Effect of arcing on DC flashover performance of contaminated porcelain insulators for various suspension patterns at high altitudes

This paper presents an analysis of the arcing and flashover performance of contaminated dc insulators of various suspension patterns at high altitudes (1970 m). The experiments tested two types of dc insulators, a bell-type insulator and a tri-shed suspension insulator. The experimental results show that dc arcs play an important role in the flashover performance since they levitate more easily from the porcelain surfaces at high altitudes than at sea level. For heavily contaminated insulators, the relationship between the insulator length and the flashover voltage per insulator unit is affected by the arc development path, and is lower for shorter insulator strings (10 to 20 insulator units). With a non-uniform contamination distribution between the top and bottom insulator surfaces, the arcs propagate close to the insulator surface, resulting in a higher flashover voltage than with uniform contamination. The Y-string configuration appears to lead to much lower flashover voltages than in I- and V-string insulators. With the latter, the arc propagation path is greatly influenced by the angle between the two insulator strings with the flashover voltages for both bell-type and tri-shed insulators increasing with the angle but apparently due to different mechanisms. Experimental results indicate that the bell-type insulator has better flashover characteristic; than the tri-shed insulator.