System recovery voltage determination by analytical and A-C calculating board methods

THE PERFORMANCE of current interrupting devices on systems is dependent not only on the characteristics of the device itself but also on the characteristics of the system. The voltage rating of the system and the connections at the time of fault have considerable influence on the recovery voltage and in turn on the application of the interrupting device. For example, the last oil circuit breaker to open must be capable of interrupting current under extreme system recovery conditions, while a deion protector tube always has at least the line section on which it is applied, connected at the time of clearing. This means that in considering broadly the current interruption problem it is necessary to have a knowledge of voltage recovery characteristics for a large number of system conditions. Tests can be made for particular system conditions, but this is expensive and it is difficult to obtain data for all possible combinations of faults and system connections. A general analysis taking into account all the factors makes calculations practically impossible, and on account of the complexity, the human factor cannot be overlooked.