*Article* **E** ff**ects of Fast Elongation on Switching Arcs Characteristics in Fast Air Switches**

**Ali Kadivar 1,2,\* and Kaveh Niayesh 1**


Received: 25 July 2020; Accepted: 14 September 2020; Published: 16 September 2020

**Abstract:** This paper is devoted to investigating the e ffects of high-speed elongation of arcs inside ultra-fast switches (*ucontact* ≈ 5–80 m/s), through a 2-D time-dependent model, in Cartesian coordinates. Two air arcs in series, one between a stationary anode and a moving cathode and the other between a stationary cathode and a moving anode in the arc chamber, are considered. A variable speed experimental setup through a Thomson drive actuator is designed to support this study. A computational fluid dynamics (CFD) equations system is solved for fluid velocity, pressure, temperature, and electric potential, as well as the magnetic vector potential. Electron emission mechanisms on the contact surface and induced current density due to magnetic field changes are also considered to describe the arc root formation, arc bending, lengthening, and calculating the arc current density, as well as the contact temperatures, in a better way. Data processing techniques are utilized to derive instantaneous core shape and profiles of the arc to investigate thermo-electrical characteristics during the elongation progress. The results are compared with another experimentally verified magnetohydrodynamics model of a fixed-length, free-burning arc in the air. The simulation and experimental results confirm each other.

**Keywords:** air arc plasma; Thomson actuator; magnetohydrodynamic simulations; fast switch
