A wall-stabilized arc in a polytetrafluoroethylene nozzle was investigated. Very similar arc properties as in the ablation dominated high-current phase of SF6 circuit breakers were expected. Spectroscopic measurements of arc temperature profiles were performed. Spectral lines of fluorine and ionized carbon were observed. The side-on intensities of optically thin spectral lines were measured. Abel inversion was applied and the emission coefficient was determined. Temperatures of 16 000 to 18 000 K in the arc centre were obtained at various times of the current pulse. The pressure values were in the range 10–30 bar and arc currents varied from 10 to 20 kA. In the framework of the model, radial temperature profiles were determined with an accuracy of ±4%.

The dielectric recovery of an axially blown arc in an experimental set-up based on a conventional HV circuit breaker was investigated both experimentally and theoretically. As a quenching gas, synthetic air was used. The investigated time range was from 10 µs to 10 ms after current zero (CZ). A fast rise in the dielectric strength during the first 100 µs, followed by a plateau and further rise later was observed. The dependences on the breaking current and pressure were determined. The measured dielectric recovery during the first 100 µs after CZ could be reproduced with good accuracy by computational fluid dynamics simulations. From that it could be deduced that the temperature decay in the axis does not depend sensitively on the pressure. The dielectric recovery during the first 100 µs scales therefore mainly with the filling pressure. The plateau in the breakdown characteristic is due to a hot vapour layer from the still evaporating PTFE nozzle surface.

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