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Pittsburgh Railways Rotary Converter Saved
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Author:  Rick Rowlands [ Sun Sep 28, 2014 8:20 pm ]
Post subject:  Pittsburgh Railways Rotary Converter Saved
Add this to the "success" column.

Youngstown Steel Heritage has acquired and will be preserving a 2000KW rotary converter that was originally used by the Pittsburgh Railways trolley car operations. It will be coming to Youngstown by the end of next week and will be cleaned up and wired in to operate for demonstration purposes.

Standing over 10 feet tall and weighing 30 tons, it is quite a large piece of equipment, and we are specially designing a structure in which to house it. The function of this machine was to convert 440VAC SIX PHASE power to 600 VDC for trolley car operations. None still operate in regular service and very few are preserved in railway museums across the US.

We are taking it because 1)nobody else wanted it, 2) converters were used in the steel industry, and 3)because its simply the coolest piece of electrical equipment I have ever seen!

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Author:  baldwin [ Sun Sep 28, 2014 8:57 pm ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Doesn't your overhead crane need 600 VDC to operate?
Author:  robertjohndavis [ Sun Sep 28, 2014 9:10 pm ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Congrats, Rick. That's awesome. Great save!
Author:  Ryan Andrews [ Sun Sep 28, 2014 10:43 pm ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Rick I just wanted to say congratulations on the new addition. By the way I attempted to go visit your organizations collection page on your website and somehow all of it got translated into Latin. I don't know if it is just my computer or what I just thought id let you know.
Author:  Pegasuspinto [ Mon Sep 29, 2014 12:02 am ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Where the heck you gonna get 6 phase power?
Author:  Rick Rowlands [ Mon Sep 29, 2014 12:13 am ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Thanks. Yeah, the website needs some work. Too busy working on stuff to work on the website it seems.

The interesting thing about rotaries is that if you run it on lower AC voltage you get lower DC voltage out. I figure if I run it at 208VAC I'll get a little shy of 300 volts which is a little hot but is manageable. Certainly there will be some experimenting to figure out the best way to run it.

We can make six phase using three rewired transformers. It can also run on three phase, as long as you tap into either slip rings 1,3 and 5 or 2,4 or 6.
Author:  Pegasuspinto [ Mon Sep 29, 2014 10:29 pm ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
I would love to see a diagram of how that transformer set up works.

A converter HAS to lower the voltage to more or less 'match' what is being fed in. It's simply a motor driven mechanical rotary switch. You will get about 1.4 times the DC voltage out as the AC voltage fed in. 480 vac will make about 672vdc, 440vac makes about 616vdc. 440vac and 480vac are basically the same 'voltage level' in the same way that old household AC equipment was rated at 110vac and now is usually 120vac, also 440vac is used as the nominal voltage to compensate for voltage drop in the system. 208vac will make 291vdc but i'm not sure the converter will like that, as it has to be at synchronous speed to work which means the amp draw will be more then double....I wonder what was better, a mechanical converter or a mercury vapor rectifier.

Other situations used a dynamotor (or motor-generator set) a different animal entirely. Just a motor hooked to a generator.

In any case be careful, DC voltages at those levels is a much nastier animal then AC.
Author:  Bob Davis [ Mon Sep 29, 2014 10:49 pm ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Yep, that's a big one! Orange Empire has a 300kW General Electric rotary converter that came from the Sacramento Northern back in the 1960s. It came with a 6-phase transformer so that wasn't a concern. It is kept in a recycled service station structure; the resistor banks are where the lube rack or the gas pumps might have been. It went into service around 1972, but a few years later the museum acquired a GE rectifier sub from a mining operation, relegating the rotary to a standby role. But it still gets turned on about once a month or when the rectifier plant is down for repairs or upgrades. Listening to the machine start up is like being in Dr. Frankenstein's laboratory with all sort of zarks, buzzes and clanks as it goes through its start up sequence.
Author:  David Johnston [ Tue Sep 30, 2014 12:15 am ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Not only is the transformer important, but as Bob said starting it up is quite a process. It probably starts at a reduced power level and after it is near up to speed, full power is applied to it. Normally most of the DC brushes are lifted durning starting. It looks like there is a brush lifting mechanism, but it may not be complete. There is usually a field flashing mechanism to get things started. There is also field control to adjust the power factor. There are three or four different fields on the machine each serving a different function.

Rotary Converters were very efficient at full load, much better than a MG, but at low load the spinning rotor used a lot of power and efficiency was poor.
Author:  John Risley [ Tue Sep 30, 2014 12:58 am ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Very cool. Go big or go home! Love it. Regards, John.
Author:  robertmacdowell [ Tue Sep 30, 2014 1:57 am ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Pegasuspinto wrote:
440vac and 480vac are basically the same 'voltage level' in the same way that old household AC equipment was rated at 110vac and now is usually 120vac,

Yes, you'll commonly hear "110vac", "120vac", "115vac", "117vac" or even "125vac" used interchangeably to describe what is exactly the same thing: household power as provisioned in the US and Canada. Really, it's close to 120v.

Ditto ditto 440, 460 and 480, really 480.

If someone had a specialty application where they /actually/ needed 440, trying to describe that to electricians would quickly devolve into the Abbott & Costello skit "Who's on first?"

Pegasuspinto wrote:
Where the heck you gonna get 6 phase power?


Aha. Well, you know 3-phase current, if you think of the face of a clock, has its phases at "noon", "4:00" and "8:00"... right?

OK, now think about power in your home. It's 240V with a center tap, and the center tap is neutral, so you have two 120V "phases" that are completely (180 degrees) opposite. On the clock face, they would be at "noon" and "6:00". Some people object to calling it a phase since it's simply another tap, but it's like a "shadow" phase.

Well imagine you did the same thing with 3-phase power. You'd have phases at noon and six as above; at 4 and its shadow at 10; and at 8 and its shadow at 2. That's six.

"Thank you, Mr. Tesla."
Author:  David H. Hamley [ Tue Sep 30, 2014 8:07 am ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
This lovely machine last served in the former Pittsburgh Railways (since 1964, Port Authority Transit) South Hill Junction substation until it was replaced by rectifiers in the 1990s. It formerly served at the PRCo Craft Ave. sub. The 2000KW was the largest size rotaries in the PRCo system.

Pennsylvania Trolley Museum has in its collection two 1920 vintage Westinghouse 500KW rotaries. One of these is of PRCo heritage and once powered a portion of the very PRCo trolley line on which the museum is now located. We also have, with one exception, all the various pieces needed to replicate a typical rotary installation. The exception is the transformer. It was loaded with PCBs and thus not available for preservation. As noted elsewhere in this string, a six phase transformer is required and that will be a custom design. Our long term plans are to put this rotary in service in an authentic brick substation. Dont rush to PTM to see this, it'll be quite a while in coming.

Our second rotary was rescued from the Duquesne Light Co.'s Stanwix St. sub in downtown Pittsburgh in the 1990s when they shut down the last of their 600VDC two wire commercial distribution system. This once served numerous office buildings for their escalators, elevators, and similar applications. Our plans for this machine are to cosmetically restore it as a "please touch me" exhibit in our visitor center. A second rotary from this location went to Baltimore Streetcar Museum.

Both of our machines weigh approximately 9900 lbs and measure about 5x5x5 feet.
Author:  Rick Rowlands [ Tue Sep 30, 2014 11:33 pm ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Making the converter run and in a way that its useful to us is going to be a bit of a challenge. To those of us who love early electrical gear, making this converter operate again is akin to the excitement in returning a locomotive to operation that has been dormant for many years.

I have a few people whose understanding of electricity is much better than mine, so we are in good hands. I believe that a three phase transformer, wired in a the opposite configuration to how the power is fed to the converter (delta vs. wye) would provide the other three phases. But in looking at the wiring diagram I'm not sure if the other three phases are even needed. Clearly more research is called for.

For our needs we will be drawing a maximum of 2.5% of the capacity of the converter to run any motors we have at the museum, and at that low of a power level you can take liberties that you can't with a machine putting out near rated capacity. I'll be sure to record our efforts as we return what is probably the largest preserved rotary back into operation. Might even be worthy of a few youtube videos.
Author:  EDM [ Wed Oct 01, 2014 9:09 am ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
Maybe 25 years ago, I had an EE as a boss, who had spent some time with ABB. He and I got talking traction power (streetcars, subways) and he described using rectifiers and transformers to get a very smooth 12 pulse DC. Basically it involved the two secondaries of a transformer, one wired into the rectifiers in wye, the other in delta. At least that is what I remember. Could this be something similar, driving a rotating machine instead of rectifiers?
Author:  Pegasuspinto [ Wed Oct 01, 2014 12:40 pm ]
Post subject:  Re: Pittsburgh Railways Rotary Converter Saved
There is only one way to hook up a full wave bridge to 3 phase AC, I would say it more resembles delta because the voltage is going to be based off the phase-to-phase voltage. Full wave rectified 3-phase AC is already pretty smooth DC.

How this converter apparently works is that it is only doing half-wave rectification but it inverts the 3 phases and half wave rectifies them again, added together they look like 3 phase full wave rectification. It's complex but in that time there was no good way to rectify AC into DC at those power levels. Same reason when diesel electric locomotives came around they started with DC generators then progressed to AC alternators with a rectifier pack-the rectifiers advanced to the point that they could take advantage of the efficiency of a alternator.

Nowadays 6 of these: http://www.mouser.com/ds/2/196/DS_D2450N_3_1-219502.pdf rectifier 'pucks' can replace that entire machine. And most of the control gear that went with it, and they only cost about $150 each.
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