TM
5-811-1/AFJMAN
32-1080
NORMAL ALLOCATlON OF VOLTAGE DROP
Figure 5-1. Normal Allocation of Voltage Drop.
basis. Voltage control is used where objectionable
circuit must be capable of serving the load over
voltage changes occur with varying voltages. Cur-
the required distance without exceeding the allow-
rent control is used when loads change, but voltage
able voltage drop. The number of circuits and
is well regulated or load power factor remains
conductor sizes will be determined by an economic
substantially constant. Current control is effective
evaluation of the possible configurations including
also when power factor varies in a predictable
construction requirements (span lengths, pole
manner with the load. Kilovar control is used when
heights, pole classes) for conductor capacities at
load voltage is regulated, but power factor varies in
the primary distribution voltage and higher volt-
an unpredictable manner to corresponding load
ages.
variations. More sophisticated current and voltage
(1) Quick check values. Table 5-1 has been
control than that covered by IEEE Std 18 can be
prepared to allow a quick check of the capacities of
provided, and manufacturers should be consulted
three-phase medium-voltage circuits at 0.90 power
for application and specification information.
factor by giving the approximate kilovolt-ampere-
mile loading for a three percent voltage drop. For
5-6.
Medium-Voltage
Circuits.
voltages not given, the use of a factor of the
a. Number. The number of medium-voltage cir-
square of the ratio of the desired voltage divided
cuits will be determined on the basis that each
by the known voltage times the megavolt-ampere-
5-3
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