Abstract
The post-arc (PA) characteristics of vacuum arcs in transverse magnetic field contacts are studied for short-circuit currents of up to 123 kA peak and transient recovery voltages below 875 V. The measured PA currents are interpreted in terms of an Electric Resistance Model and the models of Andrews-Varey, Langmuir-Child, and Slepian-Schmelzle. Whereas in the late PA period, the calculations do not agree well with the measurements, the PA behavior is well described in the early period after current-zero. It is concluded that the PA discharge is amplified by ionization of metal vapor particles in the boundary sheath due to electron impact.
Highlights
Vacuum arcs are successfully applied in switching technology to interrupt high short-circuit (SC) currents
The PA characteristics of constricted vacuum arcs moving in a small-gap cupshaped transverse magnetic field (TMF) contact system (CuCr) have been investigated for SC currents (42 Hz) of up to 123 kA peak and for transient recovery voltage (TRV)’s below 875 V
The measured post-arc current” (PAC) evolutions are strongly related to SC current amplitude, arcing time, and applied TRV
Summary
Vacuum arcs are successfully applied in switching technology to interrupt high short-circuit (SC) currents. The transient recovery voltage (TRV) of the electrical grid after current-zero removes the residual electric charge carriers of the switching arc plasma from the contact gap region. This results in a “post-arc current” (PAC) that is still flowing after vacuum arc extinction (e.g. early papers [1, 2] or recent papers [3,4,5]). Due to the fast removal of the electrons within microseconds after current-zero, the (heavy) metal ions (copper and chromium) establish a positive space charge sheath near the post-arc (PA) cathode, the “post-arc boundary sheath”, which is expanding towards the PA anode. The movement of the ions and the ionization of neutral metal vapor particles within the sheath sensitively influence the PAC characteristics
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