With the impact of summer cooling loads on systems
already extended by the increased loads caused by the
building boom following World War II, it has become
evident that the continuance of some former practices
could "pile u p " distribution investment and still leave
the system inadequate for the future loads now being
forecast.
In this author's opinion, future residential distribution
developments will depart substantially from today's
practices. T o meet the requirements of higher kw customer
demands, and to keep investment in line with
revenues, it will be necessary to develop a system which
can absorb larger incremental load increases with a
minimum of system betterment expense.
PURPOSE
THE PURPOSE of this article is to present, in light of
recent trends, a scheme for serving future residential
loads. This scheme includes some ideas for changes in
methods, equipment, and voltage classifications and is
based on the following considerations:
1. Future installations of electric cooling and space
heating equipment plus other high kw rated appliances
will be prevalent in existing residential areas, as well
as new areas.
2. An acceptable scheme must develop and make use
of investment in existing facilities and be applicable on
either a spot or group basis to both new and existing
residential areas.
3. Distribution systems along residential streets will,
for many years, continue to be overhead for reasons of
economy and accessibility for servicing. However, future
developments should anticipate the ultimate possibility
of an underground system in some areas.
4. Single-phase 120/240 volts will continue to be the
standard utilization voltage for the home.
On the premise that no one fixed set of conditions
can be applied in all areas because of differences in existing
facilities, policies, and practices, the scheme presented
herein is intended to be flexible, and somewhat
general, in scope.
It is the author's hope that this article will serve to
stimulate further interest and study in new developments
to solve the problems associated with future residential
loads.
REVIEW OF RECENT TRENDS
T o ESTABLISH a systematic approach for the future,
a brief review of recent trends will be made.
Fig. 1 will be recognized as a conventional 4-kv Y
radial system, with express feeder, primary main, series
street light circuit, lighting secondary, and power secondary,
and serving, as an example, one of the earlier
customers to have a central unit cooling system.
For illustration purposes, all circuits have been combined
on the same pole as shown on the elevation of the
pole structure, Fig. 1 (A). It is not uncommon, however,
to see such structures on many streets today.
By the following sequence of system developments,
the pole structure will be reduced to conform to present
trends and practices:
1. One Point of Delivery. Increase the size of the
lighting transformer and serve the customer's central
cooling unit from the single-phase lighting service. Remove
the open-delta power bank, power secondary, separate
power service, and meter with the results as shown
in Fig. 1 (B).
2. Common Neutral. Combine the neutrals of the
4-kv feeder and primary main, with the secondary neutral,
as shown in Fig. 1 (C).
3. Multiple Street Light Circuit. Convert the series
street light system to multiple, install individual luminaire
control, and serve from the system secondaries.
Remove the constant current transformer and series circuit,
as shown in Fig. 1 (D).