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Chapter 3 Harmonic Modeling of Networks

Tutorial on Harmonics Modeling and Simulation. Chapter 3 Harmonic Modeling of Networks. Contributors: T. Ortmyer, C. Hatziadoniu, and P. Ribeiro. Distribution System Modeling . The initial decisions:

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Chapter 3 Harmonic Modeling of Networks

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  1. Tutorial on Harmonics Modeling and Simulation Chapter 3Harmonic Modeling of Networks Contributors: T. Ortmyer, C. Hatziadoniu, and P. Ribeiro

  2. Distribution System Modeling The initial decisions: -Three phase or single phase modeling- The extent of the primary model- Secondary distribution modeling The NATURE of the issue and the GOAL of the study constrain these decisions.

  3. A Typical Primary Distribution System

  4. Things to note • Any large or unique loads • Capacitor banks/ cables(?) • Transmission supply • Any unusual operating conditions?

  5. Decision 1: Per phase versus Three Phase Modeling • The three phase model is required when: • Single phase or unbalanced capacitors are present • Ground or residual currents are important in the study • Significant unbalanced loading is present • A combination of wye-wye and/or delta-wye transformers leads to harmonic cancellation*

  6. The typical instances where a single phase model may be sufficient are: • A single large three phase harmonic source is the cause of the study • The remaining system is well balanced • Ground currents are not an issue

  7. Decision 2: The extent of the system model • Model the entire primary system • Transmission source can be modeled by the 60 Hertz short circuit impedance if no significant transmission capacitance is nearby– but check that the transmission system is not a source of harmonics • Power factor capacitors and any distributed generation should be modeled in detail

  8. Decision 3: Load and harmonic source modeling • Identify and model all significant harmonic sources • Determine present levels through measurements- also determine if harmonic levels peak at full or light load conditions • Develop aggregate load models based on measurements and load distribution • Validate with measurements taken as harmonic sources/capacitor banks are switched in and out

  9. Representative secondary distribution system

  10. Characteristics of secondary studies • Different voltage levels • Fewer capacitors, and more with tuning coils • Load data is more accessible- and more important • Measurements can be more economical

  11. Modeling transformers • Model the transformer connection • Neglect the transformer magnetizing branch (usually ignore the transformer magnetizing harmonics) • Model the harmonic reactance as the product of short circuit leakage reactance and harmonic number • Model the harmonic resistance as the short circuit resistance. Correct for skin effect if data or model available. • Include stray capacitance for frequencies above the low khertz range.

  12. Line Models • Distribution lines and cables should be represented by an equivalent pi. An estimated correction factor for skin effect can be included • Model ground path for zero sequence harmonics

  13. Capacitors • Capacitors– model as capacitive reactance– 60 hertz reactance divided by the harmonic number. • Be sure to note those single phase capacitors, and model as such. • Model the capacitor as either grounded wye, or ungrounded wye or delta.

  14. Load Models • Linear Loads • Induction and Synchronous Machines • Non-linear Loads

  15. Linear Passive Loads • TYPES: Incandescent lamps, resistive heater, electric range, water heater, space heater, etc. • CHARACTERISTICS: RL type loads with RL values independent of frequency.

  16. Line Connected MOTOR/GENERATOR LOADS Induction Motor Fundamental Frequency Per Phase Equivalent Circuit

  17. IM Per Phase Harmonic Model

  18. For synchronous generators, the per phase model of the synchronous generator is similar– use a series combination of stator resistance and substransient reactance in the model. • On all direct connected machines, make sure and account for the ground connection (or lack of one) in studies with zero sequence harmonics.

  19. Adjustable speed drives fluorescent lamps, computers and other electronic loads arc furnaces and welders These loads generate harmonic currents, and are modeled as sources at the harmonic frequencies Nonlinear Loads

  20. Load Model 1: Series Passive Load

  21. Load Model 2: Parallel Passive Load

  22. Load Model 3. Skin Effect Parallel Load Model

  23. Load Model 4. Induction Motor plus Resistive

  24. Load Model 5. CIGRE/EDF

  25. Load Model 6. Inclusion of Load Transformer and Motor Damping

  26. I. Case Study 1: Load Impedance Frequency Study

  27. Case Study 1 Parameters • Linear Load=743 kW. • PF Cap.=741kVAr, (C=5.4mF). • Injected Harmonic Currents (A): • I5 = 0.840 I7 = 0.601 • I11=0.382 I13=0.323

  28. Case Study 1: Load Model 1, 2, and 3 results

  29. Case Study 1: Load Model 4, 5, and 6 Results

  30. Sensitivity of Impedance to Motor Penetration Level (Load Model 6, fixed PFC)

  31. Sensitivity of Impedance to IM Penetration– w/changing PFC

  32. Summary • Define study needs • Determine the modeling needs • Get the data • Validate the data • Produce good results!!

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