Variability of measured railway track conductance due to test set-up

Abstract

IEC 62128-2 [6] proposes and describes in its Appendix A, section A.3, a track conductance measurement method, shown in the schematic in Figure 1. Its use is suggested in the case of a ABSTRACT One of our previous studies, published in the ACTA IMEKO journal, pointed out the probable variability in track-to-ground conductance measurements due to the use of the method indicated in A.3 of the international standard IEC 62128-2. In this work, the presence of measurement variabilities due to the connection of the negative terminal of the power supply to an earthing electrode instead of the behind section and due to the location chosen for the voltage terminal was proven by on-site measurements. A simulation model that includes undesirable soil conditions is proposed and used herein in the estimation of the correct value of track-to-ground conductance using the measured values.

Stray Current Protection and Monitoring Systems: Characteristic Quantities, Assessment of Performance and Verification

“…Amplitude accuracy. The reliability of the SCMS output does not require extremely demanding accuracy for the measurement of the physical quantities; the standard accuracy for the measurement of track quantities is usually agreed around 1%, although the output of the measurement function even for simple setups is exposed to several non-idealities, as demonstrated in [ 19 , 20 ] for track insulation and insulating rail joint efficiency.…”

“…It is, nevertheless, true that an accurate simulation result stems from a comprehensive description of the system, fed with accurate estimates of all relevant parameters (in particular for rail electrical characteristics, conductance to earth and leakage paths along the fastening system). Low-frequency phenomena can be, in principle, accurately modeled, but there are approximations when the system is quite extended and its electrical parameters are not fully and accurately documented and they may vary with time and environmental conditions: track to earth conductance [ 16 , 17 , 18 , 19 , 20 ] and longitudinal rail resistance (and inductance, for ac railways) [ 21 , 22 ]. Performance of instrumentation under severe environmental conditions is a significant point to consider for instrumental uncertainty, including the characteristics of the electrochemical electrodes used for impressed potential readings at structures.…”

“…Compliance to standards and to contractual specifications is generally required, but demonstration methods are rarely clarified. During test and commissioning, track insulation and impressed potential can be demonstrated following the methods in EN 50122-2 [ 24 ] and EN 50162 [ 25 ] integrated by good engineering practice [ 19 , 26 , 27 ]. When it comes to electrochemical potentials, great care must be given to installation, preservation of humidity and contamination, which are specific to this field of measurement.…”

“…When it comes to electrochemical potentials, great care must be given to installation, preservation of humidity and contamination, which are specific to this field of measurement. An example of non-ideality of measurement methods and of necessary precautions is given in [ 19 , 20 ] for the measurement of track insulation and insulating rail joint efficiency, which are, in principle, well defined and known, covered by standardized methods (EN 50122-2 [ 24 ]). Such methods have intrinsic systematic errors, mostly related to the quality of setup earthing (common problem trackside), to the track length included in the setup and the positioning of voltage measurement points.…”

“…A suitable reference value might be the 5 V threshold of the EN 50122-2 itself, used to specify the track-to-earth conductance limit starting from a current limit of 2.5 mA/m. [19,20,24]; it could be estimated on-line if, besides track potential V te , track leakage current I tl is also available (we will see that the estimate of I tl from the measured track current I tr is quite difficult). An alternative method suitable for tramlines and other at grade lines with minimal infrastructure is the one in Sec.…”