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Partial discharge diagnostics are common for the condition assessment of high voltage alternating current (ac) and direct current (dc) equipment. For ac applications the phase resolved partial discharge evaluation method has prevailed . Even though, numerous methods for dc partial discharge diagnostics have been proposed no agreed standard exists. This is primarily because of the fact that these methods are not as easily applicable as the well-known, intuitive, pattern based phase resolved method. Due to the often assumed unavailability of a useable phase angle information – this method has never been transferred to dc partial discharge diagnostics. However, as a dc voltage is usually not generated but obtained from a rectification process a natural ripple, which provides a phase information, will always be available. Hence, a novel dc partial discharge evaluation method that uses a phase resolved approach is introduced in this thesis. The introduction of a ripple on the dc voltage, which, in this thesis, is obtained from a half-wave rectification, might alter the discharge behaviour. Consequently, the maximum tolerable ripple below which a dc discharge behaviour is maintained has to be evaluated. Such an evaluation has never been carried out for a partially rectified voltage. Hence, for the first time, four characteristic discharge quantities have been evaluated with respect to a varying ripple. The outcome is a maximum tolerable ripple of 3 % for negative corona, 2 % for positive corona, 0.8 % for negative and positive surface discharges as well as 0.4 % for internal discharges. These newly defined values have then been used as a basis to obtain characteristic phase resolved partial discharge patterns at dc voltages. The novel patterns have been explained through the underlying physical phenomena. Therefore, for the first time, this work successfully demonstrated that a phase resolved partial discharge evaluation can be conducted at dc voltages, while the general dc discharge behaviour is maintained. This newly proposed recognition method has the potential to change dc partial discharge diagnostics in practical as well as in laboratory applications.
Dezenzo, T. (2019) Phase Resolved Partial Discharge Evaluation at dc Voltage, Doctoral Thesis, Technological University Dublin. doi:10.21427/by0j-7k53