Two speed one winding motor troubleshooting advice

[kwired]

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.

 

[Besoeker]

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.

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.

 

[phineascage]

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".

 

[milldrone]

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

 

[phineascage]

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.

 

[phineascage]

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.

 

[Besoeker]

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.

 

[phineascage]

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.

 

[phineascage]

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.

 

[kwired]

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.

 

[Besoeker]

By the way, I love your quote. I just had it translated via Google.

Ah, nothing like a bit of Latin even if it is bad Latin.....
Do you know what my user name means?

 

[JFletcher]

Next step to me would be to get an infrared gun and take measurements of the gearbox. Sometimes the simplest thing can be the problem ...to wit:

I used to run furnaces for Wastewater plants. We got an upgrade on our ID (induced draft) fans, from 150 to 250 horsepower, and appropriate upgrades to the scrubber systems as well.

One night while operating, I noticed the outboard fan bearing was warmer-than-normal. Next hour I was shut down with a seized up fan. this is a 6-foot diameter fandisc that weighs approximately a ton that came to a screeching halt.

maintenance pulled it apart, the inner race of the bearing was welded to the shaft. Cause of the failure was determined to be a very small amount of grease in the passageway from the oiler cup, causing a reduced flow of oil and subsequent failure.

Even if your gear boxes are perfectly fine, a quick scan with a cheap IR gun will at least rule them out as a problem.

How long has this problem existed with this fan? Is it possible to trace any maintenance or operational procedures to roughly when your problem started?

Since it sounds like your motor is already reinstalled and cannot be taken back out of service, it seems to me that you may want to look for non electrical sources of the problem, or at least eliminate them.

Your voltage readings were taken with the motor off? What were / are they at the motor while it is running? Excessive voltage drop could also cause higher amperage draw.

Can you measure to see if the fan is being overloaded via something like a higher differential pressure across it than the others?

 

[phineascage]

Ah, nothing like a bit of Latin even if it is bad Latin.....
Do you know what my user name means?

I'm sorry I do not. Please tell me.

 

[Besoeker]

I'm sorry I do not. Please tell me.

Visitor. In Afrikaans. It was on my ID badge at a gold mine in South Africa when I was checking some VFDs there.
We are all visitors in some sense so I thought it appropriate.
Sorry to wander off topic mods............

 

[phineascage]

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.

The motor failed in late March due to bearing seizure which damaged the rotor. I know the motor prior to failure was drawing high current just like it is doing now. The motor shop replaced the bearings and reworked the rotor and then performed winding testing and recorded the current draw. According to the shop all testing was within spec. which is another monkey wrench in my already muddled thinking. So it appears that the current draw measured at the motor shop vs. what is measured at my plant site differs by the order of 45A greater at my site. That's where it gets puzzling because that means the only difference between the two tests are the controls and conductors used in the test. All voltages and currents are balanced here. The voltage at the motor is roughly 476VAC across all phases.

 

[phineascage]

Visitor. In Afrikaans. It was on my ID badge at a gold mine in South Africa when I was checking some VFDs there.
We are all visitors in some sense so I thought it appropriate.
Sorry to wander off topic mods............

And I thought it was a play on Berserker..

One should NEVER assume.

 

[Besoeker]

Next step to me would be to get an infrared gun and take measurements of the gearbox. Sometimes the simplest thing can be the problem.

Whilst true, the OP has observed a 45A current difference with the motor uncoupled so unrelated to the gearbox. Of course, that doesn't preclude the possibility of a gearbox problem also. But it isn't the starting point since the higher current is there without the gearbox.

 

[kwired]

The motor failed in late March due to bearing seizure which damaged the rotor. I know the motor prior to failure was drawing high current just like it is doing now. The motor shop replaced the bearings and reworked the rotor and then performed winding testing and recorded the current draw. According to the shop all testing was within spec. which is another monkey wrench in my already muddled thinking. So it appears that the current draw measured at the motor shop vs. what is measured at my plant site differs by the order of 45A greater at my site. That's where it gets puzzling because that means the only difference between the two tests are the controls and conductors used in the test. All voltages and currents are balanced here. The voltage at the motor is roughly 476VAC across all phases.

Was actual voltage at motor measured on other motors being compared or when it was in the shop?

Bad connection in circuit won't last long with that kind of load being supplied, but VD because of length of circuit/size of conductor will remain constant.

At the level of current being drawn, it wouldn't take a lot of VD to see a 45 amp increase on a motor that size, enough to be a concern, but not enough to cause an immediately noticeable condition. But VA isn't exactly linear with loading either - low load typically lower power factor - which means VA is high in relation to actual input watts.

 

[phineascage]

Next step to me would be to get an infrared gun and take measurements of the gearbox. Sometimes the simplest thing can be the problem ...to wit:

I used to run furnaces for Wastewater plants. We got an upgrade on our ID (induced draft) fans, from 150 to 250 horsepower, and appropriate upgrades to the scrubber systems as well.

One night while operating, I noticed the outboard fan bearing was warmer-than-normal. Next hour I was shut down with a seized up fan. this is a 6-foot diameter fandisc that weighs approximately a ton that came to a screeching halt.

maintenance pulled it apart, the inner race of the bearing was welded to the shaft. Cause of the failure was determined to be a very small amount of grease in the passageway from the oiler cup, causing a reduced flow of oil and subsequent failure.

Even if your gear boxes are perfectly fine, a quick scan with a cheap IR gun will at least rule them out as a problem.

How long has this problem existed with this fan? Is it possible to trace any maintenance or operational procedures to roughly when your problem started?

Since it sounds like your motor is already reinstalled and cannot be taken back out of service, it seems to me that you may want to look for non electrical sources of the problem, or at least eliminate them.

Your voltage readings were taken with the motor off? What were / are they at the motor while it is running? Excessive voltage drop could also cause higher amperage draw.

Can you measure to see if the fan is being overloaded via something like a higher differential pressure across it than the others?

I have taken infrared scans of the gearbox. The inboard bearing is running around 130F and this agrees precisely with another identical gearbox. Saw nothing out of the ordinary on the gearbox body either.

I have only been at this facility for about 7 months. History on this particular motor is not what I'd like for it to be. What I do know is that in previous contracted IR scans of the MCC for this motor there have been instances of the Low speed/High speed shorted conductors showing hot since about 2002. This leads me to believe the problem has been here for a long time. These conductors would read hot since they are carrying an average of 158A each when the motor is running in high speed. These conductors are 2AWG THHN Copper 90C and are rated, I'm reading, for 130A.

I measured voltage with the motor in High both at the output of the Line to Load contactor and at the motor itself. It's roughly 480VAC(all phases) at the contactor output and about 476VAC(all phases) at the motor.

We have no instrumentation to measure air flow. Good idea though.

 

[phineascage]

Was actual voltage at motor measured on other motors being compared or when it was in the shop?

Bad connection in circuit won't last long with that kind of load being supplied, but VD because of length of circuit/size of conductor will remain constant.

At the level of current being drawn, it wouldn't take a lot of VD to see a 45 amp increase on a motor that size, enough to be a concern, but not enough to cause an immediately noticeable condition. But VA isn't exactly linear with loading either - low load typically lower power factor - which means VA is high in relation to actual input watts.

I have not measured actual voltage on our two other normally functioning fan motors. I tend to believe though that the voltage at each of their respective output contactors is roughly 480 on all phases since they are fed from the same MCC as our problem motor.

I wish I could find a voltage drop, I could stop scratching my head.