Power for trains, what system?

anamorph · Post by **anamorph** » Tue Dec 09, 2003 8:56 pm

We know dynamos are used on coaches to charge batteries etc, but with todays technology I wonder how much use could be made of high efficiency dynamo/generator combos on trains, that, once up to speed, may be able to power the train completely?

thedarkness · Post by **thedarkness** » Tue Dec 09, 2003 9:19 pm

Similar idea to dynamic braking?

jdjonny · Post by **jdjonny** » Tue Dec 09, 2003 9:26 pm

It's called perpetual momentum, and is physically impossible as power is always less than the physical energy put in...you wouldnt be able to keep it up to speed.

Has been tried by many of the worlds great physicists to no avail, so I hardly think that the likes of bombardier will get the hang of it, lol

JDJonny

nightbeaver911 · Post by **nightbeaver911** » Tue Dec 09, 2003 9:28 pm

What exactly does dynamic braking do (im aware that it slows the train) but why use it over regular brakes, and when is it most commonly used?

thedarkness · Post by **thedarkness** » Tue Dec 09, 2003 9:35 pm

Most new trains have it.
Its something to do with passing the current generated by the turning of the motors, backwards through the motors, so slowing the motor itself, instead of slowing the motor by applying friction brakes to the driving wheels.
Most new units have it, but it only works above 3mph, you have to have a friction brake back up, it has different types.
Regenerative braking - the current goes backwards through the motors, and back to the power supply, ready for use by the next train
Reostatic - The current is shunted off through a resistor

I believe it gives a far better stopping distance than friction brakes.

jdjonny · Post by **jdjonny** » Tue Dec 09, 2003 9:37 pm

better? I thought it was smoother but slower.

but then, the locos I know inside out don't boast dynamic braking, ie. 37142, 50042 etc

JDJonny

Post by **martinhodgson** » Tue Dec 09, 2003 9:46 pm

I think dynamic braking is similar (in theory) to engine braking in cars.

anamorph · Post by **anamorph** » Tue Dec 09, 2003 9:51 pm

But, even so, surely a proportion of this current could offset engine power needed?

chriscooper · Post by **chriscooper** » Tue Dec 09, 2003 10:39 pm

The advantage of Dynamic braking is that it reduces brake wear, and also reduces brake fade, where braking power is lost as the brakes heat up. It is especially useful for heavy trains on steep downhill gradients where the brakes need to be constantly applied to keep below the speed limit (such as on the loco's used on the woodhead route (when open), and the channel tunnel). It is also useful where trains are starting and stopping regularly such as on rapid transit systems, and rheostatic braking was fitted to trams very early on, although London Underground didn't adopt the system until the 1960's (1967 stock on the Victoria and C stock on the Circle). Another advantage for underground systems is the reduction of brake dust in the tunnels. The first use on British mainline loco's was on the Woodhead route as previously mentioned (regenerative braking) and rheostatic braking was fitted to the all the AL series locos used on the WCML electrification. The first mainline units with rheostatic braking were the PEPs (prototype electop pnumatic) which were the prototypes for the 313, 314, 315, 507 and 508. Since then every EMU, DEMU (voyagers) and Electric loco (and maybe some diesels) have been fitted with rheostatic braking and recently since the introduction of electronic control, regenerative braking.
On the main subject of the power in dynamos being used to power trains, this was how early southern region electric loco's were powered. A motor turned a dynamo, the output of which could either be added to or subtracted from the line voltage and sent to the motors, hence the name Booster locos. This had 3 advantages over traditional DC control systems. Firstly their was no need for large resistors for power control. Secondly due to the lack of resistors all power notchs could be used constantly rarther than only being able to hold notchs where no resistors were in the circuit. Thirdly the dynamo continued to turn after the line power was lost so trains wouldn't "gap" at brakes in the live rail, and it even enabled them to run in none electrified sidings as the momentum of the spinning dynamo could provide power for quite a time.

slipdigby · Post by **slipdigby** » Tue Dec 09, 2003 11:51 pm

anamorph wrote:But, even so, surely a proportion of this current could offset engine power needed?

Part of the Parry People mover technogy centres around flywheel energy storage. The flywheel was charged from a short bit of low voltage 3rd rail at stations, with the tram using the flywheel's energy to propel itself. On braking, the energy was used to charge the flywheel. Neat bit of technology looking for an application that.

Slip

jimbob · Post by **jimbob** » Wed Dec 10, 2003 12:38 am

anamorph wrote:We know dynamos are used on coaches to charge batteries etc, but with todays technology I wonder how much use could be made of high efficiency dynamo/generator combos on trains, that, once up to speed, may be able to power the train completely?

I think you mean motor alternators or MA's to their friends, dynamos were on Mk1's but Mk2 (dont know about early ones ie a/b/c but d/e/f are!) & upwards are definatly MA's

Christopher125 · Post by **Christopher125** » Wed Dec 10, 2003 8:00 am

Hi

one other thing, in this country Dynamic/Regenerative brakes usually work in conjunction with other brake systems, while in other countries like the USA, Dynamic brakes can be used separately, meaning it is easier to not realise they are being used.

Chris

nwallace · Post by **nwallace** » Wed Dec 10, 2003 7:29 pm

Reostatic - The current is shunted off through a resistor

Bloody hot resistor then.

Non-Electronic speed controllers in radio controlled cars use a resistor to use up the extra energy when your not going full tilt, problem is they are almost allways mounted in the easiest places to put your hand.

Removed one from one of my cars to replace with a cheap electronic speed controler but i didn't bother to get one of them for my new car, unfortunatley i didn't think about where i was putting the power switch on that one and put it on the wrong side... right next to the resistor... Douh.

jimbob · Post by **jimbob** » Thu Dec 11, 2003 1:12 am

nwallace wrote:Reostatic - The current is shunted off through a resistor

Bloody hot resistor then.

Non-Electronic speed controllers in radio controlled cars use a resistor to use up the extra energy when your not going full tilt, problem is they are almost allways mounted in the easiest places to put your hand.

Removed one from one of my cars to replace with a cheap electronic speed controler but i didn't bother to get one of them for my new car, unfortunatley i didn't think about where i was putting the power switch on that one and put it on the wrong side... right next to the resistor... Douh.

Yeah they do get quite hot, you want to stand next to the vents from the resistor banks on an 86 after its just done a run from norwich, very nice on a cold winters day, in summer its a whole different story!

nwallace · Post by **nwallace** » Fri Dec 12, 2003 12:17 pm

Jsut noticed something else.

Dynamos produce a DC Current
Alternators produce an AC Current

Using a Wheatstone bridge or similar AC can be changed to DC.

Advantage of using AC in carriage is that you can produce 230VAC which is conveniently what most electrical current in this country is made for so Microwaves, mobile phone chargers can work off it.

Problem is you have to be able to provide enough energy for whats being run. So while phones and laptops aren't particularly power hungry i think virgin woudl get a bit pissed off if you tried to use a microwave at your seat on a voyager.

Whats done on Pendolinos? Do they step down the power from the OHL or is the power generated?

Niall

Atomic Systems

Power for trains, what system?

Power for trains, what system?

Re: Power for trains, what system?