Emerging technologies associated with conductors and transmission towers require a re-evaluation of models of audible noise generated by overhead line conductors. Measurements on which existing commercial models were developed were typically performed on a single, classical design of conductor around 50 years ago. Within this paper, an ac testing facility employing a semianechoic chamber and a novel measurement procedure are proposed to give accurate determination of acoustic emission from overhead line conductors. The reproducibility of these measurements is significantly above traditional testing methods, but is shown to be heavily dependent on the chosen wetting technique. It is found that to achieve an accurate result, background acoustic noise control is essential especially for lower frequencies of power frequency harmonics. A direct comparison is reported for conductor samples with various physical characteristics. The analysis of results gives power utilities valuable information for selecting quieter conductors for overhead lines. The magnitude of high-frequency audible noise generated above 1 kHz is shown to be closely related to corona discharge activity, while the acoustic emission below 1 kHz is determined by the size distribution of droplets.

The relationship between the size of water droplets on the surface of ac high-voltage conductors, their vibration, and corona onset is investigated. Measurements have been carried out on individual droplets in high-voltage experiments, including high-speed photography, and discharge inception measurements. These have been correlated with acoustic emission from larger arrays of droplets on overhead transmission line conductors. A numerical model based on the finite element method has also been developed to simulate the vibration of the droplet enabling evaluation of the electric field and the characteristics of the droplet vibration. It is shown that the size of the water droplet is critical in its mechanical response to the field and that corona does not necessarily occur when the droplet is deformed into its most conical state as is the case under dc fields. For larger droplets the phase shift between the field and droplet vibration results in the maximum field occurring when the droplet is in a “flattened” profile rather than when it is “pointed.” The phase relationship between the droplet vibration and the electric field thus controls the onset of corona. It is argued that conductors which facilitate the development of small, uniform, stable droplets on their surface are the cause of abnormally high levels of low-frequency audible noise sometimes observed by transmission utilities. Moreover, the narrow resonant response of the droplet may lead to a difference in acoustic emissions experienced between power utilities with 50 and 60 Hz system frequencies.

Power cables connecting floating offshore wind farms will see mechanical stresses not experienced in land-based networks. Cross-linked polyethylene (XLPE) samples from power cable were subjected to compressive and tensile strains of up to 5% to examine how electrical tree growth is affected. A total of 35 samples were tested using needle-to-plane geometry and 50-Hz ac voltage at 7.5 kVrms. Compressive strain widened electrical trees along the direction strain was applied, and tensile strain led to narrower trees, distorting their rotational symmetry, and confirming a mechanical influence on growth. The distortion was linear with strain magnitude. The likelihood of increased tree branch bending or bifurcation angles linearly increased with compressive strain and reduced linearly with tensile strain. The fractal dimension of the trees was unaffected. Strain did not significantly influence the growth rate of trees until a value of 5% was reached. At this value, compressive strain reduced growth rate by a factor of approximately 2, whereas tensile strain showed no influence. Increasing compressive strain was also shown to linearly delay tree initiation. The influence of tensile strain was not quantifiable as trees initiated readily. The evolution of phase-resolved partial discharge patterns (PRPD) was unaffected by the strain applied. Time-to-failure was decreased by a factor of 1.8 at 5.7% tensile strain, which could have significance to in-service usage of high-voltage cables under dynamic forces found in floating applications.

Electric tree growth is a key ageing mechanism leading to breakdown of high voltage electrical insulation. Partial discharges (PDs) are invariably associated with electrical tree inception and propagation. In turn, the physical structure of an electrical tree influences the characteristics of partial discharge activity. Interpretation of PD patterns is therefore central to developing an understanding of the tree propagation process, and also to the use of PD patterns as an asset management tool. Our previous research indicates that the phase resolved PD (PRPD) patterns and pulse sequence analysis (PSA) patterns evolve with tree propagation. A method was proposed to estimate the point-on-wave inception and extinction voltages of PDs in tree channels within each power cycle. It was shown that the evolution of PD patterns is a consequence of changes to PD inception and extinction voltages as a tree develops. This paper provides a deterministic model of partial discharge in tree channels. Simulations of PDs in a straight non-conductive tree channel are based on experimental PD inception, extinction and residual voltages. The quantitative simulations reproduce almost all the characteristics of observed PRPD and PSA patterns. It is concluded that PD events are determined by five key parameters: tree structure, applied voltage, PD inception voltage, PD extinction voltage and PD residual voltage. Key parameters estimated by the method, and the models proposed explain PD activity in non-conductive trees. It is suggested that the PSA and PRPD patterns should be discussed together to fully understand the PD events. This model forms a platform for generating robust information for asset managers using PD measurements from high voltage equipment in service.

Bodies close to high-voltage equipment may experience discharges to metallic objects at ground potential if they are not grounded themselves. A tool which is able to predict the occurrence of such events would provide considerable benefit to transmission network operators. In this study, models of microshocks are developed. Laboratory measurements coupling a high-voltage overhead line to a simple model of a human body are compared to the predictions of a commercially available software package. The software, called current distribution, electromagnetic fields, grounding, and soil structure analysis, is widely used in the power industry. The experimental measurement of the potential of the floating body is complex because of the high field in which it sits, and this is also discussed. The software is found to represent the measured data in the simple cases examined to within 10%, and is found to be satisfactory as a platform for further development.

If not well designed, high voltage composite insulators are prone to ageing and failure due to corona and electric field stress. Particular care is required designing areas where the metal end connections meet the insulator core, otherwise a large electric field enhancement is observed. It is difficult to completely eradicate corona on any insulator, thus manufacturers try and minimise this phenomenon by designing the assembly to increase the corona inception voltage across the end connections and other metallic components. Often this involves introduction of corona rings, especially at the high voltage end of the composite insulator, to manage the magnitude of the electric field. The use of FEA to design corona/grading rings and optimise their position has recently been of great interest. The present paper reviews the use of FEA simulation to design stress relief devices across the high voltage end of a composite insulating cross-arm. Design work has been realised in practice and verified using corona inception measurements and compared to previous FEA results.