What are electrical circuit breakers?
Electrical circuit breakers is a device used for controlling and protection of electrical power system. circuit breaker means a device which breaks(Open) the circuit under abnormal conditions and protects the system from hazards. The function of a circuit breaker is to isolate the faulty point of the power system in case of abnormal conditions such as faults.
##What is an arc in circuit breaker?
During the opening of the contact in a circuit breaker of carrying high voltage, the gap between the two contacts gets ionized. This forms a low resistive path for current through the gap, which produces a conducting arc in the gap. So that even the contacts are physically separated the current continues to flow.
During the flow of electric current one contact to other, the contact becomes so heated that it glows in an arc shape. This is an arc. All the circuit breakers need to quench the medium to break the circuit.
##Air blast circuit breaker:
This type of circuit breaker uses an air blast to quench the medium to break the circuit. The air blast swipes away the arcing product to the atmosphere. This type of circuit breaks are used were system voltage is above 245kV, 420kV and even more.
Working:
The high-pressure air is blasted through the nozzle at the instant of contact separation. There is a moving contact, which moves axially so as to open and close depends on the spring pressure and air pressure. The operating mechanism operates the rod when it gets a pneumatic or electrical signal. The opens so as to send the high-pressure air in the hollow of the insulator. The high pressure rapidly enters to the arc chamber and opening the contact. Open to close the outgoing of the air through the port. The chamber gets filled with air.
During the arcing period, the air is allowed to pass to the atmosphere.
While closing the valve turned so as to close the connection between hollow of the insulator and reservoiur. The valve lets the air from the hollow insulator to the atmosphere. As the pressure drops in the chamber to the atmospheric pressure, the moving contact closes the contact by virtue of the spring pressure.
##Advantages:
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The risk of fire is eliminated
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Small size compared to other methods
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The arcing time is very small due to the rapid build-up of dielectric strength between contacts.
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Lesser energy needed
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The arcing product are completely removed by blast.
##Disadvantages:
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Air blasting circuit breakers are very sensitive to the variation of the restricting voltage
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Maintenance required for the compressor which supplies the blast air.