Switchgear
Definition
The apparatus used for controlling, regulating and
switching on or off the circuit within the electric power system is understood
as switchgear.
The switches, fuses, circuit breaker, isolator, relays,
current and potential transformer, indicating instrument, lightning arresters
and control panels are samples of the switchgear devices.
The switchgear system is directly linked to the
availability system. It's placed in both the high and low voltage side of the
facility transformer. It's used for de-energizing the equipment for testing and
maintenance and for clearing the fault.
When the fault occurs within the power grid, heavy
current flow through equipment thanks to which the equipment get damaged, and
therefore the service also get interrupted. So to guard the lines, generators,
transformers and other electrical equipment from damage automatic protective
devices or switchgear devices are required.
The automatic protective switchgear mainly consists
of the relay and circuit breaker. When the fault occurs in any section of the
system, the relay of that section comes into operation and shut the trip
circuit of the breaker which disconnects the faulty section. The healthy
section continues supplying loads as was common, and thus there's no damage to
equipment and no complete interruption of supply.
Types
of Switchgear
The switchgear is especially classified into two
types, the outside type and therefore the indoor type. For voltage above 66kV,
the output switchgear is employed. Because for the high voltage, the building
work will unnecessarily increase the installation cost due to large spacing
between the conductor and enormous size of insulators.
Below the 66kv there's no difficulty in providing
the building work for the switchgear at an inexpensive cost. The indoor type
switchgear is of metal clad type and is compact. Due to the compactness, the
security clearance for operation is additionally reduced and thus reduced the
world required.
Essential
Features of switchgear
The essential features of switchgear are:
1. Complete reliability. With continue trend of
interconnection and therefore the increasing capacity of generating station, he
need for a reliable switchgear has become of paramount importance. This is
often not surprising because switchgear is added to the facility system to
enhance the reliability. When fault occurs on any a part of the facility
system, the switchgear must operate to isolate the faulty section from the rest
circuit.
2. Absolutely certain discrimination. When fault
occurs on any section of the facility system, the switchgear must be ready to
discriminate between the faulty section and therefore the healthy section. It
should isolate the isolate the faulty section from the system without affecting
the healthy section. This may ensure continuity of supply.
3. Quick operation. When fault occurs on any a part of the facility system, the switchgear must operate quickly in order that no damage is completed to generators, transformers and other equipment by the short-circuit current. If fault isn't cleared by switchgear quickly, it's likely to spread into healthy parts, thus endangering complete shutdown of the system.
4. Provision for manual control. A switchgear must
have provision for manual control. Just in case the electrical control fails,
the required operation are often administered through manual control.
5. Provision for instruments. There must be
provision for instruments which my be required. There could also be within the
from of ammeter or voltmeter on the unit itself or the required current and
voltage transformers for connecting to the most switchboard or a separate
control panel.
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