I am trying to understand 2 speed induction motors, so I figured the 2 speed, 2 winding, 3 phase induction motor would be simpler to understand. From what I learned in my electrical engineering classes a few years ago, the more times a conductor is wound, the stronger the magnetic field and thus the higher the torque. I was then trying to understand the workings of a 2 speed motor in our plant and I was told that the winding that resulted in more volts/winding would result in the higher speed. That means, connected to the same bus that the winding with less "winds" would actually be the faster speed and would require more power (it's powering a fan). I don't understand how this works. I mean, taken to an extreme, the fastest, most powerful configuration would then be 1 wind, and the slowest, weakest configuration would be infinity. I am sure I am looking at this wrong but I can't seem to wrap my head around it.
2 Speed 2 Winding 3 Phase Motor
- Thread starter lbarber70
- Start date
- Status
- Occupation
- Licensed Electrician
You were told wrong. The speed of a three phase or single phase motor is determined by the number of magnetic poles until you get into VFD controls.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Correct.
S = f x 120/P
Where S = Synchronous RPM, f = frequency in Hz, P = # of magnetic poles and 120 is a mathematical constant.
So a 2 speed motor, whether 2 windings or 1 winding, is changing the number of poles in the configuration of the internal connections. This is done by bringing all of the coil connections out to terminals that are then connected to contactors that reconfigure them.
The stuff you remember about the magnetic field strength and the speed was probably either in relation to DC motors, or was regarding slip speed in AC induction motors from the standpoint of the initial motor design. It's not something you can change on the fly without a Wound Rotor controller or a VFD.
Last edited:
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
190425-1649 EDT
What is being taught in an undergraduate EE program today?
When I was in school both DC and AC machinery were required undergraduate courses for any EE program. And a number of other areas were considered basic, like statics, dynamics, fluid dynamics, and thermo. Drawing was even required. This was independent of your speciality area.
The electrical engineering field has greatly expanded, but a BS degree is still just a 4 year program, really should be longer. It seems too many basic concepts are being glossed over.
Even though I live about 1 mile from campus I have little contact with the school, and thus direct knowledge of the course material. However, great things are being done here. Like one of the world's most powerful lasers, and smallest complete computer with sensors and RF output that can go inside a blood vessel. We have one of only a few very clean microcircuit lab facilities in the country.
I looked at the present course outline for today's students and it is very different than what I experienced. Probably the same at other schools. See
https://www.eecs.umich.edu/eecs/undergraduate/ugee/EE_Program_Guide.pdf
Overall the new program is probably doing a good job.
I was on the radio or electronics side of things, but there was a big power area, and in earlier days the capacitor run motor motor was invented or developed by one of the professors. The AC Machinery book I studied from was written by him.
.
What is being taught in an undergraduate EE program today?
When I was in school both DC and AC machinery were required undergraduate courses for any EE program. And a number of other areas were considered basic, like statics, dynamics, fluid dynamics, and thermo. Drawing was even required. This was independent of your speciality area.
The electrical engineering field has greatly expanded, but a BS degree is still just a 4 year program, really should be longer. It seems too many basic concepts are being glossed over.
Even though I live about 1 mile from campus I have little contact with the school, and thus direct knowledge of the course material. However, great things are being done here. Like one of the world's most powerful lasers, and smallest complete computer with sensors and RF output that can go inside a blood vessel. We have one of only a few very clean microcircuit lab facilities in the country.
I looked at the present course outline for today's students and it is very different than what I experienced. Probably the same at other schools. See
https://www.eecs.umich.edu/eecs/undergraduate/ugee/EE_Program_Guide.pdf
Overall the new program is probably doing a good job.
I was on the radio or electronics side of things, but there was a big power area, and in earlier days the capacitor run motor motor was invented or developed by one of the professors. The AC Machinery book I studied from was written by him.
.
junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Fitzgerald ? Kingsley?
Not to kijack the op thoughts, but my son and his wife have EE and CS degrees from U Washington. Son wrote much of the code for Microsoft windows to cut and paste between ppt, word, excel. That said, at times I am amazed at the large gap in their knowledge for anything power or analog circuitry.
Back to OP comments, re: the more times a conductor is wound, the stronger the magnetic field and thus the higher the torque
Not a good interpretation: s
(v*dt) = N BA, so number of turns is how much voltage the motor can handle before the core saturates.
At a given voltage motor the torque is directly proportional to CURRENT (torque = K *I), which is related to wire size. For instance, you can take a 5 HP rated motor and operate at 10 HP for a few minutes before it overheats due to I^2*R losses - if you can cool the 5 HP motor you can run it at 10 HP all day long at twice the rated current.
More complex than these 2 simple relationships, but just adding turns does not automatically increase torque.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
190425-2444 EDT
junkhound:
The book was by Bailey and Gault. I never met either of them. Gault died at a young age, and his wife went to work for the Electronics Defense Group when I worked there.
A very interesting read is
http://ece.umich.edu/bicentennial/narrative.html.
I started at Michigan in 1953 following USNR active duty, January 1951 to October 1952. Previously I was at Dearborn Junior College, and the University of Colorado.
Bailey's invention of the capacitor run motor is mentioned in the discussion.
Quite interesting about several of my teachers and neighbors. Lovell was my dad's commanding officer in WWI. Attwood, Dow, Farris, Rowe, and Lyon were all ones I worked with, were teachers, or neighbors. A comment my dad made about Lovell was that he sat ram rod straight in a saddle. The WWI army engineering group my dad was in all had their own horse.
Some of my other teachers or associates mentioned were R. K. Brown, Lewis Holland (both teacher and neighbor), Lyon and Farris were neighbors, A. D. Moore, and M. B. Stout were teachers. At 102 Dow still walked around my neighborhood and his home was about 1/2 mile from mine and a substantial elevation change. He still had a good memory at 102.
Even though it was only 15 years later that I met some of those in the 1937 photo I am surprised at how young they looked in the photo.
The 1923 photo of radio class students may show my uncle at the right in the front row.
I am surprised at how small the enrollment was in the 1920s, thus the staff, and yet substantial research was going on at that time.
.
junkhound:
The book was by Bailey and Gault. I never met either of them. Gault died at a young age, and his wife went to work for the Electronics Defense Group when I worked there.
A very interesting read is
http://ece.umich.edu/bicentennial/narrative.html.
I started at Michigan in 1953 following USNR active duty, January 1951 to October 1952. Previously I was at Dearborn Junior College, and the University of Colorado.
Bailey's invention of the capacitor run motor is mentioned in the discussion.
Quite interesting about several of my teachers and neighbors. Lovell was my dad's commanding officer in WWI. Attwood, Dow, Farris, Rowe, and Lyon were all ones I worked with, were teachers, or neighbors. A comment my dad made about Lovell was that he sat ram rod straight in a saddle. The WWI army engineering group my dad was in all had their own horse.
Some of my other teachers or associates mentioned were R. K. Brown, Lewis Holland (both teacher and neighbor), Lyon and Farris were neighbors, A. D. Moore, and M. B. Stout were teachers. At 102 Dow still walked around my neighborhood and his home was about 1/2 mile from mine and a substantial elevation change. He still had a good memory at 102.
Even though it was only 15 years later that I met some of those in the 1937 photo I am surprised at how young they looked in the photo.
The 1923 photo of radio class students may show my uncle at the right in the front row.
I am surprised at how small the enrollment was in the 1920s, thus the staff, and yet substantial research was going on at that time.
.
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