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.

(c) Air Blast Circuit Breakers:

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).

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