The design of electrical plant, control gear and connections for protection against shock, fire and faults

The risks to life and plant are set out. Means for prevention are discussed in full and summarized in conclusion. In the main an endeavour has been made to collate present practice and to ventilate some demands which are in a nebulous stage, including the duplication of components, the changing over of live circuits, the meaning of the breaking-capacity rating of circuit breakers, the use and effect of reactances, charging resistances and lightning arresters, and the best means of economy in switchgear without loss of safety. In reviewing known automatic protective systems, stress is laid upon the importance of what has been termed, for the purpose of this paper, the ¿stability ratio.¿ Stability takes precedence over sensitivity. In balanced automatic protective systems stability is jeopardized by influences, some of which are of recent discovery and have been brought to light by new conditions of service. They include the unbalancing effect of high-frequency oscillations on main lines, and interference by induction between the main line and the pilot line. Suitable remedies are available and have been applied. The relation of interference with telephone service and fault occurrences on power supply systems provides a further argument in favour of good bonding, earthing the neutral and the instantaneous isolation of faults. Mechanical consideration is given to the layout of switch-gear and to the terminal construction of plant, and a diagrammatic illustration of the alternator main, field, and neutral connections is shown.