Transformer Oil Analysis

Here we are focusing on the transformer oil analysis before moving further we must know what transformer oil is? Transformer oil or insulating oil is oil that remains durable at high temperature. It has extremely good electrical insulating traits and it is widely used in oil filled transformer. It performs two major tasks, it is liquid insulation in transformer and second it consumes heat generated by transformer.


1. Partial Discharge

Signs of partial discharge were first observed in an oscilloscope in sixties. Later in Eighties, computerized data recovery became commonly accessible. This greatly intensifies storage and digital processing of discharge patterns.


Partial discharge more often than not, starts inside tiny bubbles, voids, cracks, or inclusions within solid insulator (dielectric), at conductor-dielectric interfaces with solid or liquid dielectrics, or in voids that occurs in liquid insulators used as dielectrics. Since partial discharge only occurs at a particular part in the electrode, the faults created by the discharges only partially connect the separation of the electrodes.

Partial discharge in transformers reduces the traits of the insulating materials and can lead to

possible failures. Partial discharge can be determined by using analysis from phonic calculations or by calculations of electric signals. Another preferred method is by doing chemical tests to analyze the gases produced by partial discharge,


Partial discharge causes appreciable declination to the insulation (dielectric) it occurs in.

It is worth mentioning that when gases are collected by upward delivery or downward

displacement of air, and the result of the analysis of the gases can be used to determine the type of fault that occurred. For the cause of partial discharge, hydrogen gas is produced.


Generally, and for all types of oil, the partial discharge experiments show that the rate of partial discharge is directly proportional to the age of oil. This is reasonable because during partial discharge, many chemical bonds are broken to form several gases and this productively shortens the hydrocarbon chains of the oil.

Partial discharge therefore would be worthwhile to be detected early for technical intervention; else, it can ruin the transformer.


2. Dissolved Gas Analysis (DGA)

Dissolved gas analysis is the study of dissolved gasses in transformer oil. The gasses obtained from the degradation of the materials from the container of the transformer oil. These materials include both the electrical equipment, the insulating materials for the coils and the core. Since the oil is united with the internal equipment, the gases formed by oxidation, vaporization, decomposition, insulation, oil breakdown and electrolytic action, are dissolved in the transformer oil. At the instance, the oil is hot. The heat enhances the dissolution of gases

During normal transformer operation, gasses are produced. But when there is a fault, the gasses are produced in larger quantities. The gasses produced are proportional to the fault. Below, are the most common faults and gasses produced; in increasing severity.


       2.1 Dissolved Moisture in Transformer Oil

Free water causes few problems with the dielectric strength of oil in transformers. However, it should be dried up as soon as noticed. Moisture is obtained in dissolved gas in ppm, and some laboratories also give percent saturation. Percent saturation refers to saturation of water in the 0il. This is a percentage of how much water is in the oil compared with the maximum possible saturation of water in oil. The saturation of water in oil greatly depends on temperature.

Hope you find this article useful. If you need more information regarding transformer oil, read these blogs.

Three Phase Transformer Storage and Handling

Transformer oil sampling – Study & Analysis

Why Transformer Oil Testing Is so Important?

Properties of Transformer Insulating Oil

Transformer oil filtration machine

Transformer oil Specification