A Rotating Arc Gap Switch Controlled By Axial Magnetic Field And Its Arc Motion Characteristics

Switch is one of the most important parts of the pulsed power technology. It determines the output performance of the pulsed power systems. Gas discharge switch is a popular application in pulsed power system among closing switches. It usually works at high voltage and high current. The interaction between the arc and electrode material is complicate and it determines the performance and lifetime of the switch. A rotating arc gap switch controlled by axial magnetic field is designed and built in this paper to meet the requirements of high voltage, high current, large transfers, slight electrode erosion and long lifetime. The arc motion characteristics are studied.The rotating arc gap switch makes the arc move between the electrodes; therefore, the area contacting with the arc is much larger than that in the static arc condition. It makes the arcing time on unit area much shorter and then less heat is conducted into. Therefore, the electrode erosion is slighter and switch lifetime is longer. The electrodes are coaxial cylinder configuration and its shape is optimized to make the electric field uniformly distributed in the gap. This makes the arc starts random in the gap when triggered. The current flow in inner electrode are symmetrical and opposite in direction. So their force on the arc is balanced and will not lead the arc moving in axial direction. The coils which connected to the inner electrode are placed both at the top and bottom of the switch. The resultant magnetic field is in axial direction and forms a mirror-like configuration. It makes the arc stabilized rotate in the middle of the switch where the magnetic field is weakest. The switch operation characteristics are studied by experiments. Its specifications of current and coulomb per shot can reach 250kA and about 745 Coulomb respectively.The B-dot probes are installed to measure the arc velocity. The probe voltage signal is calculated in three different measurement ways and two of them are adopted in experiments. The factors that influence the probe signal are analyzed, such as the direction of the arc, the arc column diameter and the arc current distribution. The accuracy in arc velocity calculation is discussed. The results show that the method is believable.A power supply system consist several independent modules discharging in sequence provides a trapezoidal pulse of current on the switch. The arc velocity variation is lagging behind the current variation and there is abnormally high-speed motion during the arc acceleration in one shot in some experimental conditions. The arc velocity in different amplitude of current and magnetic flux density are studied. The expression that describes the relationship between arc velocity and axial magnetic flux density is found. When the coil number is 2, the arc is stationary in the ignition place for a few microseconds, it results severely damage to the electrode.A chain model is employed to describe the arc motion in this rotating arc gap switch. The arc is assumed to be a chain of small cylindrical current elements like a string of beads, and they are linked by a certain rules. Each element moves individually which determines the behavior of the whole arc. The chain model is improvement by considering the arc root motion and surface drag force. The arc velocity and shape variation during the movement are studied based on this model. The results showed that the surface drag force is an important factor that influences the arc velocity and shape. The arc column diameter is calculated and the relationship between it and axial magnetic flux density is obtained.