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. Such circuit breakers are classified into:   a)Plain oil circuit breakers b)Arc control circuit breakers   In the former type no means is available for controlling the arc and the contacts are exposed to the whole of the oil in the tank. In the latter special arc control devices are employed to get the beneficial action of the arc as efficiently as possible 2)Low oil circuit breakers, which use minimum amount of oil. In such circuit breakers oil read more

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inoil 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 portions of the contact. The arc extinction is facilitated mainly by two processes. Firstly the hydrogen gas has high heat conductivity and cools the arc, thus aiding the deionisation of the medium between the contacts. Secondly the gas sets up turbulence in the oil and forces it into the space between contacts thus eliminating the arcing products from the arc path resulting in arc extinction and interruption of current. The advantages of using oil as an arc quenching medium read more

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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. read more

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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 the fault. Depending on the above duties circuit breaker has three ratings braking capacity, making capacity and short time capacity. Breaking capacity It is current that a circuit breaker is capable of breaking at a given recovery voltage under specified conditions. The breaking capacity is always stated at the r.m.s value of fault current at the instant of contact separation. When a fault occurs there is considerable asymmetry in the fault current due to presence of d.c component. The d.c read more

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·High resistance method – In this method arc resistance is made to increase with time so thatcurrent becomes insufficient to maintain the arc. Disadvantage of this method is enormous energy is dissipated in the arc. Hence it can be used only in dc circuit breakers and low capacity ac circuit breakers. Arc resistance can be increased by: 1.Lengthening the arc – Arc resistance is directly proportional to length of arc so to increase resistance separation between the contacts are increased 2.Cooling the arc – Cooling helps in deionisation of medium thus increasing arc resistance 3.Reducing cross section of the arc – When area of arc reduced, voltage necessary to maintain arc increased i.e. resistance is increased. Allowing the arc to pass through narrow opening can reduce cross read more

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Circuit breaker is an equipment, which can make or break a circuit manually or automatically under all conditions i.e. no load, full load and short circuit conditions. OPERATING PRINCIPLE It consists of fixed and moving contacts which remain closed under normal condition, when fault occur the trip coil are energized and the moving contacts are pulled apart. When contacts get separated an arc will be struck between the contacts, which will not only delay current interruption process but also generate enormous heat, which may cause damage to the system or to the circuit breaker itself. So the main problem with circuit breaker is to extinguish the arc within the shortest possible time. ARC PHENOMENON When fault occurs current flow through contacts before they are being separated. At the read more

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