The European railway companies had hundreds of single phase AC commutator motored electrics with dynamic braking. A batch of the Swiss Ae 4/7 electric locomotives built between 1930 - 1932 by SLM with electrical equipment by Machinenfabrik Oerlikon had dynamic brakes for service on the Gotthardbahn. With these being contemporary with the GG1 I am sure that dynamic braking ability could have been installed at that time.
beaulieu With these being contemporary with the GG1 I am sure that dynamic braking ability could have been installed at that time.
With these being contemporary with the GG1 I am sure that dynamic braking ability could have been installed at that time.
My guess is that the PRR didn't see the need for dynamic braking, figuring that it was only helpful for mountain railroading. IIRC, it took many US railroads a couple of decades or so to realize that dynamic brakes are a good thing even on low grade lines.
The obvious way of implementing dynamic braking with AC series motors is to treat them as DC series motors - i.e. provide DC excitation to the field coils. I wasn't aware of the Swiss using dynamic braking, but it does make sense that they would want to do it.
- Erik
Paul_D_North_JrThe twin motors in the geared quill drive: Would they have been 1/4 cycle out of sync with each other - kind of like the quartering of steam locomotive drivers for timing the cylinder strokes - to prevent both motors from being at zero torque at the same instant ? With that (presumably) sinusoidal variation of torque on each motor being offset by the 1/4 cycle, the sum of the torque from both motors at any instant would always be in a higher and narrower range, around 0.7 of the max. torque of any 1 motor as i'm recalling those kinds of things. This kind of explanation is what's sadly lacking from almost all of the 'stuffed and mounted' displays of locomotives. When I was too young to fully appreciate it, i was on a tour of the PRR's Electric Locomotive Shop in Wilmington as part of an NMRA Mid-Eastern Region convention. There were many parts spread out over the floor and well-labeled, and people to answer questions . . . Something like that should be done with the displays of the 'guts' from the electric locomotives. None of the GG1's would be less for having one of their axles with the twin motors and quill drive pulled out from underneath and set in front with signs and labels. [end rant] - Paul North.
This kind of explanation is what's sadly lacking from almost all of the 'stuffed and mounted' displays of locomotives. When I was too young to fully appreciate it, i was on a tour of the PRR's Electric Locomotive Shop in Wilmington as part of an NMRA Mid-Eastern Region convention. There were many parts spread out over the floor and well-labeled, and people to answer questions . . . Something like that should be done with the displays of the 'guts' from the electric locomotives. None of the GG1's would be less for having one of their axles with the twin motors and quill drive pulled out from underneath and set in front with signs and labels. [end rant]
- Paul North.
Paul,
The motors are operating in-phase, as they are driven from the same voltage source, so there would be no quartering effect as in a steam locomotive. Using twin motors as opposed to a single larger motor allows for a lower profile and the combined weight of two motors is likely less than the weight of a single motor with twice the power.
The issue with torque pulsation from a single phase commutator motor is something I picked up from an electrical machinery class.
I've been doing a bit more reading on quill drives - turns out that the original B&O electric locomotives used gearless quill drives to provide shock protection for the motors.
blue streak 1 Paul_D_North_Jr: motors in the geared quill drive: Would they have been 1/4 cycle out of sync with each other - kind of like the quartering of steam locomotive drivers for timing the cylinder strokes - to prevent both motors from being at zero torque at the same instant ? With that (presumably) sinusoidal variation of torque on each motor being offset by the 1/4 cycle, the sum of the torque from both motors at any instant would always be in a higher and narrower range, around 0.7 of the max. torque of any 1 motor as i'm recalling those kinds of things. - Paul North. PDN: You bring up a very good point. I am now wondering as well. A follow on may indicate why present day 3 phase AC diesel and electric traction motors work when the older ACs did not work as well. Makes one wonder how much more efficient todays motive power is compared to the NHs and PRRs electrics? Also the ability to regenerate or run dynamic braking?
Paul_D_North_Jr: motors in the geared quill drive: Would they have been 1/4 cycle out of sync with each other - kind of like the quartering of steam locomotive drivers for timing the cylinder strokes - to prevent both motors from being at zero torque at the same instant ? With that (presumably) sinusoidal variation of torque on each motor being offset by the 1/4 cycle, the sum of the torque from both motors at any instant would always be in a higher and narrower range, around 0.7 of the max. torque of any 1 motor as i'm recalling those kinds of things. - Paul North.
motors in the geared quill drive: Would they have been 1/4 cycle out of sync with each other - kind of like the quartering of steam locomotive drivers for timing the cylinder strokes - to prevent both motors from being at zero torque at the same instant ? With that (presumably) sinusoidal variation of torque on each motor being offset by the 1/4 cycle, the sum of the torque from both motors at any instant would always be in a higher and narrower range, around 0.7 of the max. torque of any 1 motor as i'm recalling those kinds of things.
PDN: You bring up a very good point. I am now wondering as well. A follow on may indicate why present day 3 phase AC diesel and electric traction motors work when the older ACs did not work as well. Makes one wonder how much more efficient todays motive power is compared to the NHs and PRRs electrics? Also the ability to regenerate or run dynamic braking?
Would the effciency of the modern solid state inverter have something to do with it? There's also the modern AC "Squirrel cage" traction motor...
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
blue streak 1 A follow on may indicate why present day 3 phase AC diesel and electric traction motors work when the older ACs did not work as well. Makes one wonder how much more efficient todays motive power is compared to the NHs and PRRs electrics? Also the ability to regenerate or run dynamic braking?
Keep in mind that the single phase series motors and three phase induction motors are very different beasts - something along the lines as the difference between a reciprocating steam engine and a steam turbine. The three phase induction motor is simpler, more rugged and more efficient than a single phase series motor. Another advantage is uniform torque. Use of three phase induction motors in locomotives is not new - the original GN Cascade tunnel locomotives were so equipped, along with the N&W and original VGN electrics. These were wound rotor motors, necessitated by being operated from a fixed frequency supply.
Modern AC drives make use of a variable voltage variable frequency (VVVF) drive which allow for the use of squirrel cage motors, which are simpler and cheaper than wound rotor induction motors (to say nothing about being simpler than commutator (brush) motors).
Erik: Thanks for clarifying that for us posters. Did not have timme or vocabulary to put it that well.
My understanding is that the AC motors used in both electrics and diesels are NOT truly squirel-cage synchronouse motors, with conducting bars straight across but are what are termed "hysterises non-synchronous motors" with slanted bars. But other than that, the description, with variable frequency excitation, is correct. With a true squirel-cage, at constant frequency excitation, the motor will run at the rpm corresponding to that frequency unless loaded to a specific maximum torque requirement, and then the motor will fail above that torque requirement. With the hysterises nopn-synchronous, loading increases slippage and the motor will run slower even though the frequency remains the same. If anyone has photos of the actual rotors, this question can be resolved.
erikem Paul_D_North_Jr: The twin motors in the geared quill drive: Would they have been 1/4 cycle out of sync with each other - kind of like the quartering of steam locomotive drivers for timing the cylinder strokes - to prevent both motors from being at zero torque at the same instant ? With that (presumably) sinusoidal variation of torque on each motor being offset by the 1/4 cycle, the sum of the torque from both motors at any instant would always be in a higher and narrower range, around 0.7 of the max. torque of any 1 motor as I'm recalling those kinds of things. Paul, The motors are operating in-phase, as they are driven from the same voltage source, so there would be no quartering effect as in a steam locomotive. Using twin motors as opposed to a single larger motor allows for a lower profile and the combined weight of two motors is likely less than the weight of a single motor with twice the power. [snip] - Erik
Paul_D_North_Jr: The twin motors in the geared quill drive: Would they have been 1/4 cycle out of sync with each other - kind of like the quartering of steam locomotive drivers for timing the cylinder strokes - to prevent both motors from being at zero torque at the same instant ? With that (presumably) sinusoidal variation of torque on each motor being offset by the 1/4 cycle, the sum of the torque from both motors at any instant would always be in a higher and narrower range, around 0.7 of the max. torque of any 1 motor as I'm recalling those kinds of things.
The motors are operating in-phase, as they are driven from the same voltage source, so there would be no quartering effect as in a steam locomotive. Using twin motors as opposed to a single larger motor allows for a lower profile and the combined weight of two motors is likely less than the weight of a single motor with twice the power. [snip]
Erik, I didn't think that question all the way through, and worded it poorly. Let me try again: Can the arrangement and spacing of the commutator, brushes, and coils be set-up so that the twin motors are mechanically 1/4 cycle out of sync with each other ? What I have in mind is something like whenever the twin motors were assembled or re-assembled, that someone would have to check to make sure that the one armature wasn't quite in the same relative position with regard to the same-phase electrical cycle as the other armature when engaging the pinion teeth onto the quill's drive gear . . . if that makes any sense.
Thanks again for the more-thoughtful response to my last question, and in advance for this one.
I'm not sure if it would be practical to have a mechanical means to change the timing of the torque pulsations. One problem is that a mechanical solution would likely be speed specific. An electrical solution would be to put a capacitor in series with one of the motors - which would which serve pretty much the same purpose as the capacitor in a single phase induction motor.
Rectifier locomotives would have similar problems with torque pulsation, but almost all use a smoothing reactor to filter out the ripple in the rectified DC.
How many 'segments' would the commutator on the armature of such a motor - single phase, AC series - have ? I believe it has to be 2 at minimum - 1 for current in or onto it, and another for current out or off of it, and each covering roughly 180 degrees of the circumference of the armature - and that if there are more segments, they have to be in multiples of 2 for the same reason.
The latter would be if there are multiple coils on the rotor to attempt to smooth out the torque pulsations - but wait a minute, if there are only 2 brushes, they could contact only the commutator for 2 such coils at a time, andthe others would be 'dead' . . . I need to find a diagram of one of these. Back a little later on.
My recollection was that the motors typically had 4 poles and thus would have 4 sets of brushes. I don't recall how many segments in the commutator for the GG1 motors, but I would be extremely surprised if there less than 30 segments in the commutator. The torque pulsations in AC series motors have almost nothing to do with the commutator, it has to do with the AC current supplied to the whole motor going through zero twice per cycle of the AC line - zero current means zero torque. AC cannot be Alternating Current without the current going through zero in the process of alternating back and forth between a positive and negative maximum.. The zero crossing of the current may not coincide exactly with the zero crossing of the applied voltage, but the relative phase shift between current and voltage will be the same for all the motors on the locomotive, although that phase shift can vary with operating conditions (but will vary the same way for all the motors).
Remember torque is proportional to applied B field time the armature current, the applied B field is proportional to field current (which is the same as armature current in series motors - assuming no field shunting) up to the point where the motor frame and pole pieces saturate, at which point the B field increases at a much slower rate with increasing current. Keep in mind that the magnetic circuit is unsaturated at the zero crossing of the current.
The Westinghouse article on the development of single phase Electrifications did admit that the AC series motor was a poor cousin to the DC series motor. What they did claim was that these disadvantages were outweighed by the higher power available per train and longer spacings between cheaper/simpler substations possible with single phase AC for heavy electrifications such as the NYNH&H and PRR.
erikem Paul, My recollection was that the motors typically had 4 poles and thus would have 4 sets of brushes. I don't recall how many segments in the commutator for the GG1 motors, but I would be extremely surprised if there less than 30 segments in the commutator. The torque pulsations in AC series motors have almost nothing to do with the commutator, it has to do with the AC current supplied to the whole motor going through zero twice per cycle of the AC line - zero current means zero torque. AC cannot be Alternating Current without the current going through zero in the process of alternating back and forth between a positive and negative maximum. [snip] - Erik
My recollection was that the motors typically had 4 poles and thus would have 4 sets of brushes. I don't recall how many segments in the commutator for the GG1 motors, but I would be extremely surprised if there less than 30 segments in the commutator. The torque pulsations in AC series motors have almost nothing to do with the commutator, it has to do with the AC current supplied to the whole motor going through zero twice per cycle of the AC line - zero current means zero torque. AC cannot be Alternating Current without the current going through zero in the process of alternating back and forth between a positive and negative maximum. [snip]
Erik -
Yes, that all makes more sense now. Thanks for your patience in explaining what may seem to be even simpler than 'Electric Motors 101' principles. So without the quill drive to 'buffer' the torque pulsations, the whole locomotive would have surged or 'boogied' down the track at 25 cycles x 2 = 50 times per second, between max. power and 0 power ? And in Europe, it would have been at 33 RPM - er, 33 pulses per second (16-2/3 cycles x 2). I recall that a modern - and very sensitive - dynamometer car run behind either the 610 or 614 steam locomotive as written up in Trains by Bill WIthuhn in the mid-1980's or so was able to pick up the individual pulses from the locomotive's cylinder strokes ! i suppose the same could have happened if we took one of these electrics - without the intermediate quill drive - and hooked it to such a dynamometer car.
That's kind reminiscent of what the 1960's-1970's model railroaders - i was one - did for better speed control and overcoming dirt on the rails, etc. The full-wave plus-and-minus 16+/- volt AC after being rectified would be 2 half-waves of plus-only 12+/- volt DC. By cutting one of the wires on the rectifier, only half the pulses came through, which would slow the locomotive but still provide a higher voltage to get throught the crud and overcome the higher resistance of the rails, etc., so it really helped with low-speed switching operations. It was called 'pulse control' or 'pulse power' back then - as I recall, the more advanced circuits diminished that effect at higher voltages because it wasn't needed then and to avoid motor damage from overheating, etc. No one knew or cared about the mechanical effects at that small scale . . .
Those old guys were pretty smart to figure out a decent mechanical way to cope with that inherent electrical disadvantage, which also yielded benefits with reducing the unsprung weight, etc. But then again, back then the railroads were the equivalent of today's aerospace industry or Silicon Valley enterprises and attracted the best and the brightest talent, although in this instance that talent seems to have been more at the supplier - Westinghouse - than on the railroads themselves . . . .
Thanks again. Wouldn't have been aware of that nuance or that the main purpose of the quill was to cope with it without your comment - and I consider myself to be pretty well-read on the GG1's at the 'fan' (non-EE / non ME) level.
I know from your posting and our past conversations that you have a very active curiosity, so taking the time to explain things was more of a fun project than a burden. Besides you know a lot more about the civil engineering side of railroading than I do.
Getting back to the thread topic...
There was some discussion about the relative prices of GP-7's versus the Joe's - I've read some of DPM's early Motive Power Surveys and the price of diesel locomotives ca 1950 ranged from $90 to $105 per hp. This implies that a 1500 hp GP-7 would likely cost somewhere in the range of $135,000 to $157,000. With the tractive effort of a Joe equivalent to 1.5 GP-7's and the power equivalent to 4 GP-7's, each Joe was equivalent to something like $200,000 to $500,000 worth of GP-7's. With the price per Joe of $83,000, they were quite a bargain. In 1950, the Milwaukee was only running about 17% of its freight behind diesels, so the savings from buying the Joe's would have been helpful.
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