Abstract
Partial discharge (PD) detection can be considered one of the most useful tools for assessing the insulation conditions of the power apparatus in high-voltage systems. Under AC conditions, this analysis is widely employed in online and offline tests, such as type tests or commissioning, and can be carried out by applying the phase-resolved PD (PRPD) method, since the patterns can give information about the defect classification. Under DC voltages, the classic pattern recognition method cannot be performed, and the measurements show complexities related to the nature of the phenomena. For this reason, to date, a standard for PD measurements under DC does not exist. In previous papers, a new method for PD detection under DC stress voltages has been proposed by the authors. It is based on the application of a direct current periodic (DCP) waveform useful in obtaining PRPD patterns. The dependence of partial discharge inception voltage (PDIV) and PD repetition rate (PDRR) on the δ shape parameter of the DCP for different materials, as well as the capability to recognize different discharge phenomena, provided valid indications on the behavior of PD in the transition from AC to DC. The aim of this paper is to evaluate the time dependence of PD occurring in a dielectric by applying the DCP waveform. In our previous studies, the investigations were focused on the PD behavior under different values of the DC voltage periodic part. In another work, the DCP waveform with both positive and negative polarity was applied to several dielectric materials. In the proposed work, instead, the DCP waveform is applied for a long time in order to observe its effect on the PD behavior for 72 h. In this way, due to the space charge accumulation phenomenon, the aging effect, also due to the space charge accumulation phenomenon, is evaluated. The methodological approach was to acquire PRPD patterns over time and evaluate their trends in comparison with the sinusoidal case. The experimental results show that, with a DCP waveform having δ = 0.6, the aging effect similar to that provided by pure DC stress is observed, while the acquired PRPD patterns are easily interpretated, as in the AC case.
Highlights
Partial discharge (PD) measurements are a widespread approach to determine the status of efficiency of insulation systems [1]
In this paper, a first evaluation of the time dependence of the partial discharges occurring inside a dielectric by applying the recently developed direct current periodic (DCP) waveform was carried out with the purpose of confirming the effectiveness of acquiring phase-resolved PD (PRPD) patterns under
This last aspect was widely analyzed by Pan C. et al in Reference [24], where, by means of the chopped PD (CPD) method [25], the residual charge generated during PD events was magnified
Summary
PD measurements are a widespread approach to determine the status of efficiency of insulation systems [1]. In HVDC systems, PD measurements are much less standardized, so much so that, often, the standards propose to use AC stresses for the type tests of DC components. The CIGRÈ Technical Brochure (TB) 496 [5] and the Standard IEC 62895:2017 [6] are the main international standards for testing HVDC cable systems. Both standards prescribe the prequalification and the electrical-type test on entire cable systems. They suggest the use of AC stress in order to test components employed in HVDC transmission systems, such as joints. In Reference [7], a review focused on typing, the design and testing techniques (especially for PD and space charge measurements) of extruded cable joints are reported in detail
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