a question about 460V/60Hz motor run on 380V/50Hz power supply 1

[FFrraannkk]

we have a ABB AC 460V/60Hz motor run on 380V/50Hz power supply in China. The motor is connected to a ABB drive. The nameplate of motor rating is 522KW/769Amps/1790RPM/460V/60Hz. Because the V/Hz is almost the same between 460/60 and 380/50, i think the torque and FLA should be about the same between these two. My question is that which values should we enter in the VFD for motor rated power, amps, RPM, and voltage, should we enter 522KW/769Amps/1790RPM/460V/60Hz or 435KW/769Amps,1490/380/50Hz? Or they are pretty much the same?

Thanks a lot for your help.

 

[edison123]

The power and the current will be derated in the ratio 5/6.

Muthu

http://www.edison.co.in

 

[FFrraannkk]

Thanks edison123,

do we need to derate the current? Both power and voltage is derated at 5/6, so current will be about the same?

 

[jraef]

When you have a VFD, frequency differences are irrelevant. The problem you will run into here is that your line voltage is lower. This means that you cannot get full 460V output power to this motor when in China. But you can get full torque at 50 Hz output, which will take place at 380V output. You can accept that as it is, or you can allow the VFD to give the motor 60Hz. The problem then comes back to the fact that you are stuck at 380V, because that's all you have. Ergo at 380V 60Hz, you will be losing torque, around 20% lost. If your motor was 20% larger than necessary, no problem. If not, you have to change something somewhere.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Parchie]

@FFrraannkk (Chemical)
Your VFD will report undervoltage fault when its DC link voltage falls below 65 to 51% of the nominal level. Your dc max at 480VAC will be 1.414 x 480 = 679VDC. Your fault trip would then be around 441VDC (311VAC).
Your VFD load settings will have to be conforming to the specs of the driven motor though. If your supply is 380V, try and see if your unit can be set for that system voltage.

 

[FFrraannkk]

Thanks Jraef,

The output frequency of VFD is 50Hz if I understand correctly. We will lose some speed, but 1490 is more than enough for our application (torque is more critical). How about the full load amps at 380V/50Hz? Should it be ~769amps or we also need to derate the amps at ratio 5/6?

 

[FFrraannkk]

Thanks Parchie!

Sorry that i don't fully understand your calculation (chemical engineer myself). but it seems that you think we should put in original machine specs at 480V/60Hz in our VFD load setting, correct?

 

[waross]

You may be able to use an auto-transformer boost system to raise the voltage and allow full power/torque operation at 60 Hz output.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Isn't what speed you run the motor defined by the load it is connected to? If the load demands 50 Hz and the required power, you choose a motor that meets it. Not the other way around.

Muthu

http://www.edison.co.in

 

[LionelHutz]

Your 50Hz numbers look just fine to me. I would keep it simple and use them.

You do not de-rate the current.

You could use the 60Hz numbers but that is more likely to leas to a parameter setting mistake that causes an odd knee frequency so it produce the correct V/Hz ratio. 50Hz parameters and 50Hz as the maximum frequency are easier to set.

 

[FFrraannkk]

Thank you all, waross, edison123, and LionelHutz!

 

[Parchie]

Sorry that i don't fully understand your calculation (chemical engineer myself). but it seems that you think we should put in original machine specs at 480V/60Hz in our VFD load setting, correct?

You said you have a 60HZ, 460V ABB motor! Your motor will be very happy to be fed with 460V, 60Hz power! That's just it. If your power supply to the VFD is other than 480V, that VFD of yours will still work provided the voltage at the DC link of the VFD does not go below 0.65 X 480V X 1.414 = 441VDC (or an AC input of 311VAC)

 

[ScottyUK]

Parchie,

The VFD will switch on, but the motor and VFD combination won't operate correctly at such a low input voltage. I think you're answering a different question to the one the OP asked.

 

[jraef]

Don't get excited about the drive not working. Most drive mfrs I know of do not bother to make a drive rated at 400V and another one at 480V, the components would be the same. So a drive labeled as a 480V drive will be perfectly happy with a 380V input. The only issue is that the drive cannot output more potential than was put in, so if fed with 380V, the maximum output is 380V.

As I said, your motor will be perfectly happy receiving 380V 50Hz. You WILL get full rated torque from it, just not full 60Hz speed at full rated torque. With it being a VFD, you COULD make the output be 60Hz, but still at 380V max, so it is only when you go ABOVE 50Hz output that you begin to lose torque. Since you indicated that torque is more important than speed in your application, you can run at 50Hz and have no issues.




"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Parchie]

Parchie,

The VFD will switch on, but the motor and VFD combination won't operate correctly at such a low input voltage. I think you're answering a different question to the one the OP asked.

Please see jraef's post.
By experience, a VFD designed for "480V" can run successfully when brought to any place where the power supply is 400V. It's of the same VFD class-->400V class, to cater for 380-480V systems! The equipment the VFD is driving will run successfully provided the current rating of the VFD is not exceeded. Like I said, the VFD will report an "Undervoltage" fault only if its DC link voltage drops below 65% of its nominal design DC voltage.

 

[ScottyUK]

Yes I understand that, but with an input of 311V AC the motor will be incapable of producing rated torque above about 39Hz. We have no way of knowing whether 'the equipment the VFD is driving will run successfully' at such low speed or not. In many cases it won't.

 

[waross]

When the VFD is set to run the motor at 1190 RPM the VFD will be outputting 380 Volts at 50 Hz.
Motor performance should be equal at either 460 Volts/60 Hz and 380 Volts/50 Hz, up to 50 Hz. Above 50 Hz the torque will start to fall off.
Maximum torque is developed at around 30% to 60% of rated speed.
As an example, if the maximum torque is developed at 40% of rated speed, then an output of about 40% frequency and 40% voltage will develop maximum torque at standstill. (Torque boost for starting problem loads.)
De-rate the motor to 50 Hz and set the VFD parameters according to the de-rated motor values.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

I'm a little surprised how this is confusing. The VFD will work on 380VAC. The motot will work on 380VAC, 50Hz as long as the HP is derated by 5/6th. The OP is not supplying 311VAC, That is just the lower voltage limit Parchie posted.

De-rate the motor to 50 Hz and set the VFD parameters according to the de-rated motor values.

YES!