Effect of self-magnetic field on large pulsed insulators operated at 4 megavolts and 5 megaamperes

Experiments on a large, high voltage pulsed insulator will be described. The goal was investigation of the effect of the self-magnetic field associated with current flow toward the load, on the insulator voltage hold-off capability. In principle, the self-magnetic field could improve insulator hold-off by deflecting electrons away from the insulator surface. However, it appears that no controlled experiments have been done to measure the effect of magnetic flashover-inhibition (MFI) on a 45-degree insulator. Most modern insulator stacks, including the one used here, have the insulators at 45 degrees to the power flow direction, often with reduced electric field at the cathode triple point. Results from the experiments presented in this paper do not show a significant beneficial effect from current flow in this situation. This paper will also show calculations on the effect of magnetic field on electrons emitted from the capacitively- coupled grading rings in the insulator stack