Evaluating the humidity in insulating materials is an important factor to ensure the reliability and service life of transformers. The moisture in insulating oil is constantly changing, which may adversely affect the quality. In addition, most humidity is distributed in insulating paper. Humidity will affect the dielectric breakdown strength of solid and liquid insulation materials, and affect the aging rate of cellulose insulation materials and the tendency of bubble formation during overload.
Environmental temperature, load, aging, leakage and other factors will cause changes in humidity. Therefore, with the cyclic variation of transformer temperature, continuous monitoring and diagnosis should be carried out. This is more necessary for overload or peak load transformers. The total humidity in the transformer insulation system is determined by the moisture content in the cellulose and liquid. The humidity relationship between insulating paper and insulating oil depends only on temperature. As the temperature increases, the solubility of water in the insulating oil (water content of the solution) increases, and the water will be transferred from the insulating paper to the insulating oil.
When the temperature decreases, the process reverses, but the flow of water from the liquid medium to the solid insulation material is quite slow. Therefore, the water content of the insulating oil during cooling is higher than that during heating. Therefore, in order to accurately grasp the humidity distribution in the transformer, it is necessary to know the position of the equipment in its thermal cycle. To understand the true humidity of the insulation paper by monitoring the moisture content in the liquid medium, the transformer must be in a relatively stable temperature state.
The relative saturation of water in insulating oil needs to be standardized, because the humidity in insulating oil is closely related to temperature changes, and there is a certain temperature gradient in the main box of transformer (usually the top temperature of the box is higher than the bottom).
To achieve standardization, expert system analysis needs to deduce the percentage of relative saturation at the bottom. It can be obtained by using the temperature of the sensor report and its sampling position. The analysis assumes that the temperature at the top of the transformer is 10 degrees higher than that at the bottom. If the position at the top or bottom is taken as the sampling point, the temperature deviation must be specified. Through the relative saturation of humidity and the specific measurement of temperature, the expert system will calculate the humidity of insulation paper with a certain percentage of relative saturation.
It is important to note that the calculation is based only on the results of a single measurement and may not reflect the true humidity concentration of the insulation paper, especially after the transformer has just undergone drastic temperature changes. If the expert system determines that the transformer is in equilibrium (insulation paper neither releases nor absorbs moisture), the second relative saturation percentage is calculated, which is the average of the last 30 relative saturation percentages measured when the transformer is in equilibrium.
The temperature and change recorded in front determine whether there is a criterion for balance. There are 4 kinds of alerts available. When humidity alarm is displayed, the word "P" is used as the first character. The second character is 0~3. The P0 alarm indicates the sensor failure. The P1 alert indicates no execution analysis. P1, P2 and P3 alerts all depend on relative saturation percentage. The condition of alarm: 1 is the relative saturation percentage of the humidity of the insulating oil (> 50), but < 75; 2 is the relative saturation percentage of the humidity of the insulating oil (> 75).
The above content is provided by Shandong transformer oil. If you want to know more, you can pay attention to our website: http://www.jnwdsh.com. There are more wonderful content in the website. Hope you can help each other!