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TET4115 Power System Analysis Faculty of Information Technology, Mathematics and Electrical Engineering Department of Electrical Power Engineering Electric Power Systems group Address:

7491 Trondheim

Phone:

735 94215

Fax:

735 94279

Assignment 3 – Power flow Announced:

Deadline:

12.09.2011

26.09.2010

The figure below shows the one line diagram of a simple power system. Generators are connected at buses ① and ④ while loads are indicated at all four buses. Base values for the transmission system are 100 MVA, 230 kV. The line data in the table give per unit series impedances and line charging susceptances for the nominal π equivalents of the four lines identified by the buses at which they terminate. The bus data in the table list values for P, Q, and V at each bus. The Q values of load are calculated from the corresponding P values assuming a power factor of 0.85 and presented in the table for bus data.

Fig 1. One line diagram of the 4 bus case (case4gs)

TASKS: 1. Run base case power flow: Run Power flow for ‘case4gs.m’ in MATPOWER using the function ‘runpf’. (Pgen, Qgen, U and  at all buses) Indicate the solution in a one-line diagram as in Fig 1. 2. Edit base case and re-run power flow: Reduce generation at bus at ④ to 200 MW. Set the maximum active power (Pmax) to 600 MW and maximum reactive power (Qmax) of both the buses ① and ④ to 200MVAR. Again run the power flow. Indicate the solution in the one-line diagram as in Task 1 and comment on the reactive power generation.

3. U-P curves: Consider the network in the base case. Change the load at bus ② in steps of 50 MW from 100 MW to 400-500 MW and draw the voltage versus load power curve for node 2. (Adjust the reactive load accordingly to maintain a power factor of 0.85.) 4. Enforce Q limits: Consider the case mentioned in Task 2. Set the maximum allowable Q (Qmax) for both generators at buses ① and ④ to 200 MVAr. Set up the power flow solution to enforce Q limits (See ‘help mpoption’). Increase loads as in Task 3 and draw voltage versus load power curve for node ② when Q limits are enforced. Comment on the difference. 5. Reactive compensation: Consider the network in the base case. Explore the effect of adding a capacitor bank at bus ②. Find the optimal size of capacitor bank (that minimize system losses) when the load at bus ② is 300 MW. 6. Grid reinforcement: Consider the network in the base case. Connect a new line between buses ① and ④ or ② and ③ and explore the effect on power flow and the bus voltages. Assume the line data for this new line same as that of line between buses ③and ④. Note: Download and install MATPOWER. Use the function „runpf‟ to run the power flow. You can learn how to use „runpf‟ by typing ‘help runpf’ in MATLAB command window. The changes can be made in the MATLAB file ‘case4gs.m’ to include the loads and lines. Other useful help: help caseformat help mpoption NB! A user manual can be found in the “Matpower” folder, under “docs”. This manual has more details regarding how the different components are model in Matpower.