| The atmospheric ice accretion on insulators heavily threatens to the secureoperation of power systems and is also one of the key techniques needed to solve sorely.Researchers around the world have carried out large number of investigations on icingand flashover performance of insulators through artificial icing test and natural siteobservations. However, most of these tests do not consider the effects of transmissionline operation electric field and thus have large difference from the practical situations.Based on previous achievements, this paper has conducted plenty of icing tests of fourtypical configurations of220kV and35kV composite insulators under AC and DC in themultifunctional artificial climate chamber. According to experiment results, thedifferences of icing characteristics of composite insulators under no-energized, ACenergized and DC energized are compared. The testing results and the icing mechanismare verified and analyzed through electric field simulation and other means. Thefollowing conclusions are found:(1) The AC and DC electric field have significant effects on the appearance,density and weight of ice on the surface of composite insulators. With the increase ofapplied voltage, the average density of ice reduces gradually, and the weight of iceincreases at first and then decreases. When the voltage rises to a certain value, thedescent speed of ice amount of insulators under–DC voltage is faster than under ACand+DC voltage.(2) The density of glaze under energized condition is less than that underno-energized condition. When the values of applied voltage are the same, the density ofglaze is minimum under–DC voltage and maximum under AC voltage.(3) The interior of icicles at the edge of sheds appear bubbles under energized icingcondition and the bubbles of icicles under–DC voltage are larger than that under+DCand AC voltage, which the number and volume become larger with the increase ofapplied voltage. Compared to the vertical growth under no-energized condition, allicicles at the edge of shed bend towards core rod of insulators under energized condition,which the bending degree is more obvious when the electric field is more uneven andgreater.(4) Grading ring can improve the electric filed distribution along the compositeinsulators and is helpful to the ice accretion of insulator. Under the energized icing tests with grading ring installed at the end-fitting, the ice on the surface of most of sheds iscompact, smooth and transparent, but the ice on the other sheds is still loose, fuzzy andnon-transparent, with granular ice bead.(5) Shed configuration and grading ring can improve the electric filed distributionof ice-covered insulators each other and both of them can obviously influence theflashover voltage. The improvement of electric field distribution can increase the criticalflashover voltage and the range is significantly associated with the shed configuration ofinsulators. The bigger difference the shed configuration and the longer the spacingdistance, the smaller the effect of the ice amount and appearance on the flashoverperformance and the better the improvement of icing flashover voltage under gradingring condition.(6) Regardless of AC and DC, in the process of insulator icing, the polarizationand attraction of electric field to water droplets play the main role when the electric fledintensity is low. When the electric field intensity is larger, the heating effects of leakagecurrent, corona discharge, spark discharge and arc play the leading role. |
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