486 ELECTRICAL EQUIPMENT 



circuits and the method of switching. Reliability and contin- 

 uity of service are the main considerations, but besides this the 

 protection of the apparatus from injury should not be lost sight of. 



The switching equipment is the key to the entire system, and 

 the first requisite to decide on is the system of connections, the 

 diagram of which should be worked out with the greatest care, 

 taking into consideration the various equipments and the normal, 

 as well as possible abnormal, operating conditions of the entire 

 system. The design of the control boards and the selection and 

 arrangement of the oil circuit breakers, bus-bars, etc., depends 

 greatly on the system of connections; in fact, the design of the 

 entire power-station. 



In taking up the various problems dealing with the design of a 

 switching equipment, space will only permit the fundamental 

 principles to be dealt with, and only some of the more important 

 apparatus can be briefly described. It would be of little value to 

 go into the minute details of the engineering features connected 

 with a switching equipment because the art changes so rapidly, 

 and new and improved lines of apparatus are brought on the 

 market so rapidly, that they change for almost every new impor- 

 tant installation. 



System of Connections and Relay Protection. In laying out 

 the system of connections and the protective switching and 

 relaying equipment for a high-tension transmission system, there 

 are a number of general principles which must be kept clearly in 

 mind. Chief among these is continuity of service which is now of 

 prime importance and this has been brought about mainly by 

 the steadily increasing demand for a much higher standard of 

 service than formerly. This, in turn, involves a flexibility in the 

 arrangement of the connections so as to reduce to the absolute 

 minimum the amount of apparatus which will be automatically 

 disconnected in case of trouble, and also to provide for sectional- 

 izing any apparatus for inspection and repairs. Besides this, the 

 protection of the apparatus from injury should be given careful 

 study. These considerations are, however, very closely con- 

 nected and must naturally be treated together. In this connec- 

 tion it should be noted that the function of an automatic selective 

 switching is not any longer correlated to the idea of protecting 

 the apparatus against ordinary overloads, but that the relays are 

 intended to operate only on breakdowns, although their setting 



