IEEE Draft Standard for Transient Overvoltage Protection of DC Electrification Systems by Application of Surge Arrestors

This standard is a basis for the design and application of dc surge protection devices to protect Overhead Contact System (OCS) from transient overvoltages associated with lightning and switching surges. Switching surges are inherent characteristics of electrification system and are generally considered low energy transient overvoltages. Lightning surges are natural, caused by electrical discharge that occurs in the atmosphere between clouds or between clouds and ground. Lightning surges are known for causing very high energy transient overvoltages by direct or indirect coupling with OCS. This standard covers transient overvoltage protection of OCS and third rail used in dc transit electrification system. Transient overvoltage protection of positive electrical conductors and the respective negative return system including running rails can be achieved by the application of same type of surge protection devices. Although running rails are less likely to be affected by lightning transient overvoltages due to their proximity to earth, flash-over can occur to drain surge energy away from the rails without the application of surge overvoltage protection devices. The subject of application of lightning protection devices to running rails (where such lightning protection devices may be required, especially in areas where lightning activity is severe) will require reviews and protection consideration of rail-ground shorting devices along with surge protection device rating. It is known that all modern light rail transit (LRT) projects and heavy rail transit projects use rail-ground shorting devices (when rail-ground voltage exceed set limit for certain time duration) for safety of personnel from the undesirable rail-ground voltage appearing at the train vehicle surface when train is located at the passenger station or somewhere else on the track rails. Therefore, the application of surge protection devices to rails will require special studies performing reviews and coordination of surge protection devices with the rail-ground shorting devices, as called voltage limiting devices [B37]. This type of special study can’t be covered in this standard as theree are no industry standards in North America that exist today on rail-ground shorting devices, otherre than IEC standard [B37]. The word surge arrester instead of lightning arrester and earth instead of ground have been used in this standard without affecting the technical contents of the standard.