Electrical Treeing Phenomenon And Suppression Method Of Polypropylene Under DC And Impulse Voltages

The development of environmentally friendly polypropylene insulation DC cable can improve the environmental friendliness of the power system and improve the cable operating temperature,which is of great significance for the development of DC cable transmission technology.During the operation of the HVDC cable,due to the frequent conduction and shutdown operations of the power electronic components,HVDC cable may be affected by repeated pulse voltages,which may easily cause electrical aging and insulation failure.In addition,the change of temperature will also affect the deterioration process of polypropylene insulation and threaten the safe and stable operation of power system.Based on the DC cable polypropylene insulation as object,using the typical needle-plate electrode structure,electrical tree characteristics and its growth mechanism of polypropylene under DC and impulse electric field were studied.The effects of temperature on the electrical tree characteristics was also studied.Using the method of adding voltage stabilizer into polypropylene to inhibit the growth of electrical tree.These studies lay the experimental and theoretical foundation for the development of environmental protection DC cable insulation without crosslinking.The main research work and achievements are as follows:(1)By studying the dynamic growth characteristics of the electrical tree under DC and DC-impulse voltages,it was found that the DC voltage is not easy to initial the growth of electrical tree.In the case that different amplitudes DC combined with pulse voltages,the growth rate and accumulated damage of the electrical tree increased with the increase of the DC voltage when DC voltage polarity and pulse voltage polarity are the same.The growth rate and accumulated damage of the electrical tree increased first and then decreased with the increase of the DC amplitude when DC voltage polarity and pulse voltage polarity are different.In the case that different amplitudes pulse combined with DC voltages,the growth rate and accumulated damage of the electrical tree increased with the increase of the pulse voltage amplitude.(2)By studying the growth characteristics of electrical tree under different temperatures,it was found that the growth rate of electrical tree increased first and then decreased with the increase of temperature from 50 to 130 °C under pulse voltage,and it decreased with the decrease of temperature from-30 to-196 °C.The accumulated damage of breakdown electrical tree and the width of the breakdown channels had no obvious change with temperature.The analysis of the electrical tree channel was carried out by energy spectrum analysis and infrared spectroscopy.It was found that oxygen was introduced into the breakdown channel and C=O and C-O groups were found.Under the same polarity impulse superimposed DC voltages,the growth rate of electrical tree decreased first and then increased with the increase of temperature,and the accumulated damage increased gradually.Under the opposite polarity impulse superimposed DC voltages,the growth rate and accumulated damage increased with the increase of temperature.(3)In order to inhibit the growth of electrical tree,4-phenylbenzophenone,2-hydroxy-2-phenylacetophenone and 4,4'-bis(dimethylamino)benzyl three types of voltage stabilizer were added to polypropylene.It was found that 2-hydroxy-2-phenylacetophenone can inhibit the growth of polypropylene electrical tree,adding 4-phenylbenzophenone and 4,4'-bis(dimethylamino)benzyl promote the growth of electrical tree.With the increase of 2-hydroxy-2-phenylacetophenone content,the growth rate of electrical tree first decreased and then increased.2-hydroxy-2-phenylacetophenone could capture hot electrons,inhibiting the impact of hot electrons on the polypropylene insulating molecular chains under the DC and impulse voltages,thereby inhibit electrical tree growth.