Question

A 3-core, 3-phase metal-sheathed cable has (i) capacitance of 1 µF between shorted conductors and sheath and (ii) capacitance between two conductors shorted with the sheath and the third conductor 0.6 µF. Find the capacitance (a) between any two conductors (b) between any two shorted conductors and the third conductor.

Answer 1

(a) The capacitance between two cores or lines when the third core is free or shorted to earth is given by 1/2 (3C₁ + C_S)

Now, (i) we have 3C_S = 1µ F or C_s = 1/3 µ F = 0.333 µ F

From (ii) we get, 2C₁ + C_S = 0.6 µ F, 2C₁ = 0.6 − 0.333 = 0.267 µ F,

∴ C₁ = 0.133 µ F

(b) The capacitance between two shorted conductors and the other is given by

= 0.488 mF