General Electric (GE) worked with researchers at the Princeton Plasma Physics Laboratory (PPPL) to develop a 300kV plasma switch that will convert high-voltage DC current to high-voltage AC current for consumers more efficiently. As a final step, substations along the route reduce the high-voltage AC current to low-voltage current before it reaches consumers.
The plasma tube has to operate for years with voltage as high as 300kV to enable a single unit to cost-effectively replace the assemblies of power semiconductor switches that are currently used for the DC-AC conversion. PPPL modelled the switch to demonstrate how the high current affects the helium gas used in the switch, modelling the ionisation of the gas at these higher voltages. This built upon a 2017 PPPL paper published in the journal Physics of Plasmas that modeled the effect of high-voltage breakdown without presenting an analytical theory.
“GE is dealing with much higher voltage,” said Igor Kaganovich, deputy head of the PPPL Theory Department and PPPL’s Low Temperature Plasma Laboratory and a coauthor of the two papers. “The low-pressure and high-voltage breakdown mechanism has been poorly understood because of the need to consider new mechanisms of gas ionization at high voltages, which is what we did.” The lead author of the papers was Liang Xu, a visiting Chinese graduate student whom Kaganovich advised and is now a physicist at Ruhr-University in Bochum, Germany. Co-authors of the papers included GE’s Sommerer and physicist Alexander Khrabrov of PPPL.
The findings identified three different breakdown regimes that become important when high voltage is used to turn helium into plasma. In these regimes, electrons, ions and fast neutral atoms start the breakdown by back-scattering — or bouncing off — the electrodes through which the current flows. These results contrast strongly with most previous models, which consider only the impact of electrons on the ionization process.
The findings proved useful for GE. “The potential applications of the gas switch depend on its maximum possible voltage,” said Timothy Sommerer, a physicist at GE who heads the project. “We have already experimentally demonstrated that a gas switch can operate at 100 kilovolts and we are now working to test at 300 kilovolts. The results from the PPPL model are both scientifically interesting and favorable for high-voltage gas switch design.”