The researchers established a mathematical model of water droplet motion based on the principles of hydrodynamics and electromagnetic field using composite insulators as samples and calculated the trajectory deflection rate of water droplets on the insulator surface due to the electric field force. Based on this, they calculated the local collision coefficient1 distribution of water droplets at the edge of the insulator skirt and the core bar with and without electric field, and the results showed that the trajectory deflection of water droplets under the action of the electric field was the largest for small wind speed and small droplet radius, and the percentage increase of1 value at the core bar of the insulator was more than 15%.
The researchers conducted both charged and uncharged icing tests on composite insulators in an artificial climate chamber. The results show that the electric field increases the ice cover rate by up to 30% for dry growth ice cover at a small droplet radius and causes a rougher ice cover surface, but has less effect on the wet growth ice cover rate at a large droplet radius, which mainly causes a curved growth ice prism pattern.
Ice cover in China's power grid transmission line safety operation process has been a serious problem, which can not only cause transmission lines, towers of mechanical overload, collapse but also can cause the transmission line insulator string ice flashover. For the influence mechanism of icing on the safety of transmission lines, domestic and foreign scholars have done a lot of research.
The impact caused by wire ice is mainly focused on the mechanical characteristics, so the study of wire ice mechanism, the establishment of ice model, prediction of its ice growth has been the focus of attention. Among them, the three-parameter model based on water droplet collision, capture and freezing are most widely used. The model states that the ice growth rate of the conductor is determined by the collision, capture and freezing efficiency of supercooled water droplets on the surface of the conductor, and a physical model for calculating the three parameters is established, involving the gas-liquid two-flow field and thermodynamic equations.
To improve the model, related studies point out that the electric field strength and corona discharge on the transmission conductor surface can have an impact on the ice cover pattern and rate, which must be considered in the computational model. And some studies from the collision coefficient of water droplets on the wire surface, simulation calculations of the electric field effect on the impact of this parameter, the results show that the electric field will increase the collision range of water droplets on the wire surface and the value of the collision coefficient.
The main hazard of insulator ice is the line tripping caused by ice flashover, and most of the previous studies focused on the reduction characteristics of the insulator flashover voltage by ice overlay. Researchers from the State Key Laboratory of Safety and New Technologies for Power Transmission and Distribution Equipment and Systems (Chongqing University) have investigated the influence of the DC field on the insulator surface during the process of water droplets encountering the insulator and colliding with the insulator surface to form the over-ice.