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 solution can result in better voltage regulation at the end of heavily loaded circuits, as the load
current of an existing load is reduced by the same factor. Load losses vary as the square of the
voltage, so an increase.in the operating voltage in the example by a factor of 1.732 will result in
reduced losses by a factor of three. This method cannot be used if the distribution equipment,
such as the cable, switchgear, or transformers are not rated for the increased voltage. On more
modern systems (consisting of three-phase transformers, underground cable, and metal-clad
switchgear), the equipment is usually operated at or near its design voltage ratings. A simple
increase of system voltage, therefore, cannot be used to increase system capacity. In these cases,
the practical solution is often to superimpose a new higher voltage distribution system on top of
the existing system, and to serve the old loads from transformer substations. These substations
should convert the supply voltage from the new system distribution voltage to the old one. For
example, a newer 13.8 kV distribution system might be superimposed over an older 4.16 kV
system, with several 13.8 kV to 4.16 kV substations installed to serve the old portion of the
distribution system. All new loads, however, would be fed by the 13.8 kV distribution system
with direct transformation to the utilization voltage (e.g., 13.8 kV to 480 V).
8.2.5.2 Installation of Transformer Fans. When the load increases to, or above, the
transformer capacity at an existing substation, fans are often used to increase the transformer load
handling capacity by a factor of 15 to 25 percent (depending upon the size of the transformer).
The transformer bushings, primary and secondary load cables, switchgear or fuses, and other
factors must also be investigated to assure that there are no other weak links in the system that
may prevent full capacity utilization of the transformer's inherent capability. This should be
included as part of the design criteria of the initial installation of the transformer equipment.
The primary and secondary cables, bushings, and primary and secondary switchgear should all be
sized to provide greater load carrying capability than the transformer. Then, as the need arises,
the transformer capacity can be increased relatively inexpensively by the addition of fans. The
other devices, such as bushings, cables, and switchgear cannot be inexpensively changed to
achieve the same capacity increase, therefore, this capability should be provided upon initial
installation.
8.3 MAINTENANCE MANAGEMENT. Every distribution system is unique in its
configuration, load, and types of installed equipment. This section provides general guidelines
regarding the requirements of a proper Electrical Distribution System Maintenance Program. In
both the long term and in the day-to-day operation of the system, maintenance must be performed
in order to preserve a reliable source of electric power. Often, however, it appears that an
electrical system requires no maintenance.
ANSI/NFPA 7OB-1987, Recommended Practice for Electrical Equipment Maintenance, is a
premier source of information for all levels of personnel involved with the electrical distribution
system. This document defines an Electrical Preventive Maintenance (EPM) program that is
intended to reduce the hazard to life and property that can result from failure or malfunction
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