Previous Year Question
For a transposed 3-phase transmission line, the mutual distances between the conductors are 4 m, 4 m, and 5 m, respectively. What is the equivalent mutual Geometric Mean Distance (GMD) of the line?
Correct answer: D
Explanation
For a transposed 3-phase line, equivalent mutual GMD is the cube root of the product of the three mutual spacings. Thus Dm = ∛(4×4×5) = ∛80 m.
Formula
Dm = ∛(Dab Dbc Dca) = ∛(4×4×5) = ∛80 m
Step-by-step solution
Correct Answer
D — ∛80 m
Explanation
For a transposed 3-phase line, equivalent mutual GMD is the cube root of the product of the three mutual spacings. Thus Dm = ∛(4×4×5) = ∛80 m.
Key Concept
Equivalent GMD of Transposed Line
Formula
Dm = ∛(Dab Dbc Dca) = ∛(4×4×5) = ∛80 m
Exam Point
Three mutual distances → multiply all three, then take cube root.
Common Mistake
Do not take a square root; a 3-phase transposed line uses the cube root of three spacings.
Common mistake
Do not take a square root; a 3-phase transposed line uses the cube root of three spacings.
Exam tip
Three mutual distances → multiply all three, then take cube root.
Quick method
Three mutual distances → multiply all three, then take cube root.