SWITCHING EQUIPMENT 565 



are given, which show some typical arrangements which are self- 

 explanatory. 



In laying out the structure attention should also be given to 

 the current and potential transformers. The latter with their 

 fuses require considerable space for higher voltages and have to be 

 installed in certain positions. This refers especially to oil-cooled 

 transformers and expulsion fuses, so that if in the preliminary 

 design these points are not taken into consideration considerable 

 difficulty may be encountered in finding suitable accommodation 

 for them. When current and potential transformers are installed 

 in separate compartments, holes should be left in the partition 

 walls to accommodate conduits for the secondaries between 

 phases, and in case of potential transformers porcelain bushings 

 should be provided for the primaries. 



For voltages above 15,000 the circuit breakers are, as a rule, 

 of the top-connected tank construction and compartments are 

 entirely omitted, especially for the higher voltages. The conduct- 

 ors must necessarily be spaced farther apart and at a consider- 

 able distance from the floor, so as to be out of reach. Different 

 arrangements are used for nearly every new station, as seen from 

 the illustrations, Figs. 93 to 101. 



The busbars are an important part of the installation, carry ing- 

 the whole energy of the plant in a confined space. The material 

 is usually copper and the conductors may be either cylindrical 

 rods or tubes or rectangular bars. The former are generally 

 used for the high-tension ouses and connections, but the latter are 

 essential for lower voltages where large currents are to be carried, 

 necessitating a larger cross-section. In such cases the bus is 

 laminated, i.e., it consists of a number of bars arranged side by 

 side with ventilating ducts between. This insures a large radiat- 

 ing surface, while at the same time this construction permits a 

 tapering of the bus so as to utilize the material to the best advan- 

 tage. Additional bars may also readily be added in case the 

 capacity needs to be increased in the future. 



The buses as well as the connections to the oil circuit breakers, 

 etc., should be so proportioned as not to attain an excessive tem- 

 perature rise under the maximum current which they are intended 

 to carry. For direct-current work the features affecting the tem- 

 perature rise are the size of the bar, the number of laminations, 

 spacing of laminations, spacing between poles, whether the bars 



