Influence of aluminum phosphate contaminant on discharge characteristics of suspension glass insulators

Contaminant composition affects the discharge characteristics of external insulation. This paper studies the intense discharge phenomenon at low relative humidity (77%) in an AC 500 kV substation in Southern China. Due to farming and the soil feature in the sugar cane field around the substation, aluminum phosphate is formed in the soil, and accumulates on the external insulation surface owing to blowing dust. The porous structure and four-coordinated aluminum atom lead to strong moisture absorption capacity of aluminum phosphate. Then electrical performances of aluminum phosphate as a contaminant on insulation surface were investigated by means of discharge test in a constant humidity chamber. The experimental results show that, compared to conventional contaminant, aluminum phosphate contamination insulator has lower discharge inception voltage and stronger discharge intensity when relative humidity is above 70% and the aluminum phosphate content exceeds 20% in the non-soluble deposit. Aluminum phosphate is the main cause for the discharge phenomenon in the substation under study. It needs to be considered for insulation design and maintenance in ferralsol areas where phosphate fertilizer is heavily used. The moisture absorption of contaminant merits special consideration for further research.