scope:

This document provides guidelines for performing a bushing dielectric frequency response (DFR) measurement either in the field or in the factory. The measurement technique, measuring equipment requirement, and interpretation of results based on comparison are included in the normative text.

Additional theories related to DFR such as temperature correction using the Arrhenius equation, influence of voltage, and a few case studies are described in the annexes.

Purpose

The purpose of this guide is to provide a diagnostic tool for bushing condition evaluation in the field to reduce unexpected transformer failures and unplanned outages. Bushing manufacturers performing the DFR measurement on a bushing during the factory acceptance or transformer commissioning test could act as a baseline signature that is compared with the results obtained later. Given the same test conditions, the trending of the insulation condition can be observed through comparison. This process gives the test engineers an additional way to identify defects in the bushing insulation system at an early stage.