What is switchgear?
Switchgear is essential equipment used in electricity world and present in electrical power systems, it used to control, protect and isolate any electrical device or electrical network under consideration. It consists mainly of electrical disconnecting switches equipped with fuses or may be circuit breakers So it is impossible to find any electricity system without switchgears.
Switchgear is essential equipment used in electricity world and present in electrical power systems, it used to control, protect and isolate any electrical device or electrical network under consideration. It consists mainly of electrical disconnecting switches equipped with fuses or may be circuit breakers So it is impossible to find any electricity system without switchgears.
At the earlier time our electricity power station used very simple knife
switches as the power and voltage levels was small, after that power and
voltage level increased rapidly making manually opening operated switches are
so dangerous especially when we deal with the loaded electricity circuits.
Consequently anew generation of switchgear has been manufactured
to allow large currents and power levels to be safely controlled by automatic
equipment incorporating digital controls, metering and protection devices in the electricity systems.
The technology has been improved till we can now used switchgear
for voltages up to 1100 k.v as in power substation which step up or down the voltage.
We use electrical switchgear in both the high and low voltage side
to control the high rated power transformer and also the downstream electricity distribution
circuits.
What are the main types of switchgears?
Switchgear enclosure contain a number of equipment's
that allow it to interrupt fault currents with thousands of amperes , the primary
component that interrupt the fault current is called the
circuit breaker .
Circuit breaker is carefully designed to disconnect
the electrical circuit under faulty conditions, it contains a mean to quench the
arc resulting from the on /off switching, and according to this mean we have
four types of circuit breaker:
1-Oil Circuit breaker: depend on the oil to quench the
arc.
2-Gas Circuit breaker: this type stretch the arc by using magnetic
field then use (SF6) gas to quench this stretched arc.
3-Vacuum Circuit breaker: this type also stretch the arc by small
amount and at or near the zero current, the circuit breaker will interrupt the
current as the arc is not so hot at this moment. Vacuum circuit breakers are almost
used in modern medium-voltage switchgear up to 35 k.v.
4-Air Circuit breaker: this type use
the magnetic force or the compressed air to quench the arc and usually able to
terminate all current flow very quickly typically between 30 ms and
150 ms depending on the age and construction of the circuit breaker.
How can we classify switchgears?
Many details of switchgears like rating and specifications
are set by several of standards, for example IEEE and ANSI standards are used
in North America and IEC are frequently used in the reset of the world.
We can classify switch gear according to the following parameters:
(1) Current rating.
(2) Interrupting rating which means the
maximum short circuit current
that the circuit breaker can safely interrupt.
(3) Voltage rating as following:
(a)
Low voltage "less
than 1 kV AC".
(b)
Medium voltage "
1 kV up to approximately 75 kV (AC)".
(c)
High voltage "75
kV up to approximately 230 kV AC".
(d)
Extra high voltage "more
than 230 kV".
(4) Insulation around the contact points:
"Oil - Gas (SF6) - Vacuum - Air ", as referred above.
(5) Construction type:
"Indoor – Outdoor – Marine – Industrial
– Draw out elements (removable with a tool) - Fixed elements (not removable) – Metal
enclosed – Nonmetal enclosed".
(6) IEC degree of internal separation:
(a)
No Separation.
(b)
Busbars separated
from other functional units.
(c)
Terminals for
external conductors separated from busbars.
(d)
Terminals for
external conductors separated from functional units but not separated from each
other.
(e)
Terminals for
external conductors separate from their associated functional unit.
(f)
Terminals for
external conductors separated from each other.
(7) Interrupting device:
"Fuses – Air circuit breaker – Oil circuit breaker –
Vacuum circuit breaker – SF6 circuit breaker ".
(8) Operating method:
"Manually operated – Motor operated – Solenoid operated".
(9) Type of current:
"Alternating current – Direct current".
(10) Application:
"Distribution System - Transmission system".
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