scope:

The standard covers application of dc surge arresters for transient overvoltage protection of dc transit electrification systems. These dc transit electrification systems include light rail, heavy rail, streetcar, and trolley bus systems. This standard covers selection and application of metal-oxide varistor (MOV) gapless surge arresters to divert surge energy away from the transit system components. It does not cover low-voltage SPDs that are required within dc traction power system equipment, such as rectifier units, vehicle propulsion system, or other sensitive components of the dc transit system.

Purpose

It is the purpose of this standard to provide uniform practices for lightning and switching transient overvoltage protection of dc transit electrification by proper selection of dc surge arresters based upon the surge environment and site conditions of the transit system. This standard allows the use of SPDs in dc transit systems to avoid insulation failure due to transient overvoltage. Transient overvoltage protection is just as important as short-circuit protection. this standard will minimize equipment damage caused by transient overvoltages, increasing system reliability that will result in reduced maintenance.