Transformer dissolved gas analysis are oil and fiber insulation materials that are aged and decomposed under the influence of moisture, oxygen, heat, and the catalytic action of materials such as copper and iron during operation. Most of the gas generated is dissolved in the oil, but the rate of gas generation is quite slowly. When there is an initial fault or a new fault condition is formed inside the transformer, the gas production rate and amount are very obvious. Most of the initial defects will show early signs. Therefore, proper analysis of the gas generated by the transformer can detect the fault.

As the operating time of the transformer prolongs, the transformer may develop initial failures. Certain flammable gases in the oil are precursors of internal failures. These flammable gases can reduce the flash point of the transformer oil, thereby causing early failures.

Dissolved gas analysis of transformer oil age and decompose under the influence of moisture, oxygen, heat, and the catalytic action of materials such as copper and iron during operation. Most of the gas generated is dissolved in the oil, but the rate of gas generation is quite slow. When there is an initial fault or a new fault condition is formed inside the transformer, the gas production rate and amount are very obvious. Most of the initial defects will show early signs. Therefore, proper analysis of the gas generated by the transformer can detect the fault. .
Gas chromatography is the most practical method for analyzing flammable gases in transformer oil. This method includes two processes: degassing from the oil and measurement. Mineral oil is composed of approximately 2871 liquid hydrocarbons. Usually only hydrogen (H2), oxygen (O2), nitrogen (N2), methane (CH4), carbon monoxide (CO), and ethane (C2H6) in insulating oil are identified. ), carbon dioxide (CO2), ethylene (C2H4), and acetylene (C2H2). Taking these gases out of the oil and analyzing them to prove their existence and content can reflect the type and severity of the faults that generate these gases. degree. The gases generated by oil during the normal aging process are mainly carbon monoxide (CO) and carbon dioxide (CO2). When there is partial discharge in the oil insulation (such as bubble breakdown in the oil), the gases generated by oil cracking are mainly hydrogen (H2) and methane ( CH4). When the fault temperature is not much higher than the normal operating temperature, the gas produced is mainly methane (CH4). As the fault temperature increases, ethylene (C2H2) and ethane (C2H6) gradually become the main physical gases; when the temperature is higher than 1000 ℃ (for example, when the arc temperature is above 300°C), the gas generated by oil cracking contains more acetylene (C2H2). If the fault involves solid insulating materials, more carbon monoxide (CO) and carbon dioxide ( CO2).

How to judge the nature of the fault of electrical equipment?

Use three contrasting values of five characteristic gases to determine the nature of the fault of electrical equipment:

(1) C2H2/C2H4≤0.1　0.1＜CH4/H2＜1

When C2H4/C2H6 <1, the transformer has aged normally.

(2) C2H2/C2H4≤0.1　CH4/H2＜0.1

When 0.1＜C2H4/C2H6＜1, it is a partial discharge with low energy density, which is a discharge in a gas-containing cavity. This cavity is caused by incomplete immersion, gas saturation or high humidity.

(3) 0.1＜C2H2/C2H4＜1　CH4/H2＜0.1

When 0.1＜C2H4/C2H6＜1, it is a partial discharge with high energy density (except discharge in gas-containing cavities), resulting in discharge traces of solid insulation.

(4) 1＜C2H2/C2H4＜3　0.1＜CH4/H2＜1

When C2H4/C2H6>3, there is power frequency freewheeling discharge, arc breakdown of oil between coils, wire cakes, wire turns or between coils and ground.

(5) C2H2/C2H4≈3　0.1＜CH4/H2＜1

When C2H4/C2H6≈3, it is a low-energy discharge. As the spark discharge intensity increases, the ratio of characteristic gases gradually increases to 3. The fault may be the continuous spark discharge of the suspended potential body or the breakdown of oil between solid materials.

(6) C2H2/C2H4≤0.1　0.1＜CH4/H2＜1

When 1＜C2H4/C2H6＜3, it is a thermal failure below 150℃. The gas mainly comes from the decomposition of solid insulating materials, usually the overheating of wires covered with insulation.

(7) C2H2/C2H4≤0.1　 1＜CH4/H2＜3

When C2H4/C2H6<1, it is a low-temperature thermal fault below 300℃.

(8) C2H2/C2H4≤0.1　1＜CH4/H2＜3

When 1＜C2H4/C2H6＜3, it is a medium temperature thermal fault of 300~700℃.

(9) C2H2/C2H4≤0.1　1＜CH4/H2＜3

When C2H4/C2H6>3, it is a high temperature thermal failure above 700℃.

The main reason for (7), (8) and (9) is the local overheating of the iron core caused by the concentration of magnetic flux. In practice, dissolved gas analyzer are ratio combinations not included, which may be the simultaneous existence of overheating and discharge or the on-load voltage regulating transformer. The diverter switch oil chamber is leaking.