What is Harmonics?
Harmonic frequencies are integral multiples of the fundamental supply frequency, i.e. for a fundamental of 50 Hz, the third harmonic would be 150 Hz and the fifth harmonic would be 250 Hz. The presence of harmonics in electrical systems means that current and voltage are distorted and deviate from sinusoidal waveforms. Harmonic currents are caused by non-linear loads connected to the distribution system
What is Total Harmonic Distortion?
The total harmonic distortion (THD) is a measurement of the harmonic distortion present in a signal and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency
The Harmonic Generators
Harmonic load currents are generated by all non-linear loads. These include:
Single phase loads, e.g.
Switched mode power supplies (SMPS)
Electronic fluorescent lighting ballasts_
Small uninterruptible power supplies (UPS) units
Three phase loads, e.g.
Variable speed drives
Large UPS units
Symptoms for Harmonics Study
- Blinking of incandescent bulbs
- Capacitor failure.
- Circuit breaker tripping.
- Computer malfunction or lockup.
- Conductor failure.
- Failure of electronic equipment.
- Flickering of fluorescent tubes.
- Blown fuses.
- Motor failures due to overheating.
- Excessive neutral current.
- Overheating of metal enclosures.
- Power interference on voice communication
- Transformer failure /Temperature Rise.
- Buss bar Humming.
- Cable Heating.
Problems caused by harmonic currents
Overloading of neutrals
Overheating of transformers
Nuisance tripping of circuit breakers
Over-stressing of power factor correction capacitors
Harmonic mitigation measures
A walk through study is done to understand the load profile, power structure and the common causes/effect of harmonics distortion. A portable power quality analyzer is used to measure electrical parameters including harmonics (%THD) at the Main LT incomer and at crucial harmonics generating loads (VFD, UPS, Rectifiers, Lighting ballasts etc). Based on the collected data a Harmonics Audit report is submitted to the client. The report includes ‘Analysis & Recommendation’ section that summarizes what needs to be done to mitigate the harmonic distortion.
- Creating List of harmonics generating loads.
- Listing of symptoms related to harmonics distortion.
- Taking power & harmonics data at LT Main Incomer (PCC).
- Taking power & harmonics data at major harmonics generating loads.
- Analysis of logged data.
- Creating detailed report with %THD-current & power waveforms.
- Mentioning recommendations for harmonics mitigation.
- Submission of report.