Thermal bubble-triggered breakdown under DC, AC and impulse nonuniform electric fields in liquid nitrogen

The effect of voltage waveform on breakdown phenomena in liquid nitrogen in the presence of thermally induced bubbles is investigated with a cylinder-to-plane electrode. Bubbles are produced by a heater mounted in the cylinder due to simulation of a superconducting wire in a state of quench. The result shows that AC electric fields have lesser effect on bubble behavior than DC electric fields. The reduction in breakdown voltage caused by bubbles under Ac electric field is smaller than that under DC electric field. The effect of impulse voltage application on bubble behavior is negligible even though the applied voltage reaches near the 50% flashover voltage. Under impulse voltage, bubbles´ radii are not reduced by the electric field and the reduction in breakdown voltage by bubbles then becomes serious