Convenient Procedure for Measuring the Electrical Resistance of Fastening Systems in Urban Railway Tracks

Abstract

Electrical resistance is among the characteristics that fastening systems must meet to ensure the proper functioning of signaling systems in railway infrastructure. The EN 13146-5:2012 standard specifies a laboratory testing method for determining the electrical resistance under wet conditions between running rails provided by a fastening system on steel or concrete sleepers. In urban railway tracks, the electrical resistance of fastening systems affects the stray current; however, there is no standardized electrical resistance measuring method. There is also no definition for the minimum value that the electrical resistance of fastening systems must satisfy to prevent stray currents. For this reason, this paper analysis the possibility of using the standard EN 13146-5:2012 for the measurement and analysis of the electrical resistance of fastening systems in urban railway tracks. In this study, the electrical resistance of different fastening systems used in urban railway tracks was measured. Based on the tests results, the modifications needed in the EN 13146-5 standard for it to be suitable for urban railway tracks were identified. The proposed modifications include the use of a DC current source. The test should be performed on a rail sample fastened to the concrete base, and the current circuit should be closed by the reference electrode installed in the base. Spraying water from nozzles is not applicable for this measurement. The test should be performed under dry conditions and at different water levels (water on the top of the concrete base and on the top of the levelling layer). Different water levels were used to simulate the most common conditions in urban railway tracks built as part of the road surface, where the track-drying process is very slow. The test should not be performed when the rails are immersed in water, because the current flows directly from the rail into the water in such case, and the fastening system has no influence on the measured electrical resistance value. In addition to describing the proposed changes, the calculation of the minimum electrical resistance value that fastening systems in urban railway tracks must satisfy is also presented.

Measures and Prescriptions to Reduce Stray Current in the Design of New Track Corridors

“…In the laboratory measurements of the electrical resistance of the fastening system on a concrete base, the electrical resistance was more than 3 × 10 3 kΩ [50]. Based on the results presented in [49], it can be concluded that in order to prevent stray currents, it is necessary that the metallic components of the fastening systems are not in direct contact with the rail, to prevent current leakage through the fasteners into the track base. This can be achieved by the use of insulating pads between the rail and the clip or by preventing contact between the fastening system components and the track base, i.e., by insulating the anchor bolts in indirect fastening systems like in the Zagreb 21 CTT fastening system.…”

“…When effective drainage is provided in tracks with discretely fastened rails and the rails are not in contact with the electrolyte, each fastening system provides a spot resistance to ground [48], so by using the appropriate type of the fastening system, R tg values can be increased. The electrical resistance of five different types of fastening systems on concrete base is analyzed in paper [49]. The results show that the electrical resistance of indirect fastening systems is significantly higher than resistance of direct systems, with an incomparably higher electrical resistance value found in the sample of continuously fastened rail (Figure 5).…”

“…A laboratory test method for determining the electrical resistance under wet conditions between a running rail with its fastening system anchored to a concrete sleeper is described in the standard EN 13146-5 [51]. The application of such a laboratory test method to determine the electrical resistance of fastening systems used in urban railway tracks is described in [49].…”

“…According to [47], the minimum resistance of one fastener at 500 Vdc shall be 10 MΩ when dry and 1 MΩ when wet. According to [49] , the insulation values as shown in Figure 5, which are variable below and above the 1 MΩ reference values, are determined by the straightforward application of Ohm's law for monitored samples under various wet conditions.…”