| The pollution flashover of insulators is one of the main factors threatening the safeoperation of the power grid. The process of pollution flashover can be generally dividedinto four steps, namely deposition of the contamination, damping of the contamination,dry band formation and the appearance of arc, and the arc propagation and thenflashover. The mechanism of the first three steps is simple comparatively, which ispropitious to inhibit the arc starting from the source. When the arc appears, it as airplasma interacts with the surface pollution layer and elongates till bridging the twoelectrodes, then flashover. Due to the complicated kinetic characteristic of the arc, thestep of arc propagation is the core of flashover mechanism. So far the mechanism of arcpropagation until flashover is still the hot and focal point at home and abroad.Comparison with DC arc, there is arc extinction and reignition during the ACflashover process due to the zero passage of arc current. Thus, the mechanism of the ACflashover process is more complicated for AC arcs propagation on the surface ofinsulators. Based on the existing research findings about flashover mechanism, a newAC electrical circuit flashover model of polluted insulators based on arc root voltagegradient criterion is proposed for the characteristics of AC arc. The main researchcontents of this paper are as follows:A new criterion based on the arc root voltage gradient is proposed from themicroscopic view of arc propagation. The arc propagating along the surface of pollutedinsulators is a kind of low-current dynamic arc, and the diffluence effect from surfacepollution layer exists in the process of the arc propagation ceaselessly. Therefore, a newarc circuit model which takes this diffluence effect into consideration is proposed notonly avoiding the use of arc voltage-gradient equation, but also improving the accuracyof flashover model. Combining the arc propagation criterion proposed with the arccircuit model proposed, a new static electrical circuit flashover model under AC voltagebased on the arc root voltage gradient criterion is built. The theoretical calculationresults of critical parameters from this electrical circuit flashover model are goodagreement with these of other AC flashover models and the test.Based on the static electrical circuit flashover model proposed above, a dynamicelectrical circuit flashover model is proposed by taking the time characteristic of arcpropagation into consideration, namely introducing the velocity of the arc propagation. The equivalent capacitance of surface pollution layer and the inductance of arc channelare both taken into consideration in the dynamic electrical circuit flashover model,whose circuit adopts vector equations. The dynamic simulation is carried out by thesoftware of MATLAB. The simulation results are good agreement with these of otherAC flashover models and the test.Artificial AC pollution flashover tests are conducted on the glass flat plate andstandard disc insulators respectively in order to verify the validity of the proposed staticand dynamic model based on the arc root voltage gradient criterion. The comparisonbetween static calculation values, dynamic simulation values and tests results indicatesthat these results are similar with each other whose errors are mainly less than10%,which verifies the validity of the proposed model. |
