Research of biological contamination and its effect on the properties of RTV-coated insulators

•The biofouling regularity of algae growth on the surface of outdoor RTV-coated insulators was presented.•The suitable conditions for algae growth on insulator surface were studied in detail.•The presence of algae could decrease flashover performance of the RTV-coated insulators.•The effect of algae on the aging of RTV silicone rubber was insignificant.•To inhibit and prevent biological contamination, some measures presented may be possible. However, their effectiveness needs further investigation.