ECEN 460 Power System Operation and Control Lecture 12: Power Flow Prof. Tom Overbye Dept. of Electrical and Computer Engineering Texas A&M University overbye@tamu.edu

Announcements Finish reading Chapter 6 Homework 5 is 6.38 (except change the line’s impedance to 0.02+j0.08), 6.39 (except use the 0.02+j0.08 line impedance, and just do one iteration), 6.44, 6.48, 6.52, 6.53 Lab 5 next week is again in CVLP 319 Lab 6 and the following labs will be back in WEB 115

Power Flow Application PJM Control Center Their generation capacity is about 177 GW 2

The N-R Power Flow: 5-bus Example 400 MVA 15 kV 15/345 kV T1 T2 800 MVA 345/15 kV 520 MVA 80 MW 40 Mvar 280 Mvar 800 MW Line 3 345 kV Line 2 Line 1 345 kV 100 mi 345 kV 200 mi 50 mi 1 4 3 2 5 Single-line diagram 3

Five Bus System Ybus 4 4

Ybus Details Elements of Ybus connected to bus 2 5 5

Here are the Initial Bus Mismatches 6 6

And the Initial Power Flow Jacobian 7 7

And the Hand Calculation Details! 8 8

Five Bus Power System Solved 9 9

Five Bus System With Capacitor A capacitor has been added at bus 2 to fix its low voltage 10

Example: ERCOT Competitive Renewable Energy Zones (CREZ) Study In 2005 Texas Legislature ordered a grid study in order to accommodate more renewable generation in West Texas; reactive compensation was a key aspect Starting System Topology Shunt Additions (< 0=caps) 11 Source: www.ercot.com/content/news/presentations/2010/CREZ%20Reactive%20Power%20Compensation%20Study.pdf

Chapter 6 Design Case 1 Example System has 37 bus, plus one new bus 12 12

Good Power System Operation Good power system operation requires that there be no reliability violations for either the current condition or in the event of statistically likely contingencies Reliability requires as a minimum that there be no transmission line/transformer limit violations and that bus voltages be within acceptable limits (perhaps 0.95 to 1.08) Example contingencies are the loss of any single device. This is known as n-1 reliability. North American Electric Reliability Corporation (N ERC) now has legal authority to enforce reliability standards (and there are now lots of them). See www.nerc.com/pa/stand/pages/reliabilitystandards.aspx 13 13

Design Case 1 Line Outages Playing around with the power flow can help gain an intuitive feel for how the system operates 14

Design Case 1: Voltage Control 15

Power System Operation Over Time Movie shows the hourly system variation over the course of one week for a 500 bus synthetic grid 16

Synthetic Texas 2000 Bus System As is the case with actual grids, as the system load changes with time there is a need for lots of reactive power control device changes to keep the voltages in range 17