Switch gear is
an apparatus which is used for switching, controlling and protecting electrical circuits and equipment. The requirement of
electric power has increased a lot, so in order to get a continuous power
supply. Power system must
be protected from large faults and provide protection to machinery and devices.
For the continuity of the power supply machinery such as generators and motors
are switched on and off many times and the means provide to achieve this is
called switch gear.
In general, switch gear is
the term including the entire range of switching devices and their combination
with associated control, measuring, protecting, and regulating equipment.
What are the functions of switch gear
- Carrying the normal load current
- Making or breaking the normal load current
- Clearing the fault current
Components of
·
Circuit
breaker
·
Current
transformer and potential transformer
·
Protective
relays
·
Measuring
instruments
·
Switches
·
fuses
·
Surge
arrestors
·
Isolators
Miniature
circuit breaker
What is the consideration which
must be done while using switch gear in the power system?
·
Location
of the equipment if it is indoor or outdoor
·
System
parameters such as system earthing, frequency, insulation level, ambient
conditions,
·
Erection
of switch gear – mechanical and electrical interconnections, placing the
equipment on foundation, assembly of loose supplied parts, connections of
controls and power circuits
· Switch gear commissioning – Testing must be done to ensure if the installation meets the
requirements.
What are the essential features
of switch gear?
·
Reliability
– switch gear is used in a power system to improve the reliability when a fault
occurs in system switch gear must isolate the faulty section from the remainder
circuit
·
Absolutely
certain discrimination – if fault occurs in a power system then switch gear must
be able to discriminate between the faulty section and healthy section.
·
Quick
operation – if any fault occurs in a power system then switch gear must be able
to act quickly so that no damage is done to the equipment
·
Provision
for manual control – switch gear must have manual control in case of any
electrical or electronic control fail
·
Provision
for instruments – provisions for the instruments is needed this may be in the
form of ammeter, voltmeter…
Types and classification of
Classification of switch gear can be done by;
·
The current rating
·
Interrupting rating
·
Voltage class-
Low voltage (less than 1000 volts)
Medium voltage (1000 – 35000 volts)
High voltage (more than 35000 volts)
· Insulating
medium – air, gas, oil, vacuum
· Construction
type – indoor, outdoor, industrial, metal-enclosed, metal-clad…
· Type of
current – AC, DC
· By
application – transmission system, distribution
· Operating
method – manually, motor or solenoid/stored energy
DIFFERENT TYPES OF SWITCH GEARS
Switch gear has a lot of equipment which is related
to switching and interrupting current under normal and abnormal conditions. It
includes equipment's such as fuses, relay, circuit breakers, and other equipment
HIGH VOLTAGE
Air-insulated switch gear
Air circuit breakers are used for high voltage
system it is mostly used in high voltage sub-station for voltage range up to
800Kv, these circuit breakers are used where space restriction and environment
circumstances are not severe. Electrical and mechanical components of AIS
installation are assembled on site. AIS which is used for industrial operation
is not safe to touch and it will be affected by the environment and climatic
change.
Gas-insulated switch gear
Its design is really compact and it would really be
an advantage for installation it is used in a substation where the voltage
range up to 550Kv. It is installed in the middle of the load center of an urban
or industrial area. This type of switch gear is insensitive to contamination and
it provides safety from electric shocks
Highly integrated switch gear
HIS switch gear has the advantages of air-insulated
installation and the technology of gas-insulated switch gear it is used in
voltage range up to 550Kv. This type of switch gear are suited for new
substations in a limited space and in places where environmental conditions are
extreme and it can also be used in places where the maintenance cost is high
LOW VOLTAGE
Contractors
Contractors are load breaking devices with a limited
short circuit breaking and making capacity and they are used for high switching
rates, it can be divided into two types they are air-insulated and vacuum contractor.
Circuit breakers
They make and break all currents within the scope of their rating, from small inductive
capacities load currents to full short circuit current and this is done under all fault conditions in the power supply system such as earth faults, phase opposition… it can be used to control the input from the transformer.
Molded case and miniature circuit
breaker
These circuit breakers are light weight compact
circuit breakers for mounting onto or behind the panels, they are designed for
hand operation but it also has a built-in protective tripping arrangements
Fuses
Fuses are used with low voltage switch gear as a
backup for distribution contractors or for various control and instrumentation
circuits. They are composed of fuse base and fuse-link with the fuse base an
isolated distance can be established and with the fuse link one single breaking
of short circuit current can be done
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