Measure regen'd power back to the grid?

[busarider29]

Greeting experts!

We have a new machine we just built. It is equipped with regenerative drives. The machine uses Beckhoff controls (PLC and I/O). I installed an EL3453 with the appropriate current transformer. Out of the box, the EL3453 gets various 3P power data coming into the machine off the mains - (current, voltage, active power, reactive power, apparent power, active energy, reactive energy, apparent energy, frequency, power quality factor). With all this, would it be possible to also calculate the regen'd power/current going back out to the grid??

Thanks.

 

[cardosocea]

Isn't it a matter of checking the direction?

 

[busarider29]

Isn't it a matter of checking the direction?

Perhaps? But without switching the orientation of the current transformer? I can't do that. There's two motors in the machine, where each motor can be rotating (or not), rotating forward or reverse, at any given time. The 3 legs of the incoming power pass through the current transformer right after the main cutoff switch.

 

[the_msp]

Isn't it a matter of checking the direction?

I think they meant the direction of power flow... if the active power is positive, it is being consumed, if it is negative it is being exported...

however to see if it is actually going back to grid, there should be power monitoring at the main incomer of the plant not just the machine.

 

[GaryS]

An interesting problem
I would think the way to do this would be to measure the current on the line side and motor side
Any difference would be power loss in the drive or control I don’t see any way to determine current flow direction from within a drive.

If the line side current is higher than the motor current then the system is drawing power from the grid the difference would have to be the lose in the drive. The total power draw would be the line side and the power consumed by the motor would the current flowing to the motor

But if the motor current is higher than the line current then the system is in regeneration mode
And here the power sent back into the grid would be the measured current o the line side. The difference would still be the lose in the drive.

I could see the possibility of current on the line side near zero while the motor is running that would mean the system is regenerating at a low level but the rules above would apply to determine if the system is motoring or regenerating. I would not expect to ever see zero difference in current.

It would be interesting to actually set this up and test it.
Let us know how you make out

 

[RVaughan]

Check the drive parameters. I seem to recall seeing someone's drive calculating regenerated power.

 

[busarider29]

I checked the "Help" documentation in the drive software and it appears that all of the relevant regen'd power data is there in the status parameters. Cool!! So, this will be easy then! I like easy!!