SWITCH GEAR & IT'S TYPE
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| Switch Gears |
A switch gear is the combination of electrical disconnect switches, fuses or circuit breakers used to control and protect. It is used both to de-energies equipment to allow work to be done and to clear downstream.
Switch Gear circuit breaker are illustrated below
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| Representation of Vaccum Circuit Breaker |
VCB ( Vaccum Circuit Breaker)
A vaccum circuit breaker is such kind of circuit breaker where the arc quenching takes place in vacuum. The technology is suitable for mainly medium voltage application. For higher voltage vacuum technology has been developed but not commercially viable. The operation of opening and closing of current carrying contacts and associated arc interruption take place in a vacuum chamber in the breaker which is called vacuum interrupter.The vacuum interrupter consists of a steel arc chamber in the centre symmetrically arranged ceramic insulators.The vacuum pressure inside a vacuum interrupter is normally maintained at 10 - 6 bar.
SF6 CIRCUIT BREAKER
A circuit breaker in which the current carrying contacts operate in sulphur hexaflouride or SF6 gas is known as an SF6 circuit breaker.
SF6 has excellent insulating property. SF6 has high electro-negativity. That means it has high affinity of absorbing free electron. Whenever a free electron collides with the SF6 gas molecule, it is absorbed by that gas molecule and forms a negative ion.
SF6 has excellent insulating property. SF6 has high electro-negativity. That means it has high affinity of absorbing free electron. Whenever a free electron collides with the SF6 gas molecule, it is absorbed by that gas molecule and forms a negative ion.
MCB CIRCUIT BREAKER
MCB stands for Miniature Circuit Breaker . Earlier we used fuses now instead of fuses we use Miniature Circuit Breaker. It's role is to automatically switch off the electrical circuit during abnormal condition. |
| MCB's |
Working of MCB
There are two arrangement of operation of miniature circuit breaker. One due to thermal effect of over current and other due to electromagnetic effect of over current. The thermal operation of miniature circuit breaker is achieved with a bimetallic strip whenever continuous over current flows through MCB, the bimetallic strip is heated and deflects by bending. This deflection of bimetallic strip releases mechanical latch. As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts. But during short circuit condition, sudden rising of electric current, causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts. This was a simple explanation of miniature circuit breaker working principle.
MCCB BREAKER
MCCB BREAKER
MCCB is Moulded Case Circuit Breaker. It is designed for circuit protection of low voltage distribution system.CHARACTERSTICS
Rated current up to 1000 A.
Trip current may be adjustable.
Thermal or thermal-magnetic operation.
ELCB BREAKER
ELCB is Earth Leakage Circuit Breaker. An ELCB is a sefety device used in electrical installation with high earth impedance to prevent shock.MPCB BREAKER
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| MPCB BREAKER |
MPCB is Motor Protection Circuit Breaker. This type of circuit Breaker is not used for motor infact they are used for motor's protection.
Motor protection is provided by the thermal-magnetic protection elements incorporated in the motor circuit-breaker.The magnetic elements (short-circuit protection) have a non-adjustable tripping threshold, fixed at 13 times the maximum setting current
of the thermal trips.
The thermal elements (overload protection) include automatic compensation for ambient temperature variations.The rated operational current of the motor is displayed by means of a graduated / calibrated knob. All live parts are protected against direct finger contact from the front panel. Personal protection is also provided.
The undervoltage trip allows the circuit-breaker to de-energize in the event of an undervoltage condition. The user is therefore protected against sudden starting of the machine when normal voltage is restored, since the Start button ‘I’ has to be pressed to restart the
motor.
The shunt trip provides remote tripping of the circuit.
CONTACTOR
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| CONTACTOR |
A contactor is an automatically controlled switch used for switching a power circuit, similar to relay except with higher current ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit.
RELAY
A relay is an electrically operated switch. Many relay use an electromagnet to mechanically operate a switch but other operating principles are also used such as solid state relays. It is used to control by a low power signal where several circuits must be controlled by one signal.
