Surface charge accumulation is considered to be a critical factor in flashover failure of three-post insulators. However

surface charge accumulation characteristics on three-post insulators with complex structures and uneven electric fields are still unclear. Furthermore

the temperature gradient field makes charge accumulation more complicated. In this presentation

surface charge profiles of DC three-post insulators under electro-thermal coupling stress are studied by establishing a multi-degree-of-freedom movement measurement system. The abdominal area of the three-post insulator accumulaftes charges of identical polarity as the DC voltage

while the leg area accumulates heteropolar charges. Charge density from the bottom of the leg to the center of the abdomen presents a trimodal distribution pattern

including two homopolar charge peaks and one heteropolar charge peak. Asymmetrical surface conductance distribution arising from the temperature gradient leads to a significant increase in amplitude and distribution range of the homopolar charge peak at the legs of insulator. Increase of the temperature gradient will further magnify the homopolar charge peak at the legs. When DC voltage is 100 kV and conductive pole temperature is 70°C

surface charge density of the three-post insulator can reach 100 μC/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2. Therefore

surface conductance regulation of the leg region is the key to charge regulation and insulation optimization design of DC three-post insulators.