Resistor sizing for regnerative loads?

[sfd]

I hope someone can help with this. It has been driving everyone in the office MAD.

We are involved in a project with large printing presses. The press manufacturer has told us AC drives with regenerative braking is used. Since we have generator back up, we cannot allow this regenerative load back onto the system (as is often the case)since we must avoid tripping on either overspeed or reverse power (we cannot guarantee that other loads in the building will be sufficient to absorb the regen. power). Therefore bleed resistors (dump banks)must be installed to absorb the regen. power. But how do you size these resistors?

Can anyone help? I hope the answers not too simple because its baffled many proffessionals here.

I would very much like to know and understand the maths behind this problem

Thanks for any help

 

[cbarn24050]

Hi, firstly are you really sure that you have a 4quadrant ac drive on this press as they are a very rare item. If so then the drive manafacturer will tell you the max regen that the drive can produce, but it is unlikely to be more than 2 times the forward power.So your resistors must be able to absorb that power for the braking time of the press, a few seconds normaly, I hope that helps.

 

[sfd]

cbarn,

Thanks for your thoughts - I have no knoweldge of the drive since this is being specified and installed by the press manufacturer. I didn't realise that the regen could be big ('forward' power of the press is in the order of 10mW). Also do you know (mathematically) how you size the resistors?

Thanks

 

[busbar]

Clarifying drive-operation specifics as early as possible in the project may be time well spent. Can the press vendor provide information from some of their previous projects? You might try contacting an applications person at a place like Post-Glover or Milwaukee Resistor for specification/sizing guidance. If not originally included in the drive design, switching of ‘outboard’ resistor banks may be a hurdle. The drive vendor may want to force some special conditions {not at their own expense, of course} if this is an operating mode they’re not used to dealing with. I suppose a drive is not truly regenerative if does not ‘feed’ the source. Obviously the banks would not require continuous ratings. Adjustable taps on the bank may be handy for fine-tuning in the field.

 

[cbarn24050]

Hi again, you cannot make any decisions untill you have the full spec of the drive fitted to the press.I had assumed that this was a printing press in which case the regen during emergency braking is very high.

 

[Wirenut]

It is very possible that the drive manufactor would offer these resistors as an option. At least they will know how to size it. GET ON THE PHONE!!!!!!!! Wirenut