Ensuring safety in rolling stock electrical storage and propulsion systems while maintaining the highest possible availability of equipment depends on identifying and dealing with faults at the earliest opportunity.
Operational equipment that cannot tolerate shutdown or failure is often designed as an ungrounded electrical network. This allows systems to continue running even if an insulation fault occurs, as eliminating an earth connection ensures the first fault current is typically not at a dangerous level, so it doesn’t cut out by tripping the circuit breaker. Instead, the system delivers an audio or visual alarm that ensures the fault is addressed before it escalates and causes problems.
A second fault on the same system changes the situation, because the fault current may reach a level where it could prove harmful or pose a fire threat. That makes it crucial to identify and rectify a first fault while the system can continue to operate.
Many critical ‘no fail’ industrial applications employ ungrounded systems, where unplanned shutdowns or failures can jeopardize safety and incur financial penalties and reputational damage.