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• W80638006 abstract "A large number of pipelines are routed around or through the Chicago metropolitan region of Illinois. Pipeline operators are faced with operational and maintenance challenges that include the mitigation of static and dynamic stray current interference. This interference is generated by D.C. current sources which can include foreign pipelines and DC electric rail systems. In the Chicago area, the Chicago Transit Authority (CTA) railway system is one of the sources of dynamic DC stray current that can affect pipeline operators. Preliminary testing conducted on a local 90-inch water transmission pipeline was observed to indicate the presence of dynamic stray current interference. Based on this preliminary testing, more advanced testing was initiated. Ultimately this activity lead to design services to address and mitigate the DC stray current found on this water transmission pipeline. Field testing and analysis, calculations and the final mitigation design are presented in this paper. INTRODUCTION When testing on a local 90-inch water transmission pipeline indicates the presence of dynamic stray current interference, additional confirmatory testing and design services were initiated. The focus of this work is to assess the level of stray current interference and after field testing recommend a design to help mitigate the effects of the stray dynamic DC current. PIPELINE CHARACTERISTICS The water transmission pipeline consists of approximately 9 miles of 90-inch diameter Pre-Stressed Concrete Cylinder Pipe (PCCP). The pipeline runs in the vicinity and adjacent to the CTA electric rail system. The pipeline is directly buried for the majority of the distance; however, there are two (2) sections where the pipeline is located in a tunnel. These sections are located at a point where the 90inch pipeline is routed closest to the CTA electrical rails. Running approximately parallel to the 90-inch pipeline, but with a separation of approximately 1⁄2 a mile, is a 72-inch steel water transmission pipeline. The 72-inch line has an existing DC stray current system in place. DC INTERFERENCE CONSIDERATIONS AND TESTING Existing Electrical Shielding As described above, there are two (2) sections of 90-inch water transmission pipeline which have been installed in a circular rib and lag tunnel. These tunnels are geographically the closest physical point between the CTA electric railroad and the 90-inch water transmission pipeline. The 90-inch water main as installed is not provided with any designed protection from the action of DC stray current interference. If the tunnels act to electrically isolate the 90-inch water transmission pipeline and there is no electrolyte, such as water or soil between the external pipe surface and internal tunnel surface (tunnel annulus), then stray current cannot be discharged from the pipe surface to ground within these two (2) tunnel locations. If isolated, these tunnels act to increase the electrical path resistance for the DC stray current and may act to eliminate the stray current from being discharged from the water transmission pipeline at a point which is closest to the D.C. electric rail system. These tunnels may also act to move the point of electrical interference to a point upstream or downstream of this location. As installed there is no possible means to directly measure pipe-to-soil potentials or perform any other tests related to interference at the tunneled locations. As such, it is unknown whether there is water or soil in the tunnel annulus. If the tunnel is not acting to completely shield the pipeline; it is possible that the 90-inch water main may be experiencing interference due to its’ close proximity to the D.C. rail system. Testing Outside of the Tunnel Since the section of the 90-inch water transmission pipeline contained within the two (2) tunnels and closest to the D.C. rail system could not be directly tested, a section of main was selected for more advanced testing based on a review of the pipeline route and engineering experience. The test section selected is the first pipeline section east of the second tunnel which begins at stationing (156+38) and heads east. The testing performed on this section of the 90-inch water transmission is as follows: Graphing of the Beta curves. This test included measurement of the pipe-to-rail open circuit potential Eo, and the pipe-to-soil potential Vg. These two parameters were measured during the same period of time and the values were plotted together in an x-y graph, where the Vg is the y axis and Eo is the x axis. Determination of Beta values. The slope of the best fit line formed by the data gathered during the step above is known as the Beta value and was used to interpret the level of DC stray current at that point. This value helped calculate the bond characteristics, such as the maximum bond resistance and the maximum allowable current flowing through the bond cable. Determination of Vg in the case of no interference. This value is the value of Vg when the pipe-torail open circuit potential Eo is equal to zero. This was determined as the intercept of each beta curve with the y axis. Maximum Eo value: After the point of maximum exposure was determined, the value of Eo, Vg and the Beta value were determined over a 24 hour period of time. By doing this, the variables of the worst case scenario were determined. These values were used to calculate the bond characteristics; which were the maximum current allowed through the bond, the maximum bond cable resistance and the bond cable gauge. TEST RESULTS Graphing Beta Curves To obtain the values for the worst case scenario, the 72” main was disconnected from the existing reverse current drainage switch. The existing negative connection to the rail was used as the point of connection to measure the open circuit potential Eo, between the electrical rail and the 90” pipeline. The rail was connected to the negative lead of the data logger and the 90” pipe was connected to the positive lead of the data logger. The data logger was used in a two channel mode, where one channel was use to measure the Eo value, and the other channel was used to measure the pipe-to-soil potential Vg, with respect to a saturated Cu/CuSO4 reference cell. Both values were recorded simultaneously and they were plotted on an x-y graph to obtain the best fit line equation that corresponds to each set of data. A set of data was taken at Test Station A and at 100 foot intervals along the pipeline to the east of the test station, which is located at the eastern end of the tunnel. The Eo and Vg data was recorded once every second for a total of ten minutes at each location. A total of 14 sets of data were obtained and the graphs were plotted with the pipe-to-rail open circuit potential Eo on the x axis and the pipe-to-soil potential Vg on the y axis. Figure 1 below shows an example of one of the Beta Curves. Figure 1 – Representative Beta Curve Potential when stray current source turn off The structure-to-soil potential, Vgo, is the pipe-to-soil potential when stray current affecting the pipe is turned off. Vgo cannot be determined because the rail system current source cannot be turned off. Even at night, when the rail system operates at a lower electrical load, there is still current flowing on the pipe. Vgo can only be determined when Eo is zero in the equation of the best fit line for the data points related to Eo and Vg. The equation of the best fit line is as follows:" @default.
• W80638006 created "2016-06-24" @default.
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• W80638006 date "2009-03-22" @default.
• W80638006 modified "2023-09-26" @default.
• W80638006 title "Dynamic Stray Current Interference Testing And Mitigation Design For A 90-Inch Water Main" @default.
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