13. Simulated quantitative evaluation of lightning protection measures for signalling equipment

• The RTRI proposed a lightning surge analysis model for the quantitative evaluation of lightning protection measures applied to signalling equipment installed near rails.
• It also performed an experiment to confirm that the model offered was sufficiently accurate for practical use.

The increased adoption of electronic signalling equipment in recent years has resulted in a higher incidence of lightning damage, which in turn has required that effective countermeasures be established. To validate the effects of such countermeasures, it is currently necessary to perform comparatively large-scale experiments, which are time-consuming and expensive. The fact that grounding resistance and earth resistivity significantly affect the experimental results is also a problem.

In order to quantitatively evaluate lightning protection measures without carrying out experiments, RTRI proposed a lightning surge analysis model that could be used to calculate lightning surge voltages and lightning surge currents with a focus on level crossing equipment, which is particularly susceptible to this type of damage from lightning (Fig. 1). The set-up consisted of a surge propagation model along rails (as rails are one of the main conductors on railways) and an equivalent circuit model for the equipment. Experiments confirmed that the lightning surge analysis model offered a suitable level of accuracy for practical use (Fig. 2).

Countermeasures for lightning damage were also evaluated using the proposed analysis model on grounded electronic train detector surge protection devices which are normally non-grounded. Grounding the devices reduced lightning surge voltage to at least half its present value for a lightning current of the same magnitude, thereby doubling the lightning impulse resistance of the electronic train detector (Fig. 3). As a result, it is estimated that the probability of lightning damage occurring can be reduced to 1/5 of its present value.

This lightning surge analysis model is applicable to signalling equipment installed near rails.

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  Fig. 1 Lightning surge analysis model of level crossing equipment
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  Fig. 2 Experiment to evaluate model performance
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  Fig. 3 Effect of lightning damage countermeasure