Question

Two insulator discs of identical capacitance value C makes up a string for a 22 kV, 50 Hz, single phase overhead line insulation system. If the pin to earth capacitance is also C, then the string efficiency is__________%.

• A. 75

Answer 1

The correct option is A 75
$Stringefficiency=\frac{Voltageacrossthestring}{n\times Voltageacrossthelowermostunit}$

$\eta =\frac{V_1+V_2}{n\times V_2}\times 100$

$V_2=V_1+K{V}_1$

$V_2=2V_1$

$\eta =\frac{V_1+2V_1}{2\times 2V_1}\times 100$

$=\frac{3V_1}{4V_1}\times 100=0.75\times 100=75\%$