# 2 speed one winding motor problem



## gpop (May 14, 2018)

Are the fan blades fixed or adjustable pitch.


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## MDShunk (Jan 7, 2007)

I'll get this out of the way first: Modern energy savings practices would ordinarily have your cooling tower fans wired for high speed only and modulating off a VFD against a head pressure target. Something to think about for your future capital expenditures, and has nothing to do with your problem. The ROI is super quick.

Since the uncoupled current draw is also high, I'll ignore the typical suspects like fan blade pitch, sheave size, and gearbox issues for now. 

I'd like to know: Where were the amp draw measurements taken? At the bucket or at the peckerhead? I'd be curious to know if they're different at each end, which would rule in our out the wire between the bucket and the peckerhead. 

The unevenness of the amp draw measurements, phase to phase, has me a little concerned. Makes me think motor. It's not super-dramatic, but a little concerning. 

The fact that the motor is drawing 45amps more in your install, uncoupled, vs the motor shop's measurements has me thinking starter bucket/wiring issues. Any chance you can take a hank of wire to the roof and run this motor off the feed to the motor next door to it and see what you see? I know it's a PITA, but it would be an interesting test. 

How's the conductors from the roof to the bucket meg to each other and to ground? Have you megged the motor for yourself, and taken ohm reading for each winding's resistance yourself? 

There's something really simple going on here, I feel sure. Probably one of those things I could sort out in person pretty quickly but having a hard time putting my finger on it across the internet. Do you know, beyond a shadow of a doubt, that the shorting contactor is working well?


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## Helmut (May 7, 2014)

Has anyone looked at the load?


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## MDShunk (Jan 7, 2007)

Helmut said:


> Has anyone looked at the load?


His uncoupled amp draws are also high. Substantially higher than the motor shop's testing. I was discounting the load in my comments because of this. It's possible that the motor has such a soft foot that the whole motor is in one hell of a twist and has is slightly rotor-bound, but that seems quite unlikely for now. The feet would probably break off.


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## paulengr (Oct 8, 2017)

First off disagree about VFDs. You take a 5% energy loss running one and if it's going to run wide open all the time anyway and the motor is decently loaded which they are, you lose money. Winter savings is the only place you might get something.

Second a large imbalance isn't just concerning, there is something seriously wrong. If you have a phase imbalance the extra current creates a counter-EMF which not only uses up it's own power but fights the proper current amp for amp resulting in major overheating. Usually the cutoff on a PM is 5% and on a trip setting 10%. You have way more than that on a "good" motor.

Third and getting to your problem nothing about the readings signals a motor problem and since its all balanced we can probably rule out the starter or power or loose connections because those tend to show up as imbalanced conditions. Two cases. First if the voltage drop is excessive going to the motor then this causes torque at FLA to decrease a lot so the motor responds by turning slower and developing more torque but at a much higher current. It doesn't seem likely though because on a 4 pole motor you should be at around 15% of FLA at no load and you're at 50% which is more like what an 8+ pole motor does. So my bet is the current is going some place else...high resistance ground fault. Megger at the starter or take a flexible current probe and wrap it around all three phases since phase currents sum to zero. That or you have phase to phase problems. Try disconnecting the motor and starting with no motor. If you have current draw it's in the wiring. If this doesn't find it take voltages at the motor. Otherwise how do you know the motor shop repair is good? Did you get a pdma report? Do you have the equipment to check vibration (bearings)? Sure it's wired up right at the motor shop and field? There are several two speed wiring schemes and it wouldn't surprise me if it's wired differently internally, Use a microohm meter and check motors against each other to verify.

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## MDShunk (Jan 7, 2007)

paulengr said:


> First off disagree about VFDs. You take a 5% energy loss running one and if it's going to run wide open all the time anyway and the motor is decently loaded which they are, you lose money. Winter savings is the only place you might get something.


I just did 8 of these and the green dollar savings were 30K in the last 12 months. They only needed to run flat out Jun-Jul-Aug.


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## Helmut (May 7, 2014)

MDShunk said:


> His uncoupled amp draws are also high.



Are they for a variable torque motor?

Doesn't a constant torque pull full/close to name plate current, constantly, and a high speed only pull light current when lighty loaded?

I just figured variable torque would be somewhere in the middle.


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## Helmut (May 7, 2014)

Same problem with same motor, mounted in the same place over the years, you got a reputable motor shop you deal with that has done maintenance on this same motor over the years. You've been through the controls already.....ect.

A head scratcher.....I'm in


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## gpop (May 14, 2018)

I have never trusted motor shows to give a accurate amp reading on larger motors as most motor shop really don't have the infa-structor to do across the line starting on motors about 50hp let alone 250hp.


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## phineascage (May 16, 2018)

gpop said:


> Are the fan blades fixed or adjustable pitch.


The blades are fixed.


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## phineascage (May 16, 2018)

MDShunk said:


> I'll get this out of the way first: Modern energy savings practices would ordinarily have your cooling tower fans wired for high speed only and modulating off a VFD against a head pressure target. Something to think about for your future capital expenditures, and has nothing to do with your problem. The ROI is super quick.
> 
> Since the uncoupled current draw is also high, I'll ignore the typical suspects like fan blade pitch, sheave size, and gearbox issues for now.
> 
> ...


 
The current was measured at the MCC bucket. That is a good thought however to measure at the motor junction box. Keep in mind though the motor is becoming excessively warm indicating it is indeed experiencing the high current in the windings. 

Not so sure about the unevenness of the current draw phase to phase on this motor. On larger motors, in my past experience, I have seen more excessive imbalance in motors that were operating properly. 

The conductors is kinda where I'm leaning at the moment. Unfortunately we're talking about 3 runs of 110' of 500kcmil and a jacketed cable of 3 conductors and ground of 2AWG. Not the most feasible thing at the moment, however it could happen. 

I have not megged the motor on site. I will do that today since we had an unplanned shut down. This was done at the motor shop after repair and the findings were good on the motor itself. 

I can't guarantee anything in the shorting contactor other than the voltage measurement at each leg of it while the motor is in High all read about 11.3VAC and I read 0VAC across each leg at this time also. 

Thanks for the great ideas.


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## phineascage (May 16, 2018)

Helmut said:


> Has anyone looked at the load?


I inspected the gearbox with an IR camera and it was no different than an identical unit in operation. 

The fan blades were checked by our cooling tower specialists and passed with no issues.

The motor draws higher current uncoupled onsite vs. the uncoupled test at the motor shop after repair.


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## MDShunk (Jan 7, 2007)

With the shorting contactor pulled in, it would be interesting to read the voltage line to load, across each contact, to measure the microvolt (or volts) reading to gauge the state of the contacts. The shorting contactor for the star point is the one that really takes a beating in 2s1w motor starters.


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## Helmut (May 7, 2014)

phineascage said:


> The motor draws higher current uncoupled onsite vs. the uncoupled test at the motor shop after repair.


I suspect the motor shop tested it when they were done, as a normal delta configured, high horse power motor,not as a variable torque wired like you have. They may not have the set-up that allows them to do that. 

Do you know if they have the setup you do?


(don't mind my stupid questions, if they seem that way)


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## MDShunk (Jan 7, 2007)

Helmut said:


> I suspect the motor shop tested it when they were done, as a normal delta configured, high horse power motor,not as a variable torque wired like you have. They may not have the set-up that allows them to do that.
> 
> Do you know if they have the setup you do?


For high speed he shorts three leads and sends power out three leads. There's ain't much to the setup. Wouldn't matter if you did that at the peckerhead with nuts and bolts at the motor shop or had the starter do it for you automatically onsite.


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## phineascage (May 16, 2018)

paulengr said:


> First off disagree about VFDs. You take a 5% energy loss running one and if it's going to run wide open all the time anyway and the motor is decently loaded which they are, you lose money. Winter savings is the only place you might get something.
> 
> Second a large imbalance isn't just concerning, there is something seriously wrong. If you have a phase imbalance the extra current creates a counter-EMF which not only uses up it's own power but fights the proper current amp for amp resulting in major overheating. Usually the cutoff on a PM is 5% and on a trip setting 10%. You have way more than that on a "good" motor.
> 
> ...


 
Man, those are some really great ideas. I'm going to start with megging this morning.


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## phineascage (May 16, 2018)

MDShunk said:


> With the shorting contactor pulled in, it would be interesting to read the voltage line to load, across each contact, to measure the microvolt (or volts) reading to gauge the state of the contacts. The shorting contactor for the star point is the one that really takes a beating in 2s1w motor starters.


I got 0VAC.


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## phineascage (May 16, 2018)

Helmut said:


> I suspect the motor shop tested it when they were done, as a normal delta configured, high horse power motor,not as a variable torque wired like you have. They may not have the set-up that allows them to do that.
> 
> Do you know if they have the setup you do?
> 
> ...


Hey, that's definitely a possibility. I will ask them.


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## Helmut (May 7, 2014)

..............


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## Helmut (May 7, 2014)

This is what we're dealing with?


View attachment 126914


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## MDShunk (Jan 7, 2007)

You posted a picture of the wiring diagram for two different types of 2s1w motors.


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## Helmut (May 7, 2014)

MDShunk said:


> You posted a picture of the wiring diagram for two different types of 2s1w motors.


????

I thought this page was for single winding, 3 phase single voltage, 2 speed, 6 winding motors, and how they can get wired depending upon the application?

OP is using as variable torque.


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## MDShunk (Jan 7, 2007)

Helmut said:


> ????
> 
> I thought this page was for single winding, 3 phase single voltage, 2 speed, 6 winding motors, and how they can get wired depending upon the application?
> 
> OP is using as variable torque.


You don't get to pick.


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## Flyingsod (Jul 11, 2013)

phineascage said:


> I got 0VAC.




Zero is crazy low. You were on the miilvolts scale right? I’d expect at least 10 and up to 100. More than that and it’s something to investigate 

Btw I very much admire your original post. I think it’s the most informative OP I’ve ever seen. Kudos 


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## frenchelectrican (Mar 15, 2007)

I think there is something is missing in this part but I will not pinpoint excatally but did anyone ever check the rotor to see if it was going bad or what ? 

If one of the rotor bar going bad it can cause uneven current reading.


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## Helmut (May 7, 2014)

MDShunk said:


> You don't get to pick.




Oh....


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## phineascage (May 16, 2018)

Flyingsod said:


> Zero is crazy low. You were on the miilvolts scale right? I’d expect at least 10 and up to 100. More than that and it’s something to investigate
> 
> Btw I very much admire your original post. I think it’s the most informative OP I’ve ever seen. Kudos
> 
> ...


To ground on each output of the shorting contactor I was seeing 11.3VAC. Across each internal contact of this contactor I saw 0. I was on the Volts scale. 

Thank you sir. Data is always key.


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## phineascage (May 16, 2018)

frenchelectrican said:


> I think there is something is missing in this part but I will not pinpoint excatally but did anyone ever check the rotor to see if it was going bad or what ?
> 
> If one of the rotor bar going bad it can cause uneven current reading.


It was sent to our motor repair shop. All windings and rotor were tested after the repair. I can only give them the benefit of the doubt. 

This problem has been evident for some time now.


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## Helmut (May 7, 2014)

MDShunk said:


> You don't get to pick.


You're positive? 
You can't wire this motor, for three different applications.


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## phineascage (May 16, 2018)

paulengr said:


> First off disagree about VFDs. You take a 5% energy loss running one and if it's going to run wide open all the time anyway and the motor is decently loaded which they are, you lose money. Winter savings is the only place you might get something.
> 
> Second a large imbalance isn't just concerning, there is something seriously wrong. If you have a phase imbalance the extra current creates a counter-EMF which not only uses up it's own power but fights the proper current amp for amp resulting in major overheating. Usually the cutoff on a PM is 5% and on a trip setting 10%. You have way more than that on a "good" motor.
> 
> ...


I meggered at the starters. Each phase to ground at 5kv for 20sec each:
T6 - 399k
T5 - 349K
T4 - 433k

T1 - 475k
T2 - 466K
T3 - 514K

I performed a second and third megger test for my own interest on settings of 2.5kv and 1000V and received slightly higher returns on the resistance measurement as I expected.

I checked a second identical non problematic motor in the same way and received results that were just slightly lower in terms of resistance. Again, this too is a non malfunctioning motor. 

T6 - 323K
T5 - 303k
T4 - 268K

T1 - 412k
T2 - 435k
T3 - 352K


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## telsa (May 22, 2015)

Before you go crazy, check out non-electrical issues -- such as obstructions to the air flow... coming or going. 

That much 'lost' energy would be radiant in a power circuit.

You've got to be throwing it into the atmosphere... somehow.

Pull IR temperature readings everywhere you can imagine.

If nothing's hot, then you've got a curious hidden load factor that has you stumped.

A failing motor can do strange things, like suck down energy and then blow it off with forced cooling.

So, fur sure, you've got to meg it eight ways from Sunday. You're looking for anything odd, out of balance.

I'd give you some luck, but it's on back-order, still.


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## gpop (May 14, 2018)

Really reaching but worth asking.....is the motor mounted vertical or horizontal


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## frenchelectrican (Mar 15, 2007)

phineascage said:


> It was sent to our motor repair shop. All windings and rotor were tested after the repair. I can only give them the benefit of the doubt.
> 
> This problem has been evident for some time now.


Fair enough with that one.,

but I think you did cover the FOP test ( fail of pontineal test ) if ya did that I do not know if you did record the X number of voltage drop thru the contractor escpally with shorting verison.


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## phineascage (May 16, 2018)

telsa said:


> Before you go crazy, check out non-electrical issues -- such as obstructions to the air flow... coming or going.
> 
> That much 'lost' energy would be radiant in a power circuit.
> 
> ...


 
The problem exists both coupled and uncoupled. 

I have examined everything I know to examine with our IR camera. The only components showing hot are the Motor body and the Low speed/High speed shorted conductors.

Yes thanks for the offer. My luck ran out years ago. I'm now operating off of prayers.


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## phineascage (May 16, 2018)

gpop said:


> Really reaching but worth asking.....is the motor mounted vertical or horizontal


The motor is mounted horizontally.


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## phineascage (May 16, 2018)

frenchelectrican said:


> Fair enough with that one.,
> 
> but I think you did cover the FOP test ( fail of pontineal test ) if ya did that I do not know if you did record the X number of voltage drop thru the contractor escpally with shorting verison.


The voltage across the shorting contactor is 0. The voltage across T6,T4 and T5 contactor is very low around 1 or 2 volts if that much.


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## gpop (May 14, 2018)

Everything to me points to the size of the wire you are using on 1-2-3. It account for higher amps at low speed, unbalanced 2 whe windings at high speed plus higher amps.
As the motor shop would have bugged 1-2-3 for testing you would expect a different result as they are not dealing with 200 feet of voltage drop on a undersized cable.

I would hazard a guess that you could drop 1-2-3 off the slow starter and cap for safety then bug 1-2-3 at the motor. Run in high speed and see if the amps drop.


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## Helmut (May 7, 2014)

MDShunk said:


> You posted a picture of the wiring diagram for two different types of 2s1w motors.


Ok, I think I know why I may be confused here.
The pic uses the word connections, And that's why I assumed you can connect this in different configurations.

If the word connections was replaced with the word motor, it would be clear as day. Is this what is really being conveyed in that doc?

A CT motor can not be wired as a VT or CH or vise versa. They are all built differently?


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## gpop (May 14, 2018)

Helmut said:


> MDShunk said:
> 
> 
> > You posted a picture of the wiring diagram for two different types of 2s1w motors.
> ...


Simple put yes. There is never more than one diagram for a motor. Even a 18 lead only has one diagram.
Next to the diagram is your lead connection patterns any options are listed there and the way the leads are connected


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## paulengr (Oct 8, 2017)

Helmut said:


> Ok, I think I know why I may be confused here.
> 
> The pic uses the word connections, And that's why I assumed you can connect this in different configurations.
> 
> ...




If you break all the coils out such as with 12 lead delta wyes you can make it anything you want. As you add internal connections typically joined at the yoke you lose options but gain sanity in the peckerhead. If you want your head to hurt go to a motor shop and ask a winder to show you the charts of spans, groups, and so on. It will make your head hurt.

Do yourself a favor if you’re serious. Ask your motor shop for an EASA “Uglies” electrical engineering book. We get them for a couple bucks and give them away. Second go to NEMA.org and download the condensed MG-1 standard which is also free. This gives you the data, wiring diagrams, and so on for most motors up to 500 HP. As a motor shop field service engineer this is what I use. I don’t even look at it for 3, 6, and 9 lead motors and DCs but for everything else I always pull out the book so I don’t make a mistake.


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## paulengr (Oct 8, 2017)

If your motor shop is not an EASA member go elsewhere. Same if they are not third party inspected (ISO 9000, EASA certified, etc.).


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## Helmut (May 7, 2014)

paulengr said:


> If you break all the coils out such as with 12 lead delta wyes you can make it anything you want. As you add internal connections typically joined at the yoke you lose options but gain sanity in the peckerhead.


That was my train of thought. Some motors you can make different ways, and some you can't. A typical 3 wire motor is what it is. Other 9 wire motors you can apply different voltages to and so on...

I din't think these were any different, considering the connection wording.

Tx for your help.


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## gpop (May 14, 2018)

paulengr as a motor shop field service engineer Whats your thoughts on the wire sizes going to this motor and the affect it might have.

Taking tit bits of info from different posts

500 mcm to 4-5-6
2awg to 1-2-3 
motor is 110 feet from starters

(I though the spec would have been a 4/0 min for 1-2-3)

Uncoupled motor from gear box and ran motor with no load. Recorded motor current:
High Speed:
T6 - 191.1A
T4 - 198.1A
T5 - 191.9A
High speed shorted connection current to problem fan motor: 
T1 - 161.9A
T2 - 154A
T3 - 156.6A

Low Speed:
T1 - 80.8A
T2 - 81.8A
T3 - 81.6A



Shouldn't the current on T1 be around half of the current on T6 if its a 2 wye I would have presumed that both whe would be working equally. Maybe slightly more accounting for the extra 200 feet of cable being used to join the wye but closer to half than these results. (I may be total wrong)


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## JRaef (Mar 23, 2009)

gpop said:


> Shouldn't the current on T1 be around half of the current on T6 if its a 2 wye I would have presumed that both whe would be working equally. Maybe slightly more accounting for the extra 200 feet of cable being used to join the wye but closer to half than these results. (I may be total wrong)


An engineering reference book I have says that the shorting contactor, which is what is tied to 1, 2 & 3, must be sized as a minimum of 50% of the other contactors, so that would agree with your thought.

The other thing is that when it is in 2Y (high speed) the current in each set of parallel windings should be the same. So why is it higher in one set than the other?










I think you may have hit the nail on the head... the conductors going to 1, 2 & 3 are under sized, causing a voltage drop! 500MCM is the correct size (not accounting for VD here) for the High Speed FLA (290 x 1.25), but half of that should have been 3/0, maybe 4/0 depending on VD, but #2 is WAY too small. Methinks someone sized those conductors based on the Low Speed FLA, which is erroneous. The shorting circuit for 1, 2 & 3 is only carrying current in High Speed operation.


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## gpop (May 14, 2018)

JRaef that my thought and as the 2 awg is in some kind of multi conductor it sounds like a add on after the fact. Maybe a salesman told them that during the winter they could save lots of money by installing a 2 speed. 

The part I don't understand is were are the amps going. The cable can not be burning off that many amps over 100' so its got to be a affect of the motor. (power factor, inductance or something like that ?)


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## Helmut (May 7, 2014)

If the conductor was undersized, wouldn't you see this at each motor?

I thought he has 3, all the same everything, and only has problems with one in particular.


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## gpop (May 14, 2018)

Helmut said:


> If the conductor was undersized, wouldn't you see this at each motor?
> 
> I thought he has 3, all the same everything, and only has problems with one in particular.


 
I like the way you are thinking. 

So the question is to the OP if all 3 are the same. 

Voltage drop is calculated on distance so im guessing this is the furthest from the contactors but that's just a guess. 

Its like someone said earlier in a post. If they could see it they could probably figure it out in a few minutes.

General rule of thumb when you have one out of group playing up is to look for the difference. Look for anything new. Back track the history.


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## phineascage (May 16, 2018)

As yet I finally received motor reports from our motor repair shop for our problem motor and another that was repaired some time back. They ran both motors in High at roughly 452VAC. Our problem motor in high speed drew current at roughly 160A. Our non problem motor in high speed drew current at roughly 103A. At this point we're looking to pull our problem motor and send for re-winding. 

The lesson for me is, I should have had reports in front of me instead of relying on verbatim from the motor shop. 

I would like to thank everyone for their ideas, advice, and experience. Hopefully rewinding the motor will solve my issue.


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## gnuuser (Jan 13, 2013)

I always instructed my apprentices to follow this procedure when installing a new motor:
weigh the motor and record the data, meg the motor and record the data. verify the nameplate data with the documentation and thermal imaging.

weighing the motor because often i have found rewound motors with less windings than what they should have (causing excess current draw and heat)

megging the motor gives you a baseline reading before installation and deviation of those readings is an early indicator of problems if done so on a rigid maintenance schedule.
the same applies to thermal imaging (schedule)

and last precision alignment is crucial as misalignment can cause premature wear in bearings and binding this includes the bearings pressed in the motor housing.
it does not take much of a pressed bearing misalignment to bind a motor

i suspect the op's original problem could be either the shaft binding or an insufficient winding as well. but i do not rule out undersized conductors


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## The professor 193 (May 23, 2021)

phineascage said:


> Hi,
> I’ve tried finding help for a current problem I’m having here and on other websites but can’t seem to nail down what I’m dealing with. I’m looking for some troubleshooting advice on a 3 phase 2S1W type motor problem. The motor is operated by three contactors. One contactor supplies line voltage to T1, T2, &T3 for Low speed while the other two contactors are open. For High speed another contactor supplies line voltage to T6, T4, & T5 and the third contactor shorts T1, T2, & T3. This motor is used to operate a cooling tower fan in a power plant type facility. It is a three cell cooling tower and generally all cells are in operation. In the warmer months all three cell fans will operate in high speed. My problem is that one fan continuously draws abnormally high current while operating in high speed. While in low speed the current is below FLA and appears normal. The motor nameplate information is below:
> High: 460VAC / 250HP / 290FLA / 1.15SF / 1790RPM / ENCL TEFC / 2 SPD 1 WDG Variable Torque
> Low: 460VAC / 62HP / 100FLA / 1.15SF / 890RPM / ENCL TEFC / 2 SPD 1 WDG Variable Torque
> ...


I’m not there so I’m only assuming thst the feeder wires from the main source is two small for the inrush current of the the motor. Over time the with motor has been starving it self of volts. Lowering the amps. P=IE. 

your power can’t change. voltage lowers just enough to let it run which cause your current to go up proportional to the percentage of voltage drop. 
The distance for the wires amp rating is not adequate to handle the amps of the motor draw at the lower voltage produced by the undersized wires. 

it will run normal until it runs for a period of time which excess heat is created by the high amps it’s drawing to keep up with the power draw of the motor. It also sounds like to me that you over current protection is not sized correctly.


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## paulengr (Oct 8, 2017)

MDShunk said:


> I just did 8 of these and the green dollar savings were 30K in the last 12 months. They only needed to run flat out Jun-Jul-Aug.


I highly doubt you saved anything based on your description. Proper operation of a cooling tower means you start or stop towers based on demand. If you had just one cell and on/off modulation is more efficient from about 70% to maximum capacity. But you have 8 cells. So with on/off modulation we get capacity in steps from 12.5% to 100%. If we are down to 70% of one cell or 8.75% demand or less VFDs save money. If you put VFDs on every cell then the ones that are or should be running at 100% are now using an additional 5% power so there is no scenario that saves money over the original system if it is running optimally. With 2 speed fans it gets even worse. A 2 speed fan running at half speed produces 25% of the air flow at 12.5% power. There are many more steps based on a mix of high and low speed fans. The minimum output for 8 fans is now 3.1% and VFDs are more efficient at 2.2% capacity or less with ONE trim VFD or even less with two.

But I often see stupid control strategies that aren’t optimized so the VFD improves on a suboptimal method like all off/low/high. The optimal strategy has been around for decades but above the heads of most PLC programmers who still write onion logic.


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## gpop (May 14, 2018)

paulengr said:


> I highly doubt you saved anything based on your description. Proper operation of a cooling tower means you start or stop towers based on demand. If you had just one cell and on/off modulation is more efficient from about 70% to maximum capacity. But you have 8 cells. So with on/off modulation we get capacity in steps from 12.5% to 100%. If we are down to 70% of one cell or 8.75% demand or less VFDs save money. If you put VFDs on every cell then the ones that are or should be running at 100% are now using an additional 5% power so there is no scenario that saves money over the original system if it is running optimally. With 2 speed fans it gets even worse. A 2 speed fan running at half speed produces 25% of the air flow at 12.5% power. There are many more steps based on a mix of high and low speed fans. The minimum output for 8 fans is now 3.1% and VFDs are more efficient at 2.2% capacity or less with ONE trim VFD or even less with two.
> 
> But I often see stupid control strategies that aren’t optimized so the VFD improves on a suboptimal method like all off/low/high. The optimal strategy has been around for decades but above the heads of most PLC programmers who still write onion logic.



That's a presumption based on how the towers are configured and what they are used for. No one said they were multi-cell.


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## Wirenuting (Sep 12, 2010)

A Zombie has risen


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