25kV overhead supply

[glowinganode]

Does any body know, or care to speculate how the three phase supply from the 'grid is converted into the single phase overhead traction supply?
Were M-G sets ever used?
Cheers,
Rob.

[Tedzed1]

Hello Rob, you might find this interesting:

http://en.wikipedia.org/wiki/25_kV_AC_ra...rification

and This:

http://en.wikipedia.org/wiki/Traction_substation

http://en.wikipedia.org/wiki/Railway_ele...ion_system

http://en.wikipedia.org/wiki/Railway_ele...at_Britain

[glowinganode]

Thanks Paul.
It seems that three phase to single phase conversion is (was) popular on the continent, but not here.
Many thanks, Rob.

[ed731pdh]

It depends on where you are and the kit installed. They tend to use one phase for one direction from the substation and a second in the opposite direction with a neutral sectioon between to keep the phases apart. The third phase is not normally used for traction. DC substations have rectifiers but in the old days rotary convertors were used to create a raw DC current. You usually find DC substations around 3 miles apart compared to 20-25miles for AC due to the poor efficiency of DC 3rd rail traction.

MG/MA sets are not normally used under AC conditions unless the stock is dual voltage in nature but even MG/MA sets are being phased out for solid state equipment. One exception, there is a rail in Namibia that is 25kv overhead but the locos have MA sets because of the long power sections, the volys drop down to as little as 15Kv mid section so the MA ensures the auxiliaries work correctly.

Much more impressive, look up DC booster sets, very clever design.

[glowinganode]

It depends on where you are and the kit installed. They tend to use one phase for one direction from the substation and a second in the opposite direction with a neutral sectioon between to keep the phases apart. The third phase is not normally used for traction.

Thanks, that's answered another question too.
Rob.

[ed731pdh]

Quite a clever system to keep the phases apart. You get the live 25kv supply joining onto 100m of dead wire, then 100m of wire covered with ceramic beads, then 40m of dead wire (100m on bi di lines) followed by the live 25kv supply. On the ground are two sets of APC magnets (yellow boxed), one at the entrance to the neutral section, the other at the exit. The train has a sensor fitted at bogie level that opens an air blast or vacuum breaker on the power car when it runs over the first magnet, cutting off the supply to the power car. The second magnet cuts the power back in. Quite a simple system, but can be overidden by the driver using the reset button on the desk.

The more modern traction uses electronics to wind down the power as it goes over the magnets although it is always good practice to manuall power down on the approach. On the WCML, when we had AC locomotives, the 25kv feed went straight into an AC autotransformer with the output being controlled by a hand notched tapchanging switch. Power was taken by notching up or down the transformer outputs in order to achieve the desired control. Running down for a neutral section was usually initiated a mile from the neutral section, at 110mph you would be on the section in around 30 seconds, followed by shutting off just before the start of the section. We had a notorious one at Hatch End, the rule was to start running off the taps when you saw the white public house by the canal. One weekend it was repainted pink and a number of trains went though the section under full power, pulling the 25kv line breakers, extreme arcs from the pantographs, and in some cases causing severe locomotive and infrastructure damage. You just didnt mess with 25kv, it was unforgiving.

[ed731pdh]

Found this, you can see the four traction motor ammeters and notch indicator to the rear.

http://album.atomic-systems.com/showPic....86Cab3.JPG

Normal driving technique for a 5000hp Class 86 or 7000hp Class 87 was to drive with the ammeters just peaking into the red.

[ed731pdh]

Or this video, watch the ammeters as the loco gets a workout.

http://www.youtube.com/watch?v=2fmtFYpRBSc

[glowinganode]

When I last did my PTS we were warned never to interfere with "red bonds".
Here's why...
The guy on the right's an effing idiot, not aware the running rail could now be live?
Rob.

[ed731pdh]

You only hit the jackpot once.