1. Seminar onPOWER SYSTEM HARMONICS By S.Naveen,UG102144. NIT Warangal1

2. CONTENTS 1. Introduction to Harmonics 2.Sources of Harmonics 3.Effects of Harmonics 4.Measuring indices for Harmonics 5.Methods to mitigate Harmonics 6.Conclusion 7.References 2 3. Introduction to Harmonics 3 4. The coefficients an , bn determine the magnitude of the harmonic components. From the data of the coefficients, we can obtain two spectra related to these coefficients: 1.Magnitude spectrum: shows the magnitude of different frequency components. 2.Phase spectrum: shows the phase of different harmonic components.4 5. Load Characterization: 1.Linear time invariant loads :application of sinusoidal voltage results in sinusoidal current. They display a constant steady state impedance. Eg: Incandescent lighting, Transformers and Rotating machines under normal operating conditions. 2.Non-Linear loads : application of sinusoidal voltage results in a non-sinusoidal current. They do not exhibit constant impedance during the entire period. Also non-linear loads may draw even a discontinuous current.5 6. Sources of Harmonics Adjustable drive systems Arc Furnaces Switching Mode Power Supplies Computers, TV sets HVDC Transmission Electric Traction FACTS Controllers Wind & Solar power generation Battery charging & Fuel cells Fluorescent lighting, Electronic ballasts Inrush Current Harmonics Rotating machines (slot , mmf) 6 7. AC PWM Drive7 8. TV Sets8 9. Switch Mode Power supply9 10. Microwave Oven10 11. HVDC Transmission11 12. Arc Furnace12 13. Effects of HarmonicsIncreased Cu loss leading to Excessive heating. Harmonic Torques. Voltage distortion in weak system. Harmonic voltages increase hysteresis and eddy current losses, also additional I2R losses mainly in Converter transformers.(Transformer derating) Power factor also deteriorates. Phenomenon of Flicker. Excessive neutral currents. Effects measuring instruments. Misoperation of relays.(False tripping of ground relay due to triplen harmonics) 13 14. Parallel resonance between Cable capacitance and system inductances, incase of long cables. Introduces Electromagnetic interference in adjacent signal or control cables via radiated and conducted emissions.14 15. Measuring indices for Harmonics 15 16. 16 17. 17 18. Methods to mitigate Harmonics 1.Passive filters. 2.Active filters. Filters are used to suppress harmonics as well as to support reactive power. 3.Operation with higher pulse number. 4.Using K-factor transformers.18 19. Passive Filters 1.Single tuned filter:Based on series resonance of RLC circuit. The circuit is designed to resonate at the frequency equal to the frequency of the component which needs to be filtered. It is confined to a particular frequency. 19 20. 2.Double tuned filter:This filter is tuned to two frequencies equal to the frequency of the significant harmonic components in the magnitude spectrum. 20 21. 3.High pass filters:These filters are designed such that all the components of frequencies higher than a particular frequency are filtered. Passive filters are cheap, easy design and reliable. But they cause resonance problems, fixed reactive power compensation and large size. 21 22. AC filter switch yard22 23. Active Filters Active power filters are Power electronic converters to inject harmonic currents into the system. They can eliminate voltage and current harmonics; compensate for reactive power. No resonance problems, can support variable reactive power compensation. Expensive, complex control. Active power filters can be classified as: 1.Based on type of power electronic converter: a)Current source converter(CSC) b)Voltage source converter(VSC) 2.Based on topology of converter: a) Shunt filter b)Series filter c)Hybrid filter23 24. Voltage source converterCurrent source converter24 25. Active shunt filterThe harmonic current is supplied by the shunt active filter locally at the point where it is connected. The converter is issued control signals based on monitored values of current. This will ensure that the current drawn from PCC will be sinusoidal and other loads are unaffected. 25 26. Active Series filterVoltages are injected in order to reduce the harmonics, by controlling the Converter.26 27. Hybrid active filterIt is a combination of series active filter and shunt passive filter.27 28. Conclusion It is essential to know the effects of the harmonics, sources of the harmonics for a power engineer to ensure that the systems will work well within the safety zone, owing to standards. Also, the various harmonic mitigation techniques discussed are to be understood well for a design engineer to protect the power system from harmonics.28 29. References Power system Harmonics- Jos Arrillaga, Neville R. Watson. Control of Harmonics in Electrical Power systems, from American Bureau of Shipping(ABS). POWER SYSTEM ANALYSIS, Short circuit load flow and Harmonics-J. C. Das www.wikipedia.org IEEE transactions on Power Apparatus & Systems, Power system Harmonics: An Overview, Vol.PAS102, No.8, August1983. IEEE transactions on Power Apparatus & Systems, vol.PAS-104, No.9, 1985. The effects of Power system Harmonics on Power system equipment and Loads. 29 30. THANK YOU.Any Queries30