Role of Guard Ring in Transmission Lines

The potential distribution in a string of suspension insulators is not uniform which results in a reduction in string efficiency. String efficiency can be improved using longer cross arms of transmission line poles, by grading the insulators, or by application of a guard ring.

Given below is an overview of the role of the guard ring in improving string efficiency.

The guard ring is a metal ring that is electrically connected to the conductor and surrounds the bottom insulator. A guard ring establishes capacitance between the conductor wire and metal fittings of the insulator. The figure below is an illustration of guard ring connected to a line.

Where in above figure

  • i1, i2 are shunt capacitance currents
  • i′1, i′2 are line capacitance currents

The guard ring is connected in a manner that shunt capacitance currents (i1, i2) are equal to metal fitting line capacitance currents i′1, i′2.

Once guard ring is properly installed in place, the same charging current I flows through each unit of string by the virtue of which a uniform potential distribution across the units is achived.

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