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 consists of moving contact and fixed contact.Moving contact is connected with a piston its just for the movement of the contact and no pressure build due to its motion.There are two vents on fixed contact they are axial vent for small current produced in oil due to heating of arc and radial vents for large currents.The whole device is covered using Bakelite paper and porcelain for protection.Vents are placed in a turbulator. Operation Under normal read more

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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 are two types of such breakers: 1.Self-blast oil circuit breakers – in which arc control is provided by internal means i.e. arc itself facilitates its own extinction efficiently. 2.Forced blast oil circuit breakers – in which arc control is provided by mechanical means external to the circuit breaker. Self-blast oil circuit breakers – In this type of breakers, the gases produced during arching are confined to a small volume by the use of an insulating read more

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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 7 below It consists of fixed and moving contacts enclosed in a strong weather-tight earthed tank containing oil up to a certain level and an air cushion above the oil level. The air cushion collects arc gases without generation of unsafe pressure in the dome of circuit breaker. It also absorbs mechanical shock of the upward oil movement. Under normal operating conditions the fixed and moving contacts remain closed and the circuit breaker carries the normal circuit read more

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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. 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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