3AV1FG - 72.5 kV Prototype Vacuum Circuit Breaker (Case Study with Pilot Customers)

SUMMARY Vacuum switching devices are used worldwide in all kinds of medium-voltage distribution systems. With their outstanding technical performance and their low life-cycle costing they dominate the power distribution market. So far this technology has been predominately used in distribution networks up to 52 kV. Now some manufacturers have started to expand this technology to the electrical power transmission networks. The vacuum switchgear technology represents in this case a natural extension of the existing SF6 circuit breaker portfolio. The expansion of the breaker portfolio to include vacuum circuit breakers can offer customers genuine added value. The first step is a prototype of an outdoor circuit breaker for 72.5 kV which uses a vacuum interrupter for arc-quenching and nitrogen gas for dielectric insulation of this vacuum interrupter. A common spring drive mechanism is used to switch the vacuum interrupter unit inside of the three pole columns. The developed live-tank prototype circuit breaker was delivered to three pilot customers in Europe to gather joint operational experience under realistic network conditions. In order to offer these pilot customers the highest quality standards and the highest degree of security for their energy supplies, the manufacturer carried out a complete set of type tests for the 72.5 kV live-tank prototype circuit breaker. The circuit breaker conforms to the specifications of the latest edition of the International Electrical Commission standard (IEC 62271100, 2008-04). This paper deals with the basic information about the circuit breaker design. The results of the IEC type test will be presented. In this context the vacuum interrupter unit provides a slightly different switching characteristic in comparison to other arc-quenching media. The minimum arcing times for most IEC test duties are shorter. Due to the excellent recovery of dielectric strength, the circuit breaker copes with severe values of di/dt and du/dt. It is quite clear that this different switching behaviour could influence the existing grid configurations. In addition to a successful type test, field experience is necessary to establish the vacuum technology on the sub-transmission voltage levels. The three pilot customers describe their initial experience with the prototype circuit breakers. This refers to the kind of applications, the number of switching operations and their early experience. Furthermore, the expectations of these utilities with respect to high-voltage vacuum circuit breakers are set out.