Industrial Engineer · phase 10 of 16 · noun
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.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
During VFD commissioning, the engineer verified field weakening by trending motor current, speed feedback, DC-bus voltage, and torque command.
Why these words
- field Old English feld, open land identifies the motor's magnetic field as the quantity being modified
- weakening weak, from Old Norse veikr, plus the suffixes -en and -ing names the process of making the field weaker
Where it came from
- Origin
- English engineering compound formed from field and weakening
- Entered the language
- 20th century
- What changed
- Field expanded from open land to a region of physical influence, while weakening developed from an adjective of reduced strength into a process noun.
How it is spelled
- Pattern
- The phrase is normally written as two separate words.
- Pattern
- Weak remains unchanged before the suffixes -en and -ing.
Spelled like
- flux weakening
- field winding
- weakness
- weakly
Broken into chunks
-
field
- fieldbus
- field winding
-
weak
- weakness
- weakly
-
-en
- strengthen
- shorten
-
-ing
- limiting
- switching
What it sits beside
Same subject
- base frequency
- voltage saturation
- flux reference
- torque command
- V/Hz control
Same shape
- flux weakening
- torque limiting
- current limiting
motor operating regions
- constant-torque region
- field-weakening region
VFD commissioning trends
- speed feedback
- motor current
- DC-bus voltage
- torque command
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.
