Can a VFD rated for a 184 kW motor successfully operate a motor with a much smaller rating, say 55 kW? I'm working on a project which would require VFD control for the sewage pump motors. Initially, 55 kW pumps would be installed but these would be scheduled for replacement with 184 kW after about 11 years operation when facility requirements would be higher. I intend to design for the utlimate capacity rather than for the initial size since replacing the VFD later would also be very expensive.
Eng-Tips is the largest engineering community on the Internet
Intelligent Work Forums for Engineering Professionals
-
Congratulations waross on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
VFD sizing for a range of motor sizes
- Thread starter qstorm
- Start date
Skogsgurra
Electrical
Yes. I would say that it can very well be done.
Especially if it is a scalar drive - and a pump drive usually is.
The only thing that I can think of is: Can the thermal protection be set for the smaller motor? That is normally not a problem.
If you think that a vector drive is necessary (can't see why) then you may need to check to make sure that the R:s and X:s (resistances and impedances) of the smaller motor are civered by the parameters in the drive. Again, with a 1:4 ratio between motor and inverter, that should not be a problem at all.
There might be a physical problem with the cabling. A cable for a 184 kW motor may be a problem to connect to a 55 kW motor. But that is solvable, just put a junction box close to the small motor and connect with a smaller area from there. Remember to fuse accordingly!
Gunnar Englund
Especially if it is a scalar drive - and a pump drive usually is.
The only thing that I can think of is: Can the thermal protection be set for the smaller motor? That is normally not a problem.
If you think that a vector drive is necessary (can't see why) then you may need to check to make sure that the R:s and X:s (resistances and impedances) of the smaller motor are civered by the parameters in the drive. Again, with a 1:4 ratio between motor and inverter, that should not be a problem at all.
There might be a physical problem with the cabling. A cable for a 184 kW motor may be a problem to connect to a 55 kW motor. But that is solvable, just put a junction box close to the small motor and connect with a smaller area from there. Remember to fuse accordingly!
Gunnar Englund
I for one would not waste the money on a larger drive if you don't need it for 11 years! An 11 year old drive right now is not worth repairing and is an anacronism compared to new drives. VFD technology will continue to evolve, who's to say what the predominant technology will be in 11 years. Capacitors will not likely last that long anyway, 5 - 7 years is the average, but by then you may as well take advantage of whatever the latest technology is when you need it. In addition, the way prices have been going on VFDs, the larger drive will most likely cost you a lot less in the future.
Eng-Tips: Help for your job, not for your homework Read faq731-376![[pirate]](/data/assets/smilies/pirate.gif "[pirate] [pirate]")
Eng-Tips: Help for your job, not for your homework Read faq731-376
Skogsgurra
Electrical
You are wiser than a poodle, jraef! Totally forgot about the time perspective.
Gunnar Englund
Gunnar Englund
In 11 years, we may all be using matrix drives with no capacitors to fail in 5 - 7 years!!
We may also be faced with requirements for low harmonic drives which wil require active rectifiers or similar.
Best regards
Mark Empson
We may also be faced with requirements for low harmonic drives which wil require active rectifiers or similar.
Best regards
Mark Empson
Skogsgurra
Electrical
Yes. A poodle is a very wise animal. I think that it all started with Martin Luther that said something about a poodle. Not sure though.
Gunnar Englund
Gunnar Englund
Gunnar,
If that hadn't come from you, I don't think I would have interpreted it as a complment!
Mark,
Matrix drives, good point. The technology is expensive now, but basic PWM drives were comparitively expensive 11 years ago and look at them now. That is likely the wave of the future that far out.
Eng-Tips: Help for your job, not for your homework Read faq731-376
If that hadn't come from you, I don't think I would have interpreted it as a complment!
Mark,
Matrix drives, good point. The technology is expensive now, but basic PWM drives were comparitively expensive 11 years ago and look at them now. That is likely the wave of the future that far out.
Eng-Tips: Help for your job, not for your homework Read faq731-376
- Status
Similar threads
- Locked
- Question
- Locked
- Question