Series graded gapped arrester provides reliable overvoltage protection in distribution systems

This paper compares the operating characteristics and energy handling capabilities of series graded gapped (SGG) and gapless metal oxide varistor (MOV) distribution class surge arresters. Application considerations are analyzed for both SGG and gapless MOV arresters using field results, laboratory tests and computer simulations. A large number of SGG arresters are installed on distribution systems throughout the USA. Field experience has demonstrated that they are extremely reliable devices with very low failure rates. Because SGG arresters have higher temporary overvoltage (TOV) ratings than gapless MOV arresters, they are often used to replace gapless MOV arresters when temporary overvoltage is a concern. Field experience also indicates that SGG arrester energy handling capability is at least equivalent to that of conventional arresters. This paper demonstrates that the arrester rated lightning impulse discharge capability is not properly characterized by the energy absorbed by the arrester. A proposed method is to use the I/sup 2/t value instead of absorbed energy because it correctly characterizes arrester energy handling and is easy to use.