Power in railway rolling stock originally involved traction, lighting and rudimentary signalling with typically raw 110VDC from the on-board batteries.
Switchgear on the DC bus did not have surge and transient limiters on the basis that they would degrade with time and couldn’t be guaranteed to always function so individual equipment had to stand the full level of overvoltages, drop-outs, and surges that resulted. It didn’t matter though that the lights occasionally brightened or dimmed.
Today it’s very different, modern rail vehicles are packed with electronics for communications and control with passengers also increasingly expecting cellular repeaters and Wi-Fi services with ‘clean’ AC mains and USB DC power available at each seat.
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