The short circuit fault of 66 kV dry-typeair-core reactor is introduced in this paper. It is preliminarily judged in accordance with its structural characteristics and on-site inspection that the insulation breakdown is between the 7 th and 8 th package. It is found throughout disassembly and inspetion analysis that such contamination as bird excrement and plume is obvious on the surface of the package. creepage traces along bird excrement and traces of penetrating over fire and smoke in the 7 th and 8 th package are existed. And each layer of conductor in the package has different degree of ablation and the toughness of the insulation film of theconductor around the ablation point is good. It is inferred that the fouling on the surface of package causes wet discharge

which damages the insulation of inter-strand and the inter-layer in package with gradual accumulation and deterioration

eventually resulting in short circuit of the reactor.Accordingly

such preventive measures for operation and inspection as check of anti-corrosion coating of reactor

add of cleaning items of ventilation duct for routine maintenance

reform of reactor grille and enhancement of anti-bird performance are proposed so to ensure safe operation of the equipment.