Research On The Damge And Characteristic Of Oil-paper Insulation Under The Accumulative Affect Of Switching Impulse Voltage

Power transformer is the core of power grid, which determines the safety of thegrid. Studies have shown that the main reason for the failure of transformers is the agingof oil-paper insulation, which is caused by various factors such as temperature, electric,moisture and oxygen. In order to monitor the status of the oil-paper insulation, thedamage to the oil-paper insulation caused by each aging factor must be studied. In allthese aging factors, the influence of overvoltages can’t be ignored. However, there’rejust a few research on the damage of the oil-paper which caused by overvoltages.What’s more, most of the research focused on the effect of lightening impulse. There arefew reports about the research on the influence of switching overvoltages to theoil-paper insulation.In this paper, a research about the damage and characteristic of oil-paper insulationunder the accumulative affect of switching impulse was made by establishing a testplatform. The results showed that there will be spark and arc discharges on the surfaceof insulating paper under the affect of switching impulse, which will increase thecontents of H2and hydrocarbon gases dissolved in the insulating oil. At the same time,the polar material which is produced by the discharge will increase the dielectricconstant and dielectric loss of insulating oil in the low frequency domain. The dcconductivity of insulating oil also increases while the breakdown and partial dischargecharacteristic keep steady. At the same time, the discharge will decrease the surfaceconductivity of insulating paper, which leads to the decrease of the inception voltage ofsurface discharge. Part of the molecular chains in the insulating paper will fractureunder the accumulative affect of switching impulse voltage, which leads to the decreaseof the degree of polymerization of insulating paper. The dielectric constant anddielectric loss of insulating paper will increase in the low frequency domain. At thesame time, the breakdown voltage of insulating paper under switching impulse voltagewill decrease while the breakdown voltage of insulating paper at power frequency keepsteady under the accumulative affect of switching impulse voltage. The DC conductivityof insulating paper also increases a bit under the accumulative affect of switchingimpulse voltage.A research on the V-N characteristic of oil-paper insulation under switchingimpulse voltage was also made to evaluate the endurance capacity of oil-paper insulation. The influence of the insulation aging and the waveform varying to the V-Ncharacteristic were also studied. The results showed that the endurance capacity ofoil-paper insulation under switching impulse voltage will decrease with the aging ofoil-paper insulation. What’s more, the decrease velocity is increase with the aging time.The varying of the waveform also make a difference to the V-N characteristic ofoil-paper insulation. The endurance capacity of oil-paper insulation under switchingimpulse voltage will decrease with the decrease of front time and the increase of tailtime. What’s more, the influence of front time is much more serious than the tail time.