Quantification of the performance of iterative and non-iterative computational methods of locating partial discharges using RF measurement techniques

Partial discharge (PD) is an electrical discharge phenomenon that occurs when the insulation materialof high voltage equipment is subjected to high electric field stress. Its occurrence can be an indication ofincipient failure within power equipment such as power transformers, underground transmission cableor switchgear. Radio frequency measurement methods can be used to detect and locate discharge sourcesby measuring the propagated electromagnetic wave arising as a result of ionic charge acceleration. Anarray of at least four receiving antennas may be employed to detect any radiated discharge signals, thenthe three dimensional position of the discharge source can be calculated using different algorithms. These algorithms fall into two categories; iterative or non-iterative. This paper evaluates, through simulation, the location performance of an iterative method (the standardleast squares method) and a non-iterative method (the Bancroft algorithm). Simulations were carried outusing (i) a "Y" shaped antenna array and (ii) a square shaped antenna array, each consisting of a four-antennas. The results show that PD location accuracy is influenced by the algorithm's error bound, thenumber of iterations and the initial values for the iterative algorithms, as well as the antenna arrangement for both the non-iterative and iterative algorithms. Furthermore, this research proposes a novel approachfor selecting adequate error bounds and number of iterations using results of the non-iterative method, thus solving some of the iterative method dependencies

Investigating the effects of VSC harmonic content on PD diagnostics for HVDC insulation systems

This paper reports on experimental investigations in which both HVDC and HVAC voltages were applied to solid dielectric insulation samples containing known defects. The insulation samples were subjected to HVAC and HVDC containing superimposed harmonic ‘ripple’, similar to that produced by the converter switching operation. Of particular interest were the effects of the applied voltage on partial discharge (PD) amplitude, repetition rate and pulse-spacing, which showed a correlation with harmonic amplitude and phase position. Under HVAC, the phase of the power frequency cycle is the dominant driver of PD activity and forms the basis of most diagnostic techniques for PD. However, under HVDC, PD activity can be influenced by comparatively minor features of the applied voltage. Established knowledge rules for defect identification based on repetitive PD characteristics at HVAC are therefore unlikely to be applicable directly to HVDC systems. Given the rapidly expanding HVDC infrastructure, accruing new knowledge rules through laboratory tests and online measurement trials will be essential in assisting network operators to identify incipient defects with a greater degree of confidence on these systems in the futur