ANSI Code: Non-regenerative vs Regenerative VFD anyone got experience with this?

[bdn2004]

In the power system analysis software this a pick when selecting a VFD. When you select the Regenerative button it appears to put short circuit current back through the system, through the VFD whereas the Non-regenerative button does not.

How does that work ? Is this very common ?

 

[dpc]

Normally regenerative drives are used for overhauling loads such as cranes and hoists. The rectifier section must be capable of passing power in both directions.

https://www.machinedesign.com/motorsdrives/regeneration-adjustable-frequency-drives

 

[itsmoked]

I would definitely NOT expect a fault current coming back out of a regenerative VFD. They're simply a silicon based grid-tie inverter. Anything coming back will be inverted via transistors that are NOT going to provide fault levels of returned current. At most I'd expect the peak to be only the available returned current on the VFD.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

They have a non-zero fault response, but for inverters of all sorts a 1.25 per unit response is high. So more than the zero of the non-regenerative drives but well less than a synchronous machine. They may also shut off quickly rather than waiting for something else to clear the fault.

 

[lansford]

In the world of surface mining equipment, specifically large electric draglines and power shovels, the older units were MG set (motor generator) powered. And you could observe on the utility source bus, the voltage fluctuation due to the load swings as the dragline went through its motions. A point the equipment manufacturer made, and was common knowledge, was that the regenerative power resulted in energy cost savings.
The modern drive systems on these machines is AC motors with VFDs that are regenerative. I have not personally seen any data, but it would be interesting to see a comparison of the amount of regenerative energy between the two cases.
thanks Jim

 

[LionelHutz]

I would agree with davidbeach, the current should be something like 1.25x rated as the regenerating value. The devices in the front-end of a regenerative VFD are typically rated for a maximum current that is around 2X the VFD nameplate rated current, which means it would never produce more than that much current. The duration could be very short too. Probably best to consult the VFD manufacturer to get their expected data.

lansford - you should be posting your own question if you want responses about that.

 

[bdn2004]

Attached is a 2 page pdf using some typical data- Utility, Transformer and a 100 HP motor in the power analysis software.
The first page is the Single Line, the second page is the same system short circuited.

The first motor is connected directly to the 480V bus, the second through a non-regenerative VFD and the third through the regenerative VFD.
Note the motor contribution from the first is 640 Amps, the second is 0 Amps and the third is 361 Amps respectively.

 

[jraef]

Active Front End Line Regenerative capable drives must be TOLD to allow power flow to the line side. So just sitting there they would not contribute to a fault. But that said, IF a Line Regenerative Drive was IN THE ACT of regenerating when a fault occurs on the line side, it WOULD continue supplying current to the fault from the motor, at least until it is told not to. So from the sake of safety, since you cannot predict when a fault will occur you must assume the worst.

The amount of fault current cannot of course be higher than the motor can produce.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[dpc]

FWIW, I believe EasyPower uses the suggestion in Conrad St. Pierre's Practical Guide to Short Circuit Calculations: 3.0 pu of rated current for 1 cycle - or X"d = 33%.