One of the main factors in contact force variations between the overhead contact line and pantograph is irregularity on the trolley wire, which can lead to pantograph contact loss and local wear of trolley wires. Thus, from the viewpoint of motor car train track maintenance, development of a high-precision measuring method has been demanded.
The Railway Technical Research Institute (RTRI) has developed a continuous measuring method of trolley wire that measures its inclination using two non-contact displacement gauges. A measuring device is mounted on the maintenance car to calculate irregularity conditions by integrating these measurement results, and measurements are taken continuously while running at about 5 - 10 km/h (Fig. 1). This method enables irregularity measurement on the trolley wire without contact and has the advantage of vertical vibration resistance of the maintenance car. This provides a substantial improvement in precision to within around one tenth of a millimeter, compared to around 1 mm using the conventional method.
Using this measuring method, it is possible to check the characteristics of sag irregularities at hanger intervals, drum winding irregularities of wavelength 0.3 - 1 m, and wavelike wear irregularities of wavelength of 0.1 - 0.2 m (Fig. 2). By conducting a spectrum analysis of the above irregularities, irregular spectral distribution extending over several sections can be clarified.
Since it is possible to estimate the tensile force of the trolley wire, the axial tension of the hanger, the pull-off arm lifting force etc. from the above measurements, factors such as diagnosis of electric wire conditions, error detection and prediction can be developed.