Research
Vacuum circuit breakers (VCB) have the function to interrupt fault currents in power networks. VCBs are limited in their operation to a network voltage of 36 kV. Above this level, SF6 gas filled circuit breakers are used exclusively, because of commercial considerations. The present discussion on the desire to reduce the emission of the extremely potent greenhouse gas SF6, and a possible tax on the use of SF6, will give a great impetus to the development of VCB also for high-voltage levels. Yearly, many hundred thousands of VCBs are produced world wide, including in the Netherlands (Holec). These devices are sealed for life which means that after production in vacuum furnaces, no access can be gained to internal parts. Therefore, only external measurements, such as high-resolution current and voltage measurements, can give insight into its proper working.

The project is aimed at developing `digital testing' of vacuum circuit breakers, i.e. a method for virtual testing of a model of such a device, once its characteristic fingerprints are obtained from refined measurements during standard laboratory tests. By means of the new high resolution measurement system, highly accurate information will be obtained of the interruption process of the vacuum circuit breaker. As the measurement data will be of such a high quality that is unprecedented in the world, a detailed vacuum arc model can be developed. After implementation of the model in a computer program that is suited for dealing with the rapid phenomena accompanying the switching of a vacuum circuit breaker, the developed VCB model, with its parameters obtained from the laboratory tests, can be used to represent the vacuum circuit breaker in network studies. In this way, vacuum circuit breaker interruptions and failures can be simulated under numerous conditions and in a variety of power system situations.

Utilization
The verification of the correct function of vacuum circuit breakers is extremely costly, due to the need of high-power equipment, which often has to exceed 1000 MVA of short-circuit power, installed in special high-power laboratories. In order to obtain as much information as possible on the interruption performance, degradation and operating limits of the circuit breaker from the cost-intensive tests, operators of such laboratories have a great interest in a scientific method to assess the results of tests. By offering `digital testing' as an extra service, new customers are attracted and an increase in testing activities of 20% is expected.

For the independent testing and certification authority (KEMA), the digital testing instrument offers significant advantages because the maximum possible amount of information can be extracted out of tests. Therefore, the manufacturer and/or customer can reduce their cost on circuit breaker testing, as extra information, such as arc model parameters or limitations of the breaker, is obtained. A reduction of the cost by a factor of 15% is viable.

For the manufacturing industry, the method is a valuable tool that gives the necessary knowledge to develop VCBs for the higher voltage levels and to improve their existing VCBs.

Application of `digital testing of vacuum circuit breakers' can speed up the process of the development and integration of VCBs on the higher voltage levels. This could seriously reduce the need for SF6 circuit breakers which is desirable as SF6 is the most potent greenhouse gas (24000 times as effective as CO2).

More information can be found on the website of the research group.

Four companies are involved in this project.

Project title

Digital testing of vacuum circuit breakers (DCS.5975).