The history of SF6 circuit breakers is somewhat older than that of vacuum circuit breakers, parallel to technological developments, there is no doubt that vacuum circuit breakers can be used more frequently nowadays in vacuum technology.
Without a doubt, circuit breakers are the most important relative elements among electrical switching devices. When the ideal circuit breaker is in the off (I) position it is an excellent conductor, and is a perfect isolator when in the open (0) position, and an excellent arc interrupter in the event of a fault. From past to present, when we look at the history of all breaker, known circuit breaker variants are air circuit breakers, compressed air circuit breakers, reduced-oil circuit breakers, oil-immersed circuit breakers, SF6 circuit breakers and vacuum circuit breakers. However, today air circuit breakers and oil-immersed circuit breakers are rarely manufactured anymore. SF6 and vacuum circuit breakers are the major circuit breakers types that are produced nowadays. Notwithstanding that the history of SF6 circuit breakers is somewhat older than that of vacuum circuit breakers, parallel to technological developments, there is no doubt that vacuum circuit breakers can be used more frequently nowadays in vacuum technology. Nowadays vacuum interrupters can be produced up to 110-170kV, the economic production rated voltage is up to 52kV. It is anticipated that these levels will increase even further in the future with the advance of vacuum technology.
Technically, when we actually make a one-to-one comparison, vacuum circuit breakers have many plus features compared to the SF6 circuit breakers. Vacuum interrupters have more dielectric strength at the less distance than the SF6 environment. For example, the dielectric strength provided at a 65-80mm contact gap distance in an sf6 environment, However can be provided at a 14-16mm distance in vacuum interrupters. One of the best known characteristics of vacuum circuit breaker is that they have a higher RRRV (Rate of Rise Recovery Voltage) resistance during short circuit switching and arc interruption. In SF6 circuit breakers, arc formation occurs with a single plasma. In vacuum circuit breakers, the arc plasma can be diffused through the help of magnetic forces, which means that it can be broken down into hundreds of separate layers. This feature is very important in terms of contact resistance. Depend on the value of the short circuit current, the arc plasma temperature increases arround 10,000 ° C to 50,000 ° C. The electrical endurance of the vacuum circuit breakers is generally higher than that of the SF6 circuit breakers, Owing to either their high RRRV strength or their ability to break up this arc plasma. While an average; SF6 breaker can switch 20-30 times at the full short circuit. This number can reach more than 100 times in many vacuum circuit breakers. In addition, this situation leads to higher levels of short circuit breaking capacity (Isc: kA) in vacuum interrupter.
It can be said that some of the problems observed over the past years in relation to the capacitive switching capability of SF6 breaker in vacuum circuit breakers according to IEC 622271-100 class C2, including technological development in vacuum interrupter, the selection of suitable vacuum interrupter, and NSDD (Non-Sustained Disruptive Discharges) international testing standards including IEC, ANSI, STL, have disappeared with the re-revaluation.
In addition to all these, the most important factor is without a doubt the environment and personal security. Although the SF6 gas is known as a colourless, odourless, tasteless, non-toxic gas, since the KYOTO protocol there has been some damage to human health and the environment. The toxic value, which is directly dangerous for human health, of SF6 gas, which has been switched on and used several times in arc extinguishing, becomes very high. In addition, the high pressure of the SF6 circuit breakers transforms heat-activated bursts in the event of possible failure during short circuit switching, which creates a serious safety problem.
In summary, it can be said that SF6 circuit breakers in voltages above 52 kV have dominated the market due to economic and technological reasons. Nevertheless, vacuum interrupter are widely used at voltages below 52KV.
In the preparation of national technical specifications it is advisable for companies of electrical transmission-distribution corporations to consider these aspects when selecting materials.
Sabri UZEL
Electrical Engineer