1. 1 Chapter 3 Harmonic Modeling of Networks Contributors: T. Ortmyer, C. Hatziadoniu, and P. Ribeiro Organized by Task Force on Harmonics Modeling & Simulation Adapted and Presented by Paulo F Ribeiro AMSC May 28-29, 2008

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

3. 3 A Typical Primary Distribution System

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

5. 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. 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. 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. 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. 9 Representative secondary distribution system

10. 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. 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. 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. 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. 14 Load Models Linear Loads Induction and Synchronous Machines Non-linear Loads

15. 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. 16 Line Connected MOTOR/GENERATOR LOADS Induction Motor Fundamental Frequency Per Phase Equivalent Circuit

17. 17 IM Per Phase Harmonic Model

18. 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. 19 Nonlinear Loads 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

20. 20 Load Model 1: Series Passive Load

21. 21 Load Model 2: Parallel Passive Load

22. 22 Load Model 3. Skin Effect Parallel Load Model

23. 23 Load Model 4. Induction Motor plus Resistive

24. 24 Load Model 5. CIGRE/EDF

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

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

27. 27 Case Study 1 Parameters Linear Load=743 kW. PF Cap.=741kVAr, (C=5.4  F). Injected Harmonic Currents (A): I 5 = 0.840I 7 = 0.601 I 11 =0.382I 13 =0.323

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

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

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

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

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