Rewind an induction motor (40 HP) from 25 Hz to 60 Hz

[cristi69]

I would like to rewind an old induction motor (squire cage rotor) from 25 Hz to 60 Hz. Is this transformation possible? Thank you very much.

 

[Skogsgurra]

Hello cristi69. I do not answer your question about rewinding, but I thank you for telling me indirectly that there are or were 25 Hz grids. I visited a hydroelectric power station (Cohoes, NY) two years ago and was guided by one of the operators/maintenance guys. He then told me that the generators once operated at 25 Hz and that they now produce 60 Hz.

That has puzzled me ever since. And now, you actually have one of those 25 Hz induction motors.

May it be that it is from upstate NY? In that case, don't change anything. Keep that antique motor as is and buy a new motor instead. Even if a rewind probably is possible (you need to think about the 2.4 times higher speed, or change number of poles) it will probably cost more than a brand new motor and you will still end up with an inferior machine.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Gunnar,

In my patch of the world we had legacy 40Hz systems in some of the chemical plants until fairly recent times. The plants used huge rotary frequency changers to supply their private networks. I believe that last of these retired within the last 10 - 15 years.

 

[Skogsgurra]

Heard about those 40 Hz, I think that they were mentioned in the BMI (now Dranetz) reference book on power systems.

Right now, we are working with 16.7 Hz (or 16 2/3 Hz - there IS a difference) systems. Heavy transformers...

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Canada and the US were originally 25 Hz. When I was young (and now I am almost as old as Gunnar) I worked after school for a gentleman who had worked on the changeover from 25 Hz to 60 Hz in Ontario (when he was young). When a motor was replaced or rewound for 60 Hz use (each individual motor was evaluated and most were simply replaced as I understood) the conversion crew attached a metal tag indicating that the conversion of that motor was complete.
Years later I worked in a small refinery in Toronto and in an old disused part of thw plant there were a number of motors dating back to the big changeover with the tags still attached.
Google gives these results:
Amtrak's 25 Hz traction power system

http://en.wikipedia.org/wiki/Amtrak's_25_Hz_traction_power_system

Rankine Generating Station Shut down in 2006

http://www.technology.niagarac.on.ca/people/mcsele/Rankine.html

25-Hz at Niagara Falls
end of an era on the Niagara Frontier, part I

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4412948

Harnessing Niagara Falls:
The Adams Power Station
The most famous of early hydroelectric power stations

http://edisontechcenter.org/Niagara.htm

OPG powers down generating station

http://www.timminspress.com/2010/03/01/opg-powers-down-generating-station

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Many of the giant pumps used to keep the Gulf of Mexico at bay in New Orleans were originally 25Hz, and they had their own generating system for them. Over the years many in the outlying areas were converted to 60Hz, but even up to Hurricane Katrina, a few core units which still had that dedicated 25Hz grid were still operating that way. I got indirectly involved in a project proposal to put in VFDs for them after Katrina so that they could be fed with conventional portable generators if the 25Hz grid went down. During that, I was told the 25Hz had persisted because the mismatch of frequency removed any temptation for city leaders to tap into that grid for other projects, leaving it dedicated to the pumping system.

I'm not sure what happened on that once my contractor was out of the running, but I think they may have just replaced the motors with commercial off-the-shelf 60Hz versions. Another problem they had after the flooding in NOLA was that the pump stations were flooded too, and the pump motors took a long time to be re-commissioned. There were, of course, no replacements immediately available (or at least, not enough).


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[jraef]

This does a decent job of explaining it, albeit a little dumbed down for the general public. The project I was involved in was announced shortly after this came out.

http://blog.nola.com/times-picayune/2007/05/outage_reveals_pumping_system.html

crist69,
This brings up another point. It might be simpler and faster to just put in a VFD set for 25Hz output for that motor. It will take a little custom programming of the motor data and frequency/voltage ratios, but all VFDs I am aware of are capable of that. Just be sure to size it for the AMPS, not the HP.[pre][/pre]




"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

Another issue that should be checked for the original motor:
I understand that some of the old 25 Hz systems were 2 phase systems. If this is a two phase motor, conversion to 60 Hz may be even more challenging.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Were they really, Bill? That is very interesting, and also understandable since Tesla's induction motor was based on two phases with 90 degree phase shift, which Westinghouse (I think) improved by introducing the three-phase system.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[djs]

I once was told that the biggest issue in converting an induction motor from 25 Hz to 60Hz was that the rotor resistance would be too low. The recommendation was to turn down the end bars to increase the rotor resistance. How much would be a lucky or unlucky guess. Too much and the motor is toast.

 

[waross]

An interesting excerpt:

http://www.technology.niagarac.on.ca/people/mcsele/Rankine.html

The Adams plant supplied two-phase 2200V local service as well as three-phase service to Buffalo via 11kV lines (two-phase power, produced by the generators, was converted to three-phase by a 'Scott Transformer' and sent to Buffalo that way).

There were a number of 25 Hz plants and I believe that some of them generated 3 phase 25 Hz.
I remember a paper I read years ago. I think you would have found it interesting.
A plant was using 25 Hz induction furnaces.
The power supplier was phasing out 25 Hz service.
An alternative was sought to the cost of converting the induction furnaces to 60 Hz.
The plant had a number of surplus 25 Hz synchronous motors
It was proposed to use 60 Hz synchronous motors to turn 25 Hz synchronous motors through appropriate ratios to generate 25 Hz to power the 25 Hz furnaces.
Second issue; The plant owned supply of 25 Hz motors did not include any single motor with enough capacity to supply the furnaces.
It was proposed to run two or more sets in parallel to gain the needed capacity.
Next issue; Paralleling. Generally the prime mover supplies torque and the parallel connection locks in the speed and angular position.
However, with synchronous motors driving synchronous generators, the angular position of the rotors becomes important. If the angular position of one rotor lags a few degrees that set will not carry its share of the load. If it lags a few degrees more, it will be driven or "motored".
This problem was solved by fabricating what the engineers called a micrometer coupling. This was a coupling with an adjustable driving link. The sets were started and the synchroscope was observed. The synchroscope would show the electrical angle error between the two sets. The set would be stopped and the relationship between the driving rotor and the driven rotor adjusted with the micrometer coupling. The procedure was repeated until good load sharing was achieved.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MikeHalloran]

<tangent>

According to his business card, my paternal grandfather was "Superintendent of Phase Change" for Niagara Mohawk in Cohoes, NY. Yeah, it was a frequency change, from 25hz to 60Hz, but they used the word 'phase' instead. Marketing, I guess. His basement accumulated many boxes of perfectly good but useless 25hz clock motors. NiMo exchanged the motors for customers; in those days, clocks came in nice wooden cases, most of which used the same few motor assemblies.

My father, when he was 12 or so, took up photography, and took many photos of the powerplant then under construction adjacent Cohoes Falls; it must have been around 1932.

I went back and tried to sneak a peek while the utility was tearing down most of the powerplant, but it was not long after 9/11, and they were _real_ paranoid about people even just looking through the fences.

</tangent>


Mike Halloran
Pembroke Pines, FL, USA

 

[Skogsgurra]

Mike

Is that the Cohoes station in Mohawk river? If that is so, I can tell you that they are not paranoid any more.

Me and my collegue stayed a couple of days around Schenectady in February 2013. We had been visiting GE and thought that we should visit some other interesting places before we went on to the Museum of Bad art (MOBA) in Boston. When we found that power station, we parked close to it and stared through the gate. Soon enough, one guy asked us what we wanted. We told him that we wanted to see the station. He phoned his boss and then opened the gate. We had a very interesting tour and saw those generators that had been rebuilt for 60 Hz. I took a few pictures of the control panel. It looked like 1940 - 1950 or so. I can send you pictures if you want.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[MikeHalloran]

Yes, Gunnar, the very same station.
I should be in the area again next summer.
Maybe I will try standing at the gate and looking friendly.



Mike Halloran
Pembroke Pines, FL, USA

 

[Skogsgurra]

It was a NERC guy. Look for them!

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[crshears]

Up to now I haven't made it a habit to carry my NERC Reliability Co-ordinator certification card with me, but I think I may start...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[VEBill]

I've heard that Lake Ontario is "full" (not really) of old 25Hz appliances that were traded in and replaced during the change over. The old ones were tossed into Lake Ontario (ah, the good old days...) to make sure that they weren't traded in again.

It's not accurate to say that Canada used to be 25 Hz. I understand it was just certain areas.

 

[waross]

There seems to have been a lot of 25 Hz generation around Niagra Falls and parts of New York State.
Does any one know if two phase power was used on 25 Hz, 60 Hz or both? The old text books often showed two phase to three phase convesion schemes. Scott, Fortesque and one or two others.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Why did they even start at 25Hz?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MikeHalloran]

WAG: The 25Hz frequency corresponded to the limits of confidence in then-current motor and turbine bearings.

Further WAG: Flicker didn't become a serious annoyance until tungsten replaced carbon filaments in electric lamps, and electric lamps (vs. e.g. gas lamps) became common.





Mike Halloran
Pembroke Pines, FL, USA