$25\mathrm{.}1-$

$[$Insulators$]$

A design of supported three$-$unit suspension insulator of three$-$phase line and fitted with a guard ring is given to you. The capacitance of the link pins to twoer and guard ring can be assumed to be $15\%$ and $5\%$ of the capacitance of each unit.

In this design of a three$-$unit suspension insulator string, you are asked to find the following:

a$)$ First, draw the circuit of three$-$unit suspension insulator string and show the shunt and self$-$capacitance, cross arms, guard rings and the insulators. Also, indicate the $KCL$ direction on your diagram for both designs $($with and without guard rings$).$

b$)$ In this design, determine the voltage distribution.

c$)$ Calculate the string efficiency.

d$)$ If you were asked to have an alternative design to reduce the voltage of the lowest unit and increase the string efficiency, what would be the best possible solution.