Prevent and control the transformer skeleton moisture absorption damp program
The principle and treatment of moisture absorption and dampness of body after drying of transformer skeleton
Transformer skeleton body after drying out, to body finishing, body into the box, the internal wiring, tap-changer installation process, in order to vacuum filling. The production process, the body insulation material is always in contact with the atmosphere, the insulation material must be moisture absorption, until the impact of transformer quality.
The larger the capacity, the higher the voltage level, the more complex the structure, the more the content of the insulating material in the structure, the longer the assembly and finishing time, the more serious the degree of moisture absorption.
2 moisture absorption principle of insulating material
Vapor phase drying and meet the requirements of the body, put the atmosphere. Insulation material by the vapor phase drying, the water content is very low generally 0.5 or so no more than 1. Due to environmental water vapor partial pressure is high, then the insulating material and the atmosphere of the water vapor partial pressure will appear sub-pressure difference (that is, the insulating material water vapor pressure value and the environment partial pressure value), such as a 40000kva / 110kv transformer body , Assuming that the water content of 0.8, has been baked 3h, the body insulation temperature of 65 ℃, from the Pepper curve check the water vapor pressure value of 590pa; and this time the atmospheric temperature 25 ℃, humidity 65, check the environmental water vapor partial pressure of 2050pa , Higher than the body insulation 1460pa. The environment will be the moisture transfer to the insulating material, that is to say the insulating material began to absorb moisture in the environment.
At the beginning stage, the moisture absorption is limited to the surface layer, and the moisture content is only peak and time, and the moisture moves and spreads from the surface to the inside. At the same time, the longer the body temperature decreases with the longer baking time, more serious. But the moisture gradually deepened, the water content increased, the insulation material water vapor pressure value will slowly rise until the saturation of the same water vapor partial pressure, moisture stop.
3 to prevent and transformer body moisture absorption method
Transformer products in the manufacturing process, the assembly time is longer, the greater the humidity and other reasons caused by moisture absorption and moisture phenomenon, the transformer manufacturing enterprises have occurred frequently. Many enterprise products on-site installation found that the transformer insulation resistance, absorption ratio, dielectric loss and the factory test value significantly different, power frequency pressure through. The reason is that moisture absorption to a certain extent, but the water content does not exceed 2, the insulation strength and insulation properties have not responded. In addition, the body of the scene by the heart of the examination, the body once again exposed the atmosphere, the body temperature has been room temperature, insulation material water vapor pressure value is lower than the ambient water vapor pressure value. , More or less moisture absorption point, so that water content increases, resulting in some of the above indicators deteriorate. , To prevent and control the body moisture absorption is particularly important.
Industry on the prevention and control of body moisture absorption generally have the following methods:
⑴ shorten the assembly time, keep the body height temperature. This requires the operator must have a skilled operation of the technical and standardized procedures for the production of pre-production and familiar with the drawings; at the same time require the production of the necessary staff to put into the staff, the formation of both the loss of work and spare time to quickly organize the production situation.
⑵ again into the drying tank heating to improve the body temperature. Some complex products often can not specify the time to complete the finishing box, but can not let the body temperature is reduced, once again into the tank to increase the body temperature, so that the water vapor pressure of the insulating material is always higher than the ambient water vapor partial pressure, Insulation material is not hygroscopic. , Finishing during the day, evening products into the furnace heating insulation is the company usually use the method.
⑶ body vapor drying and vacuum immersion oil treatment and then finishing body. Vacuum oil immersion, so that the transformer oil immersed in the insulation material inside the fiber, hinder the water into, slow down the moisture absorption rate, increase the assembly time. But the immersion oil time is short can not completely penetrate the insulating material, oil and atmospheric contact is also the lack of water absorption and production efficiency is low, the body susceptible to dust pollution and other issues. This method is more suitable for high voltage and high capacity products.
⑷ use of air drying generator for body finishing. Complex structure requires a longer body finishing process products, can be closed, inward through the air drying generator to deal with dry air (dew point below -40 ℃). Dry air access, the closed room always maintain a positive pressure to prevent moisture into the air. There are insulating materials to the tank assembly or internal wiring and other long work, but also to the tank into the dry air to maintain a positive pressure, protective body insulation and dilution operation operator exhaled moisture. This method is particularly suitable for installation site transformer repair, transformation.
4 body insulation surface moisture moisture dehumidification treatment
In the production process, we have taken to prevent and control the hygroscopic methods, but inevitably the impact of atmospheric humidity and moisture absorption of the body insulation material, more or less insulation surface adsorption of some moisture. If you do not mind or deal with incomplete, it will have an impact on the operation of the transformer. A vacuum dehumidification method was proposed.
When the vacuum is removed, the pressure around the insulating material in the tank is reduced. When the internal pressure of the insulating material is lower than that of the insulating material, the partial pressure difference between the insulating material and its surrounding water vapor pressure occurs, and the moisture in the insulating material starts to migrate outward The The higher the vacuum in the tank, the smaller the pressure in the surrounding space, the greater the pressure difference, the evaporation of water, the faster the migration and migration. When the vacuum reaches the dynamic stability, the residual gas contains only a small part of the total residual gas.
Measured results show that the water vapor pressure is about a few percent of the vacuum pressure, generally can be considered ≤ 3, such as take 3, when the vacuum ≤ 133.3pa, the water vapor partial pressure of about 4pa. Insulation water content and water vapor partial pressure balance curve (Pepper curve), the temperature is 10 ℃, water vapor partial pressure of 4pa to 5pa, the paper moisture content of about 0.5. It can be seen that the vacuum vacuum is high enough, the vacuum time is long enough (depending on the moisture content), to balance the state, at room temperature, the moisture content of insulation materials can reach a very low level. Such as surface insulation material is more serious moisture absorption, the higher the water content is best to use into the drying tank heating vacuum dehumidification treatment.
In short, the normal temperature vacuum dehumidification treatment of drying tank vacuum dehumidification treatment, in the final analysis should be the production process, try to shorten the body finishing time to maintain the body height, strengthen the production and design a pass rate in order to shorten the processing time, Increase productivity