Nostalgia & History > MILW Electric Question

Let's say a MILW electric locomotive set was bringing a train down a hill in regenerative braking. Then a tree or landslide breaks the wire between the train and substation. Would the loss of the circuit result in a sudden loss of the regenerative braking?

Ted Curphey
Ontario, OR



Edited 2 time(s). Last edit at 06/08/15 05:20 by funnelfan.

The train would nearly always be between two substations so if the line ahead was severed the line would likely still be hot to the substation behind the train if the line had not gone to ground.

Posted from Windows Phone OS 7

Good question Ted.  fbe, please explain how a substation used the power the regen was producing.  I thought another train needing the power was necessary.

Marty Bernard

MartyBernard Wrote:
-------------------------------------------------------
> Good question Ted.  fbe, please explain how a
> substation used the power the regen was producing.
>  I thought another train needing the power was
> necessary.
>
> Marty Bernard

Marty... I know that the Milwaukee was a DC system, but i think the operation is similar... The short answer is ya either have other locomotives usin the power; or ya simply "waste it" by running it thru large resistors... The Virginian and N&W electric grid used water type resistors in the river to dissapate any extra power; but they were "captive" systems that generated their own power...

As i remember; the Milwaukee system obtained power from an outside utility grid; they (...Milwaukee...) may have been able to "motor" with their convertors and return power to the utility power grid they were tied to, just like a normal power generation grid would work...

.Hope this helps a bit...
leroy

MartyBernard Wrote:
-------------------------------------------------------
> Good question Ted.  fbe, please explain how a
> substation used the power the regen was producing.
>  I thought another train needing the power was
> necessary.

No. When regenerating, the excess voltage drove the substation generators like motors. This forced rotation would cause the synchronous AC motors to generate alternating curent. This current flowed into the AC power grid back to the utility and ran the KW-hour meters backward, affording a credit for the railroad on power usage.

A heavy EB train on Butte Hill would regenerate more power on the long downhill 2% than it used on the 1.66% uphill. Likewise, a heavy WB train in the Bitterroots would regenerate more power on the long east side downgrade than it use on the shorter WB grade. Such trains had negative fuel costs.

A big reason why it was very hard to justify getting rid of the electrification and why it lasted until the tentative deal with BN required its removal.

Best regards,

Rob L.



Edited 1 time(s). Last edit at 06/08/15 10:11 by rob_l.

>When regenerating, the excess voltage drove the substation generators like motors.

Yes, although they were motor-generator sets, not generators.

>This current flowed into the AC power grid back to the utility and ran the KW-hour meters backward, affording a credit for the railroad on power usage.

The meter(s) didn't run backwards; there were separate meters which measured the power returned for credit.

Regnerative braking won't work unless there is a load connected to the trolley wire out there somewhere. So if the OP was asking whether the regenrative braking would work if there was a loss of trolley power, the answer is no (for the MILW, the VGN, and the N&W).

In the motor generator sets in the substations the DC generators became motors used to turn the AC motors which were used as AC generators. These were synchronous AC motors and would synchronize the frequencies of their output to that of the AC line they were connected to. The substation operator would reduce the DC line voltage below 3300 vdc so there was 'room' for the regeneration amperage in the overhead.

The common rule of thumb was a train in regeneration could provide about 60-66% of the power needed to lift a similar train up the other side of the mountain. So two trains in regeneration could lift one train up the grade without any commercial power consumed. Three down trains might lift two up the grade though MILW traffic was rarely high enough to test the equations out.

Both the Milwaukee Railroad and Montana Power were owned by Rockefeller interests. Both the electrified Milwaukee and the Anaconda Copper Company, also a Rockefeller property, provided a stable industrial base to finance the infrastructure to get Montana Power off the ground.

It made sense to return regeneration voltage to the AC transmission lines rather than using resistance grids to dissipate useable capacity when it could supply the copper company or sold to the public.

Posted from Windows Phone OS 7

To further answer your question, there was little risk of a runaway of the train if the line voltage was lost. Engineers ALWAYS set a minimum reduction when topping over the mountain even if were not needed to handle the tonnage going down. That way if regeneration was lost the train brakes were already set and warmed up. A smaller further reduction could be made to keep the train under control or bring it to a stop. If the line voltage was gone as indicated by gauges in the loco cab there was no motoring available either, the air compressors would not run to prevent the brake pipe from leaking so stopping the train either downhill or uphill was the recommended practice.

The engineer monitored the line voltage on his meter since there were no radios in most substations or with the dispatcher.

Posted from Windows Phone OS 7