An overhead line has three units in the string of insulators. If the voltage across top unit, middle unit and bottom unit are 6 kV, 8 kV and 10 KV, then find the string efficiency.

Concept

String efficiency is the degree of capacity utilization of individual SCRs in a string of series/parallel connected SCRs. 

String Efficiency 

Where, V = Actual voltage of the whole string

V1 = Voltage rating of the insulator at the bottom

N = Total number of insulators in a string

The insulator at the bottom has the highest voltage drop

Calculation

Given, N = 3

V₁ = 10 kV

V = 6 + 8 + 10 = 24 kV

String Efficiency 

String Efficiency = 0.8 = 80%