To find out the cause of chalking

embrittling

collapsing and fracturing of auxiliary silicone rubber shedin a 500 kV substation

the physical and chemical properties analysis and aging assessment of deteriorated shed arecarried out. The results from various techniques indicate that the hydrophobicity and mechanical performance ofaged silicone rubber shed decreases greatly compared to new shed. A series of complicated physical and chemical re-actions in silicone rubber

such as breakage of molecule chains

generating active groups

losing organic compo-nents and forming microvoids occurred under the influence of environment. The results show

the performance of sili-cone rubber shed degrades. The inappropriate composition is a probable cause of rapid degradation and performancereduction of sheds. The alkaline pollution enriched from adjacent cement plant accelerated the ageing of silicone rub-ber shed probably. To avoid similar faults and ensure security and stability of grid

some precautions for this issueand suggestions for maintenance are proposed finally.