Based on the arc extinguishing medium the circuit breaker can be classified into four types, Oil circuit breaker is one of them. Some important terms regarding it will be discussed through the following lesson.
What is oil circuit breaker?
Bulk oil circuit breaker: Circuit breakers that need a lot of oil to extinguish arcs are referred to as bulk oil circuit breakers. Due to the fact that their tank is maintained at ground potential, this kind of circuit breaker is also known as a dead tank-type circuit breaker. The system voltage determines how much oil is needed in a bulk oil circuit breaker.
Low oil circuit breaker: This kind of circuit breaker is set on a porcelain insulator to protect it from the ground and uses minimal oil as an arc quenching medium. Such circuit breakers have an arc chamber that is covered in bakelized paper. The porcelain supports the lower part of the breaker, and the upper porcelain encloses the contacts.
Construction of Oil Circuit Breaker.
Construction of an oil circuit breaker is very simple. It is made up of current-carrying contacts that are housed in a strong, weatherproof metal tank and the tank is filled with transformer oil. Between the live component and the earthed body, the oil works as both an arc extinguishing medium and an insulator.
Air is injected into the tank at the top of the oil, which acts as a cushion to control the displaced oil's impact on the production of gas surrounding the arc and to soften the mechanical shock of the oil's upward movement. The breaker tank is firmly bolted with the structure to withstand the vibration produced as a result of cutting off a very high current. Gas outlet for the removal of gases is built into the tank cover of the oil circuit breaker.
Working Principle of Oil Circuit Breaker.
In this type of circuit breaker some insulating oil like transformer transformer oil is used as arc extinction medium. The contacts are submerged under the oil so the contacts are open under oil and the heat produced due to the arc evaporates to the surrounding oil and dissociates it into the substantial gaseous hydrogen at high pressure.
The hydrogen gas occupies a volume about one thousand times that of the oil decomposed. Therefore, the oil is pushed away from the arc area and the expanding hydrogen gas bubble surrounds the arc region and the adjacent portion of the contacts.
Advantages of Oil Circuit Breaker:
1. It absorbs the arc energy to decompose the oil into gas which have excellent cooling properties.2. The oil acts as an insulator and permits small clearance between line conductors and earthed components.
3. The surrounding oil presents cooling surface in close proximity to the arc.
4. In the tank, hydrogen gas is created, and it has excellent cooling and high diffusion rates.
Disadvantages of Oil Circuit Breaker:
1. It is inflammable so there is a risk of a fire.
2. It may form an explosive mixture with air.
3. The arcing products(carbon) remain in the oil as a result its quality deteriorates with successive operations.
So it requires periodic checking and oil replacement.
Applications of Oil Circuit Breaker:
The oil circuit breakers are used in the high voltage applications such as in power grids, Substation, Powerlines and the transmission and distribution systems for upto 230 kVolt.
Maintenance of Oil Circuit Breaker.
A circuit breaker's contacts may occasionally burn due to arcing after being interrupted by short-circuit current. Additionally, the dielectric oil becomes carbonized around the contacts, decreasing its ability to conduct electricity. As a result, the breaker's breaking capacity is decreased. As a result, oil circuit breaker maintenance is crucial for testing and replacing oil and contacts. The following check list to be maintained during the breaker inspection.
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