What is Bulk Oil Circuit Breaker?
A circuit breaker that is used a bulk quantity of oil for arc extinction and insulation purpose is called a Bulk oil circuit breaker. it is also called a dead tank type circuit breaker because its tanks are earthed at ground potential. It is also called a plain Break Circuit breaker.
The amount of oil used in circuit breakers is depended upon the output ratings of circuit breakers. If the output rating of the circuit breaker is 110Kv then the quantity of oil used is 8000 to 10000 Kg of oil. If the output rating of the circuit breaker is 220Kv then the quantity of oil used is 50000 kg of oil.
In the bulk oil circuit breaker oil is used for two purposes
1. For the arc extinction purpose
2. For insulating the current-carrying parts of the circuit breaker from the earth.
In the Bulk oil circuit breaker, the oil used for arc extinction purposes is one-tenth of total oil, and the remaining oil is used for insulation purposes only.
Construction of bulk oil circuit breaker
The Fixed and moving contacts of the circuit breaker are immersed in insulating oil inside the metal vessel or metal tank which is at ground potential.
During normal operating conditions, Fixed and moving contacts of the circuit breaker remain in closed conditions. Whenever a fault occurs in the systems, moving contacts are separated from fixed contacts by the protective mechanism of the circuit breaker, and the arc is produced between the fixed and moving contacts.
A large amount of heat energy dissipates from the arc into the oil which vaporizes the oil and also decomposes the oil.
Due to this larger gaseous pressure developed inside the oil which displaced insulating oil from surrounding of fixed and moving contacts. So, the inner wall of the bulk oil circuit breaker withstands higher pressure. so a metal tank of the bulk oil circuit breaker is made strong enough to withstand higher pressure of oil.
The top covers of the bulk oil circuit breaker are tightly bolted with the tank and the entire structure is properly fitted with a concrete foundation otherwise the breaker will jump during interruption of higher fault currents.
The gas vent is fitted on the top cover to remove the oil gases safely. The oil tank of the breaker is not totally filled with oil some space keep in the tank which is useful during oil expansion.
Working of bulk oil circuit breaker
When the fixed and moving contacts are separated from each other during the fault by the protective mechanism of the breaker, the arc is produced between the fixed and moving contacts.
This arc produced a hydrogen gas bubble around the arc. when the moving contacts go away from the fixed contacts length of the arc increases which is increased the resistance of the arc.
This increased arc resistance lowers the temperature and reduces the formation of gases surrounding the arc between the contacts.
The arc quenching in bulk oil circuit breaker takes place when arc current passes through the zero-crossing. by this arc will be extinguished and fault current is interrupted. In this circuit breaker, hydrogen gas cools down the arc which helps in arc quenching in the oil circuit breaker.
Advantages of bulk oil circuit breaker
1. In the bulk oil circuit breaker production of carbonized gases are less due to the bulk quantity of oil.
2. The bulk oil circuit breaker is suitable for frequent operations.
3. In the Bulk oil circuit breaker, it is easy to remove gases between the fixed and moving contacts in time.
Disadvantages of Bulk oil circuit breaker
1. As system voltage increases maintenance costs increase as compared to the minimum oil circuit breaker.
3. Size of bulk oil circuit breaker more so, transportation of bulk oil circuit breaker is very difficult.
4. It requires more space area as compared to the minimum oil circuit breaker.
5. The bulk oil circuit breaker has larger tanks so the weight of the bulk oil circuit breaker increases.
6. The bulk oil circuit breaker does not permit high-speed interruption.
7. The bulk oil circuit breaker has long and inconsistent arcing time,
Applications of bulk Oil circuit breaker
1. The bulk oil circuit breaker used up to 33Kv.
2. These circuit breakers are only used for low voltage applications only where high breaking capacity is not important.
Difference Between Bulk Oil and Minimum Oil Circuit Breakers :
| Bulk Oil Circuit Breaker | Minimum Oil Circuit Breaker |
|---|---|
| A circuit breaker which is used a large quantity of oil for arc quenching medium is called a bulk oil circuit breaker. | A circuit breaker which is used a small quantity of oil for arc quenching medium is called a minimum oil circuit breaker. |
| It uses a bulk quantity of oil so a large space area is required | It uses a small quantity of oil so a small space area is required. |
| Due to the bulk quantity of oil size of the circuit breaker increases and transportation is become very difficult. | Due to the small quantity of oil size of the circuit breaker is reduced and transportation becomes very difficult. |
| As output voltage rating increases, the quantity of oil increases, and maintenance costs also increase. | It uses a small quantity of oil for all voltage ratings so maintenance cost is less. |
| A bulk quantity of oil is used so the degree of carbonization is less. | A small quantity of oil is used so the degree of carbonization is more |
| A bulk quantity of oil is used so the degree of carbonizations is less so it is suitable for frequent operations | A small quantity of oil is used so the degree of carbonizations is more so it is not suitable for frequent operations |
| It is very easy to remove gases from the contacts space in time. | It is very difficult to remove gases from the contacts space in time. |
| Bulk oil circuit breakers are used in low voltage applications up to 33kv. | Minimum oil circuit breakers are used in high voltage applications up to 132Kv. |