Improving The Properties Of Polypropylene Insulation Materials Using Voltage Stabilizers

Polypropylene(PP)is widely used as an insulating medium in high-voltage power equipment.Voltage stabilizer is widely used to improve the electrical resistance of cross-linked polyethylene(XLPE)insulating materials.However,few researchers have explored its application in polypropylene(PP)based insulating materials.In this paper,three kinds of excellent aromatic ketone voltage stabilizers,4-acryloxy-2-hydroxy-diphenyl ketone(ALRB),bimethylstyrene ketone(RBBT)and 2-hydroxychalconone(RQCT),were selected to study their effects on the electrical properties of PP based insulating materials.According to the principle of partial discharge when electric branches are initiated,a non-transparent sample AC branch initial voltage testing system is built based on HFCT current sensor.The influence of voltage stabilizer on PP electric branch initial voltage is tested by needle plate electrode.The results show that the voltage stabilizers ALRB,RBBT and RQCT can all increase the initial voltage and extinguishing voltage of PP electric branch initiation process,and the ALRB adding 0.6phr has the best effect,and the initial voltage and extinguishing voltage are increased by 33.0% and 32.5%.After that,the effects of three voltage stabilizers on the DC breakdown performance of PP were tested.The results show that the addition of 0.4phr ALRB has the best effect,and the DC breakdown field strength of PP can be increased by 34.6% at room temperature and 11.2% at 80℃.If PP is used as an insulating layer of power cable,it needs to be toughened and modified.Two elastomers,ethylene-octene copolymer(POE)and styreneethylene/butene-styrene triblock copolymer(SEBS),are selected to toughen and toughen PP.The effects of voltage stabilizer on the DC breakdown strength of two elastomer polymers and PP/ elastomer blends were tested.The results show that although the voltage stabilizer can improve the DC breakdown field strength of PP,but can not improve the DC breakdown performance of POE and SEBS.In the various PP/elastomer blends prepared according to different mixing order,the addition of three voltage stabilizers can not improve the DC breakdown field strength of PP/elastomer blends.At 80℃,three voltage stabilizers can increase the DC breakdown field strength of PP/POE by 12.7%,18.7% and 11.9%,respectively.However,the DC breakdown field strength of PP/SEBS insulating materials can not be effectively improved.In order to inhibit the migration and precipitation of voltage stabilizer in polymer,ALRB was grafted onto PP using DCP as grafting initiator,and a styrene derivative as an anti-degradation additive was added to inhibit the degradation of materials caused by the grafting process of voltage stabilizer.Firstly,the physical and chemical properties of the modified materials were characterized.Then,the electric branching initiation characteristics,DC breakdown characteristics and high temperature space charge accumulation characteristics of the modified materials were studied respectively.The results showed that ALRB could be grafted onto PP matrix in the free radical reaction initiated by DCP,and both styrene derivatives and ALRB could inhibit the macromolecular degradation of PP during the graft reaction.The grafting modified PP insulation material can significantly inhibit the initiation of electric branches and improve the DC breakdown field strength.At room temperature and 50℃,the space charge accumulation and electric field distortion caused by PP materials are not obvious,but at 80℃,the space charge accumulation and electric field distortion appear significantly and the grafted materials can significantly inhibit the space charge accumulation and electric field distortion.