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Old 11-29-2016, 05:12 PM   #21
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Originally Posted by John Valdes View Post
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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Old 11-29-2016, 05:16 PM   #22
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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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Old 11-29-2016, 05:36 PM   #23
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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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Old 11-29-2016, 09:38 PM   #24
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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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Old 12-09-2016, 12:22 PM   #25
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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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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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Last edited by chrisfnl; 12-09-2016 at 12:44 PM.
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Old 12-09-2016, 01:10 PM   #26
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Originally Posted by Electrorecycler View Post
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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Old 12-09-2016, 06:20 PM   #27
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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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Old 12-10-2016, 08:18 PM   #28
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...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%7Bed3.0%7Db.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/wegnet...le-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-s...e-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.
Attached Thumbnails
Excessively hot 160kW motor-iec60034-17-ed3.0-b.pdf.jpg  

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Last edited by Mike_kilroy; 12-10-2016 at 08:20 PM.
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Old 06-07-2017, 03:15 PM   #29
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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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Old 06-07-2017, 04:03 PM   #30
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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.
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