* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Fundamentals of Harmonics
Stepper motor wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Nominal impedance wikipedia , lookup
Electrical ballast wikipedia , lookup
Power factor wikipedia , lookup
Current source wikipedia , lookup
Power engineering wikipedia , lookup
Stray voltage wikipedia , lookup
History of electric power transmission wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Three-phase electric power wikipedia , lookup
Opto-isolator wikipedia , lookup
Zobel network wikipedia , lookup
Power inverter wikipedia , lookup
Electrical substation wikipedia , lookup
Power electronics wikipedia , lookup
Mains electricity wikipedia , lookup
Transformer wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Distribution management system wikipedia , lookup
Buck converter wikipedia , lookup
Switched-mode power supply wikipedia , lookup
• Locating Harmonic Sources • System Impedance • Impacts of Harmonics • K-factor • Interharmonics 1 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 = w L, so remember that for harmonic h, the reactance is Xh = h w0 L = h X1 2 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 3 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 4 Effects of harmonics • Impact on Capacitors • Impact on Transformers • Impact on Motors • Impact on Telecommunications • Impact on Energy and Demand Metering 5 Effects of Capacitors • Capacitors have some tolerances in ratings according to IEEE Standard 181992: 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 6 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 7 Ploss Pcu Pfe R I2 Phy st PEC Ploss R I2 PEC PEC V 2h2 If voltage distortion is being caused by harmonics in the load current: 2 2 PECh I h PEC PECR I h 2 2 h 8 Type Dry Oil filled MVA 0<S<1 PEC-R 3-8% 1<S<1.5 12-20% S>1.5 8-15% 0<S<2.5 1% 2.5<S<5 1-5% S>5 9-15% PEC PECR I2h2 h 9 PEC PECR I2h2 K I h h 2 h Ih h h2 2 2 PEC KPECR Ih KPECR Irms h 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 K I h 2 h Ih h h2 2 11 • Interharmonics and Losses 12