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Thread: Two speed one winding motor troubleshooting advice

  1. #21
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    Quote Originally Posted by phineascage View Post
    I agree and thought the same thing about the 152A observed at the motor shop. Certainly our motor service specialists could have missed something but our contact mentioned he was very impressed with the results from the winding tests performed at the shop. They have mentioned rewinding the motor as a possibility but that's probably a last resort for us right now. I tend to believe the motor was connected correctly at the motor shop based on conversations I've had with our contact. I have checked our connections here on site and know that Line connects to T1, T2 and T3 with other connections open for Slow and that Line connects to T6, T4 and T5 with T1, T2, and T3 shorted for High. At this moment I can't guarantee that the phasing is per the drawings at the motor junction box other than knowing that the fan turns in the correct direction in both Low and High, which I would think would be immediately disastrous for the motor if both Low and High phased with opposite rotations. The rotor had damage from the bearing failure and I am told the repair consisted of it being built up, turned down and balanced. The most perplexing thing, to me anyway, is that the motor operates below FLA while in Low. To my limited knowledge I'd think if there were a winding or mechanical problem within the motor the current draw would be proportional in both Low and High.

    Thank you for all for the great responses. You're all helping me grease the rusty cogs in my old brain.
    But mechanical load of the blower isn't 1:1 as speed changes. I don't know exactly how power factor and efficiency will change when speed changes on such a motor either - might not be same on high as it is on low, throwing your expectations off some as well.
    I live for today, I'm just a day behind.

  2. #22
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    Quote Originally Posted by Jraef View Post
    Yes, on 2S1W cooling tower fans in particular. Extremely low PF when uncoupled in high speed, in the order of .20 or less. So most of that current is reactive.
    That doesn't account for the difference in current between the motor in question and a normally functioning motor though.
    FWIW, as a first stab at modelling the motor performance I plugged in 95% for efficiency and 0.85 for power factor and that gave 289.8A for FLC or FLA as you guys call it. Pretty close to the nameplate value. A PF of 0.2 would be an awful lot more current.


    Quote Originally Posted by Jraef View Post
    The 45A difference when coupled to the gearbox is, in my opinion, the most suspicious aspect. As a general rule the most common gearboxes (Marley and Amarillo) are roughly 90% efficient. 45A out of 197A represents about 22% losses. A properly functioning gearbox would not be that much less efficient.
    But not really relevant since the OP has clarified it as uncoupled.
    Sounds very much like a motor problem to me.
    Si hoc legere scis nimium eruditionis habes.

  3. #23
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    Quote Originally Posted by Besoeker View Post
    That doesn't account for the difference in current between the motor in question and a normally functioning motor though.
    FWIW, as a first stab at modelling the motor performance I plugged in 95% for efficiency and 0.85 for power factor and that gave 289.8A for FLC or FLA as you guys call it. Pretty close to the nameplate value. A PF of 0.2 would be an awful lot more current.



    But not really relevant since the OP has clarified it as uncoupled.
    Sounds very much like a motor problem to me.
    I am leaning toward the motor or conductors to the motor. It has roughly 110 feet of three 500kcmil conductors feeding the High side windings and another 110 feet of three 3AWG conductors feeding the Low and also being used to short for High side. I can't understand a 45A difference at our facility running this motor in High(uncoupled), using our controls and conductors VS. what was observed at the motor shop running the motor in High(uncoupled) with their controls and conductors. Granted the voltage at the motor as connected at our facility(476VAC) is slightly higher than the nameplate(460VAC), I really don't think that is contributing to the high current to this motor as two other identical motors in the same application are not experiencing this problem. Furthermore voltage and current on each phase are pretty well balanced. For me it's a "Head Scratcher".

  4. #24
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    Have you checked the pitch angle (fan blades) and compared them, good tower to bad tower?

  5. #25
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    Quote Originally Posted by kwired View Post
    But mechanical load of the blower isn't 1:1 as speed changes. I don't know exactly how power factor and efficiency will change when speed changes on such a motor either - might not be same on high as it is on low, throwing your expectations off some as well.
    Yes, Thank you, that makes sense.

  6. #26
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    Quote Originally Posted by milldrone View Post
    Have you checked the pitch angle (fan blades) and compared them, good tower to bad tower?
    According to our cooling tower specialists that annually inspect our equipment they have found no problems with the gearbox or fan blades. It is certainly in the realm of possibility and I have yet not scratched it off my list.

    What keeps nagging me is the fact that this motor as connected at our site, uncoupled and run in High, draws about 45A higher than when tested at the motor shop, uncoupled and run in High. This 45A increase is also consistently observed when this motor is coupled to the fan gearbox VS. one of our other identical motors on the cooling tower that is also coupled and run in High.

  7. #27
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    Quote Originally Posted by phineascage View Post
    According to our cooling tower specialists that annually inspect our equipment they have found no problems with the gearbox or fan blades. It is certainly in the realm of possibility and I have yet not scratched it off my list.

    What keeps nagging me is the fact that this motor as connected at our site, uncoupled and run in High, draws about 45A higher than when tested at the motor shop, uncoupled and run in High. This 45A increase is also consistently observed when this motor is coupled to the fan gearbox VS. one of our other identical motors on the cooling tower that is also coupled and run in High.
    It's almost like there is a parallel 45A load that is present on your site that wouldn't be there at the motor shop. A long shot, really long shot. I'd still go for it being a motor problem. The 152A no-load current doesn't seem right despite what they say at the motor shop. And 197A even less plausible.
    Si hoc legere scis nimium eruditionis habes.

  8. #28
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    Quote Originally Posted by Besoeker View Post
    It's almost like there is a parallel 45A load that is present on your site that wouldn't be there at the motor shop. A long shot, really long shot. I'd still go for it being a motor problem. The 152A no-load current doesn't seem right despite what they say at the motor shop. And 197A even less plausible.
    Thank you Sir. I believe it's going to be sent out again anyway whether we really want to or not as it's getting hot enough to cook eggs on. It's also producing that old familiar burnt winding smell.

  9. #29
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    Quote Originally Posted by Besoeker View Post
    It's almost like there is a parallel 45A load that is present on your site that wouldn't be there at the motor shop. A long shot, really long shot. I'd still go for it being a motor problem. The 152A no-load current doesn't seem right despite what they say at the motor shop. And 197A even less plausible.
    By the way, I love your quote. I just had it translated via Google.

  10. #30
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    Was test at motor shop only the test they did after rewinding it or was it tested there after the higher current you measured at your facility?

    What I'm getting at is the motor may have been fine but now has developed a condition - like maybe a short between turns - which may be due to overloading or may be something that can be because of error during rewinding and took time to turn into what it is now.
    I live for today, I'm just a day behind.

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