Capacitors. Capacitors raise voltage levels by reducing the
reactive line losses associated with reactive current flow between the
capacitor installation and the power supply. It is rarely economical to apply
them for voltage improvement only. Capacitors are justified when their cost
over their service life is less than any utility company low-power-factor
penalty cost. Take into account the cost of switching equipment to meet any
functional or utility company prohibitions against a leading power factor.
Base design on shunt power capacitors that conform to IEEE 18, Shunt Power
Capacitors. Take into account the following considerations:
a) Fixed capacitance is the amount of capacitance that can be
applied continuously without excessive voltage rise at reduced load.
b) Switched capacitance is an additional amount of capacitance that
can be applied, if provision is made to switch off this additional amount when
demand is reduced.
c) Select the type of capacitor switching that is best for the
condition at hand. Possible choices include remote control of the capacitor
switching device, time clock control, or power factor or voltage sensitive
d) Install capacitors in banks on poles, at-grade, or in a substa-
tion, as near as possible to the centroid of the area where correction is
Transformers. Transformers can be mounted on poles, at-grade, or
indoors depending upon size and site requirements. Select a standardized
three-phase transformer, except where the load is small enough to justify a
single-phase transformer. Use oil-insulated transformers, except where site
conditions or economic considerations make their use prohibitive. Consider
loading, noise level, and transformer protection requirements. Do not use
askarel-insulated and nonflammable, fluid-insulated transformers because of
insulation must be economically or functionally justified. Less-flammable,
liquid-insulated units may be necessary where oil-insulated transformers
cannot meet fire-exposure requirements as listed in MIL-HDBK-1008, Fire
Protection for Facilities Engineering, Design, and Construction. Epoxy-
encased ventilated dry-type units may be appropriate in areas where liquid-
insulation loss might result in water pollution.
Pole Mounting. For single-pole mounting, limit the size of single-
phase or three-phase units in accordance with Table 3. Do not use pole-
platform mounting (two-pole structures) except in instances where other
methods are not satisfactory. It is recommended that maximum transformer size
be limited to the sizes shown in Table 3. For installations of 225 to 500
kVA, pad-mounted, compartmental-type transformers are recommended.