stan2004 posted:Ponz posted:...
Would someone please explain, in simple terms, how this would happen? If a train derails and a short occurs, doesn't all power (juice) stop at the pickups even if the transformer's circuit breaker takes a few seconds to trip?
Correct. The electrical short itself between the center (hot) rail and the outer-rail means there is 0 Volts between the two rails. The harmful transients are caused by the rapid change in current when the short initially occurs and even more so when the short is removed by the breaker/fuse.
I've posted this video before in different OGR threads showing a surge detector in action. There are 2 red LEDs. One flashes when there is a positive surge on the track, the other flashes when there is a negative surge. The screwdriver is simulating shorts. So while the screwdriver straddles the rails, the voltage between the rails is 0. No harm to the electronics from 0 Volts. It's the brief moment in time when entering and exiting the short where transients occur. All has to do with energy transfer in electromagnetic fields - very tedious math.
Since there is no electronics-harming voltage transient across the rails during the short itself, it doesn't matter if the breaker responds to the short in 1 sec or 2 sec. It's a separate discussion about why you'd want a faster vs. slower breaker.
Thanks Stan. That was a great explanation. Now this begs a question. Marty, above, as others have suggested, buying a modern transformer. Even if a modern transformer breaker trips much faster than an old ZW wouldn't there still be a rapid change in current when the short initially occurs, as you stated?
I've attached a couple of transient voltage protectors to the common and positive posts on the transformer. So - wouldn't those and an in-line fast-blow fuse, between power and track suffice?
Also - Modern / smart equipment requires 18 volts to the track and the remotes take over from there. Why would not an old ZW put out the same 18 volts and serve the same purpose regarding modern circuitry bearing equipment?
I'm not trying to be argumentative. I'm just trying to completely understand.
Thank you - Ponz
