In general it should be substantial, convenient to install or replace the heavy machines, and the layout arranged so that the apparatus can be readily operated by those in attendance.
An overhead traveling crane is the most convenient method of handling the heavy machinery, and is frequently used in large sub-stations.
[Fig. 2,776] shows a sectional view, and [fig. 2,777], a plan for a small sub-station containing two rotary converters and two banks of three single phase static transformers operating on a three phase system at 11,000 or 13,200 volts, together with the auxiliary apparatus.
Fig. 2,777.—Elevation of small sub-station, as shown in plan in [Fig. 2,776].
Ques. For three phase installations, what are the merits of separate and combined transformers?
Ans. With separate transformer for each phase, repairs are more readily made in case of accident or burnouts in the coils. The three phase units have the advantage of low first cost.
Sub-station transformers produce considerable heat, due to the hysteresis and eddy currents, and it is necessary to get rid of it.
Small transformers radiate the heat from the shell and the medium sizes have corrugated shells which increase the surface and provide more rapid radiation.