Question

In a string of suspension insulator, the maximum voltage appears across the unit
1. Most far from the conductior
2. Nearest to the conductor
3. At the middle
4. None of the above

Answer 1

Correct Answer - Option 2 : Nearest to the conductor

Important points of the voltage distribution across string of suspension insulators:

• Due to the presence of a shunt capacitor, the voltage across the suspension insulators does not distribute itself uniformly across each disc. 
• The voltage across the nearest disc to the conductor is maximum than the other discs.
•  The unit nearest to the conductor is under maximum electrical stress and is likely to be punctured.
• In the case of D.C voltage, the voltage across each unit would be the same. It is because insulator capacitance is ineffective for D.C.

String efficiency of Suspension:

It is define as the ratio of voltage across the whole string to the product of the number of insulator discs and the voltage across the insulator disc nearest to the line conductor.

\(\% String\;efficieny = \;\frac{{V_A}}{{n × V_B}} × 100\)

VA = voltage across the string

VB = voltage across disc nearest to the conductor

n = number of insulator disc

Method of improving string efficiency: 

1) Capacitance grading or grading of the unit

2) Using Gaurd ring