scope:

This guide discusses and recommends methods of testing and evaluating dissolved gases in mineral based transformer oils found in Load Tap Changers (LTCs). General types of LTC mechanisms, breathing configurations, and electrical design will be included for evaluation criteria in determining when mechanical damage or failure has occurred. Dissolved Gas Analysis (DGA) of the oil in the LTC is required. This guide will not be manufacturer specific, rather category specific.

Purpose

The purpose of this guide is to assist the responsible parties who are in charge of the operation and maintenance decisions in evaluating the condition of a load tap changer (LTC) without the need to deenergize the transformer to inspect the LTC in question. Additionally, repairs to the LTC can be made in a timely fashion based on accurate interpretation of the gas analysis minimizing premature repairs or post failure rebuilds.