Expected voltage drop with a VFD
Expected voltage drop with a VFD
(OP)
Hi,
Is possible to determine how could be the voltage drop during a start of a 550kW motor (crusher) by a MV VFD (AFE)?
Is possible to determine how could be the voltage drop during a start of a 550kW motor (crusher) by a MV VFD (AFE)?





RE: Expected voltage drop with a VFD
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Expected voltage drop with a VFD
On the other hand, you can, if necessary, program the VFD to never exceed FLA of the motor and, assuming you never need more than Full Load Torque to accelerate, take all the time in the world to do so and not cause any more voltage drop than you would running the motor in the first place.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Expected voltage drop with a VFD
Keith Cress
kcress - http://www.flaminsystems.com
RE: Expected voltage drop with a VFD
RE: Expected voltage drop with a VFD
Remember that the VFD is a power conversion device. Requiring 150% current to the motor at zero/low speeds doesn't mean the VFD will draw 150% current from the line. Real power in = Real power out + VFD losses (approximately). Inductive current going to the motor doesn't come from the line at all. You can probably supply 150% current to the motor up to around 70% speed before the VFD reaches 100% current draw from the line.
RE: Expected voltage drop with a VFD
Fresh surfer,
Lionel and I are not saying it will be zero % voltage drop, we are telling you that under the right circumstance the voltage drop will be the same as if the motor is simply running at all. That may or may not be zero %, we have no way of knowing! but you can use that.
The ABSOLUTE worst case scenario is that once your motor approaches slip speed, it MIGHT need to go higher than FLA, but will not be more than 150% of that value because the drive will not deliver it. And if you can't live with 150% for even a short time, simply tell the drive "Limit current to 100%" in programming and it will. That will force the drive to override the commanded speed/ramp time settings and extend the acceleration time, but if your motor can generate enough to torque for the load (meaning the original designer was not planning on overloading the motor on purpose to accelerate it), the drive can get you there, eventually, without going over FLA.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Expected voltage drop with a VFD
RE: Expected voltage drop with a VFD
RE: Expected voltage drop with a VFD
RE: Expected voltage drop with a VFD
Bill
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"Why not the best?"
Jimmy Carter