Abstract: The elbow head is the cable branch joint of 10 kV ring network cabinet,whose function is to separate the high voltage electric conductor and insulate the shell of the ground box,which is of great significance to the safe operation of the distribution network.In order to deal with the burning phenomenon of ring network cabinets and cable branch boxes in Yunnan power grid,the causes of the fault are analyzed from the following aspects,such as,the generation of electric charge and potential formation of the elbow head,the poor or false grounding of the elbow head,the field operation environment and so on.The results show that the “local high resistance”+“invalid grounding” cause the charge deposited in the elbow head unable to move and release,and a higher suspension potential is formed.The higher suspension potential causes the elbow head to discharge to the ground and between phases.Non-standard installation and poor operating environment cause the false grounding of the elbow head,which leads to the deterioration of the uniformity of the electric field distribution and the partial discharge on the surface or inside of the elbow head.According to the analysis results,the corresponding preventive measures are put forward based on the causes of the failure of the elbow head,which has certain guiding significance for the electric power production.