Effect of cooling mode on performance and service life of Communication Switching Power Supply

I. Effect of Temperature on the performance and life of Communication Switching Power Supply

The main component of the communication switching power supply is the high-frequency switching rectifier, which gradually develops and matures along with the development of power electronics theory and technology and power electronic devices. With the soft switch technology, the power consumption becomes smaller, the temperature is lower, the volume and weight are greatly reduced, and the overall quality and reliability are continuously improved. However, when the ambient temperature increases by 10 ℃, the service life of the main power components is reduced by 50%. The reason for the rapid decline in service life is the temperature change. Fatigue Failure Caused by various micro and macro mechanical stress concentrations. Various types of micro-internal defects will occur during the operation of ferromagnetic materials and other parts under the continuous alternating stress. Therefore, ensuring the effective heat dissipation of the device is a necessary condition for ensuring the reliability and service life of the device.

1. Relationship between operating temperature and reliability and service life of power electronic components.

A power supply is a type of electric energy conversion device. Some electric energy needs to be consumed during the conversion process, which is converted into heat for release. The stability and aging speed of electronic components are closely related to the ambient temperature. Power Electronic Components are composed of multiple semiconductor materials. Because the loss of power components during operation is caused by their own heat loss, the heat cycles of various materials with different expansion coefficients may cause significant stress and even lead to transient fracture, make the component invalid. If the power element is working in an abnormal temperature for a long time, it may lead to fracture fatigue. Due to the thermal fatigue life of semiconductors, it is required that they work in a relatively stable and low temperature range.

At the same time, rapid cold and hot changes will temporarily generate a semiconductor temperature difference, resulting in thermal stress and thermal shock. The component is subjected to thermal-mechanical stress. When the temperature difference is too large, different parts of the component may produce stress cracks. Early component failure. This requires that the power element should work in a relatively stable operating temperature range to reduce the sharp changes in the temperature, so as to eliminate the impact of thermal stress and ensure long-term reliable operation of the element.

2. Impact of operating temperature on Transformer Insulation Capacity

After the primary winding of the transformer is powered on, the magnetic flux produced by the coil flows in the core. Because the core itself is a conductor, the induction potential is generated on the plane perpendicular to the magnetic line, forming a closed loop on the section of the core and generating current is called "Eddy Current ". This "Eddy Current" increases the loss of the transformer and increases the temperature rise of the transformer core heating transformer. The loss caused by "Eddy Current" is called "iron loss ". In addition, the copper wires used for Transformer Winding have resistance. When the current flow is out of date, this resistance will consume a certain amount of power, and this part of the loss will become heat consumption, this loss is called copper loss ". Therefore, Iron Loss and copper loss are the main causes of temperature rise during transformer operation.

As the transformer operating temperature rises, it will inevitably lead to aging of the coil. When its insulation performance decreases, the impact ability of the mains resistance decreases. In this case, if a lightning strike or mains surge occurs, the high back pressure at the beginning of the transformer will break down the transformer to make the power supply invalid, and there will also be a high-voltage string into the main communication equipment, the risk of damage to the main device.

Ii. Influence of cooling mode on operating temperature of Power Supply

The heat dissipation of the power supply generally adopts two methods: Direct conduction and convection conduction. Direct heat conduction is the transfer of heat energy along the object from one end of the high temperature to one end of the low temperature, and its heat conduction capability is stable. Convection conduction is a process in which the temperature tends to be even when the liquid or gas moves through rotary motion. Since the convection conduction involves the dynamic process, the cooling rate is relatively high.

The component is installed on the metal radiator. By extrusion the hot surface, the high and low unequal energy bodies can transmit energy, and the energy that can be radiated by a large area of heat sink is not much. This heat conduction method is called natural cooling, which has a long delay on heat dissipation. Q = KA △tk heat exchange coefficient, A heat exchange area, △t temperature difference). If the indoor temperature is too high, the absolute value of △t is small, at this time, the heat dissipation performance of this heat transfer method will be greatly reduced.

Add a fan in the power supply to quickly discharge the accumulated heat from the energy conversion out of the power supply. Continuous air supply by the fan to the heat sink can be considered as convection transmission energy. It is called fan cooling, and the delay time of this heat dissipation method is short and long. Heat Dissipation Q = Km △tk heat exchange coefficient, m heat exchange air quality, △t temperature difference), once the fan rotation speed decreases, the m value will rapidly decrease, the accumulated heat in the power supply will be difficult to lose, which will greatly increase the aging speed of the capacitor, transformer and other electronic components in the power supply and affect the stability of the output quality, this eventually causes component burning and device failure.

Iii. Main methods and advantages and disadvantages of Communication Power Dissipation

The design of the Communication Switching Power Supply cold removal technology must first meet the technical performance requirements of the industry. In order to better adapt to the special environment of the communication room, the cooling method must be adaptable to the environment temperature change. At present, the common cooling methods of the rectifier include natural cooling, pure fan cooling, Natural Cooling and fan cooling. Natural Cooling features no mechanical faults, high reliability, no air flow, less dust, heat dissipation, and no noise. Pure fan cooling features light equipment and low cost. The combination of fan and natural cooling technology can effectively reduce the size and weight of the device, provide a high service life of the fan, and provide a strong adaptive capability for Fan faults.

1. Natural Cooling

Natural Cooling is a traditional cooling method in the early days of switching power supply, which relies mainly on large metal radiators for direct heat conduction heat dissipation. Q = KA △tk heat exchange coefficient, A heat exchange area, △t temperature difference ). When the output power of the rectifier increases, the temperature of the power element will rise, and the △t temperature difference will also increase. Therefore, when the heat exchange area of the rectifier A is sufficient, there is no time lag in the heat dissipation, the temperature difference between power elements is small, and the thermal stress and thermal shock are small. However, the main disadvantage of this method is that the size and weight of the heat sink are large. The transformer's bypass mechanism is to minimize the temperature rise and prevent the temperature rise from affecting its performance. Therefore, the material selection margin is large, and the transformer's volume and weight are also large. The material cost of the rectifier is high, which makes maintenance and replacement inconvenient. Due to its low environmental cleanliness requirements, the current small-capacity communication power supply has some applications in some small professional communication networks, such as power, oil, radio/TV, *, water conservancy, national security, and public security.

2. Fan cooling

With the development of Fan manufacturing technology, the fan's working stability and service life have greatly improved, and its average failure-free duration is 50 thousand hours. After the fan is used for heat dissipation, the heavy radiator can be removed, which greatly improves the volume and weight of the rectifier and reduces the raw material cost. With the intensification of market competition and the decline in market prices, this technology has become the main trend.

The main disadvantage of this method is that the average no-fault time of the fan is shorter than the 0.1 million-hour time of the rectifier. If the fan fails, the failure rate of the power supply will be greatly affected. To ensure the service life of the fan, the fan speed changes with the temperature change in the device. Its Heat Dissipation Q = Km △tk heat exchange coefficient, m heat exchange air quality, △t temperature difference ). M heat exchange air quality is related to the fan speed. When the output power of the rectifier increases, the temperature of the power element increases, however, the change in the temperature of the power element indicates that the rectifier can detect this change, and then increases the fan speed to enhance heat dissipation. There is a great delay in time. If the load changes frequently or the input voltage fluctuates greatly, the power components may experience rapid cold and hot changes. The sudden changes in the temperature of the semiconductor may lead to thermal stress and thermal shock, it may lead to stress cracks in different parts of the component. It becomes invalid too early.

3. Combination of fan and Natural Cooling

Due to changes in the ambient temperature and load, the energy dissipation during power supply operation can be quickly emitted by combining a fan with a natural cooling method. This method can reduce the radiator area while increasing the fan heat dissipation, so that the power element works in a relatively stable temperature field, and the service life will not be affected by the change of external conditions. This not only overcomes the lag of cooling regulation of Power elements caused by pure fan cooling, but also avoids the impact of low fan service life on the overall reliability of the rectifier. Especially when the ambient temperature of the data center is unstable, the cooling technology combined with air cooling and self-cooling has better cooling performance. The material cost of this type of rectifier is between the pure fan cooling and the natural cooling, which is low in weight and easy to maintain.

Especially when the smart air-cooling and self-cooling technology is used, it can make the rectifier operate at low speed with low load, and the module fan is in a low temperature. In high load conditions, the module is heated up. The module heated up more than 55 ℃. The fan speed increases linearly with the temperature change. Fan fault In-Place detection, fan fault, fan fault throttling output, and fault alarm at the same time. Because the fan operation is related to the load size, the service life of the fan is longer than that of the pure air-cooling, and its reliability is also greatly improved.

Iv. Conclusion

The Communication Switching Power Supply adopts the cooling mode combining fan and natural cooling, which can effectively reduce the working temperature and extend the service life of the transformer in the case of high ambient temperature, in addition, it can reduce the rotation speed of the fans in the case of low ambient temperature and low load, and prolong the service life of the fans. Using the radiator for heat dissipation, the device distance and the crawling distance can be relatively far away. In the case of high humidity, the security is high. The rectifier is small in size and light in weight, making maintenance easy.

To ensure reliable and stable operation of the Communication Switching Power Source, reducing the working temperature rise is a key technology. It adopts the combination of smart air cooling and self-cooling technology. It has technical advantages such as stronger adaptability to the environment, long service life, reliability and stability.