Powerflex 700 Amp readings high

[Mporter4]

I am replacing an old Allen Bradley 1336 Impact drive that operates an agitator with a new Powerflex 700 . Prior to removing the VFD I verified the amp readings using the VFD display and at full speed it showed 17.4 amps.
I replaced the VFD and did the static auto tune and Inertia auto tune etc. Everything started and operated as expected except the amp reading on the display was reading 19.2 amps...
All the nameplate data has been copied to the new parameters in the powerflex so why the change in current?
This will be a big deal because this is trended and documented.
Am I missing something?

 

[petersonra]

Did you by any chance set up the powerflex 700 as sensorless vector? I don't remember much about the 1336 drives but maybe they were only available in Volts / Hertz mode.

 

[Jraef]

I am replacing an old Allen Bradley 1336 Impact drive that operates an agitator with a new Powerflex 700 . Prior to removing the VFD I verified the amp readings using the VFD display and at full speed it showed 17.4 amps.
I replaced the VFD and did the static auto tune and Inertia auto tune etc. Everything started and operated as expected except the amp reading on the display was reading 19.2 amps...
All the nameplate data has been copied to the new parameters in the powerflex so why the change in current?
This will be a big deal because this is trended and documented.
Am I missing something?

In a nutshell, the 1336 reading was likely less accurate. The technology for sensing current has been vastly improved since then. The 1336 measured current with 2 Hall effect transducers on the transistors of A and C phases and calculated the average AC output current from those measurements. The PF700 actually measures the AC output current on the output of each phase individually using a more accurate CT specially designed for use with a PWM output.

By using a calculated values, it also may have been calculating only the active current being used by the motors, where by measuring each phase on the output side, the value will be inclusive of the reactive current as well. In other words in the 1336 = current as if it is 1.0 PF, PF700 = current with actual motor PF.

 

[adamscb]

Just an FYI (nothing to do with your question), make sure you check the grounding on those PowerFlexes. For different types of system grounding techniques, there is a jumper that you have to add/remove. We didn't do what was instructed in the manual, and we had a ground fault. This in turn ruined all of our VFDs in a particular lineup. Just letting you know.