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 operating conditions,the moving contacts remain engaged with the upper fixed contact.When a fault occurs,the moving contact is pulled down by the tripping springs and an arc is struck.The arc vapourises oil and produces gases under high pressure.This action constrains the oil to pass through a central hole in the moving contact and results in forcing series of oil through the respective passages of the turbulator.The process of turbulation is orderly one,in which the sections of arc are successively quenched by the effectof separate streams of oil ,moving across each section in turn and bearing away its gases.

Advantages

A low oil circuit breaker has following advantages compared to bulk oil circuit breaker

1. It requires lesser quantity of oil
2. It requires smaller space
3. There is reduced risk of fire
4. Maintenance problems are reduced

Disadvantages

A low oil circuit breaker has following disadvantages compared to bulk oil circuit breaker

1. Due to smaller quantity of oil,the degree of carbonisation is increased
2. There is a difficulty of removing the gases from the contact space in time
3. The dielectric strength of oil deteriorates rapidly due to high degree of carbonisation.

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