Overview ©1996 2013 ETAPOperation Technology, Inc – Workshop Notes Harmonics Harmonic Analysis Slide 2 ©1996 2013 ETAPOperation Technology, Inc Workshop Notes Harmonics Types of Power Quality Proble.
Harmonic Analysis ©1996-2013 ETAP/Operation Technology, Inc – Workshop Notes: Harmonics Types of Power Quality Problems ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Waveform Distortion • Primary Types of Waveform Distortion – DC Offset – Harmonics – Interharmonics – Notching – Noise ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Harmonics • One special category of power quality problems • “Harmonics are voltages and/or currents present in an electrical system at some multiple of the fundamental frequency.” (IEEE Std 399, Brown Book) ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Nonlinear Loads • Sinusoidal voltage applied to a simple nonlinear resistor • Increasing the voltage by a few percent may cause current to double ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Fourier Representation • Any periodic waveform can be expressed as a sum of sinusoids • The sum of the sinusoids is referred to as Fourier Series (6-pulse) I ac cos3 t I d (cos t I h cos(h t h 1 cos7 t cos11 t cos13 t 11 13 ) h ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Harmonic Sources • Utilities (Power Grid) – Known as “Background Harmonic” – Pollution from other irresponsible customers – SVC, HVDC, FACTS, … – Usually a voltage source • Synchronous Generators – Due to Pitch (can be eliminated by fractionalpitch winding) and Saturation – Usually a voltage source ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Harmonic Sources (cont’d) • Transformers – Due to magnetizing branch saturation – Only at lightly loaded condition – Usually a current source • Power Electronic Devices – Charger, Converter, Inverter, UPS, VFD, SVC, HVDC, FACTS, … – Due to switching actions – Either a voltage source or a current source ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Harmonic Sources (cont’d) • Other Non-Linear Loads – Arc furnaces, discharge lighting, … – Due to unstable and non-linear process – Either a voltage source or a current source • In general, any load that is applied to a power system that requires other than a sinusoidal current ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide Harmonic I and V ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 10 Capacitor Banks ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 26 Capacitor Banks ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 27 Capacitor Banks Say, Seventh Harmonic Current = 5% of 1100A = 55 A ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 28 Capacitor Banks Resistance = 1% including cable and transformer CAF = X/R = 7*0.0069/0.0012 =40.25 Resonant Current = 55*40.25 = 2214 A ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 29 Parallel Resonance (cont’d) Cause: Source inductance resonates with capacitor bank at a frequency excited by the facilities harmonic sources Impacts: Excessive capacitor fuse operation Capacitor failures Incorrect relay tripping Telephone interference Overheating of equipment ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 30 Harmonic Distortion Measurements • Total Harmonic Distortion (THD) – Also known as Harmonic Distortion Factor (HDF), is the most popular index to measure the level of harmonic distortion to voltage and current – Ratio of the RMS of all harmonics to the fundamental component – For an ideal system THD = 0% – Potential heating value of the harmonics relative to the fundamental ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 31 Harmonic Distortion Measurements (cont’d) – Good indicator of additional losses due to current flowing through a conductor – Not a good indicator of voltage stress in a capacitor (related to peak value of voltage waveform, not its heating value) Fi THD F1 Where Fi is the amplitude of the ith harmonic, and F1 is that for the fundamental component ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 32 Harmonic Distortion Measurements (cont’d) • Individual Harmonic Distortion (IHD) - Ratio of a given harmonic to fundamental - To track magnitude of individual harmonic IHD Fi F1 • Root Mean Square (RMS) - Total - Root Mean Square of fundamental plus all harmonics - Equal to fundamental RMS if Harmonics are zero Fi RMS ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 33 Reducing System Harmonics • Add Passive Filters – Shunt or Single Tuned Filters – Broadband Filters or Band Pass Filters – Provide low impedance path for harmonic current – Least expensive ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 34 Reducing System Harmonics (cont’d) • Increase Pulse Numbers – Increasing pulse number of convert circuits – Limited by practical control problems ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 35 Reducing System Harmonics (cont’d) • Apply Transformer Phase Shifting – Using Phase Shifting Transformers – Achieve higher pulse operation of the total converter installation • In ETAP – Phase shift is specified in the tab page of the transformer editor ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 36 Reducing System Harmonics (cont’d) • Either standard phase shift or special phase shift can be used ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 37 Reducing System Harmonics (cont’d) • Add Active Filters – Instantly adapts to changing source and load conditions – Costly – MVA Limitation ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 38 Voltage Distortion Limits Recommended Practices for Utilities (IEEE 519): Bus Voltage Individual Total Voltage Distortion Distortion (%) THD (%) 69 kV and below 3.0 5.0 69.001 kV through 161kV 1.5 2.5 161.001 and above 1.0 1.5 At PCC In ETAP: Specify Harmonic Distortion Limits in Harmonic Page of Bus Editor: ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 39 Current Distortion Limits Recommended Practices for General Distribution Systems (IEEE 519): ©1996-2013 ETAP/Operation Technology, Inc - Workshop Notes: Harmonics Slide 40 ... problems ©1996-2013 ETAP/ Operation Technology, Inc - Workshop Notes: Harmonics Slide 35 Reducing System Harmonics (cont’d) • Apply Transformer Phase Shifting – Using Phase Shifting Transformers – Achieve... converter installation • In ETAP – Phase shift is specified in the tab page of the transformer editor ©1996-2013 ETAP/ Operation Technology, Inc - Workshop Notes: Harmonics Slide 36 Reducing System Harmonics. .. ©1996-2013 ETAP/ Operation Technology, Inc - Workshop Notes: Harmonics Slide Waveform Distortion • Primary Types of Waveform Distortion – DC Offset – Harmonics – Interharmonics – Notching – Noise