Oil Circuit Breakers

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  • Topic: Circuit breaker, Distribution board, Fuse
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  • Published : March 24, 2012
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Oil Circuit Breaker Operation
By A JOSEPH

INTRODUCTION
In this study the operation and maintenance required on the Takaoka Tank Type Oil Circuit Breaker (Type L4) and the JB427 will be explored. The circuit breakers used for this study is the Diamond Vale 33kV Circuit Breaker at Mt Pleasant Substation and the #0 33kV Circuit Breaker at Barataria Substation respectively.

Figure [ 1 ] : THE TAKAOKA OIL CIRCUIT BREAKER

Figure 2 : The jb427 oil circuit breaker

CIRCUIT BREAKER MAIN COMPONENTS
The main components of the Oil Circuit Breaker are the following: * Bushing
* Tank
* Arc Extinction Chamber (Turbulator)
* Operating Mechanism (Opening and Closing Mechanism)

Bushing - Bushings must be able to withstand short-circuit currents which may flow through the circuit breaker. The bushings of both breakers are of porcelain type and can be either oil filled (Takaoka) or compound filled (JB427)

Tank - The tank contains the insulating medium for the circuit breaker which is oil. Additionally, it contains the opening mechanism, the fixed and moving contacts.
Oil Circuit Breakers can be classified with reference to the type of tank construction. The two types are minimum oil circuit breaker and bulk oil circuit breakers
The Takaoka is a minimum oil circuit breaker. This means these circuit breakers use a small quantity of oil per tank, where the oil is used only for arc extinction. For each phase, there exists a different physical compartment (tank) of oil, hence three (3) tanks.

The JB427 is a bulk oil circuit breaker. This means these breakers use large quantity oil, all of which is contained in one tank. The oil is used both for arc extinction and insulation of the current conducting parts from one another and the earthed tank.

Arc Extinction Chamber - This is a cylindrical housing which contains a fixed contact, a moving contact, baffle stacks and the interrupting medium. The arc extinction chamber as the name is implies is the area in which the arc is extinguished in the circuit breaker.

Operating Mechanism – The operating mechanism consists primarily of two tension springs, the closing spring and the opening spring.

The closing spring generates the required driving force to close the circuit breaker and charge the opening spring. In other words, a closed circuit breaker is always prepared for immediate opening.

The opening spring is directly connected to the circuit breakers link system. This means that the mechanical energy needed for the vital opening operation is always stored in the opening spring when the circuit breaker is in closed position.

The closing mechanism for the Takaoka is of the solenoid type. The closing mechanism for the JB427 is of the hydraulic spring type.

CIRCUIT BREAKER OPENING OPERATION

The trip relay sends a signal, energizing the trip coil.
When the trip coil is energized the moving contact is separated from the fixed contact.

Arc Interruption Operation
When contacts are parted on load, an arc is created. The interrupting medium (oil) is responsible for quenching the arc and establishing the nominal level of isolation between the open contacts.

The arc extinction chamber functions such that, the arc which is created when parting the contacts is stretched by the use of baffle stacks, due to their staggered alignment within the chamber. As the connecting rod is pushed out, fresh cool oil enters into turbulator from the tank from its base. as it does this, it pushes out the hot oil which in turn cools...
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