The steady-state equilibrium of parallel alternators: Some approximate solutions

The paper describes graphical methods of determining the equilibrium values of voltage and load for systems of paralleled generators working under certain specified conditions. Two main cases are considered: that of a number of synchronous machines in parallel supplying a load of constant power factor, when the operating voltage on a given load and the maximum stable load are to be determined; and that of a number of machines working on constant load, when the variation of voltage with changing power factor and the minimum power factor for stable operation are required. The principle of the methods is also extended to the determination of the reactance of the symmetrical three-phase fault which will just render unstable a system of generators each of which makes a specified contribution to a constant total load of known power factor. These solutions require certain assumptions, of which the more important are that the impedance of the interconnecting lines is negligible compared with the impedance of the alternators, and that, neglecting the resistance component and making some assumptions with regard to saturation, the impedance of the alternators can be represented as a reactance of known constant value.