Fig. 2,775.—Plan of sub-station with air blast transformers and motor operated oil switches and underground 11,000 or 13,200 volt high tension lines.
Sub-Stations.—According to the usual meaning of the term, a sub-station is a building provided with apparatus for changing high pressure alternating current received from the central station into direct current of the requisite pressure, which in the case of railways is 550 to 600 volts.
Where traffic is heavy and the railway system of considerable distance, sub-stations are provided at intervals along the line, each receiving high pressure current from one large central station and converting it into moderate pressure direct current for their districts.
Ques. Upon what does the arrangement of the sub-station depend?
Ans. Upon the character of the work and the type of apparatus employed for converting the high pressure alternating current into direct current.
Fig. 2,776.—Plan of small sub-station with single phase oil insulated self-cooling transformers and hand operated oil switches 11,000 or 13,200 volts, overhead high tension lines.