The nonuniformity in the voltage distribution over a string of suspension insulators is expressed in terms of a parameter called string efficiency.
When the voltage is applied across the suspension insulator string, it is unequally distributed across the individual unit. The disc near the line conductor is extremely stressed and takes the maximum voltage in the absence of stress. The voltage distribution on the insulator string determines the flashover voltage and the voltage at which the localized corona and radio interference are produced.
String efficiency is an important consideration since it decides the potential distribution along the string. The greater the string efficiency, the more uniform is the voltage distribution across the string. Thus 100% string efficiency is an ideal case for which the voltage across each disc will be exactly same. Although it is impossible to achieve 100% string efficiency practically, various methods are to obtain the string efficiency as high as possible.
If the voltage impressed across the string were DC, then the voltage across each unit would be same. It is because insulator capacitances are ineffective for DC. This is why string efficiency for DC system is 100%.
String efficiency is an important consideration since it decides the potential distribution along the string. The greater the string efficiency, the more uniform is the voltage distribution across the string. Thus 100% string efficiency is an ideal case for which the voltage across each disc will be exactly same. Although it is impossible to achieve 100% string efficiency practically, various methods are to obtain the string efficiency as high as possible.
If the voltage impressed across the string were DC, then the voltage across each unit would be same. It is because insulator capacitances are ineffective for DC. This is why string efficiency for DC system is 100%.
Inequality in voltage distribution increases with the increase in the number of discs in a string. Therefore, shorter strings are more efficient than longer string insulators.