Industrial Engineer · phase 13 of 16 · noun

Reflected Wave

Cable-transmission effect that can produce high motor-terminal voltage peaks when PWM pulses reflect on long leads.

The Explain card

Plain English
A reflected wave is what happens when a fast PWM pulse travels down a long motor cable and bounces back from the motor. The bounce adds to the next pulse, and the motor terminals can see nearly twice the bus voltage.
Example
A 480 volt drive feeds a motor through 120 meters of cable. Peaks of 1300 volts appear at the motor terminals, and the winding insulation fails after a year.
Why it matters
Cable length, carrier frequency and IGBT edge speed decide whether it happens, and the motor's insulation rating decides whether it matters. Load reactors, dV/dt filters and inverter duty motors are the standard defences.
Hook
The pulse comes back and lands on the one behind it.

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 used an oscilloscope at the motor terminals to check for Reflected Wave stress before setting the carrier frequency.

Why these words
  • reflected Latin reflectere, to bend back modifies wave to indicate that it has returned from a boundary
  • wave Old English wafian, to move back and forth names the traveling disturbance described by the phrase
Where it came from
Origin
English technical compound using reflected, from Latin reflectere, and wave, from Old English wafian
Entered the language
19th century
What changed
Reflect developed from physical bending backward to signal return, while wave expanded from visible motion to electrical and electromagnetic propagation.
How it is spelled
Pattern
reflected preserves the base reflect and adds -ed
Pattern
wave uses final silent e to mark the long a sound

Spelled like

  • selected
  • deflected
  • save
  • gave
Broken into chunks
  • re
    • return
    • reverse
  • flect
    • deflect
    • inflect
  • wave
    • waveform
    • wavelength
What it sits beside

Same subject

Same shape

  • incident wave
  • traveling wave
  • standing wave

wave-direction terms

  • incident wave
  • reflected wave
  • transmitted wave

VFD output-protection devices

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