The reliability of power electronic products has a lot to do with the temperature of the device. The ultra-low temperature device operates ultra-reliable. In the industry, there is a "rule of ten" and "rule of six", that is, every time the temperature of the device decreases by ten or six degrees, the lifespan increases. Doubling, whether it is the "rule of ten degrees" or the "rule of six degrees", although there is no clear and rigorous theoretical proof, engineering experience can fully demonstrate that there is a close relationship between device temperature and device life.
The operation of electronic products generates current, and the device itself produces loss, which leads to heat, and the temperature of the device rises. In order to ensure reliable operation, it is necessary to reduce the temperature of the device, and adopt various methods, optimize the control, and reduce the switching frequency. A more important aspect is heat dissipation, which quickly takes the heat away and reduces the temperature of the device. This article focuses on issues related to cooling methods.
The heat of the device is conducted from the inside to the outside. Like people, it needs to be cooled down when it is hot, otherwise there will be problems, such as heat stroke or even more serious problems. The same is true for equipment. .
There are several common ways to dissipate heat: natural cooling, forced air cooling, air-conditioning cooling, air-water cooling, and pure water cooling.
Self-heating cooling is suitable for low-power equipment in some necessary occasions. If high-power equipment adopts self-heating cooling method, to ensure reliable operation of the equipment, the equipment capacity needs to be many times the required power, and the cost and volume are very high. It is huge and very uneconomical, so it is generally not used.
Forced air cooling method: that is, ventilation cooling, just like blowing a fan to cool down in summer, it is a relatively economical method, but there are also many problems and precautions, which will be explained in detail later.
Air conditioning refrigeration: is to use air conditioning to cool the heat generated by the device, and reduce the ambient temperature, generally used in conjunction with air cooling.
Air-water cooling: that is, the fan and the water-cooling equipment cooperate to cool down. The fan draws out the heat of the equipment, cools it down by the water-cooled heat exchanger, and then blows cold air into the equipment to cool the equipment, which is relatively economical.
Pure water cooling: that is, the equipment directly adopts water cooling instead of fan cooling. The equipment radiator is a water cooling radiator, and the water circulation is used for heat dissipation. The process is relatively complicated and the cost is the highest.
The following mainly introduces the advantages and disadvantages of air cooling (including air conditioning), air-water cooling, and water cooling, and the maintenance precautions for use.
1 Air conditioning cooling
It must be a confined space. Just like our office, opening the window and turning on the air conditioner is not effective. In addition, the space must be suitable, neither too large nor too small. If it is too large, the cooling effect is not good, and it requires a lot of air conditioners, and the energy is wasted; if it is too small, the cooling effect is not good, but the heat generated by the equipment is not enough to draw the heat out, causing the internal temperature of the equipment to rise. The principle of room size is that there are 2 meters of space in the front, back, left and right of the equipment, and 1.5 meters at the top is suitable. According to the heat generation of different equipment, an appropriate number of air conditioners are selected. In addition, there must be at least one spare set in case the air conditioner is damaged and the refrigeration is insufficient, resulting in equipment failure.
2 Air-water cooling method
Air-water cooling is similar to air-conditioning refrigeration. The room also needs to be sealed. The heat generated by the equipment is drawn out through the air duct. After the hot air is cooled by the water-cooled heat exchanger, it is blown into the room to cool down the equipment temperature by circulating cooling. For air-water cooling, it is necessary to pay attention to the sufficient air volume of the air duct, as little wind resistance as possible, and do not trap the wind to prevent the hot air from being exhausted. Furthermore, the space needs to be suitable.
Air-water cooling must have a suitable water source, the water temperature should not be higher than normal temperature, and it can be recycled to ensure that the water source is clean, so as to avoid corrosion and scaling of the heat exchanger, prevent water leakage and affect the heat exchange effect. The reliability of the circulating water pump in the use process is an important issue. Only if there is a backup pump and a backup power supply to ensure the reliability of the water cooling system can ensure the reliability of the cooling effect and the reliable operation of the equipment.
3 Water cooling method
This method is relatively complicated, the cost is relatively high, and it is basically only used when the air cooling cannot meet the heat dissipation requirements in ultra-high-power equipment or when it is required to operate in a closed space outdoors.
This water-cooling method is a pure water-cooling method, which is very different from the air-water cooling method mentioned above. Air-water cooling actually relies on fans to dissipate heat. At this time, water cooling is equivalent to the role of air conditioners, while pure water cooling does not have fans to dissipate heat. The water-cooling system is directly designed in the equipment. Heaters, water-air heat exchangers use fans to cool the circulating water and reduce the water temperature. The air-water cooling mentioned above is to cool the air with water and reduce the air temperature.
The pure water cooling process is complex and requires high requirements. The water needs to use pure water to ensure cleanliness, no scaling, deionization, low electrical conductivity, and ensure insulation performance. The water temperature should be controlled appropriately, and condensation should not be formed. The water needs to be protected from freezing to avoid freezing the pipes in winter when the equipment is out of service. This cooling method has better application effect in ultra-high power products, and the cost performance is relatively high. Users need to have certain maintenance skills. Usually, pay attention to observe whether there is water leakage, seepage, etc. When replenishing water, antifreeze should be added in the same proportion.
4 Air cooling method
Most of the working conditions are still dominated by forced air cooling. The following mainly introduces some problems in the application of forced air cooling, so as to avoid it in the application, so as to avoid the situation of poor heat dissipation. If forced air cooling is not used for air conditioning, the air duct will be used to discharge the hot air outside to lower the room temperature and the inlet air temperature. There are several issues to be aware of in this way:
(1) The air inlet should be sufficient and larger than the area of the air outlet. There will be different requirements according to the calorific value of the equipment. The room should be designed strictly according to the relevant data provided by the equipment manufacturer. Since the air inlet needs to add filter cotton to prevent dust from entering, it needs to be calculated according to the effective ventilation area according to the situation of the filter cotton, and the filter cotton should be cleaned in time to prevent clogging.
(2) The air outlet should be slightly lower than the air outlet of the equipment, that is, the air duct should be inclined downward and an elbow should be added to prevent rainwater from pouring into the equipment, and a protective net should be added to the outlet to prevent small animals from entering and causing accidents.
(3) The design of the air duct is very important, which depends on the placement of the equipment in many cases. Here, the user is reminded that if they want to use the method of exhausting air from the outside of the air duct, they should plan the placement of the equipment at the beginning of the design. the airway. The air outlet of the equipment should not face beams, columns, etc. The equipment should not be too far away from the outdoor discharge outlet (such as a wall), the air duct is too long, and the wind resistance is large, which is not conducive to the external exhaust air, and the easy nest wind will affect the heat dissipation.
(4) The air duct should not have large wind resistance. Too many turns or too sharp turns will cause large wind resistance, and the wind will lead to poor heat dissipation. It is best to turn at a 45-degree angle, and try to avoid a straight turn at a 90-degree angle.
(5) Problems that are prone to occur on site
①No air conditioning, no air duct, closed room, small space, high indoor temperature.
②There is an air duct, but there is only air out but no air in, the negative pressure is large, and there is not enough air volume to take away heat, resulting in high equipment temperature.
③The inlet is too small, almost no, the negative pressure is also large, and the heat dissipation effect is poor.
5 Summary
Industrial sites are generally dirty, with a lot of dust, and there are still conductive dust in some occasions, which affects the reliability of electrical equipment. Therefore, it is recommended that users adopt the air-water cooling scheme from the aspects of economy and reliability. It can not only make the room airtight and prevent dust from entering, but also have a better cooling effect to ensure the reliable operation of the equipment, and the cost performance is high. The reliability of electrical equipment is inversely proportional to temperature, the lower the temperature, the higher the reliability, and vice versa, the higher the temperature, the lower the reliability. For the reliable operation of the equipment, it is necessary to pay attention to the selection and implementation of the cooling scheme