The stability characteristics of alternators and of large interconnected systems

The development of the national electricity supply scheme and the interconnection of large systems throughout Britain has brought into greater prominence problems of power limit and stability. The stability of a system depends upon the combined characteristics of the generating plant, load, and interconnecting lines. Instability may occur in excitation circuits, but this form is not to be confused with the several kinds of alternator instability which occur under different conditions of operation. An endeavour is made to give a clear review of the various forms of power limit and stability. The effect of various factors such as reactance, power factor, and automatic voltage regulation, is discussed. It is shown that the last factor is of considerable importance in increasing the load limit and stability of an alternator; and, with its use, the load of the system is limited only by the characteristics of the transmission line. Stability may be difficult to maintain under fault conditions, and high speed of operation of protective apparatus and switchgear is necessary. The practical aspect of mechanical and electrical resonance problems is briefly mentioned.