Modern systems usually have a UPS (Uninterruptible Power Supply) to maintain the supply if there's a power loss. That wouldn't have been practical back when the District was signalled though (1950s?)
Even in the 1950s, battery stacks were common in railroad signaling systems. More likely that some bright-eyes thought the electric supply was reliable enough (ahem, cough) or they didn't like the cost of enough batteries and maintenance. Or... did they use AC track circuits at the mains frequency?
Come to think of it, none of the books I have about UK signalling practice, not that I have many, mention backup power. is the District line signalling based on AC or DC circuits? (Which sends me at various web sites to find out.)
Post by principlesdesigner on Apr 3, 2018 3:50:07 GMT
The District line originally used AC track circuits, and in some areas still does, the frequency of these tracks was 33 1/3Hz. The signal relays, trainstop valves, points valves & detection etc. are also AC.