PowerFlex 525 and 753 current rating.

[PaulBr]

We have started using new families of Rockwell Automation drives, PowerFlex 525 and Powerflex 753. In the drives manual there is chart that showing drives input current rating and output current rating. On these charts output current rating is greater than input current rating.
It is opposite that in manuals for Fowerflex 40 and Powerflex 70. For these drives rated input current is greater than output rated current. It is kind of going alone with the fact that there will be some power losses, and resulting drive output current will be slightly less than input current.
When I ask that question technical support the answer was:

"here is the answer form engineering

The input current is a function of the power factor of the motor, the power factor of the power system and drive, and efficiencies of each part of the system. It is common to have a published output current higher than the input current for some drive ratings"

Is it really common to have rated output current higher than input current? How other drive manufacturers are rating ther drives?

PaulBr.

 

[ScottyUK]

With an active front end to give near-unity power factor on the supply side of the drive it is quite possible that the output current, at a lagging power factor, could be higher than the input. I haven't particularly noticed it in datasheets before but there is certainly some logic to it.

 

[jraef]

I think you are reading something wrong. I'm looking at a PF40 manual and a PF70 manual, both are showing the input current as lower than the output current, as does the PF525 manual. Where are you getting your information?

A VFD essentially corrects the displacement power factor of the motor as seen by the drive. So if the motor PF is .8, and the input PF to the drive is .95, then the input amps will be lower.

"Will work for (the memory of) salami"

 

[jraef]

Whoops, I typed that exactly backward! Input is HIGHER than Output amps in all cases between the PF40, 525, 70 etc., but Input current IS lower on the PF750 series. That's because the PF750 series has a built-in DC bus choke, the others do not (unless you order the PF70 with a CE filter). The DC bus choke reduces the distortion power factor as seen by the drive.



"Will work for (the memory of) salami"

 

[PaulBr]

Jraef,

I've actually noticed it with PowerFlex 525. Frame D and E of 380-460V all have output current higher than input current.

PaulBr.

 

[jraef]

Not on my chart, page 20 of the manual.
It is like that on the 575V version though.

"Will work for (the memory of) salami"