Negative damping of electrical machinery

This paper presents (1) a more nearly complete and exact criterion of instability or hunting of a synchronous machine as influenced by its armature or tie line resistance, (2) a general stability criterion which includes in one formula three previously separately treated cases: the usual steady state power limit, rotor hunting produced by armature resistance, and self-excitation produced by series capacitance in the armature circuit, and (3) an indication, by means of a numerical example, of the limitations of the previously used approximate criterion for hunting due to armature resistance. In previous treatments, hunting, self-excitation, and loss of synchronism have been considered only separately, neglecting their mutual interactions. The present paper, on the other hand, considers their mutual effects and thus provides a general analysis by reference to which the limitations and proper fields of application of the approximate formulas may be found. Application of the complete criterion given is however rather laborious, and it is not suggested for general use in place of the approximate forms.