Harmonics

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

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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