Lab: Power Transmission Lines
A one-line diagram along with bus and generator data for a power transmission system is shown below; the system will be referred to as Transmission Corridor Z. Solve the following problems using the PowerWorld Simulator. There are two additional files you may need that are also posted on the website: a list of Aluminum-conductor Steel-reinforced (ACSR) cables and a help document for the PowerWorld Transmission Line Calculator.
Transmission Corridor Z represent the transmission of power from a large generating facility into the utility service area. The generating station feeds a line voltage of 500kV with 700MW and 300MVAr of power. This power is delivered into the service area along 103 miles of 500kV transmission lines before arriving at a substation to be lowered to 220kV for local transmission. The substation is equipped with a 300MVAr shunt capacitor on the low voltage side. The power is then transmitted another 37 miles for distribution to the specific service area, represented by a 600 MW 250 MVAr load.
You are tasked with choosing the transmission lines that will deliver this power. Make sure that you use the correct conductor sizes for the load the lines will be carrying. You will explore three design cases for the transmission system. Note that your generated MW and MVAr as well as the actual shunt capacitor MVAr will vary based on your choices.
For each case you must calculate the per unit resistance, p.u. reactance, p.u. shunt charging and MVA limit using the table of ACSR cables given on the website in conjunction with the PowerWorld software. Note the code word of the selected cable and why that cable was selected. Record the p.u. values used (for resistance, first use the AC resistance at 25*C). Run the simulation and note the total losses in the transmission lines (not including the transformer) and the actual MVAr value at the shunt capacitor. Recalculate the p.u. resistance at 75*C and note how the losses and power delivery change.
If you exceed your MVA rating, you need to select new conductors. (Recall that we don't want to exceed 95% of our nominal MVA rating).
1) A single transmission line at 500kV and three transmission lines at 220kV.
2) Two transmission lines at 500kV and four transmission lines at 220kV.
3) Increase the load to 750MW and 300MVAr, also increase the shunt capacitor to 400MVAr.
Choose the number of conductors, along with correct conductor sizing, for the 500kV and 220kV lines such that the loading is between 65% and 80% on every conductor.
Make sure you choose appropriate conductors for each of these cases. If the load isn't being delivered because of a low p.u. voltage on bus 4, you may add a shunt capacitor on bus 4 to bring up the voltage.
One Line Diagram
Line Records (Base MVA = 250)
|
From Number
|
From Nom kV
|
To Number
|
To Nom kV
|
Transformer?
|
R
|
X
|
|
B
|
Lim MVA A
|
|
1
|
500
|
2
|
500
|
NO
|
?
|
|
?
|
?
|
?
|
|
2
|
500
|
3
|
220
|
YES
|
0.0085
|
|
0.06
|
0
|
750
|
|
2
|
500
|
3
|
220
|
YES
|
0.0085
|
|
0.06
|
0
|
750
|
|
3
|
220
|
4
|
220
|
NO
|
?
|
|
?
|
?
|
?
|
|
3
|
220
|
4
|
220
|
NO
|
?
|
|
?
|
?
|
?
|
|
3
|
220
|
4
|
220
|
NO
|
?
|
|
?
|
?
|
?
|
Generator and Load Records
|
Bus #
|
Gen MW
|
Gen Mvar
|
AGC
|
AVR
|
Min MW
|
Max MW
|
Min Mvar
|
Max Mvar
|
Part. Factor
|
|
1
|
700
|
300
|
NO
|
YES
|
500
|
1000
|
-400
|
400
|
10
|
|
3
|
0
|
300
|
N/A
|
N/A
|
N/A
|
N/A
|
N/A
|
N/A
|
N/A
|
|
4
|
-600
|
-250
|
N/A
|
N/A
|
N/A
|
N/A
|
N/A
|
N/A
|
N/A
|