Friday, July 27, 2012

Circuit Breaker Types

Circuit breakers can be classified by the arc-quenching media they use. The following is a brief listing of the different types, in the order of their historical development.

Air-Magnetic Air Quenching

These types of breakers date back to the early 1900s and were used in the medium voltage range to about 15 kV. They interrupt the current by drawing the arc into and extending it in a magnetic field and creating an increased air flow to extinguish it.
This type of breaker was used in industrial and power installations to about the early1960s. A well-known example is the GE or Westinghouse Magna-blast breaker, stillin service in a number of installations. They are no longer readily available. 

Oil Circuit Breakers

Oil circuit breakers were the dominant type of breakers used in both the medium- and high-voltage range up to 345 kV until the early 1960s in the North American and British practice. The arc quenching is by the turbulent flow of oil originally by the effect of the arc and later by some improved design of the construction of
the chamber surrounding the contacts. These breakers are distinguished by the relatively large amount of oil required for the effective and efficient arc interruption.

Oil circuit breakers are used to switch circuits and equipment in and out of a system in a substation. They are oil filled to provide cooling and to prevent arcing when the switch is activated.

Air-Blast Breakers

Air-blast breakers were used in Europe from the early 1930s in both the medium- and high-voltage range, but they were used in North America only from the late 1950s, and because of the advent of SF6 gas circuit breakers, only for a relatively short period of time. All air-blast breakers are based on the principle of high-pressure air, on the order of 200 psi, forced through a nozzle and passed at high speed across the arc, partly to lengthen the arc and partly to carry away the arc/plasma product from in between the contacts. To this end, a central high-pressure storage or high-pressure individual breaker air storage is used.

Air-blast breakers have been manufactured for voltages up to 800 kV, and were used for the development of 500 kV systems. Because of their good functionality at low temperatures, they were frequently used in the northern latitudes.

SF6 Gas Circuit Breakers

SF6 breakers  were developed in the 1960s and quickly became the preferred choice for wide areas of medium- and high-voltage applications. These breakers utilize SF6 gas for the extinction of arc, having dielectric properties superior to that of air, leading to a much more economical design in the construction and dimensions of the breaker. The voltage rating for a single interrupter head is mostly limited to 245 kV, hence more than one head in series is used for higher voltages. The initial development of the SF6 breaker was the so-called double-pressure breaker mimicking
the operating principle of an air-blast breaker.

This construction was replaced by the so-called puffer breakers. The SF6 gas is passed to and held in the contact chamber at a gas pressure of about 50 to 70 psi (three to five times atmospheric pressure). Upon contact parting, a piston compresses the gas and blasts it through the arc, returning it to the closed SF6 circulation loop in the breaker. SF6 breakers are the breaker type predominantly used in the HV and EHV voltage range, and widely used for medium voltages.

Vacuum Circuit Breakers

Vacuum breakers  utilize the superior dielectric nature of the vacuum for arc extinction. They consist of a vacuum- tight “bottle” housing the fixed and moving Cu or Cr contacts. The contact movement and separation is very small, on the order of millimeters rather than centimeters, which makes the operation of these breakers and their ability of arc extinction very fast. Some problems associated with this phenomenon will be discussed later.
Vacuum breakers for fault-current interrupting capabilities similar to SF6 breakers are available in the medium voltage range up to about 35 kV and at 25-kV single phase (50-kV equivalent) as dual bottle assemblies for electric traction. Vacuum switches as load-break switches consisting of a series of assembly of vacuum bottles are available up to 245 kV.

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