1. ECE 476 POWER SYSTEM ANALYSIS
Lecture 15
Power Flow, Economic Dispatch
Muhammad Abdul Retha lefte Al-Badri
Department of Electrical and Computer Engineering

2. Announcements Be reading Chapter 12.4 and 12.5 for lectures 15 and 16
HW 6 is 6.50, 6.52, 6.59, 12.20, 12.26; due October 20 in class.

3. In the News: Line Costs Increase
On Tuesday Ameren gave new costs for the proposed 138 kV line between the Bondville and Southwest Campus substations
Cost for the “preferred” 9.8 mile route has increased from $14 million in 2010 to $23.8 million currently
Also require $6 million in substation costs
Increased material and real-estate costs were the reason for the change
Source: News-Gazette, October 12, 2012

4. Wind Turbine and Power Flow
There are four main types of wind turbines:
Type 1: Induction machine; treated as PQ bus with negative P load
Type 2: Induction machine with varying rotor resistance; treated as Type 1
Type 3: Doubly Fed Induction Generator (DFIG); treated as a PV bus
Type 4: Full Asynchronous Generator; treated as a PV bus

5. Wind Farm (Park) Feeder Layout
Usually a number of wind turbines are located together, in what is known as a wind farm or wind park.
Typical turbine size is 1 to 3 MW onshore, 3 to 6 MW off-shore
A common voltage level is 600V, with the voltage stepped up to 34.5 kV in the distribution system connecting to a single transmission system interconnection point.

6. Indirect Transmission Line Control
What we would like to determine is how a change in
generation at bus k affects the power flow on a line
from bus i to bus j.
The assumption is
that the change
in generation is
absorbed by the
slack bus

7. Power Flow Simulation - Before
One way to determine the impact of a generator change is to compare a before/after power flow.
For example below is a three bus case with an overload

8. Power Flow Simulation - After
Increasing the generation at bus 3 by 95 MW (and hence
decreasing it at bus 1 by a corresponding amount), results
in a 31.3 drop in the MW flow on the line from bus 1 to 2.

9. Analytic Calculation of Sensitivities
Calculating control sensitivities by repeat power flow solutions is tedious and would require many power flow solutions. An alternative approach is to analytically calculate these values