# Excessively hot 160kW motor



## Electrorecycler (Apr 3, 2013)

Background Info: We have a Centrifuge driven by a 160kW, 460 volt motor. The motor is driven by a TECO VFD. The VFD is protected by a line reactor. The motor is fed using parallel runs of 1/0, 4 conductor, unshielded, about 20' long. This machine runs 24 hours/day, 7 days/week unless it's shut down for a tooling change or other necessary maintenance. 

We have been having an issue with this motor becoming excessively hot. This time of year, when the ambient temperature in the building is 10 - 15 degrees C, the motor runs at around 60*C. During the summer, when the ambient temperature in the building is around 30 - 35 degrees C, the motor runs upwards of 100*C. It then kicks out on excessive temperature. The only way to prevent this is to have a fan constantly blowing on it to help keep it cool. What I'm wondering is if this is simply caused by a combination of ambient temperature and overworking of the motor, or if Harmonics produced by the VFD might be contributing to this?

I ask because we had a MOL inspector (why he was asking this, I don't know since it's outside of his authority) ask why it was running hot, if it was the correct motor for the application (yes, supplied by the OEM) and if was safe to operate. Before I put anything on paper for him, I'd like a few other professional opinions besides my own.


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## Cow (Jan 16, 2008)

Have you verified for yourself it is a VFD rated motor? Class F insulation?

What speed does the motor run at a majority of the time?

What exactly is "kicking out on overtemperature?"

Does the motor have leads for an internal thermostat?

Is the air supply into the room capable of keeping the motor ventilated?


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## micromind (Aug 11, 2007)

Cow said:


> Have you verified for yourself it is a VFD rated motor? Class F insulation?
> 
> What speed does the motor run at a majority of the time?
> 
> ...


Also, how does the current reading on the VFD display compare with the nameplate? 

What is the motors service factor?


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## KennyW (Aug 31, 2013)

If it is the winding temp that is 100c, that is not hot at all for what is most likely a motor with class f insulation.


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## Southeast Power (Jan 18, 2009)

200 plus hp is a decent size motor.

I would look at the load. I suspect that a centrifuge needing that size motor would have quite a bit of surface area. The larger the surfaces, depending on the material, the more susceptible they might be to expansion.

Do you have access to a thermography service that can interpret their findings?


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## Mike_kilroy (Sep 2, 2016)

You specifically asked if VFD harmonics can cause your motor overheat issues: answer is definite - maybe.

You have received a bunch of replies asking very important questions. You need to systematically answer each of these to help identify why YOUR motor is overheating.

As for your specific VFD question: A cheap VFD will add 5-7% additional heat to the motor it runs, irregardless of load. 

So if your motor is overheating and kicking out, then your load is above what the motor can handle. Simple. If it is sized so close to the limit that this additional small 5-7% extra heat causes issue, then the motor is undersized for the application.

Answer the other questions so you can be sure you do not have OTHER problem(s) causing this. 

Be sure to pay close attention to the speed you are running: I assume your centrifuge load increases by the square of the motor speed, so a small increase in speed above its OEM rating may be your issue. Or you may have the VFD programmed slightly wrong and are on wrong v/hz line - either too hi or too low and you add current to the motor. 

Without more info, one cannot say "put an output reactor between the motor and VFD to reduce that 5-7% to maybe 3-5%" but it may also be an option.


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## varmit (Apr 19, 2009)

From the OP, I will assume that this equipment has "always worked before". 

1.) Is a thermal sensor in the motor tripping?
If so some condition has changed- mechanical misalignment, bearing failure, material change, excessive material loaded into the centrifuge, possible winding insulation breakdown, dirt or material build up interfering with motor cooling, running motor faster than rated speed, loose or corroded terminations.

2.) Is the VFD tripping on over temperature? 
If so, is there a motor temperature sensor connected to the VFD "enable"?
If so, all items in (1.) may apply.

3.) If there is no temperature feedback from motor to VFD and the VFD is tripping on "over temperature", there could be a VFD problem.
It could be as simple as a failed cooling fan on the VFD.
It could also be the VFD dying.
Often the indicated VFD fault is not the actual problem. VFD component failure is a possibility.
Check the VFD fault history to see if there are other faults.


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## John Valdes (May 17, 2007)

Centrifuges do not use standard motors. They are specially built for this application.
For one thing they must operate at above standard base speeds.
I found this out the hard way once when trying to replace one. We ended up rewinding and installing new bearings in the one in question. There was also machine work involved with both end bells. I also believe the shafts needed attention as well.

We need the nameplate info from the OP and especially the design code and the RPM.
Centrifuge motors are designed to run at very high speeds, so knowing what the nameplate says will be required before anyone can help the OP.

Also OP. Whats the drives carrier frequency set too.


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## Electrorecycler (Apr 3, 2013)

Wow, I guess I should check this over the weekend. 

The insulation class is H...I suppose I should have included that. 


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## Electrorecycler (Apr 3, 2013)

By "kicking out on over temperature", I'm referring to the motor thermistor. My technical terminology ends up getting dumbed down at work. How else do you explain things to management? 


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## Electrorecycler (Apr 3, 2013)

We've had considerable issues with this equipment over the years. Over heating and motor rewinds have been a consistent thing (2 rewinds in my almost 5 years here). I'll check into the VFD carrier. 

As for speed, the centrifuge runs consistently at 1220 rpm. The rated motor rpm is 1780. 


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## Electrorecycler (Apr 3, 2013)

The OEM allows for a maximum speed of 1450 rpm. Sorry for all the posts, there's a lot of information to fill in here. 

One more piece of info, the VFD is oversized for the application. I believe it's sized for 250 kW. 


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## oliquir (Jan 13, 2011)

whats the frequency the the vfd operates ( 1-2-3khz,..., maybe it is set too high and add heat to the motor


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## John Valdes (May 17, 2007)

Electrorecycler said:


> By "kicking out on over temperature", I'm referring to the motor thermistor. My technical terminology ends up getting dumbed down at work. How else do you explain things to management?


I always called the type that opens at a certain temp a Klikson. To hot it opens and then closes when the temp has come down low enough. Like whats in a hair dryer.
On drives this would be connected to a digital input. And that input is programmed to alarm or to shut the drive down.
You may have a thermistor. (RTD or thermocouple) In the drive parameters you set the temperature value.



Electrorecycler said:


> We've had considerable issues with this equipment over the years. Over heating and motor rewinds have been a consistent thing (2 rewinds in my almost 5 years here). I'll check into the VFD carrier.
> As for speed, the centrifuge runs consistently at 1220 rpm. The rated motor rpm is 1780.


You sure you are using the correct term for a "centrifuge"? I have not seen one that was that slow. 
Are you guys using gearing and or mechanical option to get higher speeds?
The RPM you have is not special and this may very well be a standard or OEM motor? What does the nameplate say.



oliquir said:


> whats the frequency the the vfd operates ( 1-2-3khz,..., maybe it is set too high and add heat to the motor


This why I asked what the "carrier frequency" was set too.
It very well could over heat a motor if set to high.


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## JRaef (Mar 23, 2009)

+1 on the carrier frequency. Carrier Frequency (CF) is the pulse rate of the PWM going to the motor, not the motor speed frequency. It is responsible for the "whine" sound coming from the motor, and people sometimes increase the CF to "get rid of" that whine. It doesn't really get rid of it, but by adjusting it above 10kHz the pitch moves out of human hearing (or if you are 50+, 5kHz does it). The problem with that is that it increases the switching losses inside of the drive and it increases the motor heat. The fact that the drive is over sized is a possible indicator that the OEM KNEW that they were going to run this at a high CF in order to make the motor run quieter, and thereby sacrifice the motor life, knowing that the motor would likely outlast the warranty anyway. On something as big as 160kW, you definitely want that CF to be as close to 1kHz as you can get it. The motor will whine, but usually the machine makes more noise than that anyway.

If the CF is already as low as it can get, you might also want to check the control method. It's best to use Sensorless Vector Control for something like a centrifuge, but depending on the age of the drive, that may not have been an option, Teco were a little late to the party. So if it is in V/Hz mode, check the V/Hz pattern; it will be programmable. In a V/Hz drive, if you need extra torque to accelerate a load, and that is common on centrifuges, then you must "boost" the voltage at low speeds. If the settings on that are done incorrectly, you might end up boosting the voltage excessively at higher speeds, which would over flux the motor and heat it up.

Post a catalog number of the VFD and many of us can help further.


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## Electrorecycler (Apr 3, 2013)

John Valdes said:


> I always called the type that opens at a certain temp a Klikson. To hot it opens and then closes when the temp has come down low enough. Like whats in a hair dryer.
> On drives this would be connected to a digital input. And that input is programmed to alarm or to shut the drive down.
> You may have a thermistor. (RTD or thermocouple) In the drive parameters you set the temperature value.
> 
> ...




The thermistor ties to a PTC relay, not the VFD. That in turn sends an input to the PLC when the internal motor temp reached alarm point....I'll have to check AB's specs to see what that temperature is. 

As for Centrifuge being the correct term, yes, that's exactly what it is, however we use this one to delaminate plastics from metals. It's actually called a "delamination mill". The operation is similar . It spins at high speeds and processes material between hammers and stators. The rpm of the mill is actually about 7% slower than the motor. 


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## Electrorecycler (Apr 3, 2013)

Thanks JRaef. And a minor correction, the VFD is stamped TECO on the front, but is actually a Sinus Penta. The catalog number (I think) is: ZZ0124051.74013

And yes, it seems that the control method is V/Hz. I'll check the carrier frequency ASAP, but it is definitely in the audible range.

To be honest, I think the overheating issues are caused by high ambient temperatures and operator error, but I've been asked to investigate every possible reason for this, so investigate I will.


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## JRaef (Mar 23, 2009)

The Sinus Penta drives are made by Elettronica Santerno, an Italian company. kind of an impressive drive actually, I almost went to work for them at one time. So for them, the operating mode we call "V/Hz" is called "IFD" which supposedly stands Inverter Frequency Drive, which if you ask me, is redundant... But whatever.

Now, the one thing I have never liked about that drive is in fact the carrier frequency issue. They have made it WAY too complicated, because they allow you to program a rate of CHANGE in the CF as the motor speed changes. If left at the factory defaults, the CF will climb as the speed increases, up to 16kHz at full speed! That can DEFINITELY cause the motor to over heat. I think that is a dangerous default position, I would expect to see a fixed LOW CF as the default, then ALLOW a user to change it and maybe even vary it (although most people will not fully understand the consequences).


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## Electrorecycler (Apr 3, 2013)

> If left at the factory defaults, the CF will climb as the speed increases, up to 16kHz at full speed! That can DEFINITELY cause the motor to over heat.


I was reading into this in the manual today before I left. It seemed rather complicated and a little confusing, but what you're saying was the gist of it. I'm going to stop the machine tomorrow and make the changes to the lowest carrier frequency I can. Time will tell if it helps with running temperature.


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## Electrorecycler (Apr 3, 2013)

Update: I checked the carrier frequency this morning. Apparently Sinus Penta drives of this frame size come default with the carrier frequency set to 2khz. The "silent modulation" setting (increasing carrier frequency with increasing speed) comes turned off as default. I lowered the carrier to 1.6khz, which is lowest that this particular vfd will go. The only setting I didn't change in regards to this was the "Pulse Number", which apparently has no effect unless the "silent modulation" is turned on.


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## Mike_kilroy (Sep 2, 2016)

John Valdes said:


> 1) You sure you are using the correct term for a "centrifuge"? I have not seen one that was that slow.
> Are you guys using gearing and or mechanical option to get higher speeds?
> The RPM you have is not special and this may very well be a standard or OEM motor? What does the nameplate say.
> 2) This why I asked what the "carrier frequency" was set too.
> It very well could over heat a motor if set to high.


1) Might you be thinking of a COMPRESSOR? I have "high speed" compressor motors of this size running at 40,000rpm with our drives... to take nitrogen out of the air for oil companies...

2) Not so fast: HIGHER VFD freqs will REDUCE motor heat and INCREASE VFD heat.... Higher is good for his motor....


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## Mike_kilroy (Sep 2, 2016)

Electrorecycler said:


> Update: I checked the carrier frequency this morning. Apparently Sinus Penta drives of this frame size come default with the carrier frequency set to 2khz. The "silent modulation" setting (increasing carrier frequency with increasing speed) comes turned off as default. I lowered the carrier to 1.6khz, which is lowest that this particular vfd will go. The only setting I didn't change in regards to this was the "Pulse Number", which apparently has no effect unless the "silent modulation" is turned on.



Contrary to some folks beliefs, this 1.6khz should make your heating issue WORSE... Lower VFD PWM CF freq heats the motor more, not less.


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## Electrorecycler (Apr 3, 2013)

Mike_kilroy said:


> Contrary to some folks beliefs, this 1.6khz should make your heating issue WORSE... Lower VFD PWM CF freq heats the motor more, not less.


I'll be observing the motor for some time. I'm taking regular trips with a thermal imaging camera. If the carrier frequency is having a negative effect, it should be obvious sooner rather than later. The motor is running hotter today than yesterday, but the ambient temperature is also higher. I've recommended that we monitor the motor temp, ambient air temp and motor current through historical trends for the next few months to have the data to properly come to a conclusion.


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## JRaef (Mar 23, 2009)

Mike_kilroy said:


> Contrary to some folks beliefs, this 1.6khz should make your heating issue WORSE... Lower VFD PWM CF freq heats the motor more, not less.


Hmmm, well sort of.

This is true if considering only the harmonic current per se, because the wave form looks a little worse at 1.6khz compared to 15kHz. So at full speed, yes, that is true. But you rarely run the motor at full speed when you have a VFD, in fact that's WHY you have VFD.

When running at a reduced speed, you have another factor that causes motor heating, the virtual frequency of the higher CF compared to the real speed of the rotor. So lets say we are running at 50% speed, so a 4 pole motor rotor is spinning at 875RPM. If the CF is 2kHz, the virtual speed of the number of magnetic lines of force being cut by the rotor is (120 x 2000/4) = 60,000RPM, compared to the actual speed of 875RPM. The energy represented by that higher virtual frequency is not doing any useful work and becomes pure heat in the rotor. If you lower the CF to 1.6kHz, the virtual frequency is (120 x 1600/4) = 48,000Hz, so the wasted rotor heat is 80% of what takes place at 2kHz.


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## chrisfnl (Sep 13, 2010)

Electrorecycler said:


> Wow, I guess I should check this over the weekend.
> 
> The insulation class is H...I suppose I should have included that.
> 
> ...


100degC isn't excessively hot if you've got Class H insulation...

Just wondering if maybe you're over complicating the problem.

Is the over temperature shut down just set too low? If the motor housing is 100degC it's hotter in the windings, but may not be that much hotter if it's running constantly.

I know you mentioned the motor has been a problem before and has been rewound, but have the shutdowns always been an issue?

I assume it's the winding temperature shtting it down not the bearing temperature? Is there temperature monitoring on the bearings? Have you compared drive end and non-drive end temperatures?

Don't fixate on just the motor or the VFD either look at everything, is the connected machinery operating correctly? Is ventilation for the space working properly?


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## Mike_kilroy (Sep 2, 2016)

Electrorecycler said:


> I'll be observing the motor for some time. I'm taking regular trips with a thermal imaging camera. If the carrier frequency is having a negative effect, it should be obvious sooner rather than later. The motor is running hotter today than yesterday, but the ambient temperature is also higher. I've recommended that we monitor the motor temp, ambient air temp and motor current through historical trends for the next few months to have the data to properly come to a conclusion.


I for one am curious; any data yet on temp vs PWM freq change?


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## Electrorecycler (Apr 3, 2013)

Mike_kilroy said:


> I for one am curious; any data yet on temp vs PWM freq change?


So far the motor temp has done as expected. Higher ambient temp = higher running temp and higher running current = higher running temp. Changing the PWM frequency seems to have effected the motor in no way, at least nothing observable so far.


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## Mike_kilroy (Sep 2, 2016)

Electrorecycler said:


> ...Changing the PWM frequency seems to have effected the motor in no way, at least nothing observable so far.


Keep tracking! It will be good info to share once you have the month or two of data you projected!

In the meantime, I will add some backup for my prediction that higher PWM frequency should reduce your motor heat, and show why dropping 2khz to 1.6khz will not have a measurable effect on temperature rise.

Attached is an IEC chart showing each area in a motor where heat comes from. Not just for across the line (pure sinewave voltage) but also PWM. You can see the added rotor heat (lower PWM=good) is an order of magnitude LESS than the added iron loss heat (higher PWM is good).

[ref: http://www.teias.gov.tr/IEC/iec60034-17{ed3.0}b.pdf ]

copied from a Weg motor white paper on invert use with their motors:

_ switching frequency increase results in the
motor voltage FFT improvement and so tends to improve the
motor thermal performance besides reducing noise. _

[ref: http://ecatalog.weg.net/files/wegne...by-pwm-50029350-technical-article-english.pdf ]

Loss Factors for Various Motors/Inverter Combinations

Loss factor @4kHz PWM Loss factor @ 2kHz PWM
Inverter frequency motor	1.1 1.2
General-purpose motor	1.2 1.3

[ref: http://powerelectronics.com/motion-systems/motors-efficiency-and-adjustable-speed-drives ]

So for your complete heat rise tests you owe it to yourself to try a significantly higher PWM frequency too. See if that gains you the 3-5% (of the total heat rise) or so less heat that it might. Of course if you need to reduce heat rise by more than 5% total, you need a different solution.

I did not go back reread the other posts but IIRC there were a lot of questions about details of the motor and drive that were not answered yet? There may still be a parameter mismatch causing an added 10-20% temp rise? If you answer all those questions, maybe someone's thought might point out an issue.


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## macbeton (Jun 7, 2017)

Can't read such crap, eyes start to bleed.
If you can't check motors current and don't understand maintainance - tell your boss to hire a part time competent guy.


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## The_Modifier (Oct 24, 2009)

macbeton said:


> Can't read such crap, eyes start to bleed.



Maybe ask your janitor boss to see if you have an eye care plan available to you. If not, maybe check into a health care facility and get it checked out.:thumbsup:


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