A $3-$phase system is suspended by a string of $3$ identical insulators. Consider that, the self $-$captcitance of each disc is C and the shunt capacitance between metal pin and earth is $\frac{1}{5}$ times of the self$-$capacitance.

i$.$ calculate the string efficiency.

ii$.$ calculate the string efficiency of the module if a guard ring is introduced between lowest metal link and line, whose capacitance is $\frac{1}{10}$ times of the self$-$capacitance of each disc.

$($With Proper diagram and explanation$)$