On our forms: CMA - circular mills/amp, AGD - air gap density (lines/sq. inch), THD - tooth density (lines/sq. inch), BID - back iron density (lines/sq. inch). I hope this helps.
Thanks for answers.
Seems to me that in this case AGD is not air gap density. The most common case is when the value of air gap density is below the 50 000 lines per sq. inch. In exceptional cases, this value may be 65 000.
BTW, my earlier example is from an EASA publication.
Zlatkodo
zlatkodo, the values that I gave are from our EASA Motor Winding Verification Program (in USA units). I am attaching a copy of one that happens to be sitting on my desk.
Hi, Starkopete,
Probably, you're right.
I was confused by the value of AGD = 105 (105 is too small value, 105 000 is too high value). Must be an error.
Thanks for the explanation.
Zlatkodo
I have researched some more and found many similar AGD values, between 90 and 100.
Apparently, there is AGD expressed in another unit, not in lines per sq. inch. The unit is not written but I guess it could be lines per sq. millimeter. This makes some sense.
Also, some other important information is omitted or written in a unmarked units, so it is often necessary to guess.
Zlatkodo
zlatkodo:
Yes, the AGD figure of 105 most likely is 105 lines per square millimeter. This would be equivalent to 10500 lines per square centimeter OR 10500 Gauss OR 1.05 Tesla. An air gap flux density of about 1 Tesla is quite a reasonable figure.
starkopete:
Your example mentions lines per square inch. The AGD figure of 45713 lines per square inch is equivalent to 7087 lines per square centimeter OR 7087 Gauss OR 0.7087 Tesla. Tooth density is 1.29 Tesla (a bit low) and back iron density is 1.49 Tesla (a bit high), but I'm more familiar with large generators.
Thanks, Wolf,
BTW, I think, maximum and minimum value of flux densities in air gap, tooth and back iron for LV induction motors are well known.
With HV motors and generators, it is not the case. It would be interesting to see what are the most common values of these flux densities for large generators and HV motors.
Zlatkodo
wolf39:
You are correct about the densities not being dead on. This particular job was a rewind from 2300 volts to 480 volts and we maintained the densities that the original factory winding yielded. I am attaching the charts we use for reference when winding motors.
Most, if not all, hydro generators are salient pole machines. The air gap shape of salient poles can vary between constant and sinusoidal (turbogenerators always have constant air gaps around the stator circumference). Because of the variety of air gap forms, the air gap flux density of hydro generators can vary between 0.7 and 1.0 Tesla. Tooth flux densities can be as high as 1.7 Tesla and back iron flux densities may reach 1.3 Tesla. These figures are somewhat lower for cases when the generator specification is specifying high loss evaluation figures. Some recent loss evaluation values reached and even exceeded US$ 15000 per kilowatt.
I'm a little late to the discussion but here is my answer to zlatkodo.
AGP on zlatkodo's form definitely means 'air gap density' and the value is given in lines per square millimeter.
The EASA Motor Winding Redesign data sheet that is attached was made using zlatkodo's winding data. Note the similarity in the two forms. However, I do not believe that zlatkodo's form is a computer generated calculation sheet from the same program as mine. His looks like a an empty form or maybe a database that someone entered data into. I can explain why I think that if anyone is interested.
The units of measure for my USA version are millimeters for dimensions and lines per square centimeter for flux. I guess-estimated the back iron depth and tooth width based on the zlatkodo's core dimensions in order to have complete data for the calculations. THe tooth width is a good estimate but the back iron depth is a wild guess.
The results from the EASA Motor Winding Redesign program show 10,533 lines per square centimeter for AGP. This corresponds to a value of 105.33 lines per square millimeter as shown in zlatkodo's data sheet.
The only thing that I would add is that the flux densities look a little high for the air gap (AGD) and the stator teeth (THD) but otherwise this data looks good.
I cannot judge the back iron flux density (BID) since there is no way to reliably guess-estimate the back iron depth reading required to determine that value. It must me measured.
If you are rewinding this motor and currently have a bare core I would recommend taking accurate measurements for the back iron depth (and stator tooth width) and making the calculations so that you can know for sure what the densities are.
Hi, Rhatcher,
Thanks for your explanation.
I agree with everything you said. For one thing I am particularly interested.
I also think that the AGD = 1 T (64 516 lines / sq. inch or 100 lines / sq. mm) too large value for LV induction motors, for continuous work.
Perhaps it can be used in exceptional cases if the value of the BID and THD is in acceptable limits. What do you think about it?
During the calculations, I use the maximum and minimum allowed values for AGD, BID and THD in much more ranges, depending on the number of poles and the core - diameter (or power). In this way I get more reliable data.
I do not have this redesign-program but I am interested in further proceedings in the case, when some of the values is too high.
I guess, you will slightly increase the number of turns / coil and repeat the calculation. Sometimes you will need to repeat this several times until all values are within permissible limits. That's fine but now the new problem may occur with the values of the CMA. You're so increased the number of coils (reduced cross-section of wire) so that you got as a result, for example, a motor of 18 HP instead of 25 HP. What to do in such cases? This is something that often happens in practice, especially with small motors. If you're going to make a calculation with your program for many of the original windings, you would often get results with too high values of some of the flux densities.
Zlatkodo
Correction in text .
Instaed of:
You're so increased the number of coils (reduced cross-section of wire) so that you got as a result, for example, a motor of 18 HP instead of 25 HP.
should be:
You're so increased the number of turns/coil (reduced cross-section of wire) so that you got as a result, for example, a motor of 18 HP instead of 25 HP.
Zlatkodo
zlatkodo,
For what it is worth, I am attaching an excerpt from EASA's AC Motor Redesign book that deals with the relationships that you are talking about.
