Study on Reliability and Selection of Silicone Grease Used for Coating at the Interface Between Cable and Accessory

Silicone grease coated at the interface of cables and accessories performs a good role in lubricating and sealing during installation, but the swelling impact of silicone grease on rubber insulation of accessories greatly affects the long-term reliability of the interface between cable and accessory. Until recently, no standard has been proposed to guide accessory manufacturers in choosing the best silicone grease. In this study, nine different silicone greases that were widely used for accessories installation were chosen. First, three types of silicone greases with outstanding anti-swelling properties were tested using a silicone rubber (SiR) swelling experiment. The properties of the three silicone greases chosen were then investigated further, including electrical and mechanical properties, moisture resistance, and corona resistance. The results reveal that dimethyl silicone with high viscosity or by inserting phenyl side groups can minimize SiR swelling and then enhance its mechanical qualities. However, perfluoropolyether grease outperforms dimethyl silicone in terms of swelling resistance, chemical inertness, and excellent thermal stability. Thus, SiR coated with perfluoropolyether grease can maintain excellent mechanical properties after different aging. However, because of its high polarity, it can cause significant charge buildup at the interface between cables and accessories, particularly under direct current (dc) electrical stress. Consequently, perfluoropolyether grease will have a negative effect on the use in dc environment. Moreover, silicone greases after inorganic doping absorb moisture easily, resulting in a high relative dielectric constant that will have a negative effect on the use in a humid environment.