IEEE Power & Energy Magazine - March/April 2022 - 67

began an effort with suppliers to develop
those relays. In 1920, the Palmer Electric
and Manufacturing Company perfected
an automatic switch that would
detect a reverse current from the network
to protect the primary feeders and
transformer. It would open on the magnetizing
current of the transformer
and close when the current stabilized
but not close on a crossed connection.
The Palmer network switch was
operated by relays in the secondary circuit
to trip on reverse flow of power. In
the event of an outage on the primary
side, it would prevent reverse flow from
the network into a faulted transformer.
It closed only upon the flow of true (actual)
power from the transformer into
the network.
The Sexton and Orcutt report credits
the Palmer relay as the key to the success
of the United effort. Earlier network
protectors such as those marketed in 1913
by the Metropolitan Engineering Company
(a Murray company) protected the
network by isolation of a defective transformer
but appa rent ly not from
reverse current from the network into
a faulted transformer.
The United Automatic
Network
The Upper West Side of Manhattan
had developed rapidly after the
opening of the first subway line in
1904. Large apartment buildings with
elevators presented a heavy load and
United captured much of that business.
That success was bolstered by innovation
in transformers, system design, and
reactive power compensation. The radial
distribution feeders from a United
transformer substation on 146th Street
supplied local transformers with twophase
power by three-wire 2,100-/
3,000-V feeders. Lighting transformers
were connected to the pair of 3,000-V
wires to supply single-phase customers
at 110/220 V. Two-phase power was supplied
from all three wires of the feeder
by two-phase transformers that delivered
220-V two-phase power by threewire
circuits to customer motors.
As customer load increased with
additional building construction, a
march/april 2022
new transformer
substation
was constructed
on West 97th Street in
1922. The most modern
of similar United installations,
it was supplied
by 13,200-V three-phase
feeders, a new transmission
scheme that supplanted,
and in time,
replaced the 3,000 V
two-phase lines.
Ten years of research
and experiments proved
successful on that April
day in 1922 when the
automatic network assumed
the load that extended
from 93rd Street
to 101st Street and from
Broadway to Riverside
Drive. Four sets of threephase,
three-wire 2,750 V
primary feeders from the West 97th Street
transformer substation fed 29 transformer
banks. The transformer secondaries were
connected to form a network throughout
the area. The total capacity was
1,275 kVA on two separate three-wire
low-tension networks. One network carried
single-phase lighting loads on threeThe
Palmer
network
switch
proved highly
successful as
detailed event
records of
the first year
of network
operation
showed it
to be nearly
trouble free.
wire 110-/220-V circuits,
the other supplied power
loads on three-wire,
220-V two-phase circuits
as two-phase distribution
for power customers
was still the norm. Each
transformer bank held a
25-kVA transformer for
the lighting network and
a pair of 50- or a pair of
100-kVA transformers for
the two-phase power network.
The lighting cables
were 200 mcm, and the
power used 80 mcm (see
Figures 2 and 3).
The secondaries were
spliced at intersections,
customer connections
were made in manholes,
and no additional junction
boxes were required.
In dense areas, lines were placed on both
sides of the street; this improved efficiency
by the reduction of load on the
lines, which reduced the reactance in the
lines. Moreover, it decreased the length
of customer laterals. The transformers
were located at each street intersection.
An external reactance of 8.7% was
figure 1. The interior of the United West 45th Street ac distribution substation, similar
in capacity to the West 97th Street location, showing the operator's board and
synchronous condenser in the lower-right corner. (Courtesy of Electrical World.)
ieee power & energy magazine
67
IEEE Power & Energy Magazine - March/April 2022

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