High-Voltage Circuit Breakers:

High-voltage circuit breakers (including breakers rated at intermediate voltage) are used for service on circuits along with voltage ratings higher than 600 volts.  The Standard voltage ratings for these circuit breakers are from 4,160 - 765,000 volts and 3-phase interrupting ratings of 50,000 -50,000,000 kVA.

Within the early stages of electrical system development, the main portion of high-voltage circuit breakers was oil circuit breakers. Therefore, magnetic and compressed-air type air circuit breakers have been established and are in use present day.

The magnetic air circuit breaker is rated up to 750,000 kVA at 13,800 volts. That type of circuit breaker interrupts in air among two separable contacts along with the aid of magnetic blowout coils. As the current-carrying contacts divided during a fault condition, an arc is drawn out horizontally and transferred to a set of arcing contacts. Concurrently, the blowout coil gives a magnetic field to draw the arc upward into the arc chutes.  The arc, accelerates upward into the arc chute, aided through the blowout coil magnetic field and thermal effects, where it is elongated and separated into several small segments.

A construction of this category of circuit breaker is similar to in which of a huge air circuit breaker used for low-voltage applications, except in which they are all electrically operated.

Compressed-air circuit breakers or air-blast circuit breakers and depend on a stream of compressed air directed toward the separable contacts of the breaker to interrupt the arc formed while the breaker is opened. Air-blast circuit breakers have presently been established for use in extra high-voltage applications along with standard ratings up to 765,000 volts.

OCBs (Oil circuit breakers) are circuit breakers which have their contacts immersed in oil.  Current interruption takes place in oil that cools the arc developed and thereby quenches the arc. The pole of small oil circuit breakers could be placed in one oil tank; thus, the large high-voltage circuit breakers have every pole in a separate oil tank. An oil tanks in oil circuit breakers are generally sealed.  The electrical connections among the contacts and external circuits are made by porcelain bushings.