Question

A 3-core, 3-phase metal sheath cable had a capacitance of 0.8 $\mu F$ between shorted conductors and sheath, capacitance between two conductors shorted with the sheath and the third conductor is 0.4 $\mu F$. Then the capacitance (in $\mu F$) between any two conductors is

• A. 0.0666
• B. 0.1
• C. 0.1333
• D. 0.2667

Answer 1

The correct option is A 0.0666

When all conductors are shorted,

Capacitance between shorted conductors and sheath is $3C_s$

$\therefore$ $3C_s=0.8\mu F$
$C_s=\frac{0.8\mu F}{3}=0.2667\mu F$

When two conductors are shorted with sheath

$\therefore$
$C_{AS}=2C_C+C_s$
$\therefore$ Capacitance between two conductors shorted with sheath and the third conductor is $2C_C+C_S$
$2C_C+C_S=0.4\mu F$
$2C_C+0.2667=0.4$
$2C_C=0.1333$
$C_C=0.0666\mu F$