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Understanding and Troubleshooting Real-World Power Quality Problems

Understanding and Troubleshooting Real-World Power Quality Problems

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Understanding and Troubleshooting Real-World Power Quality Problems

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  1. Understanding and Troubleshooting Real-World Power Quality Problems Troy Ledford Schweitzer Engineering Laboratories

  2. Class Content • Introduction to power quality (PQ) • Causes of poor PQ and impact of application • PQ characteristics • Tools for monitoring PQ • Case studies

  3. PQ Involves Voltage and Current Characteristics Poor PQ refers to changes in an electric power supply that can cause equipment to fail, misoperate, or degrade NoisyTransformers OverheatedEquipment BlownFuses

  4. What Is the Cost of Poor PQ? Equipment failures, misoperations, and degradation

  5. PQ Problems Can Affect Metering AccuracyANSI C12.20-2015, Accuracy Class 0.1 Adds Tests

  6. Several Factors Affect PQ Faults Nonlinear Loads Large Load Changes

  7. Nonlinear Loads Distort WaveformsIncandescent Bulb With Dimmer Voltage 169 V peak 120 V rms Current 0.15 A peak 0.07 A rms

  8. LED Lights Provide Energy Efficiency But Distort Waveforms Incandescent Bulb With Dimmer0.60 A Peak 0.44 A rms LED Light0.11 A Peak 0.04 A rms

  9. High Sampling Rates Accurately Capture Waveform ContentLED Light Bulb Waveforms 8 kHz – 0% Error 1 kHz – 2.2% Error

  10. Customer and Utility Share Responsibility • Customer limits current distortion • System owner or operator limits voltage distortion by modifying supply system impedance characteristics IEEE 519-2014 applies to point of common coupling

  11. Outages EPRI 2001 Study of Typical PQ Phenomena 5% Line Noise 5% 10%Spikes, Transients 46% Voltage Sags Harmonics 5% 5% Frequency Variations 7% Overvoltage 10%Voltage Swells 7% Undervoltage

  12. Voltage Sag, Swell, and Interruption (VSSI)

  13. Analyze Sag Event Using Waveform or RMS Plots

  14. VSSI Are Described by Depth and Duration 85 V Sag Peak 60 V rms ~3 cycles

  15. Combined Waveform and RMS Plot V rms V inst

  16. Overvoltage and Undervoltage Are Long-Term Phenomena

  17. Lightning Strikes Cause Voltage Sags Lightning Strikes Power Pole Flashover Insulators Flash Over and Fault Current Flows Instantaneous Voltage Drop Occurs Protective Relays Operate Circuit Breakers Open

  18. Power System Faults Can Cause Voltage SagsVoltage Profile of a Three-Phase Fault No Load Voltage Voltage disturbance effect is more at fault point and less away from it

  19. Fault on Transmission Line Causes Sag and Interruption

  20. Restoration Event Causes Damage to 3D Printer Asymmetric waveform indicates presence of second harmonic

  21. Motor Operation Can Cause Voltage Sags Mechanical Load Motor

  22. University Uses Voltage Sag Data to Continue Operations and Buy Planning Time 700 hp pump

  23. Optimized Motor Shutdown Reduces Sag and Eliminates Problems

  24. Voltage Sag Ride-Through Characteristics

  25. Voltage Events Damage Motors and Sensitive Processing Equipment $1,300 $1,300 $65,000

  26. Voltage Events Damage Motor Fan and Compressor and Degrade Power Supply

  27. VSSI Data Reveal Stuck Load Tap Changer

  28. IEC 61000-4-30 Standardizes PQ Measurements Class A: For contractual applications andverifying compliance Class S: For surveys and assessment IEC 62586-2 specifies functional test requirements for IEC 61000-4-30

  29. Voltage Unbalance Damages Motors • Causes temperature rise • Reduces life expectancy Photo courtesy of Electrical Apparatus Service Association

  30. Unbalance Occurs When VA + VB + VC ≠ 0 VBalanced Three-Phase Waveforms 1.0 0.5 Magnitude (pu) 0 –0.5 –1.0 0 0.5 1.0 1.5 2.0 2.5 3.0 Cycles A-Phase B-Phase C-Phase Unbalance

  31. Unbalance Occurs When VA + VB + VC ≠ 0 VUnbalanced Three-Phase Waveforms 1.0 0.5 Magnitude (pu) 0 –0.5 –1.0 0 0.5 1.0 1.5 2.0 2.5 3.0 Cycles A-Phase B-Phase C-Phase Unbalance

  32. Typical Voltage Unbalance Levels in U.S.Three-Phase Power Delivered to Industrial Plants >3% Unbalance <1% Unbalance Operates normally Can cause significant damage 1–3%Unbalance Causes overheating and premature aging 66% 32% 2%

  33. Facilities Operator Uses Data to Balance Loads

  34. Common Causes of Unbalance • Faulty distribution equipment • Random phase loading (arc furnaces) • Unbalanced distribution feeders

  35. Unbalanced Magnitude Phasor 150 100 50 Magnitude(V) 0 –50 –100 –150 0 0.33 0.67 1 1.33 1.67 2 Time (cycles) A-Phase C-Phase V0 B-Phase

  36. Harmonics Occur as Multiples of 60 Hz Fundamental Third Harmonic Fundamental + Third Harmonic Fundamental: 60 Hz Third harmonic: 60 • 3 = 180 Hz

  37. Harmonics Occur as Multiples of 60 Hz Fundamental Third Harmonic Fifth Harmonic Fundamental + Third Harmonic + Fifth Harmonic Fundamental: 60 Hz Fifth harmonic: 60 • 5 = 300 Hz

  38. Harmonics Cause Humming in Transformers

  39. Spectral Analysis Displays Harmonics, Subharmonics, and Interharmonics 60 Hz FundamentalHarmonic Component SubharmonicComponents Second-HarmonicComponent Interharmonics65–115 Hz

  40. Harmonics Described as Percent of Fundamental Frequency

  41. Total Harmonic Distortion (THD) Is High Under Low-Load Conditions Although Impact Can Be Low Incandescent Bulb With DimmerCurrent THD: 20% 0.44 A rms LED LightCurrent THD: 45% 0.04 A rms

  42. IEEE 519-2014 Uses Total Demand Distortion (TDD)

  43. Third-Order, Odd Harmonics (Triplens) Align With A, B, and C Phases Peaks align with fundamental peaks of other phases

  44. Harmonic Currents Produce Heat and Cause Damage Losses = l2R Use K-factor measurements from advanced meters to size transformers to serve distorting loads without overheating

  45. Fifth Harmonic Counters Torque Normal (ABC) Rotate Angles to 5x Position Fifth Harmonic (ACB)

  46. Harmonic Trending Pinpoints Cause of Lighting Ballast Failures

  47. Electronic Ballasts Cause Fifth-Harmonic Disturbance

  48. Adjustable Speed Drives Cause Harmonics Six-pole adjustable speed drive creates fifth and seventh harmonics

  49. HVdc and Industrial Interties Cause Harmonic Issue for Georgia

  50. Low Harmonics Are More Common in Power System Fifth Order Fiftieth Order Third Order