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The Impact of Non-Linear Loads on Wiring Requirements in Power Systems

Explore the effects of harmonics from new load types like energy-efficient lighting on wiring requirements in power systems. Dive into NEC wiring requirements, harmonics fundamentals, and their impact on conductors. Learn about changing energy consumption trends and the importance of properly sizing neutrals for a reliable and efficient electrical system.

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The Impact of Non-Linear Loads on Wiring Requirements in Power Systems

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  1. Impact of Non-Linear Loads on Wiring Requirements Jens Schoene December 06, 2011

  2. Who we are • EnerNex is a consulting company with headquarter in Knoxville, TN • Power System Studies • Power Quality • Wind and Solar (design, generator modeling,…) • T&D (bulk system analysis, SSR, CSS) • Safety (arc flash, grounding, electromagnetic coupling) • Smart Grid Engineering Studies • Advanced Metering Infrastructure (AMI) • Utility Communication Architecture • Security

  3. Outline • Motivation • Fundamentals of Power Quality • Changing Energy Consumption and Changing Loads • Characteristics of “New” Lighting Technologies • Case Studies • Conclusions and Recommendations

  4. Motivation

  5. Background • Higher penetration of “new” load types: • Energy-efficient lighting • Consumer electronics • Residential appliances • Plug-in Electric Vehicles • What is the impact? • Wiring requirements • Efficiency, reliability, power quality

  6. NEC Wiring Requirement NEC 310.15(B)(5)(c) • No information regarding harmonic limits for which the neutral has to be considered a current carrying conductor • No information regarding required size of neutral conductor in the presence of harmonics • Old buildings have undersized neutral or neutral size equals the size of the phase conductor. • New commercial buildings commonly employ oversized neutral.

  7. Fundamentals of Power Quality

  8. What are Harmonics? • Harmonics are sinusoidal voltages and currents with frequencies that are integer multiples of the fundamental frequency (60 Hz in the United States). • Value of the multiplier corresponds to the harmonic order.

  9. General Effects of Harmonics Harmonics can cause • Transformer overheating resulting in the shortening of the expected lifetime • Capacitor can failure due to excessive harmonic currents or overvoltage stress on dielectrics • Increased ohmic losses and shortened lifetime of cables • Overloaded neutral conductors (odd harmonic currents do not cancel in the neutral conductor) • Nuisance tripping of breakers and fuses • Motor heating • Control misoperation • Communication system interference • Degrade meter accuracy

  10. Effects on Wiring Requirements • Measure of heating in conductor is product of squared current I and impedance Z (I2Z) • Harmonics increase heating in conductors due to • additional load current flowing throughconductor • current redistribution inside conductor (skin effect)

  11. What is special about 3rd Harmonics? • Add arithmetically in the Neutral (assuming balanced 3-phase system) • Many electronic loads produce them. • Neutral size in commercial building of particular concern.

  12. How to Quantify Harmonics • Individual Harmonic Distortion (IHD) LevelPercentage of individual harmonic relative to fundamental • Total Harmonic Distortion (THD) LevelPercentage of RMS of all harmonics relative to fundamental • IEEE 519 specifies limits

  13. Changing Energy Consumption andChanging Loads

  14. Increasing Electricity Consumption Residential Electricity Consumption in the U.S.A. 1990-2006 source: International Energy Agency, 2009

  15. What consumes Electricity? Distribution of USA Electricity Consumption in 2005 source: Energy Information Administration, 2008

  16. Changing Electricity Consumption Changes in Electricity Consumption in the USA from 1998 to 2008 source: International Energy Agency, 2009

  17. Changing Electricity Consumption Global CE and ICT Electricity Consumption 1990-2030 (Business As Usual) source: International Energy Agency, 2009

  18. Changing Electricity Consumption Global CE and ICT Electricity Consumption 1990-2030 (BAU, LLCC, BAT) source: International Energy Agency, 2009

  19. Lighting • Lighting is 16% of residential load • Most incandescent lamps phased-out by 2014 • Compact Fluorescent Lamps • Color Rendering Index around 80 • Some are dimmable (most are not) • Some are high power factor / low harmonics (most are not) • White LED • Even more efficient than CFL

  20. Characteristics of “New” Lighting Technologies

  21. Increased Energy Efficiency

  22. How does a CFL work? Electronic Ballast in Energy-Efficient Lighting

  23. Harmonic Characteristics Incandescent Compact Fluorescent White LED

  24. Case Studies

  25. Currents and Voltages Measured at Different Locations (PQube Data) • Comp. 1: Office Building in Knoxville, TN • Comp. 2: Manufacturing Facility in Alameda, CA • Comp. 3: Office Building in Santa Clara, CA • Comp. 4 Manufacturing Facility in Karlsruhe, Germany

  26. Phase Currents Industrial Industrial Commercial Commercial Industrial

  27. Neutral Currents Industrial Commercial Commercial Industrial

  28. Conclusion and Recommendations

  29. Conclusions & Recommendations • Electricity consumption and load characteristics changing • 3rd harmonics produced by power electronics are concern • NEC does recognize neutral as current carrying conductor, but no guidance/requirement regarding size. • Neutral sizing requirements should be based on statistically significant data from measurements of neutral currents in different environments (office buildings, residential building, etc.)

  30. Backup

  31. Power Factor: Displacement vs. True Not all Power Factors are alike

  32. Resonances

  33. Series Resonance

  34. Parallel Resonance

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