Safeguards against interruptions of supply

Abstract

The paper is intended to present a perspective of the safeguards that have an economic utility in a supply system to ensure an uninterrupted supply of electricity to consumers. The safeguards are classified broadly under the headings of general, routine, protective, and ultimate. Although the most consistent application of general and routine safeguards can never completely eliminate the risk of faults, the appropriate blending of these with protective safeguards, which isolate faults automatically in their initial stages, should prevent any fault from developing into a breakdown of the major order, such as to involve the functioning of ultimate safeguards.After a general discussion of the application of protective safeguards to supply systems according to whether they include cables or overhead conductors (which, owing to differing conditions, have to be dealt with differently), there follows a survey of protective safeguards available for use with various components of a supply system against short-circuits transient faults, and excess voltages. These include feeder and busbarzone protective systems; methods of reducing unnecessary outages of overhead lines; and rapid operation of circuit breakers. Particulars are given of high-speed small-oilvolume circuit breakers developed on the lines of utilizing in improved ways well-tried principles and components, and of an automatic reclosing 132-kV oil circuit-breaker with an arc duration of one cycle at full rating.It is claimed that, when a fault has developed in a component of a supply system provided with protective safeguards such as automatic instantaneous protection and fast-acting circuit breakers, the result is a switching operation with very little if any damage of the faulty component, and, depending upon the system layout, an outage with either no interruption or only a slight interruption of supply. If, however, a fault develops in an unprotected component of a supply system, the sustained feeding of power into it may lead to severe breakdown and fire, with risk of serious interruption of supply.The authors suggest that, if the supply industry is of the opinion that it is detrimental to have such interruptions of supply as have occurred in the past (for example, because of outages from transient faults on overhead lines or because of outages due to fires resulting from sustained arcing on unprotected apparatus), and that such interruptions are an uneconomic risk for the future, one of the first steps to be taken is a consideration of safeguards adequate to prevent them.