Electric “flashover” or insulation breakdown has occurred on “hot stick” safety tools used on live AC transmission lines at Manitoba Hydro in 1997 and 2002. Investigations showed pollution flashover as the cause, whereby leakage currents cascade into flashover. Prior to reinstating live-line work with mitigation procedures, DC voltage experiments suggested an atypical flashover uncharacteristic of pollution flashover without leakage currents, which may require a different mitigation strategy. In this thesis, statistical analysis shows that relative humidity has a greater correlation than voltage with the type of flashover. Labeled a “fast flashover”, it seems to be distinct from pollution flashover, although not statistically significant. A time-stepping computer model was developed to calculate a critical voltage for flashover as a function of relative humidity. However, lack of data prevents the model from making firm conclusions. A list of recommended research is proposed to remedy these deficiencies to allow future model refinement.

Electric “flashover” or insulation breakdown has occurred on “hot stick” safety tools used on live AC transmission lines at Manitoba Hydro in 1997 and 2002. Investigations showed pollution flashover as the cause, whereby leakage currents cascade into flashover. Prior to reinstating live-line work with mitigation procedures, DC voltage experiments suggested an atypical flashover uncharacteristic of pollution flashover without leakage currents, which may require a different mitigation strategy. In this thesis, statistical analysis shows that relative humidity has a greater correlation than voltage with the type of flashover. Labeled a “fast flashover”, it seems to be distinct from pollution flashover, although not statistically significant. A time-stepping computer model was developed to calculate a critical voltage for flashover as a function of relative humidity. However, lack of data prevents the model from making firm conclusions. A list of recommended research is proposed to remedy these deficiencies to allow future model refinement.

This thesis deals with the online measurement of partial discharge (PD) in a high-voltage direct current (HVDC) converter station. The HVDC station is a particularly challenging environment for PD measurement due to elevated interference levels caused from the switching of the thyristor-controlled converters. Online PD measurements are performed on two specimens, one is an HVDC converter transformer and the other an HVDC converter wall bushing. The measurements are performed in the high-frequency range between 400-kHz to 30-MHz with a modern PD measurement instrument that employs a signal processing technique known as feature extraction. The results demonstrate that online measurement of PD in an HVDC station environment is possible. Input filtering and feature extraction methods can mitigate the converter interference. The feature extraction methods can also isolate individual PD phenomena, and allow for the trending and monitoring of insulation degradation. Furthermore, specific strategies for PD measurement and analysis are developed.

This thesis deals with the online measurement of partial discharge (PD) in a high-voltage direct current (HVDC) converter station. The HVDC station is a particularly challenging environment for PD measurement due to elevated interference levels caused from the switching of the thyristor-controlled converters. Online PD measurements are performed on two specimens, one is an HVDC converter transformer and the other an HVDC converter wall bushing. The measurements are performed in the high-frequency range between 400-kHz to 30-MHz with a modern PD measurement instrument that employs a signal processing technique known as feature extraction. The results demonstrate that online measurement of PD in an HVDC station environment is possible. Input filtering and feature extraction methods can mitigate the converter interference. The feature extraction methods can also isolate individual PD phenomena, and allow for the trending and monitoring of insulation degradation. Furthermore, specific strategies for PD measurement and analysis are developed.

Thesis (doctoral)--Universität Freiburg.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 144-146).

No description available.

A static electrochemical discharge machining (ECDM) tester, where the tungsten needle is used as the cathode and the platinum as the anode and the glass as the specimen, and the depth of electrode is set to be 1mm in the aqueous electrolyte of 30wt% KOH at the test time of 10s, is employed to investigate the influence of geometry and size of the electrode, supply voltage and gap on the characteristic of electrochemical discharge machining. According to the current/voltage measurements combined with the photographs of the bubble layer on the cathode and the behavior of discharge under different geometry and size of the electrode during the ECDM process, three regimes have been identified as: (I): non-machining. (II): glow discharge. (III): spark discharge. From the observation on the surface of machined glass specimen by using SEM, the experimental result show that damage of the glass increases with the increase of supply voltage.

No description available.

No description available.