Comparison of dynamic stability of superconducting and conventional synchronous alternators

Superconducting alternators have many advantages such as high efficiency, high power density and large unit capacity. In addition, they have reactance as small as one-fourth to one-third that of conventional alternators. Therefore superconducting alternators are very useful from viewpoints of steady state and transient stability and also from the viewpoints of reactive power supply to bulk power transmission lines and underground cables. At present, Westinghouse Electric Co. is attempting to construct a 300-MVA superconducting alternator. Since we have very little experience in operating superconducting alternators, it is very important that we analyze their stability behavior. In the first part of this paper, we analyze quantitatively the effects of the automatic voltage regulator, speed governor, line impedance, machine constants (particularly electromagnetic shielding constants) on the dynamic stability. The analysis is based on the eignevalue method. In the second part of this paper, we derive the block diagram of the superconducting alternator for the small disturbance around an operating point