Abstract
This paper informs on the flashover strength of three materials: Delrin (polyoxymethylene), HDPE (high-density polyethylene) and Ultem (polyetherimide) with smooth surface finishes, in zero-grade air at −0.5, 0 and 0.5 bar gauge, and at 90% relative humidity (RH). Both negative and positive polarity impulse voltages were applied to investigate the potentially asymmetrical electrical performance of the geometrically-symmetrical electrode arrangement. In all tests, high voltage (HV) impulses with a nominal 100/700 ns wave-shape were applied. Each test conformed with the ASTM D3426-97 standard of ‘step up’ testing, to find the average flashover voltage for each set of conditions. For negative polarity, each solid dielectric material demonstrated a decrease in flashover voltage as the RH was increased. For positive polarity, however, the flashover voltages were similar for all levels of RH, with the exemption of HDPE. A decrease in flashover voltage was found as the permittivity of the material increased for negative polarity, irrespective of humidity and pressure. Overall, the highest flashover voltage recorded for negative polarity was ~200 kV with an HDPE spacer, at 0.5 bar gauge and 90% RH, at a value of ~53 kV. For positive polarity, the highest flashover voltage was for a Delrin spacer at ~50% RH and 0.5 bar gauge, with a voltage of ~180 kV; the lowest flashover voltage of ~60 kV was recorded with an HDPE spacer, at −0.5 bar gauge and >90% RH.
Highlights
Solid insulation is important within pulsed power systems as it provides mechanical support between conductors at different potential, but the inclusion can lead to surface flashover of the gas-solid interface created, which can occur at a lower applied voltage than that for a gas gap without a solid spacer
This paper focuses on similar methodology to that used in the literature discussed previously, under the high dV/dt conditions encountered in pulsed power applications, in order to determine the effect of environmental conditions on the relative flashover performance of the different solid materials, thereby, allowing conclusions to be drawn on the synergistic effect of multiple environmental and material parameters on the flashover voltage
A permittivity effect on the flashover strength of the composite insulation system is apparent in Figs. 5a, 5b and 5c, where a decrease in the flashover voltage was seen with increasing relative permittivity of the solid spacer; these decreases, are not statistically significant
Summary
Solid insulation is important within pulsed power systems as it provides mechanical support between conductors at different potential, but the inclusion can lead to surface flashover of the gas-solid interface created, which can occur at a lower applied voltage than that for a gas gap without a solid spacer. It is desirable to have information on the flashover strength of different materials within a system, in order for design processes to be tailored to the intended application. Solid spacers were tested in sub-optimal conditions, and the performance recorded throughout. HDPE (high-density polyethylene), Delrin (polyoxymethylene) and Ultem (polyetherimide) were tested in conditions of varying humidity, polarity and pressure
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