Harmonics

Harmonics

“Harmonics are not a problem unless they are a problem!”

Synthesis_square

 

Negative side effects of harmonics

Harmonics create heat in units proportional to the square of the harmonic order

  • 50Hz or 60 Hz = 1 heating unit (amp)
  • 5th order = 25 heating units (amp)

Excessive heat in a distribution system can have many adverse effects

  • Cable insulation breakdown
  • Transformer failure
  • Limits on generator & UPS capacity

Common symptoms of harmonics

Heating

  • Cable insulation breakdown
  • Random thermal breaker tripping
  • Fuse blowing
  • Transformer failure

Random logic faults

  • CNC
  • PLC
  • Drives
  • UPS
  • Computers

Thyristor (SCR) converter shorting

  • DC drives
  • Battery chargers
  • DC power supplies

Power factor capacitor incompatibility

  • Harmonic heating effect
  • Tripping on over-current
  • Resonating power factor capacitors

AC motor winding and bearing destruction

  • Path to ground for harmonics

Limits on generator & UPS capacity

  • Harmonic heating effect

Generator faulting

  • Not able to regulate to frequency
The power quality industry has developed certain index values that help us assess the quality of service as it relates to distortion caused by the presence of harmonics. These values, or harmonic indices, serve as a useful metric of system performance. The two most frequently used are Total Harmonic Distortion (THD) and Total Demand Distortion (TDD). They are measures of the effective value of a waveform and can be applied to both current and voltage. While K-factor shows how much more heat is produced from a non-linear load, it doesn’t portray anything about distortion of the sine wave.
 
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