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The effect of relative humidity on the surface electric field (SEF) strength and a new non-contact assessment method based on space charge density were studied. The purpose of using space charge was to assess the SEF accurately, particularly after corona occurs. Space charge measurement and SEF evaluation were conducted at a relative humidity of 40% to 90%. The change law of SEF after corona occurs at different relative humidity was obtained. Results showed that under the same relative humidity, the space charge density increases with the applied voltage, while the SEF decreases with voltages after corona occurs. As the humidity condition aggravated, SEF first increases and then decreases, and the turning point is about 70%. The distribution of charge density has an opposite change trend. The variation of charge density and SEF demonstrates that the two have mutual inhibition. Meanwhile, the change formula of SEF shows that the electric field intensity on the wire surface is not constant after corona occurs. The corona discharge experiment and theoretical research can be further carried out based on the results in this paper.

Corona performance of transmission lines in foul weather conditions, icing particularly, have attracted widely attentions recently. In this research, the influence of freezing water conductivity on positive corona performance of soft rime ice-covered conductor is studied in corona cage via energized artificial icing method. The most important finding of this research is that the maximum deviation of the corona inception voltage obtained by the compared three corona inception method could reach 14.7% in soft rime icing condition, and the quadratic law method is recommended. The formed soft rime is composed of the divergent dendritic layer and the ice layer. Based on the ultraviolet photon videos and the corona current pulses waveform, the corona development process of soft rime ice-covered conductor is divided into four stages: feeble discharge mode, positive onset streamer mode, positive glow mode, and positive pre-breakdown streamer mode. Moreover, with higher freezing water conductivity, the obtained icing weight and icing thickness are bigger, consequently, the corresponding corona loss and audible noise are also larger.

This research studies the impact of icing severity on audible noise (AN) characteristics of a rime ice-covered smooth conductor. The conductor is energized with positive polarity voltage during artificial icing experiment and corona performance experiment. The experiments are performed in a corona cage located in an artificial climate chamber. Test results show that harsher icing severity causes higher AN and the AN approaches saturation. The empirical formula for different icing severities is also given, which can help predict the AN, once the icing thickness and nominal electric field intensity are given. The studies of the one-third octave band spectra indicate that the audio frequency can be divided into three sections: background noise section, transitional section, and corona discharge section. The A-weighted AN is independent of the frequency components in the background noise section. However, in the corona discharge section, the differences between A-weighted AN and frequency components are constant once the frequency component is designated. Especially, the 3.15-kHz component is recommended to extract the corona-generated AN during the long-term AN monitoring, and its relative error is less than 3.6%.

Corona performance of transmission lines in foul weather conditions, icing particularly, have attracted widely attentions. In this research, the influence of voltage polarity on corona performance of two icing categories, glaze and soft rime icing, is studied in corona cage via artificial icing method. The most important finding of this research is that a linear relationship is found between audible noise (AN) and the corona loss (CL) in dB above 1 W/m for the first time, the slopes of the line are voltage polarity-dependent. A 10.4 dBA and 13.7 dBA variation in the AN value for a 10 dB increase in the CL for negative and positive voltage respectively, with little influence icing categories. Moreover, the negative polarity conductors are attending to accumulate much more glaze ice than positive polarity conductors. Taylor cones and hemispheres are observed on the tip of glaze icicles when subjected to DC and AC electric field, respectively. For both icing categories, the CL of negative polarity conductors are bigger than that of positive polarity conductors, the contrary is the case of AN. When the voltage gradient is greater than 18.0 kV/cm, contrary to popular perception, the generated CL and AN of glaze ice-covered conductor are bigger than that of rain condition and fair weather, respectively.

Wind turbines often suffer from blade icing issues in cold regions, which causes the degradation of the blade aerodynamic performance and the loss of power production. In the paper, a 3D numerical simulation model of the wind turbine rotor is put forward by using a commercial computational fluid dynamics (CFD) solver ANSYS Fluent to estimate the blade aerodynamic performance after icing. The multiple reference frame (MRF) model, Reynold Averaged Navier Stokes (RANS) and k-ω SST turbulence model are used in the simulation. Results show that CFD computational results are in accordance with the experimental results for clean and rime-iced rotors within rated wind speed, and overrated for glaze-iced rotors at high wind speed. As the wind speed increases, the rotor speed and output power of wind turbines decrease more dramatically under icing conditions. Besides, ice shapes mainly affect pressure distribution at the leading edge of airfoils, and thus reduce the normal force and tangential force significantly at approximate 62%–89% radial position. Influenced by ice shapes, blades are more likely to work in stall region at the same wind speed. In addition, flow separation around the iced blade is more serious at larger wind speed, which will produce more momentum and frictional loss, especially for glaze ice. The results provide a valuable reference for the wind farms operation and generator system evaluation in cold regions.

As the most common precipitation form, rain-lead corona problems are inevitably faced by designers of transmission lines. Through long-term observations of corona inception process under rain conditions by ultraviolet camera, a definition of minimum steady corona inception voltage is presented, which is more useful for practical application. To predict the minimum steady corona inception voltage, water droplet deformation model of smooth conductor is promoted based on the principle of minimising energy in this publication, which takes the influence of electric field force into consideration. Critical breakdown voltage and corresponding critical geometric dimensions of specific water droplet are calculated through the deformation model. The accuracy of the presented deformation model is proved to be >95%, by verification tests performed in a corona cage. Corona discharge model presented in the previous work is adopted to predict the water droplet corona inception voltage of given geometric dimensions. Finally, through the calculation results of both models, the defined minimum steady corona inception voltage of smooth conductor is calculated when there exist rain droplets on conductor lower surface. Also, the calculation error of minimum steady corona inception voltage is ∼8.0% when compared with the validation experiments.

This paper presents the results of laboratory experiments carried out on an ac-energized stranded conductor subjected to simulated glaze icing, which were conducted in a corona cage located in an artificial climate chamber. With the increase of icing duration, the grow of icing severity of conductors lead to the corona onset voltage fell from 54.8 to 41.9 kV, correspondingly, the surface irregularity of stranded conductor decreased from 0.41 to 0.31. Through the ultraviolet photon frame and ultraviolet photon curve, corona development process of glaze ice-covered conductor were divided into three stages, that is, burst corona mode, comprehensive corona mode and glow mode. The impact of icing severity on the corona loss and audible noise was investigated. With regard to corona loss, it is in proportion to icing severity at a given surface gradient, whereas no obvious impact was observed with audible noise could be established. In addition, corona performance in comparison with rain condition was also studied, the corona loss of glaze ice-covered conductor was higher than that of rain, instead the audible noise of glaze ice-covered conductor was lower than that of rain after a certain surface gradient. The presented results could provide references to the design of ac overhead transmission lines crossing cold regions.

Flashover of ice-covered insulators seriously affects the safe operation of transmission lines. It is necessary to study the electric field distribution for flashover analysis of ice-covered insulators. The electric field of ice-covered insulators was mostly calculated by a two-dimensional (2D) axisymmetric model that cannot be well corresponded to actual icing situations. In this study, a 3D electric field simulation model of ice-covered suspension insulators under moderate icing condition with applied DC voltage was established. Two characteristic parameters, E(av) and E(max) were proposed to measure electric field distortion degree. Based on the simulation results, the effects of water film conductivity, icicle length, icicle deviation angle, and icicle distribution on E(av) and E(max) were studied. The results showed that icicles have a significant influence on the electric field distribution of insulators. E(av) increases with the increase of icicle length and decreases with the increase of icicle deviation angle. E(max) increases with the increase of the icicle length, icicle spacing and adjacent icicle length difference. When the icicle deviation angle is 45°, E(max) is the largest. Lastly, the possible flashover paths were analysed based on the simulation results, which would provide a theoretical basis for building a flashover model of ice-covered insulators.