Relative merits and demerits of different types of conventional circuit breakers (bulk-oil circuit breakers, minimum oil circuit breakers and air-blast circuit breakers) are given below:
1. Bulk-Oil Circuit Breakers:
Merits:
Simplicity in construction, high rupturing capacity, suitability for automatic as well as manual operation; possibility of locating CTs in bushings.
Demerits:
ADVERTISEMENTS:
Larger size and greater weight, fire hazard, explosion hazard, unsuitability for indoor installation, requirement of large volume of high grade mineral oil (scarcely available in our country), necessity for periodic inspection of the quantity and quality of oil in the tank, greater wear and tear of the contacts resulting in their frequent replacement, unsuitability for repeated cycles of operation in connection with automatic reclosing. Becoming obsolete now.
2. Minimum-Oil Circuit Breakers:
Merits:
Requirement of lesser quantity of oil, smaller space requirement, smaller tank size, less weight, low cost, reduced risk of fire and reduced maintenance problems, easier access to the contacts, suitability for both automatic and manual operation.
Demerits:
ADVERTISEMENTS:
Increased degree of carbonisation due to smaller quantity of oil, rapid deterioration of oil dielectric strength due to high degree of carbonisation, greater contact damage, comparatively low rupturing capacity, difficulties in removal of gases from the contact space in time and locating CTs, necessity of more frequent inspection and replacement of oil and total unsuitability for repeated cycles of operation. Now superseded by SF6 circuit breakers.
3. Air-Blast Circuit Breakers:
Merits:
High speed operation, suitability for frequent operation, facility for high speed reclosure, negligible maintenance, elimination of fire hazard, reduced size, comparatively less weight, less contact damage, very easy access to the contacts, very high rupturing capacity.
Demerits:
ADVERTISEMENTS:
Requirement of a complete compressed air system consisting of air compressor, electric motor, airtight tubes etc. more complicated construction, higher cost, requirement of highly trained personnel for maintenance, problem of current chopping, sensitivity to circuit severity i.e. RRRV. Becoming obsolete now.