Inverter Rated Motor vs ordinary Squirrel Cage motor

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W@ttson

W@ttson

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Hello,

When using variable frequency drives "Inverter rated" squirrel cage motors are used. I know typically for these motors the insulation is more durable so that it can withstand the corona inception voltage produced by drives. However, I have also seen that these inverter rated squirrel cage motors are specified to not be used Across the line started.

What is the reasoning for limiting some inverter rated motors from being operated across the line?
 
spraymax6 said:
Hello,

When using variable frequency drives "Inverter rated" squirrel cage motors are used. I know typically for these motors the insulation is more durable so that it can withstand the corona inception voltage produced by drives. However, I have also seen that these inverter rated squirrel cage motors are specified to not be used Across the line started.

What is the reasoning for limiting some inverter rated motors from being operated across the line?
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None that I know of. I've used both very frequently.
 
spraymax6 said:
I have also seen that these inverter rated squirrel cage motors are specified to not be used Across the line started.

What is the reasoning for limiting some inverter rated motors from being operated across the line?
Click to expand...

I'm thinking that they probably don't correspond to any particular NEMA characteristic for starting and torque characteristics.
Also, it's possible that their impedance could be relatively low because they would not need to limit the high current of across-the-line starting.
 
synchro said:
I'm thinking that they probably don't correspond to any particular NEMA characteristic for starting and torque characteristics.
Also, it's possible that their impedance could be relatively low because they would not need to limit the high current of across-the-line starting.
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Here's one I used :



Locked rotor is usually abound 6 limes full load current. Another was 5.5 times. That was a 700 kW, 3.3 kV fan drive.
 
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I have never seen nor heard of any such restriction nor can I think of any reason for it technically. It’s most likely an internal policy someone came up with so as to not needlessly spend extra money for a motor that doesn’t need the other features.
 
Jraef said:
I have never seen nor heard of any such restriction nor can I think of any reason for it technically. It’s most likely an internal policy someone came up with so as to not needlessly spend extra money for a motor that doesn’t need the other features.
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Actually I have. This was in a pumping station. The drives were 350 kW. The drives started failing at around a month. The motors were random sound. The supplier (not us!) had to repair the motors with mesh wound. A costly mistake.
 
Besoeker3 said:
Actually I have. This was in a pumping station. The drives were 350 kW. The drives started failing at around a month. The motors were random sound. The supplier (not us!) had to repair the motors with mesh wound. A costly mistake.
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I was referring to restricting inverter rated motors to not be used Across-the-Line (DOL).
 
I could imagine a motor optimized for high efficiency at the cost of starting torque, used on a constant torque load.

Such a setup might be incapable of starting across the line and require a VFD to get moving.

Jon
 
it will take me quite some time to find the job where I got the submittal with the warning of "Variable speed drive only, no across the line". So I tried to see if google had any info. Here is a website link that briefly mentions this phenomenon:

Avoid over-specifying inverter-duty motors | Plant Engineering

Today adjustable-speed drives (ASDs) are commonly used to regulate the flow of air and water from motor-driven fans and pumps. In doing so, old-style | Plant Engineering
www.plantengineering.com www.plantengineering.com

The applicable text is as follows:

Only applications requiring a motor to produce constant torque over a wide speed range require a true inverter-duty motor. Such a motor may have a standard premium-efficiency winding (for use with a bypass or line start) or be supplied with a special winding optimized for use with an inverter and may not be capable of starting across the line. In addition to TENV and TEFC enclosures, inverter-duty motors may also have a separately powered constant velocity fan to ensure cooling at low speeds and are totally enclosed blower-cooled (TEBC). These motors usually have a 1,000:1 CTSR and with a flux vector drive can provide full torque at zero speed. Families of vector-duty motors are similar to inverter-duty but usually provided with encoder feedback for more precise speed regulation than can be done with an open-loop vector control. Inverter-duty and vector-duty motors are made in conventional NEMA and IEC frames and may provide increased performance in a drop-in solution.

For what its worth, my applications are typically Constant torque applications with TENV enclosures. Maybe that is why I have bumped into it in the past?
 
Another link:

Your questions answered: What is inverter duty anyway? | Consulting - Specifying Engineer

Reece Robinson, senior technical training specialist at Grundfos Pumps Corp. in Olathe, Kan., tackled unanswered questions from the May 24, 2016, webcast | Consulting - Specifying Engineer
www.csemag.com www.csemag.com

Applicable text:
Q: What happens if we use an inverter duty motor without an inverter? Does it provide better service/performance?

Robinson: Definite-purpose, inverter-fed poly-phase motors are not designed for across-the-line starting. Therefore, they must be used with inverters. Successive across-the-line starts can damage the motor.
 
winnie said:
I could imagine a motor optimized for high efficiency at the cost of starting torque, used on a constant torque load.

Such a setup might be incapable of starting across the line and require a VFD to get moving.

Jon
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I am thinking the links I pasted above are directly hitting at what you are saying. Since I typically have constant torque motors, this maybe the case, although my starting torque requirements are rather high.
 
Jraef said:
I was referring to restricting inverter rated motors to not be used Across-the-Line (DOL).
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Maybe. There was a problem that we had once about High-efficiency motors replacing a conventional induction motor (old one). Just like you said, the short-time setting of the motor breaker tripped and the guys didn't report immediately causing a delay in the production lines. The setting was reviewed and adjusted to correspond to a higher starting current (but the guys got scolded for forgone production, 1-hour delay for a $3M a day process line)
 
spraymax6 said:
Another link:

Your questions answered: What is inverter duty anyway? | Consulting - Specifying Engineer

Reece Robinson, senior technical training specialist at Grundfos Pumps Corp. in Olathe, Kan., tackled unanswered questions from the May 24, 2016, webcast | Consulting - Specifying Engineer
www.csemag.com www.csemag.com

Applicable text:
Q: What happens if we use an inverter duty motor without an inverter? Does it provide better service/performance?

Robinson: Definite-purpose, inverter-fed poly-phase motors are not designed for across-the-line starting. Therefore, they must be used with inverters. Successive across-the-line starts can damage the motor.
Click to expand...
I haven't encountered any polyphase except that single one that ought to have mesh wound All others have been suitable for both inverter duty or DOL.
 
W@ttson said:
A bit of an old post, but here is the proof of a real life motor with the warning:
View attachment 2565490
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I think you are misinterpreting…

It says “For PWM VFD use only”, meaning it is NOT suitable for other older VFD technologies, like 6-Step or Current Source inverters. All those other older technologies are long gone now, everything in LV is now PWM, but that wasn’t always the case.

Just above it and to the left are data points starting with “X-Line”, which would mean they are relating to Across-The -Line starting and running. Why have that if it were “VFD use only”?

That, by the way, is one of the most detailed motor nameplates I have ever seen! Bravo to whomever made that (you seem to have blacked out the manufacturer).
 
Jraef said:
I think you are misinterpreting…

It says “For PWM VFD use only”, meaning it is NOT suitable for other older VFD technologies, like 6-Step or Current Source inverters. All those other older technologies are long gone now, everything in LV is now PWM, but that wasn’t always the case.

Just above it and to the left are data points starting with “X-Line”, which would mean they are relating to Across-The -Line starting and running. Why have that if it were “VFD use only”?

That, by the way, is one of the most detailed motor nameplates I have ever seen! Bravo to whomever made that (you seem to have blacked out the manufacturer).
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Hmmg, I can buy that argument. Thank you for explaining what "X line" was referring to.

Ok, the search is still on! Next time one comes through my desk I will add it to this post.

To get rid of some of the anticipation, its a custom order Marathon motor.
 
Besoeker3 said:
Actually I have. This was in a pumping station. The drives were 350 kW. The drives started failing at around a month. The motors were random sound. The supplier (not us!) had to repair the motors with mesh wound. A costly mistake.
Click to expand...

Could you expand on the terms here?

I've heard of random wound and mush wound, as synonyms, and I've heard of mesh connected as another term for delta.

But I've not heard 'mesh' wound.

Thanks
Jon
 
winnie said:
Could you expand on the terms here?

I've heard of random wound and mush wound, as synonyms, and I've heard of mesh connected as another term for delta.

But I've not heard 'mesh' wound.

Thanks
Jon
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Arranged with the conductors arranged in an orderly way as opposed to random.
 
Besoeker3 said:
Arranged with the conductors arranged in an orderly way as opposed to random.
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As in a form coil machine, where the conductors are carefully placed into insulated coils which then get inserted into the slots?

Or are you describing something built with loose magnet wire (like a random wound machine), but somehow the position of the wire is held in an ordered fashion? (Sort of an intermediate between a full random winding and a full formed coil?)

Thanks
Jon
 
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