Corrosion control for the Dallas Area Rapid Transit system

Abstract

The Dallas Light Rail Transit System (DART) operates it's traction power system at 800 volt direct current (DC). Several generations have passed since electrified transit operated in Dallas, the possible dynamic effects of stray current have not been realized by local utility companies. Stray current corrosion is caused by an earth path of direct current from a source external to an underground metallic structure. DART, like most modern transit systems, incorporates corrosion control measures to insure that the DC traction return current travels along the running rails and does not generate stray current interference on surrounding metallic structures. Other routine corrosion control methods must also be addressed such as galvanic corrosion on metallic structures, which results from electro-chemical reactions. This is mitigated by barriers, which prevent a chemical reaction from taking place on the structure. Another method of controlling corrosion is the use of cathodic protection, where sacrificial anodes are installed to afford protective currents to mitigate the corrosive effects on a buried metallic structure. DART is active in coordinating corrosion control methods with other utilities that own and operate underground structures subject to corrosion damages. This paper explains the interaction of the traction power, signal, and corrosion control disciplines and methods used for the effective control of corrosion. The interaction of these disciplines, and coordination with local owners of buried metallic structures will keep corrosion under control and maintain a high level of engineered protection.