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 3.7.4.1 Pole-Mounted. Pole-mounted capacitors (Figure 3-17) are packaged as a complete
unit containing all necessary items for a switched distribution capacitor bank installation. The
banks consist of an aluminum or steel mounting frame that supports the capacitor units,
interconnecting wiring, and capacitor switches. Overcurrent protection is usually provided
by group fuses.
3.7.4.2 Metal-Enclosed. Metal-enclosed capacitor banks (Figure 3-18) consist of a factory
assembled group of individual capacitor units mounted in a protective housing complete with bus
connections, controls, and protective and switching equipment within the enclosure. Personnel
safety and compactness are the major benefits. Each capacitor unit is normally protected by an
individual current-limiting fuse.
3.7.4.3 Open-Rack. An open-rack capacitor installation (Figure 3-19) is a field-assembled
group of capacitor units mounted in an open-rack structure without enclosing plates or screens.
Open-rack installations are normally made up of several stack-type capacitors connected in
parallel to provide desired kVar capacity. All the units in a given stacking unit are normally
connected in parallel with the steel frame forming one terminal and the insulated bus forming the
other. For open-rack installations the capacitor units are protected by individual fuses, group
fuses or relays, and a circuit breaker.
3.7.5 Fixed Capacitors. Fixed capacitor installations are those that are continuously on-line.
Fixed capacitor banks are connected to the system through a disconnecting device that is capable
of interrupting the capacitor current, allowing removal of the capacitors for maintenance
purposes. Fixed capacitor banks should be applied to give a voltage boost to the system during
heavy load periods. Caution must be used, however, to ensure the boost will not be excessive
during light-load conditions. To isolate or deenergize a fixed capacitor installation, the
disconnecting switches should be opened with rapid positive action. The successful switching of
capacitors depends, to a considerable extent, on the technique of the operator and the speed of
opening. It is more difficult to deenergize a capacitor bank than it is to energize it, because the
ease with which capacitor current is interrupted depends on the point on the voltage wave when
the switch contacts separate. If the arc is reestablished and maintained with the disconnecting
device open, the switch should be reclosed at once to avoid damage to the switch. Another
attempt should then be made to open the disconnecting device. After the disconnecting device
has been opened, the capacitor installation is isolated but still charged. The capacitors should be
left open from the line for at least five minutes before they are returned to service. This
precaution will prevent a buildup of the line voltage above normal, which may occur if a fully
charged capacitor bank was closed on a line.
3.7.6 Switched Capacitors. Switched capacitor installations are those where the capacitor
bank is switched in and out of service depending upon system operating conditions. They are
usually switched on when the load requirements are the greatest and switched off during
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