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Enclosed Distribution Cutout |
Figure 4-29.—Capacitors, open-rack installation.
Experience has shown that the following schedule
normally will keep the equipment operating properly:
TYPE CONTROL
YEARS
Time clock
3
Voltage
3
Dual temperature
5
Temperature only
8
Time clock and temperature
8
The capacitors switches usually are removed from
the distribution line by the lineman and replaced with a
spare unit during the season in which they normally are
not operated. The capacitor switches can be
maintained efficiently in a distribution shop by the
lineman.
Protective/Interrupting Devices
A power distribution circuit, like any other
electrical circuit, requires the use of special devices to
provide control and to protect the system from internal
or external influences that may damage the circuit.
Overcurrent/overvoltage protection and personnel
safety, requirements are provided in a power
distribution system by the use of lightning arresters,
cutouts, fuses, air switches, and oil switches.
LIGHTNING OR SURGE ARRESTERS.—A
surge arrester is a device that prevents high voltages,
by providing a low-impedance path to ground for the
current from lightning or transient voltages. and then
restores normal circuit conditions.
Surge arresters perform a function on the electric
system similar to that of a safety valve on a steam
boiler. A safety valve on a boiler relieves high pressure
by blowing off steam until the pressure is reduced to
normal. When the pressure is reduced to normal, the
safety valve closes and is ready for the next abnormal
condition. When a high voltage (greater than the
normal line voltage) exists on the line, the arrester
immediately furnishes a path to ground and thus limits
and drains off the excess voltage. Furthermore, when
the excess voltage is relieved, the action of the arrester
must prevent any further flow of power current. The
function of a surge arrester is, therefore,
twofold-first, to provide a point in the circuit at which
the overvoltage impulse can pass to earth without
injury to line insulators, transformers, or other
connected equipment and, second, to prevent any
follow-up power current from flowing to ground.
DISTRIBUTION CUTOUT.—A distribution
cutout provides a high-voltage mounting for the fuse
element to protect the distribution system or the
equipment connected to the system (fig. 4-30).
Distribution cutouts are used with installations of
4-20
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