Cascade Protection Scheme for Wayside Signaling Surge Protection

Damage from lightning and transient over voltages cost railways millions per year. Exposure to the forces of lightning is unavoidable in the rail environment. To protect (and mitigate damage to) critical network equipment, an approach whereby surge protection devices (SPDs) cascade across electrical and electronic components that work in conjunction to provide greater protection and coverage is recommended. This paper will introduce an enhanced protection scheme through a Cascaded Surge Protection (CSP) system, which includes discussion on surge protection device specifications, recommendations for SPD selection and information on wayside signalling applications. The primary goal of the ‘cascaded protection scheme’ is to reduce the voltage experienced at the equipment to be protected during a transient event, by reducing the voltage at each SPD stage. Robust electronic equipment, like motors and switches, can sustain energy behind a first stage of protection whereas more sensitive electronics, like signalling and measuring devices, should be placed behind a second or even third stage of surge protection.