What is harmonics ?
Harmonics are defined as the sinusoidal components of a non-linear periodic waveform with a frequency that is a whole multiple of the fundamental frequency. Putting this simply; any switching operation of the mains supply sine wave will produce lots of other sine waves at higher frequencies. These are not apparent but they are harmful.
harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency being 50 or 60hz (50hz for european power and 60hz for american power). For example, if the fundamental power frequency is 60 hz, then the 2nd harmonic is 120 hz, the 3rd is 180 hz, etc. In modern test equipment today harmonics can be measured up to the 63rd harmonic. When harmonic frequencies are prevalent, electrical power panels and transformers become mechanically resonant to the magnetic fields generated by higher frequency harmonics. When this happens, the power panel or transformer vibrates and emits a buzzing sound for the different harmonic frequencies. Harmonic frequencies from the 3rd to the 25th are the most common range of frequencies measured in electrical distribution systems.
How do harmonics affect us?
Harmonics are responsible for a number of undesired events and malfunctions.
- Measurement errors in analog instruments since these can not detect harmonics. Only tru-rms digital instruments can detect parameters at harmonic frequencies.
- Nuisance tripping of micro-processor based protective relays & earth leakage circuit breakers.
- Greater risk of interference with communication network.
- Overheating due to overloading of capacitors, motors, transformers, cables.
- Rise in iron losses in transformers, motors & chokes due to high frequency.
- Risk of short circuits at power factor correction capacitors due to parallel resonance.
- High currents in neutrals due to triplents.
Harmonic Analysis
Management of harmonics is an important aspect in power quality. It begins with comprehensive analysis of harmonics and periodic monitoring of total harmonic distortion.
- Power factor correction capacitors are protected from short circuits as a result of occurrence of parallel resonance by using de-tuned filters.
- Tuned filters are used to suppress individual harmonic orders.
Active or dynamic filters are used to suppress various harmonics considerably, to balance three phases, regulate voltage, suppress other abnormalities like noise, rf interference, spikes etc.
