Question

The positive, negative, and zero sequence impedance of a solidly grounded system under steady state condition always follow the relation ________.

• A. \( Z_1>Z_2>Z_0 \)
• B. \( Z_1<Z_2<Z_0 \)
• C. \( Z_0<Z_1>Z_2 \)
• D. \( Z_0 = Z_1 Z_2 \)

Hint:

Solidly grounded system: \( Z_1>Z_2>Z_0 \). Zero-sequence sees ground return, so lowest impedance.

Answer 1

The Correct Option is A

Step 1: Understanding Sequence Impedances
In power systems, unbalanced conditions are analyzed using symmetrical components — positive, negative, and zero sequences:
- \( Z_1 \): Positive sequence impedance (normal operating impedance).
- \( Z_2 \): Negative sequence impedance (seen under unbalanced faults).
- \( Z_0 \): Zero sequence impedance (involved in ground faults).
Step 2: Practical Relations in Solidly Grounded Systems
In solidly grounded systems:
- Positive sequence network represents the usual load path — has the highest impedance.
- Negative sequence is slightly less, as it's influenced by machine asymmetries.
- Zero sequence is often the smallest due to path via neutral or ground return.
Thus, the relation \( Z_1>Z_2>Z_0 \) holds. Conclusion:
Option (1) is correct based on the standard impedance behavior of solidly grounded systems.