Question

The valid positive, negative and zero sequence impedances (in p.u.), respectively, for a 220 kV, fully transposed three-phase transmission line, from the given choices are

• A. 1.1, 0.15 and 0.08
• B. 0.15, 0.15 and 0.35
• C. 0.2, 0.2 and 0.2
• D. 0.1, 0.3 and 0.1

Hint:

Sequence impedances play a crucial role in fault analysis. The zero sequence impedance is typically higher than the positive and negative sequence impedances, especially in transmission lines.

Answer 1

The Correct Option is B

Step 1: Understanding the question.
The question refers to the sequence impedances of a three-phase transmission line. The positive, negative, and zero sequence impedances are important in the analysis of unbalanced faults in three-phase systems. Step 2: Analyzing the options.
- (A) 1.1, 0.15 and 0.08: The values provided here are inconsistent with typical values for a three-phase transmission line. - (B) 0.15, 0.15 and 0.35: This option is a valid set of sequence impedances commonly used in transmission line calculations, making it the correct answer. - (C) 0.2, 0.2 and 0.2: These values are unlikely for a fully transposed transmission line as the positive and negative sequence impedances are typically not equal to the zero sequence impedance. - (D) 0.1, 0.3 and 0.1: This option does not match typical impedance values for a transmission line.
Step 3: Conclusion.
The correct answer is (B) because the given values are in accordance with standard transmission line impedance calculations.