html5-img
1 / 35

The Whys of Distribution System Analysis

The Whys of Distribution System Analysis. W. H. Kersting Milsoft Utility Solutions. Why???????. Planning studies Unbalanced studies Non-transposed lines Phasing important Power losses important Power factor important Exact transformer connections No symmetrical components

pearly
Télécharger la présentation

The Whys of Distribution System Analysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Whys of Distribution System Analysis W. H. Kersting Milsoft Utility Solutions

  2. Why??????? • Planning studies • Unbalanced studies • Non-transposed lines • Phasing important • Power losses important • Power factor important • Exact transformer connections • No symmetrical components • Exact induction motor model • R and X settings on voltage regulators

  3. Why Not Use Transmission System Power Flow Programs? • Distribution lines are not transposed • Distribution lines can be • Three-phase • Two-phase • Single-phase • Loading is not balanced

  4. What is the goal? • Under all operating conditions the ANSI voltage standards must be met • Nominal Utilization voltage = 115 volts • Max. Service voltage = 126 volts • Min. Service voltage = 114 volts • Min. Utilization voltage = 110 volts • Voltage Unbalanced less than 3%

  5. Secondary Voltage Drop Assumption

  6. What Actually Happens

  7. Why Unbalanced Studies? • Confirm that voltage unbalance is within limit • Determine how to balance loading • Reduce losses

  8. Why is Phasing of Lines Important? • Mutual coupling between phases is different because of different spacings between phases • Need to know phasing for load balancing

  9. Genera Feeder Component Model

  10. IEEE 13 Node Test Feeder

  11. Line 632 - 671

  12. Untransposed vs. Transposed Line Z

  13. Voltage Unbalance Error

  14. Power Losses

  15. Power Loss by the Numbers

  16. Neutral and Dirt Power Losses

  17. Finally

  18. IEEE 13 Node Test Feeder

  19. Why Voltage Regulators? • Voltage at Node 671 • Need to balance voltages and increase magnitude

  20. R and X Settings • CT primary rating = 500 • Pt = 2400/120 = 20

  21. With Regulator • Voltage Level = 120 volts • Bandwidth = 2 volts

  22. Why Power Factor Correction? • With regulator the complex power out of the substation is: • Can add 300 kvar/phase

  23. 900 kvar at node 671

  24. IEEE 13 Node Test Feeder

  25. Induction Motor PQ Model? • Modeled as constant 21 kW + j9 kvar

  26. Induction Motor Exact Model: • 25 Hp, 240 Volt • Zs = 0.0774 + j0.1843 Ohms • Zr = 0.0908 + j0.1843 Ohms • Zm = j4.835 Ohms

  27. Exact Motor Model Results

  28. Why is it necessary to model the exact transformer connection? • Transformer bank at Node 633 • Ungrounded wye-delta • Phase A: 25 kVA • Phase B: 15 kVA • Phase C: 15 kVA • Loads • Single phase on phases a-b (15 + j10) • Three-phase induction motor (25 Hp)

  29. IEEE 13 Node Test Feeder

  30. Case 1: Lighting transformer on phase A

  31. Case 2: Lighting transformer on phase B

  32. Case 3: Lighting transformer on phase C

  33. Case 4: Grounded Wye – Delta Lighting Xfm on Phase A

  34. Case 5: Open Wye – Delta Lighting Xfm on Phase A

  35. Conclusions • Engineers performing power-flow studies need to know the answers to the “why” questions presented in this paper. • Of primary importance an example system demonstrated • Why un-transposed lines must be modeled • How to computed power loss • Why voltage regulators are necessary • The importance of power factor correction • Why an exact model of induction motors must be used • The importance of the choice of three-phase transformer connections for given load conditions

More Related