Voltage Distribution by Standard Formula

Voltage Distribution by Standard Formula

When the number of units in a string of suspension type of insulator increases, calculation of voltage across each unit and the string efficiency becomes tedious, laborious and time consuming by the method discussed earlier. In such a case, following formulae can be used.

Let     V = Voltage across string

k = Ratio of shunt to mutual capacitance

n = Number of units in the string

V₁, V₂, V₃ ... = Voltages across the units starting from the line unit. Note that V_{1 ,} V₂, V₃  ... are defined from bottom to top. Then voltage across xth unit is given by,

Example 5.8.1 A string of suspension insulator consists of 6 units. The peak voltage per unit is 33 kV. The ratio of shunt to mutual capacitance is 0.15. Find the maximum voltage for which string can be used and the string efficiency. Use the standard formulae.

Solution : The maximum voltage is always across the unit which is V1 while using standard formula.

Review Questions

1. Explain the voltage distribution across a string of insulators by standard formula.

2. A string of 8 units is used as suspension insulator. The self capacitance is 10 times the pin to earth capacitance. How much % of the total voltage V across the string will be across the line unit ? Use standard formula.  

[Ans.: 0.275 V, 45.45 %]