Question

A $3-\varphi$ transmission line is being supported by three disc insulator. The potential across top unit (i.e near to the tower) and middle unit are 10kV and 12 kV respectively. The string efficiency is ______________%

• A. 78.05

Answer 1

The correct option is A 78.05


$C_1=kC$
$KCLatjunctionA,I_2=I_1+i_1$
$V_2\omega C=V_1\omega C+V_{1}k\omega C$
$V_2=V_2(1+k)$
$1+k=\frac{V_2}{V_1}$
$1+k=\frac{12}{10}$
k = 0.2

KCL at junction B

$I_3=I_2+i_2$
$V_3\omega C=V_2\omega C+(V_1+V_2)k\omega C$
$V_3=(1+3k+k^2)V_1=16.4kV$
$Stringefficiency=\frac{38.4}{3\times 16.4}=78.04878{}^o{/}_o\approx 78.0{}^o{/}_o$