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It has been found that most of the line faults on overhead transmission system are transient in nature. About 90% of faults are caused by lightning, birds, vines, tree branches etc. these conditions result in such arcing faults that if the fault energy is interrupted for a short period, the arc extinguishes and the line [...]
Written by John on October 12th, 2008 with 1 comment.
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In this breaker, vacuum is being used as the arc quenching medium. Vacuum offers highest insulating strength, it has far superior arc quenching properties than any other medium. When contacts of a breaker are opened in vacuum, the interruption occurs at first current zero with dielectric strength between the contacts building up at a rate [...]
Written by John on October 12th, 2008 with 5 comments.
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In this circuit breaker, sulphur hexaflouride ( SF6 ) gas is used as the arc quenching medium. The sf6 gas is an electro negative gas and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high pressure flow of sf6 gas and an arc is struck between [...]
Written by John on October 12th, 2008 with 7 comments.
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Depending upon the direction of air blast in relation to the arc;air blast circuit breakers are classified into: (i)Axial-blast type in which air-blast is directed along the arc path as shown in figure below. (ii) Cross-blast type in which air blast is directed at right angles to the arc path as shown in figure below [...]
Written by John on October 11th, 2008 with no comments.
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These type of breakers employ ‘air blast’ as the quenching medium.The contacts are opened by air blast produced by the opening of blast valve.The air blast cools the arc and sweeps away the arcing products to the atmosphere.This rapidly increases the dielectric strength of the medium between contacts and prevents from re-establishing the arc.Consequently the [...]
Written by John on October 11th, 2008 with 4 comments.
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Construction There are two chambers in a low oil circuit breaker,the oil in each chamber is separated from each other.The main advantage of this is that low oil is required and oil in second chamber wont get polluted.Upper chamber is called the circuit breaker chamber and lower one is called the supporting chamber.Circuit breaking chamber [...]
Written by John on October 10th, 2008 with no comments.
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In case of plain oil circuit breakers artificial control of arc is less therefore long arc length is necessary for arc quenching. Its necessary that final arc extinction should occur while the contact gap is still shorter. For this some arc control is incorporated and the breakers are then called arc control circuit breakers. There [...]
Written by John on October 10th, 2008 with 3 comments.
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In this circuit breaker the contacts are separated under the whole of the oil in the tank. There is no special arc control system other than increasing length caused by separation of contacts. Arc extinction occurs when a critical gap is reached between the contacts. Double break plain oil circuit breaker is shown in fig [...]
Written by John on October 10th, 2008 with no comments.
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Oil circuit breakers can be classified into following types: 1) Bulk oil circuit breakers, which use a large quantity of oil. In this circuit breaker the oil serves two purposes. Firstly it extinguishes the arc during opening of contacts and secondly it insulates the current conducting parts from one another and from the earthed tank. [...]
Written by John on October 10th, 2008 with no comments.
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in oil circuit breakers insulating oil is used as an arc quenching medium. The contacts are opened under oil and an arc is struck between them, heat of the arc evaporates the surrounding oil and produce hydrogen at high pressure. The oil is pushed away from the arc region and the gas bubble occupies adjacent [...]
Written by John on October 10th, 2008 with no comments.
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Circuit breakers are classified on the basis of medium used for arc extinction as follows: 1. Oil circuit breakers 2. Air blast circuit breakers 3. Sulphur hexafluroide circuit breakers 4. Vacuum circuit breakers.
Written by John on October 10th, 2008 with no comments.
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A circuit breaker is required to perform the following three duties: 1. It must be capable of opening the faulty circuit and breaking the fault current. 2. It must be capable of being closed on to a fault 3. Must be capable of carrying fault current for a short time while another breaker is clearing [...]
Written by John on October 9th, 2008 with 1 comment.
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