subtransient impedances of synchronous machines

A METHOD of measuring the direct-axis and the quadrature-axis subtransient impedances of a synchronous motor or generator by impressing three-phase voltages on the machine at standstill is described in this paper. With respect to the two methods at present prescribed in the Test Code for Synchronous Machines and elsewhere,^1,2,3 the proposed method for measuring the subtransient impedances has the advantages that it does not involve the taking of oscillograms and the consequent uncertainties in their analyses, nor does it require that the rotor of the machine under test be set in certain definite positions. This latter requirement, called for in the single-phase test, is frequently troublesome, particularly if the machine is large. Moreover, as three-phase, rather than single-phase voltages are impressed, the measurements are made under conditions more nearly simulating those of normal operation