Small inductive current switching with high-voltage vacuum circuit breakers

Circuit breakers are appropriate devices to energize and de-energize electrical circuits. The requirements for standard switching applications are typically covered by the standards of the International Electrical Commission (e.g. IEC 62271-100 and IEC 62271-1). Switching of small inductive currents are not automatically qualified by type tests in accordance to IEC 62271-100 and -1. The range of requirements for these applications is extremely wide, ranging from switching of unloaded transformers to the high currents of tertiary winding applications at power transformers. Gas circuit breakers are the present solution to cover high-voltage applications for these inductive loads. Circuit breakers with a point-on-wave switching device for the individual poles are used to operate the circuit breaker in the reignition-free time window to ensure a safe and sustainable operation. The increased application of vacuum circuit breakers (VCB) in high-voltage systems creates the need for technology that also covers these requirements.This paper explores the usage of a three-pole operated high-voltage vacuum circuit breaker (one drive for three poles) in combination with a filter circuit. We determine that it is a suitable combination to avoid switching overvoltages and internal winding resonance overvoltages when small inductive loads are de-energized.The approach is to simulate the circuits with an electromagnetic transient program with high-frequency models of the relevant grid components to evaluate appropriate dimensions and locations for RC filter circuits. This simulation study determines the optimized parameters for the filter circuits and then verifies the results by means of simulation of breaking operations with a vacuum circuit breaker model. The methodology is based on the long-term experience in the medium voltage range and can also be applied to the high-voltage applications. On this basis also the acceptance criteria are derived from medium voltage know-how.