A Suspension insulator string is an assembly of two or more suspension insulators in tandem. String efficiency of suspension insulators should be thinking about.

In electrical systems, most suspension insulator string used on transmission and distribution lines. We should that how to increase String efficiency of suspension insulators.
According to some resources of porcelain disc insulator string, the formula is string efficiency = Voltage across String/{n×Voltage across disc nearest to conductor}

There are three methods to improve String efficiency of suspension insulators
◆ By using longer cross-arm
◆ By grading the insulators
◆ By using a guard ring

String efficiency of suspension insulators is an important consideration since it decides the potential distribution along the string.

Relative Articles:
Composite suspension insulator
Porcelain suspension insulator
Disc suspension insulator
Suspension insulator string