Industrial Engineer · phase 9 of 16
Derating
Required reduction in drive output capability for conditions such as high temperature, altitude, switching frequency, or unusual load duty.
The Explain card
- Plain English
- Derating is the reduction in what a drive can deliver when it is used outside the conditions its rating assumes. High ambient, high altitude, high carrier frequency and unusual duty all cost capacity.
- Example
- A drive rated 40 amps at 40 degrees and 1000 meters is installed in Denver at 1600 meters with the carrier frequency raised for a quiet motor. The manual's curves take it down to about 32 amps.
- Why it matters
- A derated drive that was sized on its nameplate number runs at the edge and fails in the conditions that caused the derate, which is exactly when you need it. Read the derating curves before the order goes in.
- Hook
- The rating on the box is for the box's ideal day.
Where it sits in the deck
Phase 9: VFD Ratings, Sizing, and Motor Data
Nameplate arithmetic, where the currents, voltages and duty ratings decide whether a drive can actually run the motor you bolted it to.
