“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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