I like the idea of the third rail at ground level it's aesthetically more pleasing than gantries . But why does it need to be constantly energised ? Only small sections need to be say 0.5 mile to 1 mile segments. Similarly the underground should have the section close to the station deenergised except when the train is present.
Cyclist hospitalised after riding across live rail
- Thread starter Fordulike
- Start date
I reckon the cost of doing that is the reason. I don't know what would be involved to switch large currents of DC voltage on in small track sections, but it does sound very expensive.
Train travel is expensive enough as it is, without the companies passing on that cost to us.
The trouble with the third rail system is it's low voltage DC inefficiency and low speeds, compared to the 25 kV AC overhead system.
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Except it's not switching large currents. When the train has not arrived at the segemnt there is no current and when it has passed there is no current.so no arcing . Sort of like a giant Hornby trainset
I was thinking more of the cost of the circuitry to perform the switching, whether that be some kind of relay array etc..
As I say, I really don't know how they would perform selected track switching.
Anyone???
I think it would actually be very doable. It would need a third insulated power line running the length of the entire line and a number of electromechanical relays with nice big contacts for each segment .As d8veh has pointed out the currents are a bit large for semiconductors, and in any event the switching is very low speed . Using modern computing techniques, each relay would be addressable an switched in as required. Train management would know where on the line the train actually was. The insulated cable could also serve as a supply to remote hamlets etc.
And flecc, I am not sure of the advantages of AC versus DC in this context. There has been significant advances in the role of DC transmission , particularly HVDC over long distances in recent years. The latest UK Ireland undersea interconnector commissioned is HVDC . The key has been in the development of very high power, high voltage semiconductors used in static invertor.
Because it's private land the American idiot was trespassing, and as it is private land, the train operating companies can do what they want: In many high density traffic areas (in most cities for example) the trains already run head to toe at maximum capacity with a train in every section. There is no opportunity or even a point to "switching current off and on".
But there are idiots with total disregard for both the law and personal safety everywhere:
Agreed, but using HVDC the current losses from a ground level bolted down open rail could be considerable.
The installation costs would probably pay for an overhead system gantry system, not suffering the losses and considerable safety problems of surface level HVDC.
But apart from all technical considerations, no new ground level system would get acceptance. The only reasons the present Southern system is permitted is that it so long preceded modern safety standards and the high cost of replacing it.
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That was horrific. At least the end was quick!. Was he an idiot or was he just ignorant?. It is easy to assume that everyone is aware of the risks.
But coming back to more technical details, while the uk train system may be congested, there is nothing like a train every minute so that probably 80% to 90% of the railroad is unoccupied at any time. The congestion is done to none optimum scheduling.
The decision to use 500v as the transmission voltage, must refer back to the dawn of electrical engineering where insulation was much poorer than now. With every doubling of voltage , the transmission power loss will drop by a factor of 8. , So even a 1000v rail would be significant.