Motor power Factor and VSD operation

[niallnz]

Hello all,
Do you have any experience of running low speed (365rpm, 16 pole) motors with low power factor (0.56 @ 100% load, to 0.38 @ 50% load) on a VSD. In this instance the motor is 25kW with rated current of 80Amp. The VSD has been sized to the motor rated current not the motor kW, hence it a 45kW VSD. The motor in question is on a propeller pump and the mechanical engineer is certain that the hydraulic conditions are within the pump specifications but we get no flow, so naturally they suspect that the VSD is some how not spinning the pump at 50Hz. They also do not believe the current reading from the VSD which confirms that it is drawing full load current. Is there any chance that the poor power factor is upsetting the operation of the VSD?

Cheers Niallnz

 

[niallnz]

A little bit more info.

When the VSD is set to 50Hz it only reaches 48.7Hz and current is 80Amp. This would indicate that the VSD is limiting its output for self preservation purposes. I don't know the drive set up, but if it is set for V/Hz operation rather than vector control would that be a likely cause of poor performance at the top end of the speed range?
Cheers Niallnz

 

[Skogsgurra]

When you say that you get no flow, is the flow zero? Or is it just a bit too low?

The first thing to check is motor speed and check the flow rate against that speed. If hydraulic data don't match the speed, the pump guy has to do his part of the job.

You can always trust the VFD's display. It usually shows a lot more than Hz, voltage and amps, but those basic variables are always present and they are (mostly) correct within one or two percent.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ozmosis]

niallnz
has the VSD been set up with the correct motor settings?
This seems to be quite a special motor and the equivalent circuit may not be in the scope of the standard settings available within the VSD if you are looking to control the motor correctly, and protect the motor correctly.
Whether this is vector controlled or simply V/F setup, you typically need to input some motor parameters and most VSD's rely on a 'standard' range of motor parameters to determine their internal calculations.
If not, it might be necessary to delve deeper in the settings of the VSD to determine if this particular motor is capable of being set-up correctly.

 

[Skogsgurra]

Sidetrack: Need to mail you Patrick. Lost your address. Pls mail me./G.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

If it is in V/Hz mode, what ozmosis is saying may mean that indeed, the motor is not spinning at the speed indicated on the VFD display. Without feedback, the VFD only knows what it TOLD the motor to spin at, it has no way of knowing if that is happening (short of detecting an overload and if a pump is not pumping, it will not overload unless it is jammed). But if it is in Sensorless Vector mode, the motor model it used as a default would not be correct for a motor with that many poles as he said. I'm also not sure an "Autotune" function would correctly interpret it either. Most likely you will need to enter the motor data manually.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[edison123]

Jeff

For non-standard motors such as these, what are the data needed by VFD ? Winding resistance, inductance, impedance ?

Muthu

http://www.edison.co.in

 

[waross]

There have been times during a rewind when someone has decided to clean up a dirty rotor and his efforts have resulted in an increased air gap. This will cause the power factor to drop and the FLC to increase.
Have you checked the air gap?

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

 

[Marke]

Hello niallnz

If the pump is operating at 47Hz and drawing 80 Amps, and is producing no flow, there is a lot of energy going somewhere and there will be heat developing!!
If the VFD is set as V/Hz and it is true open loop V/Hz, then provided that the v/Hz matches the motor characteristics, there will be no problem due to the low pf of the motor.
Many of the modern VFDs, when set to V/Hz, are still not a true V/Hz and need to be tuned to the motor. Look for an auto tune mode or similar and run that.

Best regards,

Mark Empson
Advanced Motor Control Ltd

 

[niallnz]

Thanks for all your suggestions. As often seems to be the way the solution is perhaps obvious in hind site. The very muted feedback from the site is the motor was star connected instead of delta. This may explain why the VSD failed to complete the Automatic Motor Adaption and not just because the power factor was so far out of its expected range.
Cheers Niall

 

[Marke]

How does the rotor look?
There will have been a lot of heat dissipated in the rotor with the motor basically partially stalled!!

Best regards,
Mark.

Mark Empson
Advanced Motor Control Ltd

 

[DickDV]

Sure would have helped to know the drive could not complete it's motor ID run or Automatic Motor Adaptation, as you call it.

That would have been a dead giveaway!

 

[niallnz]

As I said every is clear in hindsight, but when the VSD supplier says don't worry that the AMA failed "its because the motor as a power factor that is outside of the range expected by the VSD's motor model" you tend to go and focus on something else.

Just one of those things to keep in the back of your mind for the next time something unexpected happens.

Cheers Niall