IEEE Power & Energy Magazine - March/April 2022 - 69

the goal and an opportunity appeared
in the Times Square Theater District.
United had established a substantial load
in the form of animated advertising signs
in which the complex relays used ac
to reduce arcing. New York Edison's
dc distribution system ducts were " saturated "
with cables for the heavy load from
lighting hotels and restaurants while both
companies supplied the heavy load of
the refrigeration plants of theater air conditioning
systems.
Once again, the Upper West Side was
the test area. An experimental threephase,
four-wire combined light and
power network was initiated in July 1923,
located between Columbus Avenue and
Central Park West, a residential area of
large apartment buildings and small
stores. The goal was a network free of
light flicker from motor operat ion.
Three banks of transformers, each
with a trio of 25-kVA units and a pair of
12.5-kVA units, supplied the lighting
and power loads, the latter included 15
two-phase elevator motors. Each elevator
motor received 220 V, as two
phase from auto transformers supplied
at 190 V three phase from the
network. Those transformers had only
3% reactance; the load distribution was
found to be very good on motor starting.
The elevator motors were found to
impact voltage by less than 3% with no
noticeable impact on lighting.
The first complete three-phase,
four-wire automatic network for combined
light and power went into operation
in the Times Square area on 28
October 1925. Forty-four transformers
provided 4,950 kVA to the network
from five radial three-phase, 3,000-V
feeders powered from the West 45th
Street transformer substation. The protection
was provided by Westinghouse
CM relays that had begun to supplant
the Palmer type two years prior. By
the end of 1925, the techniques of
multiple-feed automatic networks had
been established. Furthermore, the
replacement of two-phase distribution
by three phase had been initiated
in 1923 as new calculation methods
(Fortescu equations and Clark
calculat ion tools) made practical
march/april 2022
the equal balance of single-phase
lighting loads
on three-phase circuits.
The stage was set for the
final breakthrough.
The Final Goal
Achieved
On 1 April 1926, threephase
13,200-V feeders
from the generating stations
at Sherman Creek
and Hell Gate were connected
directly to the
network transformers;
initially supplemented
by 3,000-V feeders
from the transformer
substations that were
in place. In time, both
The protective
relays that
worked well
on lower
voltages were
not always
usable for
the higher
voltages, and
new designs
were needed.
the transformer substation and heavy,
3,000-V feeder cables from those substations
were eliminated. The distribution
networks fed directly from the
power station reduced the cost of ac
distribution to 20-25% of that of an
equivalent dc system.
United continued experiments to
determine voltage drop in cables and
also to improve reliability. The protective
relays that worked well on lower
voltages were not always usable for the
higher voltages, and new designs were
needed. The early relays
were relatively simple,
triggered by the transformer
magnet izing
current produced by the
flow of cable charging
current. Those relative
values changed at the
higher voltages, and
separate lockout relays
were required to prevent
" pumping " (repetitive
opening and closing)
of the protective
relay. In one instance,
the regenerated current
of elevator motors
was sufficient to trigger
pumping when loads
were light. New relay
connection schemes were necessary.
In late 1928, the validity of the
United network was key in New York
Edison President Matthew Sloan's decision
that the entire dc distribution
system in Manhattan would no longer
be expanded and would be changed to
ac over time. He stated specifically
that " given the economy, reliability,
and efficiency " of the United network,
there was " no justification for
continued extension of the Edison dc
system. " Subsequent announcements
(a)
(b)
figure 3. The Network Street vault. (a) The relays and switches and (b) network
feeder transformer. (Courtesy of AIEE Transactions.)
ieee power & energy magazine
69
IEEE Power & Energy Magazine - March/April 2022

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