Presents an actual case history of stray current interference from a LRT system on a three circuit 69kV pipe-type cable system, the corrective action taken, and its results.
Construction of the Dallas Area Rapid Transit (DART) light rail transit (LRT) starter system, comprising slightly more than twenty miles of dual track right-of-ways (R/W) began in 1993. The rail guideway was constructed in conformance with modern LRT construction practices. The following standards were established for acceptance testing of the various segments of track work:
• 625 Ohm/1000 track feet (304.8 track meter) - concrete tie and ballast track work
• 625 Ohm/1000 track feet (304.8 track meter) - direct fixation track work
• 150 Ohm/1000 track feet (304.8 track meter) - at-grade imbedded track work
• 150 Ohm/1000 track feet (304.8 track meter) - special track work (wood tie and ballast)
• 150 Ohm/1000 track feet (304.8 track meter) - grade crossing track work
• 50 Ohm/1000 track feet (304.8 track meter) - Service and Inspection (S&I) Yard wood tie and ballast Franchise owner water lines crossing the track R/W were replaced with new, utilizing PVC pipe up through ten inch diameter. Larger diameter water lines were replaced with ductile iron pipe, employing pipe joint continuity bonds, protective coatings, dielectric isolation from existing lines, and cathodic protection. All of these measures resulted in an
system that was a good neighbor, producing essentially no stray current interference problems on the franchise owner utilities. We documented one utility that was directly affected by initial operation of the
system. This was a three circuit pipe-type cable (P-TC) system with a north south orientation just beyond the east fence of the S&I yard . Pipe-Type Cable Circuits A local electric power supplier (power company) operates a city wide pipe-type cable underground system in the City of Dallas. The newly constructed DART
system crossed these pipe-type cables at several locations throughout the City. Additional test stations were installed at or close to each of these new crossings. Pipe-to-soil potentials and pipeline currents were monitored at each of these locations with train passage. No significant electrical influence was noted at any of these crossings. However, a different situation was encountered on the three P-TC circuits at the Service and Inspection Yard. Normal train movement within the yard would not cause significant stray current influence on the nearby P-TC system even though the yard trackwork was designed for limited electrical isolation. This is due to slow train speeds and limited accelerations within the yard. The yard lead track was provided with insulating joints (IJ) at the tie-in to the main line to avoid stray current in the yard. The S&I yard was provided with its own separate traction power substation (TPSS) to power train movement within the yard. At the junction of the yard lead track with the mainline a knife switch was provided between the two overhead catenary systems (OCS). Another knife switch was provided across the yard lead IJs.
