MEASUREMENTS AND ANALYSIS OF ELECTROMAGNETIC INTERFERENCE IN A RAILWAY SIGNAL BOX - A CASE STUDY

In general railway infrastructure operates in a complex and non homogeneous environment where low power electronics has to function in the similar environment as large voltages and currents from the trains. The environment close to the railway tracks is heavily polluted by electromagnetic (EM) noise from the railway systems itself. The reliability of the railway signalling-, communication-, and control system depends on the degree of isolation from EM noise. It is important to observe the real system and its characteristics in real situation. The complexity of the infrastructure is not easy to simulate or calculate, and therefore measurements were performed on real system in operation. A large number of measurements were made on site at signalling systems and installations of Banverket (the Swedish Rail Administration). By studying and analyzing these measurements, the extent of EMI (Electromagnetic interferences)-related faults can be estimated. In situ measurements must be performed on systems that have obvious problems show increasingly fast and high transients in a DC signalling subsystem. The statistics also show an increased activity of transients during a period before a certain circuit in this system gets out of order. The presented results clearly show how the electromagnets interference effects he signalling system in a signalling box. The measurements in this case study have provided new information on a railway subsystem and have revealed frequencies that are difficult to explain at this moment.