Static Stability Limits and the Intermediate Condenser Station

The principal features of this paper may be summarized as follows: For static stability calculations, power systems may be represented by a network with constant impedance and admittance branches with as many terminals as the number of synchronous machines requiring individual consideration. This method is justified because, as developed in the paper, loads may be represented by the equivalent constant admittances and synchronous machines may be replaced by their equivalent impedances. A criterion for static stability of systems is presented together with formulas for the calculation of the two-, three- and four-machine cases. It is shown that the maximum angle between machines for which synchronism can be maintained is, in general, somewhat dependent upon the inertia of the synchronous machines. Under some conditions synchronism can be maintained between two machines operating at angles greater than π/2. The delivered power corresponding to definite excitation of machines will, in general, be a maximum for a smaller angle than the maximum stable angle. While the investigations have shown that synchronism can be maintained in regions heretofore considered inherently unstable, operation in such regions is held to be inadvisable. There are a number of generalizations which may be made as to the limiting stable condition.