OPERATING BOARD—SUB-STATION NO. 11
In order to further diminish the risk of interruption of the service due to failure of power supply, each sub-station south of 96th Street receives its alternating current from the power house through cables carried on opposite sides of the subway. To protect the lead sheaths of the cables against damage by electrolysis, rubber insulating pieces 1/6 of an inch in thickness are placed between the sheaths and the iron bracket supports in the manholes.
Cable Conveying Energy from Power House to Sub-Stations
The cables used for conveying energy from the power house to the several sub-stations aggregate approximately 150 miles in length. The cable used for this purpose comprises three stranded copper conductors each of which contains nineteen wires, and the diameter of the stranded conductor thus formed is 2/5 of an inch. Paper insulation is employed and the triple cable is enclosed in a lead sheath 9/64 of an inch thick. Each conductor is separated from its neighbors and from the lead sheath by insulation of treated paper 7/16 of an inch in thickness. The outside diameter of the cables is 2-5/8 inches, and the weight 8-1/2 pounds per lineal foot. In the factories the cable as manufactured was cut into lengths corresponding to the distance between manholes, and each length subjected to severe tests including application to the insulation of an alternating current potential of 30,000 volts for a period of thirty minutes. These cables were installed under the supervision of the Interborough Company's engineers, and after jointing, each complete cable from power house to sub-station was tested by applying an alternating potential of 30,000 volts for thirty minutes between each conductor and its neighbors, and between each conductor and the lead sheath. The photographs on [page 98] illustrates the construction of this cable.
Sub-Station
The tri-phase alternating current generated at the power house is conveyed through the high potential cable system to eight sub-stations containing the necessary transforming and converting machinery. These sub-stations are designed and located as follows:
