Production Process And Influencing Factors Of X-wax In Oil-paper Insulation

Oil-paper insulating bushing is one of the core components of the transformer.Casing failures have occurred frequently in recent years,and yellow waxy substances are often found when the failed casing is disassembled.This substance has no fixed chemical formula and is called X-wax.After X-wax is produced,it will adhere to the insulating paper and enter the pores,resulting in increased overall loss and local temperature rise.At present,the cause and composition of X-wax are still unclear,and X-wax cannot be detected.It is urgent to carry out research on the generation principle,generation path and influencing factors of X-wax.This thesis focuses on Karamay No.25 naphthenic oil,which is commonly used in China.Materials Studio software is used to establish a naphthenic oil simulation model to calculate the bond breaking energy at different positions of the main constituent molecules,and the ReaxFF-MD method is used to dynamically simulate the generation of free radicals at 473 K,393 K and 373 K.The bond breaking position of the reaction initiated by each structure is determined,and it is found that two free radicals will be formed after the molecular bond is broken.The large molecular free radical recombines to form X-wax,and the small molecular free radical recombines to form gas.It is found that the minimum bond energy of the carbon-carbon bond is about 360kJ/mol,and the transformer cannot provide enough heat energy to break the chemical bond to initiate the reaction at the normal working temperature of the transformer.The high temperature above 150℃ will cause the X-wax to decompose into small molecules with less than 6 carbon atoms.Temperature alone cannot produce X-wax,and the formation of X-wax requires partial discharge in the oil.After determining the location of each molecular chemical bond break and the path of X-wax generation.Combined with free radical theory,the chain initiation,chain transfer and chain termination reactions of X-wax are analyzed,and the reaction equations of each stage are written.It is found that X-wax is formed by mixing solid alkanes with more than 16 carbon atoms,which is similar in composition to insulating oil,and is accompanied by the formation of gaseous and liquid products.Gaseous products include gases such as hydrogen and methane,and liquid products include alkanes with 5 to 16 carbon atoms.In view of the lack of X-wax detection method,the accompanying products of X-wax formation were analyzed.X-wax can be detected with the help of the colloidal properties Tyndall effect and the chang,e in resistivity of insulating oil.Experiments prove that the detection results of the two methods have good correspondence.Measuring the resistivity change of insulating oil can be used in engineering to detect X-wax.Real-time measurement of the resistivity of the insulating oil.When the resistivity is lower than 60%of the initial value,a rebound phenomenon occurs,and it can be judged that X-wax is produced in the oil.Aiming at the problem of unclear X-wax generation mechanism,the influence of different temperature,moisture,partial discharge,oil quality and catalyst conditions on the formation of X-wax was explored.It is found that there is a partial discharge threshold at a certain temperature,and X-wax cannot be produced when the partial discharge is lower.Factors such as temperature,moisture and catalyst can promote the production of X-wax,while the oil quality has little effect on the production of X-wax.It is verified that the energy generated by discharge is the main energy to provide chemical bond rupture.The thermal energy provided by temperature can promote the rupture of chemical bonds.The presence of moisture makes the partial discharge more likely to occur in the oil.The catalyst reduces the activation energy of the reaction and promotes the reaction to occur faster.