Would anyone have an accurate count of the bars and slots in a:

1500 HP, 2300 Volt, Ideal Electric Motor with a FLA of 316 at 1786 RPM and Frame Th-1901-Z?

Jim,
Only the manufacturer knows it or a repair shop that once may have counted and filed the number of slots and bars.
This is the trick to derive the requested data from a vibration measurement:
For this type of motor you will find a set of frequencies around 1200 .. 1800 hz, equally spaced 120 hz or 2*Fline. Divide each frequency component by fundamental speed frequency and the one that is most close to an integer should be the number of rotor bars. This requires a high resolution setting (number of lines 3200 or 6400 at a frequency range of 2000 hz). The result should never be a multiple of 6.
Usually the number of stator slots is more than the number of rotor bars. Also, the number of stator slots is basically a multiple of 6 for a three-phase machine. So, par example, if you find rotor bars is 58 (rather than 54, 50 or 62 or 66, then the number of stator slots could be 60, 66, 72. Most likely 72 for a 4-pole machine.
Look how the machine itself reveals a lot!
Hope this may help.
Regards,
Arie
NL

Jim

Ideal Electric still exists and is located in Ohio. I am not sure if I still have a contact there, but will check and email you directly. As I remember, they did not have too much trouble providing that type of information.

As mentioned by Arie, we have also been recommending that our clients' repair specifications require the counting of rotor bars, stator slots and bearing information on the repair report. There was some moaning from the repair shops, but the information is starting to be provided. In other cases, if you have a close relationship with your repair shop, they can contact the manufacturer directly.

You may also want to check with either PdMA, if you are still using your EMax or Baker, I seem to remember you started using that system, as they may have the information in their database. I checked mine and I do not have Ideal motors.

Howard

Arie & Howard,

Thanks for the information, sorry I didn't respond sooner but I had a log-in issue to deal with.

Even though this facility has added bars and slots to their motor shop repair specifications, this motor is not included because it was repaired prior to the bar and slot spec being added to the spec sheet. (This repair was done prior to the start of the online testing capability).

I also checked the AREVA ANP Framatome database and the other generic listing that I have with negative results. So, it looks like I'll take Arie's suggestion and look for the eccentricity peaks in the current spectrum and back calculate it that way.

Thanks again, Jim

quote:

Originally posted by Jim Zuidema:
Would anyone have an accurate count of the bars

If you are really desperate for the accurate number of the rotor bars you can use the following method. Accelerate the motor to the full speed, shut the AC power and inject the DC current to 2 phases of stator.
Take several current readings of the DC current as the motor decelerates (only one average per reading). On the second channel take a simultaneous reading of the pulses from the tachometer.
The slotting of the rotor will cause a ripple in the DC current. The current clamp will pick up the ripple as a bar count.
Attached are the spectra from the early experiment. The bottom is a spectrum of the tachometer pulses. The top is the current spectrum of the DC excitation. The first peak of the tachometer spectrum is the speed at that particular moment (1x). The peak in the current spectrum marked 28 is the bar count.
Despite the fact that this method works in principal I do not think that it will be widely used. Too complicated, and the safety people will scream at you. But using it in the shop is not a problem.
At the same time the incomplete knowledge of the number of the rotor bars cannot prevent me from performing a succesfull and conclusive current analysis.

jank

counting_the_bars.pdf (154 Kb, 68 downloads)

Jank,

I'm impressed! I may have to try this some day, thanks for the tip.


Jim