Double-cab electric locomotives

[PATTBAA]

"Tap changing which is how speed control on 'modern' NH AC (electric) locomotives was done."--The EP-1 prototype was operational in 1905 (I have the photo).There were only six "steps" , or "notches" for AC acelleration, far less than for D.C. For D.C. the traction-power motors could be connected to only one voltage-value, the 3rd rail voltage, which required for starting a two-motor series connection in series with resistors.For A. C. acelleration the motors were connected to six "taps" off the 11,000 volt transformer winding, each connection with a specific voltage-value.----"connecting the motors to the transfomer power is only used at starting." Then what are the motors connected to for "running"?.

[daveklepper]

Nonsense.  All AC electrics pass power through transformers under all conditions.

The word "taps" was missing.   Transformer taps are only used on acceleration?

Probably also nonsense, unless the railroad had a rule:

"Once up-to-speed, full power or coast."  The IND New York subway had that rule at one time.  Supposedly saved power.

 

 

 

[CSSHEGEWISCH]

Chicago Surface Lines conducted coasting experiments on a line through congested commercial areas where it was considered difficult to coast.  The experiments did show reduced power consumption and coasting instructions were extended systemwide as a result.

[Overmod]

PATTBAA

... "connecting the motors to the transformer power is only used at starting." Then what are the motors connected to for "running"?

I suspect this is a construction artifact being explained leaving fundamental electrical control out.

No practical railroad motor runs effectively on 11kV power directly, even larger 'industrial' ones adapted for jackshaft drive.  (There were experiments to run DC motors in permanent series on 5000Vdc just before WWI, but the 'big savings' weren't worth the fun).

Accordingly there is 'something' that steps the 11kV down to whatever the motors use for continuous running.  That will likely be a transformer, and if it has no speed-regulation taps in its winding structure it would be connected and disconnected via contractors (probably with hefty blowout and arc chutes!!).  The implication from the language is that the six stages of tap are on a separate 'starting' transformer that is sized for acceleration and then 'switched out' for the running one once the train has gathered momentum.

In my hymble opinion such a design would be transitory, perhaps even experimental, and perhaps limited by available materials or equipment.  Certainly the EP-3 and GG1 used multiple-tap control on their main transformers -- in part through the miracle of Pyranol.

[blue streak 1]

Discussions of motor voltages can best be addressed by using the ultimate motor voltage / output voltages of hydro electric generators .  Most generators are motored continously at speed so can immediately become generator as soon as water power is applied.

https://www.gepowerconversion.com/sites/gepc/files/product/Hydro%20Generator%20Brochure.pdf 

https://en.wikipedia.org/wiki/Hydroelectricity 

20,000 volts

https://www.brighthubengineering.com/power-plants/45558-electric-power-generators-how-they-work/

 

[Overmod]

Interesting that at least some hydro generators are kept motored to reduce effective cold start times; I had thought it was only done for synchronization or to reduce shock if the supply piping had high head or other characteristic mitigating against stable acceleration in ~60-90sec.  Keeping them spinning at some speed would also mitigate need for high-pressure prelubing of the step bearing during the early stage of spinup.

Interesting to see the professional take on this.

[Erik_Mag]

Overmod

There were experiments to run DC motors in permanent series on 5000Vdc just before WWI, but the 'big savings' weren't worth the fun.

GE had investigated the use of 5000VDC for the Milwaukee, with the overall costs for the 3000VDC and 5000VDC being about the same. The savings in copper with 5000VDC were eaten up by the increased cost of the locomotives. It was also thought that the investment in copper was easier to salvage than the investment in locomotives.

There has been some work done in replacing standard iron core distribution transformers with switching power supplies acting as a transformer. High voltage side was 14.4kV and it would seem that such a beast could be adapted for 14kVAC or 20kVDC catenaries.

[MidlandMike]

Erik_Mag

The savings in copper with 5000VDC were eaten up by the increased cost of the locomotives. It was also thought that the investment in copper was easier to salvage than the investment in locomotives.

Am I remembering correctly that someone from Anaconda sat on the MILW Board, so choosing the more copper alternative may have been preferred?

[Erik_Mag]

You are remembering coorectly about the Milw board, but don't think it had much to do with the 3kV vs 5kV decision. OTOH, Anaconda was interested in promoting electrification as a market for copper.

[Overmod]

Erik_Mag

OTOH, Anaconda was interested in promoting electrification as a market for copper.

If I remember correctly, it's a bit deeper than just board representation: some of the finance of the PCE came from people or entities specifically concerned with 'maximizing the amount of copper' in the construction.  I have my suspicions that the fancy doubled trolley structure stems at least in part from some behind-the-curtain input into engineering.

It was my opinion years ago that 5000kV operation with twin motors (the armatures in series as in the Grass Valley experiment) would have been a sensible alternative -- this was still the era of larger twin motors that didn't handily fit between the backs of wheels at standard gauge, like the GG1 motors or the 428As that followed, but still a known and good alternative.  

Is there a reason why Batchelder bipolar motors couldn't run effectively on 2500kV apiece in series under load?

[PATTBAA]

Because of the weight of a single  11,000 volt traction-power transformer, the EP-1 was equipped with two which were "auto-transformers" , an auto-transformer a single- winding design. Refer ( via hathitrust ) to the Street Railway Journal ,Volume 30 , Aug. 1907 , pags 278-285 , for an illustration of the transformer-motor connections thru "unit-switch" contacts with "blow-out" coils.You don't "start" a locomotive as you do an engine; you advance it from zero speed to full-speed.

[Erik_Mag]

Overmod

It was my opinion years ago that 5000kV operation with twin motors (the armatures in series as in the Grass Valley experiment) would have been a sensible alternative -- this was still the era of larger twin motors that didn't handily fit between the backs of wheels at standard gauge, like the GG1 motors or the 428As that followed, but still a known and good alternative.

Sounds like you're proposing a remake of the Westinghouse "Quills" with 1250V motors instead of the 750V motors used. One issue with running a bunch of motors in series is insulating the motor windings for 5kV and figuring out how to prevent arcing between the brusholders and motor frame.

OTOH, some of the Thury system implementations were running 75kV or more with lots of motor's in series, albeit the motors were on insulated mounts and had insulated shaft couplings.

Is there a reason why Batchelder bipolar motors couldn't run effectively on 2500kV apiece in series under load?

The bipolar motors were lacking interpoles, so it would have been a challenge to go higher than the 1000V on the Milw Bipolar's. Note that traction motor voltage pretty much topped out at 600VDC prior to interpoles. IIRC, the motors for the M-G sets were 2 pole design to allow enough commutator bars between brushes, but had interpoles to improve commutation.

Note that the 5kV proposal made sense with the existing traffic and number of locomotives. An increase in traffic would have lead to a higher cost for the 5kV locomotives than with the 3kV locomotives.

[Overmod]

PATTBAA

You don't "start" a locomotive as you do an engine; you advance it from zero speed to full-speed.

Actually this is the definition for any voltage-controlled electric motor, and technically includes bringing up a rotary converter.  It can be confusing to those only familiar with internal combustion to read about 'starting resistances' too.

I was fortunate to have people explain to me both on IRT subway equipment and on PRR MP54s how to get smooth physical car starts from rest and then controlled acceleration with restricted tap control.  It's something of an art.

Incidentally there is more required when opening HV contactors than when initially closing them: when you look at the action of blowout coils, arc chutes, etc. you will gain a greater appreciation for the practical joys of switching heavy inductive loads...

[SD60MAC9500]

 

MidlandMike

Some freight motors were single ended, such as the PC E-33 and E-44, and the Black Mesa E-(60?).  Most of the US double enders were either historic, or modern passenger units that are reversed often.

 

Add BC Rails GF6C to the single cab club. Yes the 1st gen E60C were single cab. The E60C-2 was the only modern domestic freight double cab electric built. Seven are still in operation on the Desert-Western located in the Uinta Basin.

 

[rdamon]

[Overmod]

Very interesting video, another example of a moving picture being worth thousands of words.

Note that this is still comparably low-voltage; if division as shown is into '30-volt arcs' this is no more than about 277V.  Presumably there is a version for up to ~480V, but you're starting to get into the range even there where a combination of (induced by arc current) magnetic field and air blast is desirable to clear the conductive plasma from between the opening contacts.  How the energy is dissipated from the extended plasma is another matter, one of more than trivial concern in 'arc flash' safety.