The occurrence of heavy rain may cause rain curtains on transmission lines, towers and insulator strings. In severe cases, rain streams will form, which will shorten the insulation distance of the air gaps among transmission equipments, causing raining flashover fault and posing a great threat to the operation of the power grid.In order to study the break-up performance of the water streams and its influence on the discharge characteristics under rain conditions, this paper focuses on the DC discharge characteristics of rod-plate short air gap with experiment and finite element method.The results indicate that the break-up process of the water streams in rod-plate short air gap is mainly affected by external electric field force, surface tension of rain column and viscous force. The electric field force is opposite to the two force directions, which promotes water streams breaking up. The break-up of water streams goes through three stages in turn:  jet zone, transition zone, break-up zone. When the water streams is in the jet zone, its surface is smooth and there are few ripples; the water streams in the transition zone has a large surface curvature with multiple ripples of different wavelengths; The water streams in the break-up zone have broken, with morphological characteristics such as long and short faults and satellite drops. The break-up length of water streams decreases with the increase of applied voltage under different flow velocities, but the decreasing trend becomes slower. The critical length of the water streams increases with the increase of the velocity. Meanwhile,The break-up length decreases with the increase of water conductivity, but the decreasing trend increases accordingly. In addition, the break-up diameter and break-up time of water streams decrease with the increase of applied voltage, and both of the change rates are positively correlated with the diameter of water streams. By comparing the simulation results with the test results, the break-up diameter and length have the same variation trend with rainfall intensity and voltage. The deviation of the data of break-up diameter is about 10%, and the deviation of break-up length is within 15%.The research results can provide theoretical support for transmission line design and insulation selection.

 

Rain conditions; DC discharge; short air gap; water streams break-up performance; finite element simulation; simula-tion experiment