Vacuum circuit breaker

IEEE, Results of an investigation on the over voltages due to a vacuum circuit breaker when switching an H. V. motor, IEEE 85 SM 370-2(1985). 

Ramaswamy, R., Vacuum circuit breakers, Siemens Circuit, XXIII, April (1988). 

Vacuum is finally judged to be the best medium to quench the arc plasma and interrupt a circuit undci the most adverse conditions. Figure 19,24 gives cross-sectional views of one pole of a vacuum circuit breaker and a typiciil construction of the arcing contacts and Figure... 

Figure 19.23 General arrangement of a 7.2-36 kV vacuum circuit breaker in a housing (Courtesy Siemens)...

Figure 19.25 A pole assembly of a vacuum circuit breaker...

Hollomon s ethos, combined with his ferocious energy and determination, and his sustained determination to recruit only the best researchers to join his group, over the next 15 years led to a sequence of remarkable innovations related to materials, including man-made diamond, high-quality thermal insulation, a vacuum circuit-breaker, products based on etched particle tracks in irradiated solids, polycarbonate plastic and, particularly, the Lucalox alumina envelope for a metal-vapour lamp. (Of course many managers besides Hollomon were involved.) A brilliant, detailed account of these innovations and the arrangements that made them possible was later written by Guy Suits and his successor as director, Arthur Bueche (Suits and Bueche 1967). Some of these specific episodes will feature later in this book, but it helps to reinforce the points made here about Hollomon s coneeption of broad research on materials if I point out that the invention of translucent alumina tubes for lamps was... 

High voltage circuit breaker, enclosure and terminal boxes in increased safety, control box has a flameproof enclosure, flameproof vacuum circuit breaker ... 

Vacuum circuit breakers show a very small stroke due to the high insulating capacity of vacuum. In a gas, the mean free path length ZF of molecules, atoms or ions is reciprocal to the gas pressure p /p 1 Ip. 

Vacuum and SF6 devices were developed at about the same time as competitors. There is little to choose between them since they are both simple mechanisms. Some engineers in the past considered the possibility that the vacnnm conld be lost while the circuit breaker was in its on state was a serions disadvantage. However, the technology has greatly improved and thousands of vacnnm circnit breakers are in service. Vacuum circuit breakers are limited to about 13.8 kV due to insulation difficulties across the open contacts. Current ratings at 13.8 kV are limited to about 3000 A, with corresponding fault making duties up to 100 kA peak. SF6 equipment tends to be preferred to vacuum equipment. 

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. 

When the arc is extinguished through vacuum, the breaker is called a vacuum circuit breaker. Since a vacuum cannot theoretically sustain an arc, it can be an effective medium. However, owing to imperfections present in vacuum, a small arc of short duration can be produced. The construction of vacuum circuit breakers is simple, but the maintenance is more complex. 

Another precaution against the risks associated with the use of oil-filled switchgear is to replace it with switchgear that uses an alternative insulating medium. Options include sulphur hexafluoride (SFe) gas-filled enclosures, air insulation, and vacuum circuit breakers. The SFe variety is beginning to lose favour because of the environmental and toxic hazards that the gas poses, so vacuum and air-insulated gear is now preferred by most high... 

Notwithstanding its complexity and elusiveness to quantitative analysis, the vacuum arc has been harnessed to serve a number of useful purposes. A modem example is the high-power vacuum circuit breaker. 

FIGURE 7 Interruption of a feult current by a vacuum circuit breaker and the subsequent transient recovery voltage. 

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