General transformer maintenance: oil test

General transformer maintenance is required for on-line detection and elimination of various defects to avoid failures in emergency situations.

In this article we will talk about transformer oil testing. The tests determine the current state of both the oil and the transformer parts. The results may serve as the criteria to undertake general maintenance.

Let’s start with the fact that transformer oil serves as an insulator, removing heat from the hot parts of the transformer. During operation, the oil is exposed to various negative factors: high temperature, air, mechanical particles, etc. It results in deterioration in the dielectric properties of oil and decrease of breakdown voltage.

Generally, samples are taken every 5000 switchings, at least once a year. The main purpose of sample analysis is to determine breakdown voltage and the presence of moisture. If the moisture is found in the amount exceeding the established norm, and the breakdown voltage is too low, the oil should be immediately replaced.

Insulating liquid is replaced when the transformer is offline. First, the tank is washed to remove oil decomposition products and moisture, and then filled with dry fresh dielectric fluid. Filling the transformer with oil can be performed with the help of a UVD unit by GlobeCore.

Sampling should be performed very carefully, with a dry and clean glass jar. Dielectric strength is determined with the help of special equipment.