Bulk-oil circuit-breaker, minimum oil circuit-breaker and air circuit-breaker are examples of high voltage circuit-breakers. Tank circuit-breaker is another name of bulk oil circuit-breaker which is reliable, cheaper and can be maintained easily. They are almost free from current chopping and is simple in design. They are unaffected by air pollution and is available for a large range of current and voltage ratings. But the main drawback is that it is not suitable for above 220 kV applications and requires frequent maintenance. The major parts of a bulk-oil circuit breaker are oil tank, arc-control device, bushings, moving-contact assembly and operating mechanism. The tank is filled with mineral oil and it absorbs and dissipates energy released during current interruption. Bushing is insulation across a high voltage conductor passing through a frame or metal sheet at earth potential. Bushings used here can be plain single dielectric bushing, condenser bushing, oil-filled bushing or dielectric fluid-filled condenser bushing. Minimum oil circuit-breakers which are also known as small oil volume breakers contain low quantity of oil in their tanks. In air circuit-breakers, arc is extinguished by applying the principle of lengthening and increasing the power loss of the arc. Some other high voltage circuit-breakers are air blast circuit-breaker, vacuum circuit-breaker, sulphur hexafluoride (SF6) circuit-breaker and high voltage direct current (HVDC) circuit-breaker.
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