20 Questions
What is the purpose of the per-unit impedance diagram in Figure 27?
To simplify the analysis of power systems by reducing the number of variables
What is the significance of the '¾»' symbol in the one-line diagram of Figure 28?
It represents a step-up transformer
In the per-unit system, what is the advantage of using a base value for voltage and current?
It provides a normalized representation of the power system, enabling easier comparison of different components
What is the purpose of G1 and G2 in the per-unit impedance diagram of Figure 27?
They represent the generators in the power system
What is the significance of the 'µ´' symbol in the per-unit impedance diagram of Figure 27?
It represents the per-unit value of a component
What is the purpose of the one-line diagram in Figure 28?
To visualize the complexity of a power system
What is the value of S2 in pu?
1.848 + j0.066
What is the value of V3 in pu?
1.06 0°
What is the value of I3 in pu?
-j0.2
What is the line-to-line voltage at bus 2?
126.5 kV
What is the value of I2 in pu?
1.68 - j0.06
What is the line-to-line voltage at bus 1?
27.6 kV
What is the per-unit value of S2 in the given problem?
0.1848 + j0.0066
What is the value of V3 in per-unit?
1.06 0°
What is the line-to-line voltage at bus 2 in kV?
440 kV
What is the value of I2 in per-unit?
0.054 + j0.332
What is the transformer reactance in percent?
20%
What is the value of S3 in per-unit?
0 MW + j0.20
What is the line impedance in ohms?
j66.125
What is the line-to-line voltage at bus 1 in kV?
480 kV
Study Notes
Problem 3.11
- The per unit impedance diagram for Problem 3.11 is shown in Figure 27.
- It consists of two lines: Line 1 with a voltage of 220 kV and Line 2 with a voltage of 110 kV.
Problem 3.14
- The one-line diagram for Problem 3.14 is shown in Figure 28.
- The three-phase power and line-line ratings are given as:
- S2 = 15.93 MW - j33.4 Mvar = 0.1593 - j0.334 pu
- S3 = 77.00 MW + j14.0 Mvar = 0.7700 + j0.140 pu
- The line-to-line voltages at buses 2 and 1 are calculated as:
- V2 = 440 kV
- V1 = 480 kV
Problem 3.17
- The one-line diagram for Problem 3.17 is shown in Figure 33.
- The transformer reactance is 20% on a base of 100-MVA, 23/115-kV.
- The line impedance is Z = j66.125Ω.
- The load at bus 2 is S2 = 184.8 MW + j6.6 Mvar and at bus 3 is S3 = 0 MW + j20 Mvar.
- The voltage at bus 3 is held at 1156 0◦ kV.
- The voltages at buses 2 and 1 are calculated as:
- V2 = 126.5 kV
- V1 = 27.6 kV
Solve problem sets related to power system analysis, including impedance diagrams and one-line diagrams. Calculate power and line-line ratings, and determine line-to-line voltages at buses.
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