HV switchgear (part 1)

Electrical switchgear is an essential element in the protection and safe, uninterrupted operation of a high-voltage network.

Its history is rich in diverse inventions, high-performance cut-off principles, and a wide variety of technologies using media as different as atmospheric air, oil, compressed air, sulfur hexafluoride and vacuum for isolation and cut-off. However, there are a number of common features throughout its evolution:

• arcing between two contacts, as a basic principle for breaking alternating current;

• use of arc energy to promote cooling and interrupt the current;

• ongoing efforts to reduce energy consumption in order to produce more reliable and economical equipment;

• the reduction of overvoltages generated during operation, thanks to the insertion of closing resistors or the synchronization of operation with voltage.

It's interesting to note that the self-blast breaking technique, which has just become established for SF ₆ high-voltage circuit breakers, had already been envisaged as far back as the 1960s. It's thanks to major advances in arc modeling and gas flow simulation that arc energy has been tamed and used effectively to define high-performance interrupting chambers.

Simulation resources have also made it possible to increase the voltage per switching element from 145 to 420 kV in the space of 25 years, without the voltage reached constituting a technical limit.

Part 1 of this article describes the different classifications of high-voltage (HV) devices and their main characteristics. Part 2 examines the main types of fundamental problems (disconnection, dielectric, overheating, contact resistance) that the designer needs to master in order to design a new device.

Type tests, which are carried out to verify the performance of a device, will be presented in the third fascicule, along with the other tests that are essential to guarantee that the devices produced do indeed have the advertised performance. Also in this fascicule, the formidable evolution of high-voltage circuit breakers will be described, from compressed-air technology to the current one using SF ₆ .

The evolution of high-voltage switchgear is not over yet; new prospects are opening up with the introduction of electronics, enabling the state of a device to be constantly monitored. New metal-enclosed cubicles and conventional circuit-breakers incorporate the newly-developed electronic current and voltage measurement reducers. This makes...