This concept is interesting to me but leaves a few questions. When dynamics are applied, I would imagine power is cut from the prime mover and the power that is now generated by the motors is shunted to the cooling grid? Am I close to being right?
I think that it is a “heating grid” which is then cooled by fans, but I think you’ve got the basic idea right.
So I’d imagine there’s a series of relays that when the brakes are applied, power is disconnected from the generator and feed to the heating grid?
Yes, that’s essentially true. When switching into (or out of) dynamics in our Alco’s, there is a very pronounced sound of relays and contactors operating in the cabinet in the back wall of the cab.
Steve will be amused to know that on some railroads making transition in Alcos was called the ‘hunting season’ because of the scattered rifle-shot pops as the relays and contactors did their thing not quite in sync. Presumably the effect is similar engaging dynamic…
Incidentally, the Diesel prime mover may be operating at a ‘power’ notch while the engine is in dynamic. This is to give better reliability to some fan drives – there is a temptation like that of regenerative braking in electrics, to try using the ‘free’ power from the motors to run the various fans and auxiliaries, which in theory would let you idle or even shut down the prime mover to save fuel or wear and tear. It may be instructive to study why this was never implemented successfully on American road power…
Regenerative meaning you’re using the brakes own bi-product to cool itself? Interesting. It appears there’s never a dull moment in railroading.
I believe, and I’m not a Engineer, that on todays AC’s with extended range Dynamics - the prime mover gets notched up to generate a higher field strength to provide the higher braking force. I could be wrong. Additionally a higher notch on the prime mover also operates the various cooling fans (traction motor & dynamic braking grid) at higher speeds thus generating a higher volume of cooling air.
Regenerative braking is a technique used in straight electrics. The motors are set up as generators and the electric current produced is fed back into the catenary.
A few things about dynamic braking:
The difference between dynamic and regenerative braking is what happens to the electric power generated from braking. In regenerative braking, the power goes back to the source (trolley wire, third rail or battery), while dynamic braking the power is dissipated in resistors.
On locomotives with DC motors, the motors are turned into generators by separately exciting the field windings by a generator (or alternator) driven by the prime mover. Braking ability falls off at low speeds because the armature falls off with decreasing speed.
On locomotives with inverter driven induction motors, the drive frequency is set less than synchronous frequency and the motors become induction generators. That is the rotating field is rotating slower than the armature. At sufficiently low speeds, the rotating fields needs to revolve in the reverse direction to provide braking torque, meaning that braking effort can take place at zero speed.
This was particularly important for railroads like the Milwaukee, where downgrade trains could help power the upgrade trains.
Capital costs notwithstanding, it was free power.
Can the lead loco control the dynamics of the other DPU’s?
I recall reading about the Milwaukee’s running their first freight over the electrified “Western Expansion” from east to west generated enough power on the downslope to cover all but some minor single dollars’ worth of power needed for the entire trip. I remember when I toured the NYNH&H RR’s Cos Cob power plant with its manager in the 1950’s that all that regenerative power was factored into the management of the power flow and its “cleanness” or balance in the catenary.
Of course, the practical issue soon arose that the trick required an actual ascending freight to be present and operating precisely in sync with the descending one. Aside from traffic conditions on the PCE it would be difficult in practice to coordinate this…
The reality was that Montana Power’s laod base was large enough that the Milwaukee could use it as a battery.
By 1918 it was clear that the real cost saving from regeneration was from the reduction in brake wear and accidents.
It was in “The Electric Way Across the Mountains.” After that first run, the power company owed the railroad (IIRC) a $1.40. The railroad had an agreement for the power company to buy back any electricity produced. Not all power companies agreed to that option.
Jeff
Yes. Either in sync mode with the lead control or, with the ‘fence up’ independently from the head end. The only thing that can’t purposely be done is to put the DPU(s) in dynamics while the head end is in power.
Jeff
Amusingly, though, it is perfectly possible to set the DPU up to turn the other way, actively powering when the head end is in power; there is at least one kooky Canuck crew that did this with interesting results for the two units involved… I think I heard the story through Bob Smith and he will remember the details even if he’d really rather not from love of country [;)]
If you mean to set up the DP consists in a way that they want to pull away from the lead control unit, yes. It’s happened accidently a few times that I’m aware of. I pulled one like that some years ago.
Went over 150 miles. Even started out from a stop on the subdivision’s ruling grade, without pulling it apart. I knew the DP wasn’t loading right. It would load, then drop it, then start loading again, but never to full tractive effort. I talked to locomotive maintenance and they thought it was dirty fuel filters. We even picked up a MOP (Manager of Operating Practices-AKA road foreman of engines) who didn’t pick up on what was really wrong. When we reached the crew change, a mechanic came out and changed the filters.
I talked to the outbound engineer a few weeks later. He told me they were still having problems when they were stopped about 60 miles down the road. When he started out, he started up the DP first. It started going backwards and he realized then what the problem was.
Back then, except for starting the
back when we still had the Harris Box there was a little trick that could be used that would allow the rear DP unit to be in Dynamic brake mode while the lead controlling unit to be in power, couldnt do it after the DP system was built in. whenever we first linked up a DB consist we would do a “bump test” to confirm the direction the DP consist was set up .