2.1 Several air humidity concepts related to condensation The atmosphere surrounding the earth's surface is a mixture of dry air and water vapor. The air that can be contained at a certain temperature has a maximum amount of water vapor. When the content of water vapor in the air reaches a maximum, it is called saturated air. To measure the amount of water vapor in the air, depending on the application, people introduce the concept of absolute humidity, moisture content, relative humidity and dew point temperature.
The absolute humidity of the air. Refers to the mass of water vapor contained in a unit volume of air.
Moisture content. It refers to how much water vapor in 1kg of dry air directly reflects the increase or decrease of the amount of water vapor in the humid air.
The relative humidity of the air. Refers to the ratio of the absolute humidity of the air to the saturated absolute humidity at the same temperature, often expressed as a percentage, directly reflecting the degree to which the air is near saturation at a certain temperature. The air humidity referred to in our daily life is relative humidity. When the relative humidity is 0, the air is dry air, and when the relative humidity is 100, the air is saturated air. The greater the relative humidity, the more humid the air.
Dew point temperature. In the case where the moisture content of the air does not change, the temperature of the air is lowered, and the saturated absolute humidity becomes small, so the relative humidity increases. When the temperature drops to a certain temperature, its relative humidity increases to 100, and the air reaches a saturated state. This temperature is called the dew point temperature. Condensation occurs when the air temperature is below the dew point temperature. The greater the moisture content of the air, the smaller the temperature decrease as it reaches saturation, ie the higher its dew point temperature. On the contrary, the smaller the moisture content, the lower its dew point temperature. Therefore, the dew point temperature can also indicate the amount of air humidity.
Causes that the relative humidity of the air is too high or even condensation. Various wet sources continuously emit moisture, which increases the absolute humidity. According to the different wet sources, it can be divided into: First, the amount of fresh rheumatism. If the outdoor high temperature and high humidity air enter the lower temperature of the plant, it will increase the relative humidity and even condensation. Second, the surface of the water and the wet surface are wet. In Example 1, the substation is located beside the Weihe River, and the Weihe River is the main surface wet source. In the underground plant water pump layer in Example 3, due to leakage of water pipes and equipment, dew condensation, cracks in the walls and ceilings, or capillary water seepage, the water accumulated during maintenance or cleaning will form a wet surface on the equipment and the enclosure. Like open water surfaces such as uncovered gutters and still water pools, it continuously emits water vapor to the air, the amount of which is related to the temperature, humidity and flow rate of the indoor air. The third is the moisture transfer. Underground plant enclosures The water inside the rock can reach the rock wall through the capillary of the rock in liquid and gaseous form. When the partial pressure of water vapor in the air outside the ground building envelope is higher than the inner side, the water will also be directly introduced into the room through the capillary of the enclosure structure in a gaseous form, although there is no obvious visible moisture on the inner surface of the building envelope structure. But this kind of moisture transmission is always going on. This direct propagation of water vapor in the envelope is referred to as gaseous propagation. The fourth is the body is wet. When there are more people in the factory, the amount of moisture should be considered. But in a factory with fewer people, it can be ignored.
Due to the presence of a heat absorbing source, the temperature is lowered and the relative humidity is increased. As in Example 2, when the air in the tank suddenly drops due to the outside temperature, the outside air forms a main heat source.
When the hot and cold air meets, the relative humidity increases at the junction. As shown in Example 3, in the case of natural ventilation, when the hot air of the motor layer and the cold air of the pump layer meet at the cable layer, the relative humidity increases, and a serious condensation phenomenon is formed.
Excessive air humidity or condensation on electrical equipment from the three examples in this article is not difficult to see, do not pay attention to the impact of air humidity on the operation of electrical equipment, let the humidity problem freely develop, will seriously affect the normal operation of electrical equipment, and even cause ACCIDENT. Its influence on the operation of electrical equipment is mainly manifested in the following aspects: when the air humidity is high or even condensation occurs, the insulation of the electrical equipment is damp and the insulation performance is degraded. For example, if the motor or equipment controls the relay coil that is not charged on the panel, the long-term operation will be in the environment with high relative humidity, the moisture will enter the inside of the coil insulation, so that the coil is damp and the insulation is lowered. For electrical equipment that relies directly on air as an insulating medium, insulation capacity is greatly compromised under conditions of high relative humidity or even saturation. If condensation forms on the insulating surface or inside of the equipment, it will directly trigger the insulation "flashover" of the electrical equipment.
When the air humidity is high or even condensation, the surface of the metal structure of the electrical equipment will be electrochemically reacted to form "electrochemical corrosion". When there is obvious condensation on the electrical connection point, the water deposited on the surface of the metal structure will dissolve the salt on the surface of the equipment. The electrolyte is formed, and an electrochemical reaction occurs under the action of an applied electric field or due to the difference in the activity of the metal, so that the metal structure is changed by oxidative corrosion, which is loose, stratified, and powdered, thereby losing the properties of the metal. In addition, the heat released at the same time by the electrochemical reaction will cause aging to be intensified on the insulating materials such as bakelite and epoxy resin, and the insulation performance is lost in advance.
Scientific research has shown that the critical value of relative humidity of metal for oxidative corrosion of metals is 70% for steel, 60% for copper, 76% for aluminum, 63% for iron and 60% for zinc. The metal is stored in an environment above this critical value. The oxidative corrosion rate is continuously accelerated as the relative humidity value of the air increases.
As the degree of automation of electrical equipment increases, the proportion of electronic products in equipment components continues to increase, and most electronic products require storage under dry conditions. Otherwise, the capacity of the capacitor will be reduced after damp, and the integrated circuit will easily cause internal faults after being damp. The damp will also oxidize the pins and connectors of the computer CPU and the card gold finger and electronic equipment, resulting in poor contact or poor solderability. The crystals are oxidized and the like. According to the relevant information, it is safe to store the electronic device in an environment with a relative humidity of 40%.
3 Control measures to solve the problem of excessive humidity or condensation on electrical equipment should be based on the principle of moisture prevention, dehumidification supplemented, all majors must closely cooperate, comprehensive consideration, take "guide, block, separate, seal, remove â€
And other measures.
To prevent water from accumulating around the electrical equipment and to eliminate the wet source, the drainage system must be done. The size and slope of the gutter should not only meet the requirements of the design in the design, but also pay attention to the construction quality, and can not produce slopes and blockages. Drains and collection wells should be closed to eliminate unnecessary open water. Also make a waterproof finish so that it does not leak or leak. After the construction is completed, if there is a leak point, use a water conduit to introduce water into the drain or fill it with grout.
For the electrical equipment panel, the cable should be waterproofed and fireproofed at the inlet and outlet of the cable to cut off the gas source. It is advisable to use a bushing structure for the underground powerhouse; a moisture-proof partition wall should be added to the inner side of the water retaining wall below the generator floor of the surface hydropower plant. The cracks and capillary permeated water of such a structure are cut by the interlayer space, and the remaining only moisture is transmitted, and the moisture transmission amount thereof is small.
The technical supply and drainage pipes in the isolation workshop shall be laid by dark pipes as much as possible. If laying with open pipes, maintenance management should be strengthened to reduce water leakage. In order to prevent condensation on the outer surface temperature of the tube below the dew point of the air, it is necessary to include heat insulating material on the outer surface of the tube.
The important electromechanical equipment for sealing should be arranged in a dry room; the automation components, terminal boxes, etc. should be placed in the sealed control box, and the control box should not be close to the wet wall.
Dehumidification and moisture treatment can greatly reduce the amount of moisture produced in the plant, but dehumidification is still indispensable. Generally, the following methods should be used: heating and cooling method. In humid areas with particularly low temperatures, such as pump chambers, main valve chambers, etc., there are fewer equipments, and the amount of moisture produced is large. It is uneconomical to use a comprehensive dehumidification method. The electrical equipment can be placed in a box containing incandescent lamps, electric heaters or infrared lamps to increase the temperature of the air inside the box and reduce the relative humidity, so-called local heating and dehumidification. This kind of measure is simple and can solve some problems. In this method, the moisture content of the air does not change, and although it does not take away the wet load, it can reduce the relative humidity of the air.
Ventilation and dehumidification method. In this method, the outdoor air is sent to the wetted part, and the wet load is absorbed and discharged. For example, in the initial stage of commissioning of a groundwater power station or a pumping station, the water content in the envelope structure is large, and the moisture production is large. The ventilation method is often used to dehumidify, and the effect is good. As long as the room air dew point temperature is higher than the temperature of the air supply point, this method can take away the room wet load. However, as the ratio of indoor thermal load to wet load is different, the relative humidity in the room may decrease or may not change or increase. In the low temperature and humid parts where the heat and humidity are relatively small, the purpose of reducing the relative humidity cannot be achieved by the ventilation and dehumidification method.
Heating and ventilation dehumidification method. In order to solve the problem that the relative humidity increases when the ventilation and dehumidification method is applied to low temperature and wet parts, an electric heater can be provided on the air supply system to send hot air to these parts. This method is essentially a combination of Method 1 and Method 2, so it is called a heating and ventilation dehumidification method, or a heating and cooling method. As in the example 2, we installed a heater and a fan, and the effect was remarkable when it was put in a thunderstorm.
Since it is uneconomical to put in the heater for a long time, in the pumping station or the hydropower station, the generator layer generates a large amount of heat to exclude the heat load; the heat generating parts below the generator layer have a small amount of heat to exclude the wet load. The method commonly used in pumping stations or hydropower plants is to introduce air that absorbs the heat load of the heat generating parts such as the generator layer to the following parts of the generator floor, so that these areas heat up and reduce the relative humidity, and also take away The wet load of these rooms.
Air conditioning dehumidification method. For the hydropower station buildings in the high temperature and high humidity areas in the south, the outdoor ventilation calculation temperature is higher in summer. If the temperature is used for ventilation and dehumidification, the temperature of the desiccated parts is often high. The outdoor air must be cooled and dehumidified, and then sent to the factory to achieve the purpose of dehumidification. This is the air conditioning dehumidification method.
Dehumidifier dehumidification method. This method is suitable for dehumidification of parts that are important and not suitable for the above methods. The dehumidifier can be placed directly in the room, or it can be placed outside the room with a return air duct. The dehumidification principle includes several types such as freezing condensation, liquid absorption, and solid adsorption.
(Responsible Editor: Qiu Yanan) First: Guo Binbin, male, born in October 1973, Lingchuan County, Shanxi Province, graduated from the Electrical Engineering Department of Taiyuan University of Technology in 1996, engineer, Shanxi Wanjiazhai Yellow River Diversion Project Administration Running the branch office, No. 217, Nan Neihuan Street, Taiyuan City, Shanxi Province, China, 030012. AEBCRDS: lctriccg book her 3nden sweet visit to move the twisted 昼 仙 仙
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