Transient Voltage and Current Requirements of Main-Field Circuit Breakers for Synchronous Machines [includes discussion]

The purpose of this paper is to analyze a number of the basic design and application requirements of main-field circuit breakers forsynchronous machines. The general functions and requirements of main-field circuit breakers are described with typical circuit diagrams. Transient voltages and currents in the excitation circuit are analyzed under normal switching and fault conditions. A basis is suggested for selecting a value of discharge resistance which will bring about the maximum limitation of armature fault damage without creating undue risk of damage to insulation components of the excitation circuit. Equivalent circuits are developed for testing the interrupting performance of the breakers. Suggested constants for interrupting-test circuits are tabulated, as well as values for momentary, short-time, and high-potential tests, over the range of main-field currents and voltages which is anticipated. Interrupting performance tests and a view of a new field breaker for a 250-volt 1,600-ampere circuit are given.