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AC to DC conversion

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AC to DC conversion
Posted by SouthPenn on Sunday, October 29, 2017 10:53 AM

I am looking for a good description of how AC current was/is converted to DC current in train engines. I have found one mention of synchronous motors turning DC generators. But it did not mention reducing 11000V to a usable voltage. A transformer I would presume. I have worked on 4160V synchronous motors but 11000V motors in a train engine seems to be absurb and dangerous.

Thanks

South Penn
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Posted by RR_Mel on Sunday, October 29, 2017 11:30 AM

There is a pretty good site on your subject.
 
 
I’ve read through the info several times but much of it is over my EE education.  The general perception of traction motor and generators is understandable.   
 
Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
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Posted by 7j43k on Sunday, October 29, 2017 12:09 PM

Great Northern had a section of electrification.  Originally, it was 3 phase, with two parallel wires overhead.  But that's another story.

When they went single phase, they used a nominal 11,000 Volts, 25 cycle AC.  They had three classes of electric locomotives.  Each used a transformer to step down the voltage, variously to 1240 V., 2300 V. and 1350 V.  AC.  A motor generator then generated, also variously, 600 V., 750/1500 V. and 500 V. DC to drive the traction motors.

These were, incidentally, the classes Z, Y and W, in order (built 1926-1929, 1927-1930, 1946).

 

Since steam locomotive classes generally started with A (on the GN, an 0-6-0), the wise folks at GN decided to start at the other end of the alphabet.  And skipped X.  They never did "crash", as T, U and V were never used.

Well, actually they DID sort of crash, as GN also had class Z steam engines.  But, as they say, that's another story.

 

Ed

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Posted by gmpullman on Sunday, October 29, 2017 3:29 PM

GE built 66 E44 Locomotives for the PRR in 1960 through 1963 based on the successful design of the EL-C of the Virginian railroad (later to become the E33 on the New Haven).

Initially these used a Mercury arc rectifier:

https://en.wikipedia.org/wiki/Mercury-arc_valve

In the 1970s Conrail swapped out the Ignitrons for silicon diode rectifiers.

https://en.wikipedia.org/wiki/Pennsylvania_Railroad_class_E44

If I recall correctly, PRR supplied cast bronze bells for these locomotives that were harvested from scrapped steam locomotives.

I have bits-&-pieces of documentation from a GE training seminar on the E44:

 PRR_E44_GE by Edmund, on Flickr


 

 PRR_E44_W by Edmund, on Flickr


 PRR_E44_0001_W by Edmund, on Flickr 

 


 

 PRR_E44_0002_W by Edmund, on Flickr


 

 PRR_E44_0003_W by Edmund, on Flickr


 

 PRR_E44_0004_W by Edmund, on Flickr


 

 PRR_E44_0005_W by Edmund, on Flickr

 The above is only the first six pages of twenty-four. The diagram, unfortunately, was lost in a fire.

I hope this is legible for you. One day I'd like to be able to find the time to scan and post some of my railroad documents for anyone to access but that has yet to happen.

The above is either fascination OR a great cure for insomnia...

Good Luck, Ed

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Posted by 7j43k on Sunday, October 29, 2017 5:07 PM

I may be misreading the document, but it looks like the transformer had a range of outputs from 780 Volts to 2490 Volts.  And that after rectification, that voltage was applied to the traction motors.  Quite a step up from the common 600 Volts.  But note the the GN Y-1's motors could (apparently) be given 1500 Volts.  So, with improvements in design over 30 years, I suppose that 2490 is not all that unreasonable.

And, you don't need a motor-generator.

One of the few electrics I have (no overhead--SAD!) is a Bachmann rectifier.  Visually appealing, and affordable at the time.

 

 

Ed

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Posted by BMMECNYC on Sunday, October 29, 2017 5:12 PM

RR_Mel
There is a pretty good site on your subject.   http://members.localnet.com/~docsteve/railroad/en_info.htm  

Yep, before solid state electronics became a thing, you placed a AC motor on a shaft with a DC generator.  

Now its all done solid state, and the traction motors could be either AC or DC.

Rule 108: In case of doubt or uncertainty, the safe course must be taken.
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Posted by SouthPenn on Tuesday, October 31, 2017 7:36 PM

Thanks for all your replys. Lots of reading to do. Fortunatly I was an electrician in a rolling mill for 35 years and over 90% of the motors were DC. We had almost every type of AC to DC conversion method available. Motor/generator sets, thyratron tubes, and SCR (silicon controlled rectifier ) electronics.  

But I have never seen a good explanation of the AC to DC conversion in a locomotive; until now.

Thanks

South Penn
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Posted by BN7150 on Wednesday, November 01, 2017 3:29 PM

I do not know if you are satisfied or not, but let me show you one example of Japanese electric locomotives. Unfortunately I am a mechanical engineer, so I am not good at English explanation.

The attached diagrams show the main circuit and the operation of JNR's ED78 type manufactured in 1967 (under 20 kV AC system). It has a thyristor phase controller with 4 DC 750 V series-wound traction motors. During power running operation, all 4 traction motors are parallelized. During regeneration braking, the 4 armatures are arranged in parallel, and the 4 fields are connected in series with a field excitation dedicated circuit. So, the thyristor pure bridge is used as a separately excited converter for regenerative operation. The figures are quoted from a Twitter (https://twitter.com/t_shigeno/status/901459618232123392).

JNR ED78 main circuit

JNR ED78 main circuit operation

Tags: JNR Electric
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Posted by ATSFGuy on Wednesday, November 01, 2017 4:51 PM

Do DC locomotive's run well on flat territory vs mountain territory?

 

Are AC motors more reliable than DC motors? Is it true you can "lock rotor" an AC motor where on an DC motor it burns up?

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Posted by SouthPenn on Wednesday, November 01, 2017 11:04 PM

DC motors run well across flat ground and mountains. Series wound DC motors make a tremendous amount of torgue. DC motors are easy to regulate their speed. There no problems having a stalled ( locked ) armature as long as you control the current. DC motors are ( were? ) used in cranes and elevators because of their high torgue and speed control.

Up until the 1990s AC motors were hard to regulate their speed and if the rotor stalled, they would burn up. Now with the electronics controlling the voltage, current, and frequency they can be speed controlled and the rotor can be locked for short periods of time.

Reliability? A DC motor requires a lot of maintenance to maintain it's reliability. The carbon brushes wear, the comutator wears, and the carbon brushes deposit carbon dust every where inside the motor. The dust can cause shorts inside the motor. The AC motor has none of these problems. In my 35 years at work, I would say 30% or more of my time was spent cleaning and repairing DC motors. The AC motors had their bearings greased once a year.

The AC motor is more reliable and requires minimal maintenance. 

South Penn
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Posted by BN7150 on Thursday, November 02, 2017 3:08 AM

The locomotive of the attached photo is a NH EP-1 model by NJICB/Tamac in 1982. The prototypes were manufactured in 1905-1908 and ran with both 11,000 V AC and 650 V DC. However, neither rectifier nor DC-converter was equiped with. The traction motors were single-phase series commutator motors, also known as universal motors. The configuration is the same as the DC direct current motor. Yes, the motor was used for mixers, vacuum cleaners and our O-gauge locomotives of the past. It was used also for PRR GG-1 and etc. I expect this to solve your doubt.

NH EP-1 model by NJICB/Tamac in 1982

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Posted by ATSFGuy on Thursday, November 02, 2017 11:01 AM

Have DC Locomotives been discontinued? 

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Posted by 7j43k on Thursday, November 02, 2017 11:29 AM

ATSFGuy

Have DC Locomotives been discontinued? 

 

 

I don't see any for sale on the GE website.  I think the last DC loco BNSF bought was in 2010.  So, it does look that way.

 

Ed

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Posted by ATSFGuy on Friday, November 10, 2017 5:29 PM

BNSF ordered ES44DC locomotive's from GE a while back, Are they still in service?

UP had them as well.

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Posted by 7j43k on Friday, November 10, 2017 6:30 PM

ATSFGuy

BNSF ordered ES44DC locomotive's from GE a while back, Are they still in service?

 

The last ES44DC BNSF ordered was BNSF 7920 delivered August 2010.

I would think they are very much in service, since they're newer than the C44-9W's.

 

UP had them as well.

 

I'm not finding them on my rosters.

 

Ed

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