Difference between bulk oil and minimum oil circuit breaker

In electrical power systems, oil circuit breakers (OCBs) are used to interrupt electrical faults and prevent damage to the system. There are two types of oil circuit breakers: bulk oil circuit breakers and minimum oil circuit breakers. The main difference between them lies in the amount of oil used and the design of the breaker.

Bulk Oil Circuit Breaker (BOCB):

A bulk oil circuit breaker uses a large quantity of oil (typically 10-20 liters) to cool and insulate the electrical contacts and the arc that forms during fault clearance. The oil is contained in a tank within the breaker and is used to:

  1. Cool the contacts: The oil helps to dissipate the heat generated by the arcing during fault clearance, reducing the risk of contact damage.
  2. Insulate the contacts: The oil provides electrical insulation between the contacts, preventing the flow of current and ensuring safe operation.
  3. Quench the arc: The oil helps to extinguish the arc that forms during fault clearance, reducing the risk of re-ignition and ensuring reliable operation.

BOCBs are commonly used in medium-voltage applications (up to 36 kV) and are suitable for applications with high fault currents.

Minimum Oil Circuit Breaker (MOCB):

A minimum oil circuit breaker uses a small amount of oil (typically 1-5 liters) to cool and insulate the electrical contacts. The oil is contained in a small tank or reservoir within the breaker and is used to:

  1. Cool the contacts: The oil helps to dissipate the heat generated by the arcing during fault clearance, reducing the risk of contact damage.
  2. Insulate the contacts: The oil provides electrical insulation between the contacts, preventing the flow of current and ensuring safe operation.

MOCBs are commonly used in low-voltage applications (up to 1 kV) and are suitable for applications with low fault currents.

Key differences:

  1. Oil quantity: BOCBs use a larger quantity of oil than MOCBs.
  2. Application: BOCBs are used in medium-voltage applications, while MOCBs are used in low-voltage applications.
  3. Fault current rating: BOCBs are designed to handle higher fault currents than MOCBs.
  4. Size and weight: BOCBs are generally larger and heavier than MOCBs due to the larger oil tank and the need for more robust construction.
  5. Maintenance: BOCBs require more frequent maintenance than MOCBs due to the larger oil tank and the need for regular oil changes.

In summary, bulk oil circuit breakers are used in medium-voltage applications with high fault currents, while minimum oil circuit breakers are used in low-voltage applications with low fault currents. The choice between the two depends on the specific requirements of the electrical power system.