Vacuum Circuit Breaker Postarc Current Modelling Based on the Theory of Langmuir Probes

Abstract

High-resolution measurements on the postarc current in vacuum circuit breakers (VCBs) reveal a period, immediately following current-zero, in which the voltage remains practically zero. The most widely used model for simulating the interaction between the postarc current with the electrical circuit lacks a proper explanation for this event, and hence, it needs to be complemented. We demonstrate that the breaker's electrical behavior during this zero-voltage period can be explained by using the theory of a Langmuir probe. Such probes are used to investigate plasma properties such as the ion density and the electron temperature, and we extrapolate its theory to the VCB. After the voltage-zero period, when the transient recovery voltage starts to rise, the breaker's electrical behavior is mainly determined by the expansion of an ionic space-charge sheath in front of the cathode. In addition to the current from the Langmuir probe model, the time change of the electric field inside the sheath gives a displacement current. Instead of solving the complicated plasma equations to find the displacement current, we use an approximation by simulating it with the aid of a voltage-dependent sheath capacitance. We programmed the model as a function block in Matlab's SimPowerSystems to facilitate its application in different electrical circuits.

Relationship Between the Voltage Distribution Ratio and the Post Arc Current in Double-Break Vacuum Circuit Breakers

“…The Langmuir probe is a kind of measurement probe for plasma density which can measure the electron temperature, the electron density, and the voltage in the vacuum interrupter [9]. Using these values, the post arc current i pa in the vacuum interrupter can be written as…”

“…If T e , m i , q i , and A are considered to be constant, the model requires four parameters n i (0), c 1 , c 2 , and τ [9]. These four parameters are then adjusted to make the simulated results fit the measured results.…”

In search for performance indicators of short-circuit current interruption in vacuum

“…Earlier research, combining current-zero measurements and modelling [1,2,3] has contributed to the understanding of the post-zero processes of current interruption in vacuum [4].…”

Two dimensional simulation of Post Arc phenomenon in Vacuum Interrupter with Axial Magnetic Field contacts

“…When the arc extinguishes in CZ crossing, it leaves conductive plasma behind, making an electrical feature possible, which is called the post arc current [1]. Since Post Arc Current (PAC) might indicate the performance of VIs, it has been investigated thoroughly in previous studies [2]- [6]. First attempts to model PAC was done with Andrews and Varey [7] and further research has been done to improve this model during last four decades.…”

“…First attempts to model PAC was done with Andrews and Varey [7] and further research has been done to improve this model during last four decades. For instance, the limitation of Andrew and Varey's model to explain the voltage zero region just after CZ is discussed in [2] and a model based on Langmuir Probes is introduced to explain this region.…”