Merits and Demerits of Types of Conventional Circuit Breakers:
Having studied the operational principles, the constructional features and fields of application of the bulk oil, minimum oil and air-blast circuit breakers, it would be worthwhile to consider their relative merits and disadvantages of Conventional Circuit Breakers.
(a) Bulk Oil Circuit Breakers:
The main advantages of this type of Conventional Circuit Breakers are:
- Simplicity of construction.
- High rupturing capacity.
- Suitability for automatic as well as manual operation.
- Possibility of locating current transformers in bushings.
The disadvantages are :
- Fire hazard.
- Explosion hazard.
- Necessity for periodic inspection of the quality and quantity of oil in the tank.
- Large volume of high grade mineral oil which is not only costly, but is scarcely available in our country.
- Necessity of storing large quantity of oil in the generating stations and
- Unsuitability for indoor installation.
- Unsuitability for repeated cycles of operation in connection with automatic re-closing.
- Greater wear and tear of the contacts resulting in their frequent
- Comparatively large quantities of steel required for the construction of the tank.
- Larger size and greater weight.
(b) Minimum Oil Circuit Breakers:
These Conventional Circuit Breakers have the following advantages:
- Comparatively smaller quantity of oil.
- Comparatively less weight and size.
- Lower cost.
- Suitable for both automatic and manual operation.
- Easier access to the contacts.
They however, suffer from the following disadvantages:
- Fire and explosion hazards do exist in this type of circuit breaker, although to a lesser extent than in bulk oil circuit breakers.
- Totally unsuitable for repeated cycles of operation.
- Requires a more frequent inspection and replacement of oil.
- Greater contact damage.
- Difficulty in locating current transformers.
- Comparatively lower rupturing capacity.
These circuit breakers are finding a much wider application in the high voltage power systems in our country because of the following advantages:
- No explosion or fire hazard.
- Very fast in operation.
- Suitable for rapid re-closing.
- Very high rupturing capacity.
- Opening unloaded transmission lines or highly capacitive systems do not present much difficulty..
- Less contact damage.
- Very easy access to the contacts.
- Comparatively less weight.
These Conventional Circuit Breakers, however, do have a few disadvantages:
- They require the installation of a complete compressed air system consisting of electric motor, air compressor, air tight tubes, etc.
- Their construction is much more complicated.
- Their cost is higher.
- Requires highly trained personnel for their maintenance.
- They are more sensitive to RRRV (rate of rise of recovery voltage).