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Locating Harmonic Sources System Impedance Impacts of Harmonics K-factor Interharmonics

Locating Harmonic Sources System Impedance Impacts of Harmonics K-factor Interharmonics. System Effects. Harmonic currents in a radial distribution system will generally flow back to the source (fig 5.23) unless they are diverted to a nearby capacitor bank (fig 5.24).

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Locating Harmonic Sources System Impedance Impacts of Harmonics K-factor Interharmonics

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  1. Locating Harmonic Sources • System Impedance • Impacts of Harmonics • K-factor • Interharmonics

  2. System Effects • Harmonic currents in a radial distribution system will generally flow back to the source (fig 5.23) unless they are diverted to a nearby capacitor bank (fig 5.24). • System impedance is generally inductive reactance XL = wL, so remember that for harmonic h, the reactance is Xh = h w0 L = h X1

  3. Capacitor banks • Capacitor impedance Zc = -j Xc where reactance Xc = 1/(w C) = 1/(2p f C) • Since capacitor banks are rated in terms of voltage and reactive power: Xc = (kV)2/MVAr = 1000(kV)2/kVAr • Again remember that Xc is proportional to 1/f, so at harmonic h: Xch = Xc1/h

  4. Effects of resistance • Resistance does not “damp out harmonics” • Resistance will tend to damp out resonance, which may alleviate (to some extent) effects of harmonics • Power factor correction capacitors are likely to cause some low-order harmonic resonance problems even with resistance in the circuit

  5. Effects of harmonics • Impact on Capacitors • Impact on Transformers • Impact on Motors • Impact on Telecommunications • Impact on Energy and Demand Metering

  6. Effects of Capacitors • Capacitors have some tolerances in ratings according to IEEE Standard 18-1992: 135% of nameplate kVAr 110% of rated rms voltage (including fundamental and harmonics) 180% of rated rms current (including fundamental and harmonics) 120% of peak voltage

  7. Effects on Transformers • Harmonics affect transformers by • increasing the rms current which increases the transformer copper loss (winding resistance loss) • increasing the eddy-current losses, which usually increase as the square of the frequency

  8. If voltage distortion is being caused by harmonics in the load current:

  9. K indicates how much extra loss is incurred due to harmonic currents increasing eddy-current losses.

  10. K factor Harmonics increase losses in transformers K factor is used to derate transformers 11

  11. Interharmonics and Losses 12

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