h an extensive tool equipment for a
repair and machine shop, which is located on the main gallery at the
northerly side of the operating room.

[Illustration: 5,000 K. W. ALTERNATOR--MAIN POWER HOUSE]

CHAPTER V

SYSTEM OF ELECTRICAL SUPPLY

[Sidenote: _Energy from
Engine Shaft
to Third Rail_]

The system of electrical supply chosen for the subway comprises
alternating current generation and distribution, and direct current
operation of car motors. Four years ago, when the engineering plans
were under consideration, the single-phase alternating current railway
motor was not even in an embryonic state, and notwithstanding the
marked progress recently made in its development, it can scarcely yet
be considered to have reached a stage that would warrant any
modifications in the plans adopted, even were such modifications
easily possible at the present time. The comparatively limited
headroom available in the subway prohibited the use of an overhead
system of conductors, and this limitation, in conjunction with the
obvious desirability of providing a system permitting interchangeable
operation with the lines of the Manhattan Railway system practically
excluded tri-phase traction systems and led directly to the adoption
of the third-rail direct current system.

[Illustration: SIDE AND END ELEVATIONS OF ALTERNATOR.]

[Illustration: SIDE ELEVATION AND CROSS SECTION OF ALTERNATOR WITH
PART CUT AWAY TO SHOW CONSTRUCTION.]

It being considered impracticable to predict with entire certainty the
ultimate traffic conditions to be met, the generator plant has been
designed to take care of all probable traffic demands expected to
arise within a year or two of the beginning of operation of the
system, while the plans permit convenient and symmetrical increase to
meet the requirements of additional demand which may develop. Each
express train will comprise five motor cars and three trail cars, and
each local train will comprise three motor cars and two trail cars.
The weight of each motor car with maximum live load is 88,000 pounds,
and the weight of each trailer car 66,000 pounds.

The plans adopted provide electric equipment at the outstart capable
of operating express trains at an average speed approximating
twenty-five miles per hour, while the control system and motor units
have been so chosen that higher speeds up to a limit of about thirty
miles per hour can be attained by increasing the number of motor cars