Effect of electrode surface roughness on the breakdown jitter of a nanoparticle-infused dielectric oil spark gap switch

Abstract

Electrode surface roughness is generated over the lifetime of an oil spark gap by high-temperature arc discharges during normal circuit operation. These electrode pits and spikes create macroscopic electric field enhancements allowing electrons to initiate breakdown at lower switch voltages. Nanoparticles with a high dielectric constant are thought to polarize and interact with these enhancements to smooth the electric field profile on the electrode surface, thus reducing the spurious low-voltage breakdowns generated by local field maxima. Experimental testing to isolate the effect that electrode roughness has on the breakdown jitter of a single-shot oil spark gap switch using a pressurized oil dielectric has been completed. The dielectric oil utilized is a synthetic hydrocarbon-based liquid, designated Nycodiel, which conforms to military specification MIL-PRF-87252C [1]. Nycodiel has experimentally demonstrated significantly lower switch self-break voltage percent standard deviation (jitter) when infused with a suspension of high-dielectric constant BST nanoparticles with polished electrode surfaces. Further tests examine the effect that nanoparticle-infused oils have on the breakdown jitter of switches whose electrodes have roughened surfaces. The results of these breakdown tests determine if the benefits of the particles scale with the magnitude of the electrode field enhancement at various pressures. The results are obtained from experiments performed on the HVADTS system at UMC. The HVADTS is a single shot oil spark gap switch test stand capable of applying a 250 kV, 21 J pulse to a planar 1.2 mm gap with a `1-cos' rise-time of 1.6 μs. A recirculation pump and filter allows the oil to be reconditioned between pulses. Both oil pressure and electrode surface roughness are controlled variables in these experiments as pressure has been shown to be a significant factor in jitter behavior. Simulations of the effect of surface roughness on the electric fields in the breakdown gap with a nanoparticle suspension have been performed concurrently with this experiment.