Where are these mounts used?
Switches and control panels are located in
power generating stations, transformer stations, distribution substations,
commercial and institutional buildings, industrial plants and factories,
refineries, paper mills, metal foundries, and any other place where electrical
power or power is used. electrical power is distributed to any number of zones
c
There are a few common types of assemblies
that cover almost any application. A broad classification based on the location
of the switch assemblies is whether the gear is installed indoors or outdoors.
An additional rating for indoor equipment
is vented as standard indoors, indoors with drip hood, indoors for sprinkler
area location, indoors in hazardous locations, arc-proof (type a, boc) and
indoors in corrosive environments. Exterior switchgear can also be classified
as having an island or not (walking instead of not walking in types) with or
without a work area.
Another method of classifying the switch is
whether it is a bottom or top entry, the power and control cables are entering
from the bottom or top of the gear.
Devices in Switchgear
The switching device can contain as
switching / interrupting device (s): a circuit breaker (cb), a switch / fuse
combination, a contactor / fuse combination (for motor switching), for low
voltage assemblies (lv): a switch or switch in series with a contactor (for
switching the motor).
Certain configurations come only as
non-pull back construction, others as removable. If special requirements for
the gear are needed, the special property can be used as a criterion to define
the gear, for example, if a dust-tight enclosure is required due to the
presence of dust (fine or bearing) in the atmosphere, this gear is designated
as dust tight.
For switchgear assemblies, as heat is
generated, due to the high current flowing, a dust-tight enclosure is almost
impossible, so a dust-proof one is used. The main standards that govern the
design, manufacture and testing of these assemblies are: CSA, ANSI, IEC, EEMAC,
NEMA.
Distribution equipment assemblies and motor
control centers (starters) can be classified according to their voltage
classes. The LV equipment is rated in the range of 120/208 V single phase or
three phases to 750 VAC. The medium voltage ones are from 2400 / 4160V to 44KV.
The enclosures for all low voltage constructions are metallic. Some
constructions include partitions and barriers to provide safer operation over
standard construction.
For medium voltage distribution equipment,
both types of construction, metal clad and closed metal, are common. In this
section the main components of switch assemblies, motor starters and associated
auxiliary elements will be given.
Major components
Low voltage switchgear assemblies
·
Molded Case Circuit Breakers
(MCB) or Power (Magnetic Air) (withdrawable or fixed) complete with or without
integral overcurrent protection device (magnetic thermometer,
·
Solid state or microprocessor
based) with or without zone interlock arrangement
·
Cradle (only for removable
versions)
·
Fixed power transformers and
power control.
·
Current transformers
·
Interframe and rear barriers.
·
Main bus bars, sliders, bus
risers and cable lugs (compression or mechanical)
·
Protection fuses for switch
control circuits, instrument compartments.
·
Circuit Breaker Accessories,
Breaker Lifting Devices (Integrated with Gears)
·
Fused or unfused breaker
switches
·
Auxiliary protection and
surveillance relays.
·
Measurement devices (ammeters,
voltmeters, wattmeter’s and DMP digital measurement packages)
·
Control switches and indicator
lights.
Medium voltage switchgear
The main components are:
·
Removable Circuit Breakers
(Oil, Air, SF6, Vacuum)
·
Switching device (load rest or
disconnect) with or without fuses (Power current limiting or power draw type.)
With or without fuse / blown fuse indicator
·
Instrument transformers
·
Capacitor trip device
·
Relays
·
Meters and instruments
·
Main bus
·
Control and indicating devices,
jumpers, cable lugs, cable holders and headers
·
Barriers and shutters
·
Instrument compartments
·
Test Switches and Switch
Accessories
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