Impulsive Flashover Characteristics and Weibull Statistical Analysis of Gas-Solid Interfaces With Varying Relative Humidity

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 <10%, ~50% and >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 <10% RH. The poorest performance was for a Delrin spacer in negative polarity, 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.

Flashover of Smooth and Knurled Dielectric Surfaces in Dry Air

“…1b, for the gap spacing and parallel-plane electrodes used here, there is an asymmetrical field distribution within the gap when one electrode is earthed. This phenomenon has been previously discussed in [13], being a result of the ratio of the inter-electrode gap to the radius of the electrode edge. Asymmetric electric field distributions in (geometrically) symmetrical electrode arrangements have also been witnessed by researchers investigating sphere gaps in [15], toroidal electrodes in [16], and for a plane-parallel setup in [17].…”

“…The insulation system was designed for use nominally at atmospheric pressure; however, HV tests were conducted at −0.5, 0 and 0.5 bar gauge, in order to quantify the effect of pressure fluctuations either side of atmospheric pressure. A detailed description of the methodology and testing procedures, based on the 'step up' procedure detailed in the ASTM D3426-97 standard [12], can be found in [13]. A new spacer was used for each set of 20 flashover events, in order to avoid changes in breakdown behaviour due to material degradation from successive flashover events.…”

Implementasi Jaringan Syaraf Tiruan - Backpropagation dalam Pengenalan Flashover Isolator 150 kV

“…Jumlah elektron yang ditangkap oleh molekul air meningkat seiring dengan jumlah jalur bebas rata-rata elektron. Karena itu, peningkatan kelembaban relatif mengubah kinerja sistem isolasi.Seperti kelembaban, kepadatan udara sangat mempengaruhi karakteristik flashover [11], [14], [12], [15].…”