The design of the high-voltage
substation must include consideration for the safe operation and
maintenance of the equipment. Switching equipment is used to provide
isolation, no load switching, load switching, and/or interruption of
fault currents.
The magnitude and duration of the load
and fault currents will be significant in the selection of the
equipment used. System operations and maintenance must also be
considered when equipment is selected.
One significant choice is the decision
of single-phase or three-phase operation. High-voltage power systems
are generally operated as a three-phase system, and the imbalance
that will occur when operating equipment in a single-phase mode must
be considered.
Metal-enclosed low-voltage power
circuit breaker switchgear indicates a design which contains low
voltage ac or dc power circuit breakers in individual grounded metal
compartments. The circuit breakers can be either stationary or draw
out; manually or electrically operated; fused or unfused; and
either 3-pole, 2-pole or single-pole,
construction.
The switchgear may also contain
associated control, instruments, metering, protective and regulating
equipment as necessary. Definitions, ratings, design and production
tests, construction requirements, and guidelines for application,
handling, storage, and installation are covered in IEEE C37.20.11.
Low-voltage metal-enclosed switchgear
is typically installed in industrial plants, utility and cogeneration
facilities, and commercial buildings for the protection and
distribution of power for loads such as lighting, machinery, motor
control centers, elevators, air conditioning, blowers, compressors,
fans, pumps, and motors.
Low-voltage switchgear is available in
ac ratings up to 635 V and 5000 A continuous and in dc ratings up to
3200 V and 12000 A continuous. Short-circuit current ratings are
available up to 200 kA.
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