Industrial Engineer · phase 13 of 16 · noun

DV/dt Filter

Output filter that reduces the rate of voltage change and peak motor-terminal voltage from PWM switching.

The Explain card

Plain English
A dV/dt filter is a small inductor and capacitor network on the drive output that slows the rise time of each PWM pulse. The voltage still switches, and it does so gently enough that the cable and the motor survive it.
Example
A retrofit drive feeds an old motor through 100 meters of conduit. A dV/dt filter at the drive keeps the terminal voltage peaks under the motor's insulation rating.
Why it matters
It does more than a reactor and costs less than a sine filter, which makes it the usual answer for long cable runs and older motors. It does nothing for common mode voltage, so bearing currents need a separate fix.
Hook
The same pulses, with the sharp edges filed off.

Word knowledge

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

The engineer installed a dV/dt filter between the VFD and a long-lead motor before commissioning the conveyor.

Why these words
  • dV/dt calculus notation using d for differential, V for voltage, and t for time specifies the electrical quantity associated with the filter
  • filter French filtre, from Medieval Latin filtrum, felt names the device class within the phrase
Where it came from
Origin
an English engineering compound formed from calculus notation dV/dt and the electrical sense of filter
Entered the language
20th century
What changed
Filter moved from naming a porous straining material to naming a selective electrical network, while dV/dt became standard engineering shorthand for voltage change with respect to time.
How it is spelled
Pattern
The notation keeps a lowercase d before each variable and a slash between the numerator and denominator.
Pattern
The variable V is capitalized for voltage, while t remains lowercase for time.
Pattern
Filter is written as a separate word after the symbolic modifier.
Breaks the pattern
Technical sources also print the modifier as dv/dt, dVdt, or DV/DT, although dV/dt preserves the variable capitalization most clearly.

Spelled like

  • dI/dt reactor
  • dV/dt reactor
  • dV/dt protection
Broken into chunks
  • dV/dt
    • dI/dt
    • dx/dt
  • filter
    • filtered
    • filtration
What it sits beside

Same subject

Same shape

  • dI/dt reactor
  • dV/dt protection

VFD output components

rate-of-change notation

  • dV/dt
  • dI/dt
  • dx/dt

Where it sits in the deck

Phase 13: VFD Power Quality, Wiring, and Motor Protection

Harmonics, reflected waves, shielded cable and bearing currents: the side effects a drive inflicts on everything around it.

Neighbours in this phase