Circuit breaker vacuum type

The two comparatively new type of breakers, vacuum and SFg are exceptions and have gained favour in view of their reliability and durability. For details on these breakers, see Sections 19.5.5 and 19.5.6, which also deal with their switching behaviour and phenomenon of arc reignition. Figures 12.44 and 12.45 illustrate typical power and control circuit diagrams respectively, for a 6.6 kV breaker-operated motor starter. 

Vacuum arcs. This type of low-pressure arc, operating with cathode spots, is special because the gas-phase working fluid is provided by erosion and evaporation of the electrode material. This type of arc is of importance in high-current electrical equipment, high-current vacuum circuit breakers, and switches. 

Insulating oil plays a vital part in many types of electrical equipment, not only as an insulant but also as a coolant in transformers and as an arc extinguishing medium in circuit breakers. In each case, efficient operation of the equipment depends upon the purity of the insulating oil, which in service can be contaminated by oxidation, condensation and the presence of solids, such as colloidal carbon, formed by arcing in circuit breakers. The electrical and physical properties of the oil may be seriously affected, resulting in reduced operating efficiency or even equipment failure. Frequent replacement of the oil wiU be too costly, and reconditioning by filtration and vacuum dehydration to remove all contaminants is the economic answer. 

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