EMD Extended Range Dynamic Braking

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EMD Extended Range Dynamic Braking

Postby Engineer Spike » Mon Feb 27, 2017 9:10 pm

I have noticed that the units with dynamic brakes seemed to do some sort of transition. It seemed to happen at about the speed where normal range DB fades out (10-12 mph). How does this work? Is extra resistance added somewhere, or does the circuit between the motors, and the grids change, as in parallel-series?
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Re: EMD Extended Range Dynamic Braking

Postby Pneudyne » Tue Feb 28, 2017 4:20 am

As far as I know, extended range dynamic braking with DC traction motors is obtained by reducing the braking resistance in several steps starting at the speed at which regular dynamic braking is starting to reduce, and progressing as speed further reduces.

I do not have any EMD curves on hand, but the attached set provide a general illustration. At each resistance reduction, there is a significant spike in traction motor current, which might be felt on the locomotive as being much the same as a power transition spike.

Extended Range Dynamic Brake Curves.png



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Re: EMD Extended Range Dynamic Braking

Postby WVU » Thu Mar 16, 2017 6:33 pm

Maximum Dynamic Braking on the EMD Dash 2 Locomotives will happen in the area of 24 to 28 mph with 700 Amps on your Loadmeter if things are set right. What Extended Range Dynamic Braking does is this, it shorts out Grid Resistance to enable you to have greater dynamic braking effort at lower train speeds. Step 1 will pick up in the area of 19 mph +/- and Step 2 will happen around 14 mph +/- and Step 3 will come in around 8 mph +/-. By this happening, it will allow you to have up to 700 amps of grid current at these lower speeds other then only having it at 24 to 28 mph. This by the way is not being controlled by the Axle Alternator, it just so happens in these speed ranges but this is controlled by Traction Motor Field Amps and Dynamic Braking Grid Current. When the Traction Motor Field Amps are greater then the Grid Amps, extended range contactors will pick up and when Grid Current becomes greater then Traction Motor Field Amps the Extended Range Contactors will drop out. Traction Motor Field Amps are set for 960 Amps and the Grid Current is set for 700 Amps.
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Re: EMD Extended Range Dynamic Braking

Postby Pneudyne » Sat Mar 18, 2017 2:07 am

Thanks for that. I’d guess then that the general form of the EMD extended dynamic range braking curve would be similar to the example that I posted, with a spike at each point where the grid resistance is switched.

I was not aware that the extended range switching of grid resistance was done by measuring the current differential between the grid current and the field current.; I had assumed that it would have been controlled by speed as measured by an axle alternator. But the current differential approach is rather neat, as then the braking is being controlled by actual events rather than by an assumption of what is happening at a given speed. It is one of those things that looks obvious once you know it, but that you don't think of when you don't know it!


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Re: EMD Extended Range Dynamic Braking

Postby WVU » Sat Mar 18, 2017 1:24 pm

Even though EMD was comparing Field Amps to Grid Amps, GE and the CSX new rebuilt 38-3, 40-3 and 50-3 units do use the axle alternator or speed probes to control Extended Range.
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