VFD Motor Load

Status
Not open for further replies.
laketime

laketime

Senior Member
I am sizing a generator to back up one 3 phase 460v motor with a namplate rating of 20hp and 23.5 amps. The motor is fed by a Danfoss VLT Aqua Drive which is converting the incoming 240v single phase to the 3 phase 460v. What would be calcualted load from that motor seen at the main service with all that is going on inside the pump house?
 
If the VFD is sized properly for converting from single phase to three phase (Probably a 40HP drive if its a standard drive). Just use the name plate values on the drive (input). Is the drive a standard 40 HP drive or is it a 20HP drive that says single phase input/3 phase out?
 
And is it a drive that will take 240V in and produce 480V out, or do you have a transformer in play as well? (Apparently there are VFDs with 'voltage doubling' input stages)

Jon
 
winnie said:
And is it a drive that will take 240V in and produce 480V out, or do you have a transformer in play as well? (Apparently there are VFDs with 'voltage doubling' input stages)

Jon
Click to expand...
Not alot of information on the face of the drive but there is no transformer involved.
 
SSDriver said:
If the VFD is sized properly for converting from single phase to three phase (Probably a 40HP drive if its a standard drive). Just use the name plate values on the drive (input). Is the drive a standard 40 HP drive or is it a 20HP drive that says single phase input/3 phase out?
Click to expand...
I ddi not see a name plate. I imagine its a 40hp drive as it is running a 20hp motor. It is single phase in/three phase out. They want to back it up with a generator and I need kw load for generator.
 
Now that I am thinking about it. The motor is multi voltage and I think the drive is merely adding a 3rd leg but keep volatge at 240v. I need another visit to verify that. I think the maintenance guy is leading me down the wrong path.
 
laketime said:
... I think the maintenance guy is leading me down the wrong path.
Click to expand...
He is.

Danfoss does not make a VFD that will double the voltage from 240V to 480V. Although it is POSSIBLE to make one, it would cost more than using a transformer, so nobody does it.

Nor does Danfoss make a VFD that can accept single phase input without de-rating the drive (above 2HP), and although as a generalize rule, many people SAY that drives can be used at a 50% derate, that is not universally true and you must check with the manufacturer first.

And just to give you fair warning: In the case of the VLT Aqua drives, Danfoss** never tells you the amount of derating it requires, it just says that when it detects an imbalance in the incoming 3 phase, it will automatically derate the drive by lowering the output speed until it is OK with it, but without saying how much that will be, other than it might be anywhere between 50% and 100% of the drive current rating. I did one a while ago with a 50% derate and it would not allow the pump to get past 75% speed. We had to go with a 65% derate to get full speed out of it.

** The DISTRIBUTOR told us we could use a 50% derate, but when it didn't work, DANFOSS said they never claimed that and that it doesn't say that in their manual (which is correct). The distributor had to eat the extra cost to get us the larger drive, I had to eat the extra time on the jobsite because of it (and had to pull larger conductors because of the VFD size being larger to meet 430.122)
 
laketime said:
I ddi not see a name plate. I imagine its a 40hp drive as it is running a 20hp motor. It is single phase in/three phase out. They want to back it up with a generator and I need kw load for generator.
Click to expand...
20 hp x .746 = 14.92 kW say it is 93% efficient you need at least 16 kW, that is what it needs to run at full rated 20 HP.
 
Yep. You size the generator to the motor load. The VFD will allow the pump to start without exceeding FLC, so that allows the generator to not need significant oversizing. But you do need about +30% to handle harmonic current if you have a line reactor ahead of the VFD, more if not. I would probably look at around 25kW at least.
 
Jraef said:
Yep. You size the generator to the motor load. The VFD will allow the pump to start without exceeding FLC, so that allows the generator to not need significant oversizing. But you do need about +30% to handle harmonic current if you have a line reactor ahead of the VFD, more if not. I would probably look at around 25kW at least.
Click to expand...
Thanks
 
Jraef said:
He is.

Danfoss does not make a VFD that will double the voltage from 240V to 480V. Although it is POSSIBLE to make one, it would cost more than using a transformer, so nobody does it.

Nor does Danfoss make a VFD that can accept single phase input without de-rating the drive (above 2HP), and although as a generalize rule, many people SAY that drives can be used at a 50% derate, that is not universally true and you must check with the manufacturer first.

And just to give you fair warning: In the case of the VLT Aqua drives, Danfoss** never tells you the amount of derating it requires, it just says that when it detects an imbalance in the incoming 3 phase, it will automatically derate the drive by lowering the output speed until it is OK with it, but without saying how much that will be, other than it might be anywhere between 50% and 100% of the drive current rating. I did one a while ago with a 50% derate and it would not allow the pump to get past 75% speed. We had to go with a 65% derate to get full speed out of it.

** The DISTRIBUTOR told us we could use a 50% derate, but when it didn't work, DANFOSS said they never claimed that and that it doesn't say that in their manual (which is correct). The distributor had to eat the extra cost to get us the larger drive, I had to eat the extra time on the jobsite because of it (and had to pull larger conductors because of the VFD size being larger to meet 430.122)
Click to expand...

It is certainly possible but I don’t think I’ve seen a voltage doubler drive over about 5 HP. In addition I haven’t seen a voltage doubler to 480’from ANY vendor. Single phase to 3 phase is more common an most motors can be wired 460 or 230 except that’s not common with submersibles. Not sure why you want the AQUA. Clearly your vendor doesn’t have a clue. The AQUA drives are not very maintenance friendly. I’ve had big problems even finding the DC bus terminals on them.
 
paulengr said:
It is certainly possible but I don’t think I’ve seen a voltage doubler drive over about 5 HP. In addition I haven’t seen a voltage doubler to 480’from ANY vendor. Single phase to 3 phase is more common an most motors can be wired 460 or 230 except that’s not common with submersibles. Not sure why you want the AQUA. Clearly your vendor doesn’t have a clue. The AQUA drives are not very maintenance friendly. I’ve had big problems even finding the DC bus terminals on them.
Click to expand...
I ran into a single phase input, three phase output with voltage doubler maybe about 20 years ago, was new concept to me at the time. That one was 240 volt input and 480 three phase output and was driving a 20 HP submersible well. I don't recall any name on it anymore.
 
Dzboyce said:
Here is a company that make voltage doubling vfd's

I have not used any of their products, though I have heard good thing about their line of single phase to 3 phase vfd's for submersible pumps.

Click to expand...

They appear to make VFD's with diode-based voltage doublers up to 15 HP. However, they have ones rated up to 50 HP and provide a 460V 3-phase output that use a switching supply (i.e., active front end) to supply the DC bus from a 240V single-phase input.

Diode-based voltage doublers will need larger electrolytic capacitors relative to the rated HP of the drive. This is because they use two series connected electrolytic capacitors where they are charged by opposing half-cycles of the 240V input. All of the current supplied to the DC bus has to flow through capacitors because both 240V line inputs are never connected to the DC bus by diodes at the same time during a 60 Hz cycle. I think these considerations make diode-based voltage doublers less practical for higher HP levels.
 
The one I mentioned a couple posts back I was called in because it wasn't working. Something on the board failed, been long enough ago I don't even recall, but took it to a shop that could repair it, seems like that bill was $6 or 7k at that time. Replacement unit wasn't a whole lot more but was going to take longer to get so we had it repaired. This was well for small village that didn't have three phase distribution and phase conversion was the major reason they had the drive. We were using a portable generator while the drive was being repaired to run the pump.
 
The technology to make a larger voltage doubler is not difficult, it’s just not practical in my opinion. It’s more expensive than just using a transformer and much less reliable.
 
laketime said:
I am sizing a generator to back up one 3 phase 460v motor with a namplate rating of 20hp and 23.5 amps. The motor is fed by a Danfoss VLT Aqua Drive which is converting the incoming 240v single phase to the 3 phase 460v. What would be calcualted load from that motor seen at the main service with all that is going on inside the pump house?
Click to expand...
Side note. I would adjust the ramp up time to at least 20 seconds to limit in rush current. At the large hospital/research center/ ambutory care care campus we used more great Danfoss VFD'S then other companies. I could replace the 220 volt fan on top of the old Danfoss 20 to 150 HP VLT drives in 10 minutes without shutting down drive. The newer FC 100 & 200 took longer. Would take up to a hour on 100 to 200 HP drives to replace fan dead center and behind buss bars & plate. We had old air handlers that on winter start ups would often trip one of the freezestats so they had a 5 to 7 minute ramp up time.
 
Status
Not open for further replies.
Top