Thursday 15 July 2021
Wednesday 5 May 2021
Switchgear and control panel assemblies
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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Tuesday 27 April 2021
Safety distance and electrical transformers
There's good reason to leave electrical work to the experts. For any transformer maintenance job, our team of experts follows a complete safety protocol. Part of this is maintaining a safe distance from the transformer when testing. Read on to learn more about this distance.
What is meant by a safety distance?
The safety distance is the free space
between one or more people and, in this case, the electrical transformer. This
space allows an adequate reaction time in case of difficulties during the
execution and maintenance tasks.
The staff must also have the relevant
safety elements, such as a helmet, gloves, boots and all the necessary
requirements. Both the safety distance and the protective equipment are
intended to prevent risks.
Electrical transformers and the
necessary distance
To work with the safety distance, it is
necessary to consider that there are different levels within it. The first
point to clarify is that the distance will be different between low, medium and
high voltage works.
Low voltage
In the event that the transformer is
located in an urbanization, protection systems must be considered to prevent
radiation from affecting people who live nearby. The transformers found in
these places are low voltage. The most common protection is usually concrete
envelopes in specially designed cabinets.
Medium and high voltage
On the other hand, medium voltage
transformers that transform to low voltage are usually installed inside
buildings. In this case, there is a regulation in charge of regulating the
installation conditions inside, taking care that there are no radiation leaks.
This is also useful for high voltage transformers. The latter, in the long
term, could harm people's health. For this reason, it is essential to have the
necessary safety equipment.
Is it dangerous to be near a
transformer?
With the necessary equipment and respecting
the safety distance, it is not. The World Health Organization (WHO) sets the
maximum limit for electromagnetic field emissions at 100 microtears. In the
case of medium to low voltage electrical transformers, once installed, they
generally do not reach these amounts. However, it is recommended to maintain a
distance of at least 5 meters from a transformer in operation, especially if
you do not have the necessary protective equipment.
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