The audible noise (AN) of DC transmission lines is a crucial factor affecting environmental assessment and electromagnetic design. In recent years, the public has paid increasing attention to the audible noise after the emergence of the HVDC technique. This paper emphatically reviewed the work investigating audible noise characteristics in both time and frequency domains, especially the correlation between sound and discharge. The proposed mechanisms of DC audible noise and the mitigating techniques are summarized, including the noise generation process, the physical models, the measurement method, and the mitigating technologies. It is found that the existing literature mainly focused on the prediction and characteristics of AN, the environmental factors which influence AN, and the methods to minimize AN emission. However, existing achievements still need to be improved to fully understand the mechanism of AN generation and solve the adaptability problem of AN prediction methods. The following aspects are valuable in future research: The correlation between audible noise and other corona effects will help solve the problem of difficulty in measuring audible noise in field condition; The corona discharge mechanism and weather resistance anti-corona coating when raindrops are attached to the surface of the transmission line, which will help guide the development and application of anti-corona coatings for the transmission line. Future research should also understand the mechanism of sound wave generation when considering the space charge effect.

When modeling the propagation of an electric discharge on an ice-covered insulator, the diameter and temperature of the discharge column are vitally important. This paper studies the thermal expansion characteristics of a discharge column occurring after electrode–ice gap breakdown both experimentally and theoretically. It is found that the air part of the discharge channel expands faster and has a higher temperature and larger diameter than the surface part. To provide a quantitative explanation of this phenomenon, a physical model is established based on the gap breakdown process, discharge channel heat conduction, and molecular thermal relaxation theory. The results of theoretical calculations show that the experimentally observed differences in discharge column thermal expansion characteristics result from the heating effect of brush discharge and from differences in heat conduction around the column.

In recent years, the number of high-voltage transmission lines has sharply increased with the rapid development of modern industry. However, a corona discharge phenomenon often occurs on the exposed high-voltage transmission lines, leading to energy loss and noise pollution. Herein, we have proposed a facile spraying method to prepare a superhydrophobic and thermally conductive coating to restrain the corona discharge phenomenon of high-voltage transmission lines, with vinyl silicone oil and hydrogen silicone oil as the main materials and modified boron nitride (BN) as a thermal conductive filler. The obtained composite coating exhibited superhydrophobicity, with a high water contact angle of 162°. In addition, the coating also showed a good self-cleaning capability, non-adhesion capability, mechanical stability, and chemical stability. Owing to the construction of the thermally conductive pathways with BN, the thermal conductivity of the coating reached 1.05 W/m·K, which was beneficial to quickly dissipating the heat generated by the current heating effect. Moreover, the corona losses of the positive and negative electrodes under simulated rainy conditions were decreased by 7.43% and 8.05%, respectively. The findings of our work have provided a new strategy to effectively restrain the corona discharge phenomenon of transmission lines, showing great application potential in the field of high-voltage power networks.

The E-I characteristic of an arc propagating over the ice surface is an essential input parameter when applying the ice flashover model. The numerical calculation and prediction of the E-I characteristic are essential to promote the numerical simulation of the discharge on the ice surface. Considering the energy balance of an arc propagates on the ice surface, this paper establishes an E-I characteristic model based on the mole ratio of the arc composition. The particle composition, transport, and E-I characteristics are obtained, and the model’s rationality is verified by comparing it with the existing data. Finally, the influence of the arc’s mole ratio and the arc radius on the E-I characteristics is analyzed. The results show that the E-I characteristics increase linearly with the increase of H2O molar ratio and decrease with the increase of arc radius, which has a saturation trend. The research results can provide a reference for the numerical simulation of an arc propagating over the ice surface.

DC corona audible noise (AN) is one of the electromagnetic interference from power grids and the key factors affecting the electrical design of power transmission and distribution equipment. The measurement method is crucial to study the generation mechanism of audible noise. This paper proposed a Schlieren optical measurement with a corresponding numerical reconstruction method to measure the audible noise within DC corona discharge and quantified it with the pressure field. Numerical experiments are conducted to verify the accuracy of the pressure field re-construction method. The relationship between the pressure field and sound pressure during DC corona discharge is experimentally studied. Results show that the reconstruction error is within 5%; the Schlieren system captures the gas expansion process and pressure field in the discharge region at the microsecond timescale. During corona discharge, the radial radius of the discharge region increases while its pressure decreases and overpressure increases. A relationship of non-linear proportional increase appears between the pressure field and audible noise, and only a small portion of the pressure field is converted into audible noise. The new method demonstrated in this paper is an effective way of measuring and analyzing the pressure field in the DC corona discharge, which would be the key to understanding the mechanism of acoustic wave (or AN) generation from DC corona discharge on transmission lines.

An in-depth study of the thermal characteristics of the discharge channel is critical to revealing the discharge mechanism on the ice surface. This paper uses the calibrated Schlieren method to study the discharge channel’s thermal characteristics (time-domain thermal radius and temperature characteristics) in the arc formation and propagation stages on the ice surface. The effects of the applied water conductivity, electrode-ice gap distance, and ice thickness on the thermal characteristics of the discharge channel are obtained. Results show that in the arc formation stage, the corona and brush discharge’s temperature is 440 K ~ 550 K, and the thermal radius is 0.4 mm ~ 0.64 mm. The discharge channel’s growth rate of the temperature and thermal radius during the transition from spark to arc decreases with the increase of the ice thickness, the gap distance, and the applied water conductivity. The discharge channel’s thermal radius increases exponentially with the increase in temperature. In the arc development stage, the arc temperature increases with the increase of the arc’s thermal radius, and the arc’s thermal diameter increases logarithmically with the increase of leakage current.