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Inverter Duty Motor's

Inverter Duty Motor's

Inverter Duty Motor's

I have a 50HP 1775 RPM horizontal motor with Class H insulation. The motor nameplate is marked with a 1.0 S.F.

No where on the motor does it say its inverter duty designed.  But according to MG-1 Section 31 no inverter duty motor will have anything but a 1.0 service factor on the nameplate.

Let me continue by asking if the motor is used at less than 3300 feet will the sign wave carry a 1.15 S.F. and a 1.0 S.F. at inverter duty conditions?

Keep it simple so I can explain this to another guy - thanks.

Wayne E. Lovison

RE: Inverter Duty Motor's

I can't find your reference to section 31 of NEMA MG-1 about inverter duty motors, but I'm really baffled by your question: "if the motor is used at less than 3300 feet will the sign wave carry a 1.15 S.F. and a 1.0 S.F. at inverter duty conditions?"
Your reference to sinewave(I'm assuming) and inverter duty may indicate that you intend to use some form of VFD.
What is the 3300 feet you are referring to? The distance between the drive and the motor?
I'll make a stretch here and assume that you're asking if:   
  you have a motor marked 1.0 SF, class H insulation, but not inverter duty,
  can you assume that it is inverter duty(because of your NEMA MG-1 reference that I cannot find), and
  can you use it with a VFD as long as the cable length is less than 3300 feet, and
  does this mean that the SF of 1.0 for inverter duty corresponds to a SF of 1.15 for non-inverter(pure sine-wave) operation?

If this is what you're asking, I believe the answers are: no, possibly, and no.

RE: Inverter Duty Motor's

According to MG 1-1998 part 31 section 31.3.7 the service factor on the nameplate will be 1.0.

The motor mfg. (Baldor) say's they don't nameplate the motor inverter duty.  They got the spec and it called for a 1.15 service factor plus the abilty to operate with a VFD.

They came back quoted a 50HP motor with Class H.  They said that the motor will have a 1.15 SF (not nameplated same) and a 1.0 SF under inverter duty and made reference to this MG 1-1998 spec.

Wayne E. Lovison

RE: Inverter Duty Motor's

Aparrently, I do not have the complete MG-1 spec, just a condensation; it has no reference to the section you mention.
In any case, let's assume that your motor is inverter-duty, as you state the manufacturer says. (get it in writing)

What are you asking?

Are you planning to use the motor with a VFD, with a cable length less than 3300 feet? If this is the case, I would contact the manufacturer of the VFD and verify that the installation is acceptable. It varies with different drives.

Do you want to know if a SF of 1.0 with a VFD is the same as a SF of 1.15 without? In this case, I would contact the motor manufacturer.

If there is some other question, please ask.

RE: Inverter Duty Motor's

It's reasonable to assume that a motor that has a 1.15 SF on a sine wave will have something less than that on an adjustable frequency drive.   How much less will depend on a lot of factors.  We typically limit bhp to not more than 87% of motor (with 1.15 SF) when operating on an AFD.  But this is just a conservative rule of thumb.  Your mileage may vary.

The issue of feeder length is a completely different problem related to standing waves on the feeder due to the high frequency noise on the drive output.

Contact the drive supplier for recommendations on maximum feeder length.  You may need to add a snubber or some type of filtering on the output.  If you really have a 3300 foot feeder at 480V, you may have a lot of other problems as well.

RE: Inverter Duty Motor's

They (Baldor) are correct.  There are several specs which prohibit putting anything but 1.0 S.F. on an inverter duty rated motor.
However, Baldor does label motors with labels that says "Inverter Duty".  I know, because I buy about 10,000 of them a year from Baldor.  But, they aren't as big as yours.
And, you definitely want class H, if it is available.

RE: Inverter Duty Motor's

I think the 3300ft refers to elevation, because it translates to 1000m, the standard altitude rating for electrical devices without derating.

Lewish is right, "inverter duty" motors cannot be labeled anything but 1.0 SF. Harmonic currents in the motor as a result of inverter operation will make it run hotter even at full speed. Cooling is reduced at low speeds as well. Having a 1.0 SF keeps that fudge factor from a 1.15 designed motor available to cover these circumstances. It then makes sense that the same motor could be capable of 1.15 SF when connected X-Line (sine wave, as you put it). I'd still get the mfgr to put it in writing though. It appears from Lewish's post as though Baldor will apply the label, yet yours do not have it? I smell fish, and I don't mean fresh fish.

Quando Omni Flunkus Moritati

RE: Inverter Duty Motor's

Hi Lovinson
Giving it a shot.MG1.31.30.7 states that when VFD motors are operated at rated voltage and frequency they shall have a SF of 1.00.
Your particular motor has a Class H windings,but its nameplate states that it has a SF of 1.00.Nothing will change that.
Because it has a SF of 1.00 does not necessarily make it an Inverter duty rated motor.
  The size of this motor ,would most likely have mhush windings and if it was designed for inverter use most likely would be wound with MagnetWire or Inverter Spike duty wire.
Its Class H windings would be a plus in any case.

Hope it helps


RE: Inverter Duty Motor's

If the motor is nameplated for 1.0 SF... and absent any statement on the N/P about use on inverter power, I think that you can reasonably conclude that the motor S.F is stated for sine-wave power ... and not inverter power.

Be that as it may.... much has to do with the design of the inverter and the modulation employed therein. There are inverters that produce less than 5% harmonics in the motor and so, harmnic heating is minimal.

That said, you still need to consider the type of duty to which the motor will be subjected. If it is constant torque, how far down in speed will you operate it... and will the motor get sufficient coolng to get rid of the heat.  If it's variable torque.... I know of lots of applications out there where the inverter reduces the voltage to the motor as the square of the speed decrease, and so, such operation is not a problem with a 1.0 SF motor, so long as.... the inverter induced harmonics into the motor do not exceed 1-2 % ideally...and max of 5%  as a limit.

Oh...and as far as MG-1; part 31 is concerned, most (if not all) manufactures of inverter duty motors do not so state on the N/P because of one teenie-tiny part.... that is; that the direction of rotation needs to be pinned to the phase rotation of the applied power. IEC motors do this as standard; that is, the specify the phase rotation for a given direction of motor rotation.  Here in the good ole USA .... we don't ... never have....  and probably won't... if anything.... that requirement will get dropped from part 31 ... and then all of the other requirements being complied with, USA mfgrs will be able to state "Inverter Duty" or complies with MG-1 part 31.. on their nameplates.  

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