Electric Motors with VFD
Electric Motors with VFD
(OP)
Is it common practice to operate a motor above it rated nampeplate RPM using a VFD? The direct drive fan has a 900 RPM motor but the design fan RPM is 1,250 RPM. The vendor is saying you can use the VFD to operate the fan at design RPM.





RE: Electric Motors with VFD
RE: Electric Motors with VFD
RE: Electric Motors with VFD
I doubt that the fan vendor knows anything at all.
If you want to know if you can run a motor above the nameplate ratings, you need to ask the motor manufacturer. He will need to know how much POWER the fan will be drawing.
Remember that power is proportional to torque X rpm.
RE: Electric Motors with VFD
RE: Electric Motors with VFD
RE: Electric Motors with VFD
I'm with RossABQ - something is wrong with the thinking on this project.
RE: Electric Motors with VFD
who's going to pay for the new motor when the existing one fries?
RE: Electric Motors with VFD
However, the increase in speed seems to be high. I have operated fans at speeds upto 20% higher than the rated speed of the motor. If your fan supplier is selling you the idea to reduce the cost of the fan, better avoid it.
There is a thread somewhere in the electrical fora that discusses this issue.
RE: Electric Motors with VFD
You are going to need almost 3-times the horsepower of the current motor as per Artisi. And it needs to be a motor that will tolerate the higher speed as well as be VFD ready... Chances are the 900 wasn't balanced at 1450, and a 1200 might not hold balance either....And you will need to change your coupling hardware cause that new motor is most likely a different shaft size...And if you are going to live more than momentarily at the higher speed and horsepower draw you are going to change the coupling anyways cause its not going to be intended for that HP...And the overclocked 900 RPM motor is most likely going to make a lot more torque than a 1750 of the same HP running slow, so your anchoring may have to be modified.... And then you got to consider your conductors and circuit protection cause the new set up will want to draw MORE THAN 3-times the current, cause your 60-Hz motor is going to be running at 85 Hz. And you might encounter some inductions at 85 Hz & clipping that you wouldn't have with 60-Hz modulated. That means some analog conductors and instrumentation may start acting up.
Short version: Can of Worms.
RE: Electric Motors with VFD
The vendor sais these motors can do it and they are smaller frame sizes.
RE: Electric Motors with VFD
7.5hp at 1800 is 15hp at 2250 rpm
RE: Electric Motors with VFD
The HP number that is written on a motor is the MAXIMUM power that motor can continuously produce without destroying itself. (Subject to modification by the service factor)
A motor will attempt to produce as much or as little power as necessary to turn the connected load.
A synchronous AC motor will valiantly attempt to rotate as fast as the field frequency - right up until it either overheats, overspeeds its bearings, or the slip angle gets so large that it dies in whatever mode an excessive slip angle causes.
You need to look at the PERFORMANCE CURVE for the FAN. At 6000 CFM against the static pressure that is imposed by your system, what is the POWER that the fan requires. If the answer is less than the 7.5 HP rating of the motor, then the windings will PROBABLY not overheat. You still need to look at the bearings.
RE: Electric Motors with VFD
RE: Electric Motors with VFD
RE: Electric Motors with VFD
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Electric Motors with VFD
The value of the constant varies for each fan.