Regen brakes to be tested at last

[Foghut]

According to issue 585 of Rail magazine the Southern has started Regenerative braking tests with its Class 377s on the line between Dorking and Horsham. Results are to be knwon in the Spring, whenever that is.

Fellow company SouthEastern is also 'investigating' Regen braking on its Electrostar fleet.

If both companies decide to instigate this form of braking it will be the largest type in Europe, involving 329 EMUs.

(There's no mention of SouthEastern's 465/6 Networker fleet which is also capable of this mode of working).

HTH
Foggy

[pavorossi]

Could someone please explain what this regenerative braking is all about?

[EuroStar]

I don't know much about it but have found something here:

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

HTH
EuroStar

[pavorossi]

Thanks for that Eurostar.

[Foghut]

I've never driven 375s but I did use to sign 465/6s which are similarly configured.

The process that is occurring here is.

1) When the driver applies the brake, the train initially applies the friction (disc) brake at 100% force, ie a step 2 application would give 2 bar brake pressure.

2) Rheostatic or regenerative braking will then be progressively introduced. By changing the excitation field of the AC motors and putting a load across them it is possible to extract energy from them and thereby slow the train down. This is very effective and is usually much better than disc brakes. Engineers tell me that strictly speaking this is not the same as "reconfiguring the motors to become generators", so I have avoided using that expression (I hope !).

3) On DC systems the train will return the energy back into that electrical section ONLY if there is another train taking power out. This is Regen braking.

4) If there isn't anything to absorb the power, the train will revert to Rheostatic braking - whereby the power is dissipated by the train's own resistor bank.

5) Once either of the two dynamic braking techniques is established, the friction (air) braking drops to a holding level (usually about half a bar pressure). This system of mixing dynamic & air braking is called brake blending and the system works to ensure that the required braking force is always maintained.

6) If the train passes over a gap in the third rail or the Traction Current is interrupted for any reason the Brake Blending valve will reintroduce full friction braking. Similarly if the driver puts the controller into Emergency Brake the dynamic brakes are excluded and 100% friction braking is used.

And finally, a little bone of contention with the above mentioned Wiki definition at http://en.wikipedia.org/wiki/Regenerative_braking
In Europe, Both rheostatic and regenerative come under the heading of Dynamic Braking, because they only work whilst the train is moving....hence the name dynamic. For the same reason it's important to understand that if the train is at a stand only friction brakes can be used.
I don't know whether the author of the article was confused or maybe it's different in the US. Over there they first had Rheostatic braking on their lovely great diesel locos, and so the name Dynamic came to be associated just with Rheo.

HTH,
Foggy

[Trev]

Is this the same system that was used on the MSW 1500vdc lines?

[Foghut]

Hi Trev, I don't know anything about the MSW 1500V locos. All I could find was a link.....http://www.27000electra.co.uk/tec.html

I couldn't see any reference there to them having Dynamic braking, so I can't say either way ?

One thing's for sure though - These modern units (37x/46x) are using AC motors, so they've got some fiendishly complex control systems, which are only possible with microprocessor electronics.

It's possible that the Electra locomotives could have had their DC motors configured to work as a retardation system - do you know anything more about this ?

Cheers,
Foggy

PS - Looking at the photos on the above site scared the living daylights out of me, as I see that it's possible to raise the Pantograph on one of these locos without there being a catenary system above. If you try this on some modern traction units you will seriously damage the gear as it will over-extend, and then the Automatic Dropping Device will bring it crashing back down in a heap of tangled metal.