INVESTİGATİON OF CARBON GAS İN OİL TRANSFORMERS
Authors: Vahid Bodurov Vahid Bodurov , Maryam Giyasi Atrafi Maryam Giyasi Atrafi 
Published: January 2022

By their structure and design, transformers are devices that are reliable in operation and easy to maintain. In the operation of transformers, the main factors are timely inspection, performance of current and major repairs, as well as the necessary preventive tests. One of the important conditions for the correct use of this device is the correct introduction of the temperature regime and observance to the allowed overloading.
Monitoring the condition of the oil is fundamental to the correct operation of the transformer. During the period of use, the oil ages and it loses its original properties. In addition to the deterioration of the properties of the oil due to aging, there is also a change in its properties under abnormal operating conditions of the transformer. So with local heating, build-up of insulation between the steel sheets of the magnetic circuit, poor contact in the tap changer or at the winding terminals under the transformer cover, and with turn short circuits in the windings, oil decomposes.
Transformer oil has at least three functions in transformers. Task of transformer oil in oil-filled transformers cooling function, extinguishing the arc, and providing insulation is the main [1].
The appearance of defects caused by both electrical and thermal faults is accompanied by the formation of gases, and their further dissolution in transformer oil. In addition to normal operation, during the operation of the transformer, local thermal overheating (of an insulated conductor, core, etc.) and electrical discharges (partial, spark and arc discharges) can occur. Such defects lead to the destruction of insulation, physical wear and tear, and irreversible damage to the active part of the transformer.
To determine the state of oil-filled electrical equipment, gases are used: hydrogen (H2), methane (CH4), ethane (C2H6), ethylene (C2H4), acetylene (C2H2), carbon monoxide (CO), carbon dioxide (CO2). In addition to the above gases, oxygen (O2) and nitrogen (N) are also present, and their concentration varies depending on the tightness of the transformer tank and gases such as propane, butane, butene and others can be released. The study of these gases for diagnostic purposes is not widespread [2].
In this regard, the method of analysis of gases dissolved in oil (DGR) has proven itself all over the world. The main advantage of this method is the timely diagnosis of the malfunction, identification of the nature and control of the defect, which leads to lower economic costs and time savings. Fault diagnostics can be performed using various methods, such as: the ratio of pairs of gas concentrations using the Duval triangle, Japanese ETRA, monogram method, etc. The most important tool for diagnosing the condition of a transformer is observing the evolution of gases by comparing different analyzes of the amount of dissolved gases and understanding this information.
The Duval Triangle Method is based on the existing IEC 60599 Gas Ratio Method. Within this triangle there are six potential damage zones. Zones include partial discharges, electrical and thermal damage. The use of this triangle method is based on three main gases (CH2, C2H4 and C2H2). Firstly the concentration levels of these gases are calculated. Then lines are drawn along three sides of an equilateral triangle: on each side, the relative value of a certain gas is laid, which can vary from 0 to 100% clockwise. The sum of the values of the concentrations of these gases is taken as 100. When drawing the boundaries of the zones of defects, the lines are drawn parallel to the lagging side of the triangle. The considered method not only clearly shows the "location" of the defect, but also allows you to observe the trajectory of its development [3].
The oil analysis results reflect the overall condition of the transformer. For this analysis, the oils are sent to a laboratory for testing. The most important indicators are the rate of formation of the total amount of combustible gases and individual gases. Carrying out timely sampling makes it possible to track the dynamics of malfunctions and take appropriate decisions in time.
To obtain more reliable results, you must follow the sampling rules, store the samples and transport the samples to the analysis site correctly.
Some gases dissolved in transformer oil (ethylene and acetylene) may indicate overheating in the contacts of switching devices, heating of the shield attachment points and bushing pins, short-circuiting of the winding conductors and other defects.
The main goal of this article is to solve the problem associated with the extraction of hydrocarbon gases from oil, and to correct the interpretation based on the obtained data [4].
Keywords: DGR, Duval triangle, transformer oil, gas discharges.