ANHOLE TO CONTACT RAIL]

The function of the electrical apparatus in sub-stations, as has been
stated, is the conversion of the high potential alternating current
energy delivered from the power house through the tri-phase cables
into direct current adapted to operate the motors with which the
rolling stock is equipped. This apparatus comprises transformers,
converters, and certain minor auxiliaries. The transformers, which are
arranged in groups of three, receive the tri-phase alternating current
at a potential approximating 10,500 volts, and deliver equivalent
energy (less the loss of about 2 per cent. in the transformation) to
the converters at a potential of about 390 volts. The converters
receiving this energy from their respective groups of transformers in
turn deliver it (less a loss approximating 4 per cent. at full load)
in the form of direct current at a potential of 625 volts to the bus
bars of the direct current switchboards, from which it is conveyed by
insulated cables to the contact rails. The photograph on page 102
is a general view of the interior of one of the sub-stations. The
exterior of sub-stations Nos. 11 and 18 are shown on page 107.

[Illustration: CONTACT RAILS, SHOWING END INCLINES]

The illustration on page 108 is from a photograph taken on one of
the switchboard galleries. In the sub-stations, as in the power house,
the high potential alternating current circuits are opened and closed
by oil switches, which are electrically operated by motors, these in
turn being controlled by 110 volt direct current circuits. Diagramatic
bench boards are used, as at the power house, but in the sub-stations
they are of course relatively small and free from complication.

The instrument board is supported by iron columns and is carried at a
sufficient height above the bench board to enable the operator, while
facing the bench board and the instruments, to look out over the floor
of the sub-station without turning his head. The switches of the
direct current circuits are hand-operated and are located upon boards
at the right and left of the control board.

A novel and important feature introduced (it is believed for the first
time) in these sub-stations, is the location in separate brick
compartments of the automatic circuit breakers in the direct current
feeder circuits. These circuit breaker compartments are shown in the
photograph on page 93, and are in a line facing the boards which
carry the direct f