Industrial Engineer · phase 10 of 16
Field Weakening
Operation above base frequency where voltage cannot rise proportionally, reducing available torque as speed increases.
The Explain card
- Plain English
- Field weakening is what happens when the drive raises frequency past the base and cannot raise the voltage to match. The flux in the motor falls, and so does the torque it can make.
- Example
- A spindle motor with a 60 hertz base runs at 120 hertz. It turns twice as fast and can produce about half the torque, so the cutting load has to be light up there.
- Why it matters
- Field weakening lets a motor run faster than its nameplate without a gearbox, which is a gift for spindles and fans. It is a trap for conveyors and hoists, where the load needs full torque and gets less as the speed rises.
- Hook
- More speed, bought with torque.
Where it sits in the deck
Phase 10: VFD Electrical and Motor Fundamentals
The physics under the parameters: slip, torque, flux, and the relationship between frequency and voltage that every drive is really controlling.
