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Harmonics

Harmonics. Is a distortion in an electrical network created by non-linear electrical devices which use solid state switching hardware

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Harmonics

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  1. Harmonics • Is a distortion in an electrical network created by non-linear electrical devices which use solid state switching hardware • Is a component of a periodic wave which has a frequency which is a multiple of the fundamental power line frequency of 50 Hz: i.e. 150Hz is third order harmonic frequency • Is a steady-state phenomenon, not a transient condition

  2. Harmonics • 3-phase non-linear loads typically create 5th, 7th, 11th and 13th harmonic • 2-phase non-linear loads typically create 3rd order harmonics and higher order multiples of 3 • Total harmonic distortion of a waveform (THD) = the level of voltage or current harmonic distortion existing at any point on a power system

  3. Harmonics • Usual side-effect of harmonics: • Higher peak-to-peak voltage resulting in insulation failure of motors, transformers and capacitors • Higher rms currents resulting in higher equipment operating temperatures • Overheating cables • Nuisance trips or damage to CB’s and fuses

  4. Harmonics and capacitors • Capacitors do not generate harmonics BUT they can amplify them significantly • When harmonic levels are elevated, there is a significant risk of harmonic resonance between the PFC capacitors and the supply transformer • Amplification of harmonics by the capacitors has a negative impact on the life of the capacitors as well as the rest of the plant equipment • Harmonics can be absorbed or “filtered” through the fitment of reactors in series with pf correction capacitor banks

  5. Harmonic Filtration • A reactor is placed in series with each of the capacitor banks of a PFC system • The reactor creates a inductive impedance path to those currents created at harmonic frequencies (typically blocking any frequency above 135 Hz) • The capacitors can no longer amplify harmonic voltages and currents, eliminating the risk of parallel resonance • If the total non-linear load of a plant is above 25%, harmonic filters will almost always be required for power factor correction purposes • Blocking reactors have a significantly cost implication for PFC equipment

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