Excitation Systems Their Influence on Short Circuits and Maximum Power

Since 1920, when the general subject of excitation systems was reviewed at the White Sulphur Springs Convention, two important problems regarding these systenms have arisen: One relates to the required excitation characteristics during system disturbances, and the other to the characteristics which are necessary in order to increase the maximumn power above the steady state or static limit¿i. e., in order to operate the synchronous machines under the condition of dynamic stability. With respect to the former problem, the advantages and disadvantages of quick response excitation are considered. Such excitation tends, of course, to hold up the voltage during system disturbances, and is thus advantageous. However, it also increases the short-circuit current which circuit breakers must interrupt. The general trend in installing such systems is, therefore, in the direction, of requiring larger circuit breakers. Such an excitation systemn is justified in many cases, and, indeed, it is essential in some. The extent to which the quickness of response and the maximum value of the excitation voltage are carried, is a question which, at present, should be settled by the conditions of the particular case. As to increasing power limits, results are given which are very promising with respect not only to long distance transmission, but also to power systems which have approached the power limit as determinied by the condition of present normal operation. A new regulator, unique in its operating characteristic, has been.