introduction
The communication DC power supply is the basic telecommunication equipment, which provides power supply guarantee for the communication main equipment. The battery pack is an important part of the communication DC power system, which is equivalent to the backup power supply and is the last line of defense for the communication DC power system.
In the initial development of the telecom service, the operator pays less attention to the battery, and the battery can be powered when the AC power failure occurs. In recent years, the competition in the field of telecommunications operations has intensified and intensified. Operators are paying more and more attention to the service life, maintenance workload and TCO of batteries.
With the development of communication networks and technological advancement, in order to save construction costs and speed up the construction cycle, operators often do not build computer rooms or mobile cabins in urban and rural areas, small towns and rural areas, but use outdoor cabinets to plan communication masters. Equipment and DC power system. In recent years, the proportion of outdoor base stations in new base stations of the world's mainstream operators has increased year by year. For countries with low latitudes and desertification (such as South Asia, Africa, etc.), high temperature has a great impact on outdoor base stations. Outdoor base stations are generally in remote areas with poor power security, especially in developing countries. Outdoor base stations often face the harsh working environment of high temperature and frequent power outages. Outdoor applications of communication DC power systems are becoming more and more mainstream, and batteries are often in a harsh environment with high temperatures and frequent power outages.
Problems faced by batteries in harsh environments
With the increase in the application of outdoor base stations, battery faults have become more prominent in harsh application environments. For example, South Asia, such as Pakistan and India, has caused economic losses to operators and damaged customer satisfaction. In response to the extensive damage of batteries in harsh application environments, ZTE conducted extensive research to gain an in-depth understanding of the application scenarios of batteries and investigate and analyze the causes of battery failures. The key to the problem is not the battery itself. The problem is that the outdoor battery cabinet does not consider high temperature protection of the battery. In order to solve the problem fundamentally, it is necessary to provide a comprehensive solution for the application of the battery in harsh outdoor environments.
Comparative Analysis of Active Cooling Technology for Outdoor Battery Cabinets
There are many options for the heat dissipation method of the outdoor cabinet. Which heat dissipation method is suitable for the outdoor battery cabinet? This starts from the product characteristics of the battery. For lead-acid batteries in communication DC power systems, users are most concerned about the service life. The main factors affecting the service life of lead-acid batteries are ambient temperature and grid conditions.
The service life of lead-acid batteries is closely related to the ambient temperature. The higher the ambient temperature, the shorter the battery life. When the ambient temperature is higher than the battery design life required temperature (25 oC), the service life is reduced by half for every 10oC increase in temperature.
The number of discharges and depth of discharge of the battery directly affect the service life of the battery. The more the number of discharges and the deeper the depth of discharge, the shorter the service life of the battery. That is to say, frequent power outages in the power grid will reduce the battery life.
For outdoor base stations, the cost of the operator's inability to improve the grid conditions or improve the grid conditions is usually too high to bear, so we start by reducing the working temperature of the battery to improve the service life of the battery.
The traditional heat dissipation method of the outdoor cabinet is direct fan ventilation or heat exchanger, but neither of the two methods can make the temperature inside the cabinet lower than the ambient temperature outside the cabinet. For high-temperature areas (generally above 40 °C), active cooling is required to make the temperature inside the cabinet of the outdoor battery cabinet lower than the ambient temperature outside the cabinet. ZTE broke through the conventions and combined innovations to introduce refrigeration components into outdoor battery cabinets.
The communication main equipment (such as GSM, transmission, etc.) and the power change part (rectifier) ​​of the DC power supply will generate heat during the operation of the equipment, but the battery will be different. According to the electrochemical mechanism of battery charging and discharging, the battery does not generate heat when discharged. When charging normally (but charging), it does not heat up. That is, the heat generated by the battery during normal use can be neglected. Therefore, there is no heat source in the outdoor battery cabinet, and the required cooling capacity is small. According to calculations, the outdoor battery cabinet usually has a cooling capacity of 200-400 W. Thermoelectric Cooler (TEC) air conditioners use emerging semiconductor refrigeration technology. For outdoor battery cabinet applications, TEC air conditioners have many advantages over traditional compressor air conditioners:
1) Simple structure and high reliability. The whole refrigerator is made up of thermoelectric refrigeration modules and wires. It does not require a compressor and has no mechanical rotating parts, so it has no vibration, no friction and no noise. High reliability and long life (more than 100,000 hours in 32 ° C environment).
2) Refrigeration is not affected by AC power outages. The DC 48V power supply is used to supply power to the TEC air conditioner during AC power failure, and the outdoor battery cabinet can still achieve cooling.
3) Refrigeration efficiency and cooling capacity. In the case of large capacity, the efficiency of thermoelectric cooling is not as good as that of vapor compression refrigeration. However, the efficiency of the vapor compression refrigerator decreases with the decrease of the capacity, and the compressor cannot be made too small, and the efficiency of the thermoelectric refrigeration has nothing to do with the capacity, and has an advantage in an application field with a small cold load. For outdoor battery cabinet applications (small cooling load), TEC air conditioning is an ideal choice.
4) Small size. Especially suitable for outdoor cabinet installation.
5) Cost performance. Based on the above analysis, the outdoor battery cabinet adopts TEC air conditioner, which is cost-effective.
6) Easy to maintain. TEC air conditioners do not require refrigerant circulation, no compressor rotation, and regular attention to the insect net should not be blocked, the maintenance workload is small.
7) Green and environmental protection. No Freon refrigerant, no damage to the atmospheric ozone layer, green and environmental protection.
Based on the above analysis, we use TEC air conditioners with better performance than traditional compressor air conditioners as the refrigeration components of outdoor battery cabinets.
Series TEC outdoor battery cabinet with good high temperature protection ability
TEC outdoor battery cabinet is composed of TEC air conditioner, cabinet body and thermal insulation layer. In order to meet the needs of installing different capacities and different types of batteries, ZTE has designed a series of TEC battery cabinets. Two typical cabinets are shown in Figure 1. The left cabinet can be installed with up to 2 sets of narrow 12V 150Ah AGM or gel batteries. The right cabinet can be installed with up to 6 sets of narrow 12V 150Ah AGM or gel batteries (3 sets of wide body 12V 150Ah or 200Ah gel batteries can also be installed). In order to achieve the desired cooling effect, the cabinet is required to have good thermal insulation effect. We have designed the insulation cotton, and use the whole raw material as much as possible to reduce the opening and cutting. The insulation cotton is 40mm thick. It has the same IP55 protection rating as the TEC module.
TEC battery cabinets take into account the cooling effect and product reliability in product design, using advanced refrigeration chips, high-reliability fans, and insulation wool with good thermal insulation. TEC battery cabinets have good high temperature protection.
Figure 1 Outline drawing of two typical TEC battery cabinets
Integrated solution improves battery life and reduces TCO
For outdoor applications of communication DC power systems in harsh applications, the main point of the integrated solution is to significantly improve the high temperature protection capability of the outdoor battery cabinets by using TEC air conditioners, and significantly improve the working environment of the battery. The experimental test results of the outdoor battery cabinet using TEC air conditioner show that when the ambient temperature outside the cabinet is above 40 °C, the temperature inside the cabinet is 15 °C lower than the temperature outside the cabinet, and the battery works within the optimal operating temperature range. Compared with the ordinary outdoor battery cabinets of the operator's existing network, the service life of the battery is increased by 1.5 times, and the increase is very large.
The integrated solution uses TEC outdoor battery cabinets, adds some cost investment to the battery cabinet, and obtains valuable high temperature protection capability, so that the battery works within the optimal operating temperature range, avoiding the batch replacement of the battery due to the low service life. The battery purchase cost, related transportation cost and replacement labor cost required for batch replacement of the battery in the field are avoided, thereby reducing the operation and maintenance cost of the operator. The substantial increase in battery life effectively ensures the safe and reliable operation of the communication network and significantly improves the operator's customer satisfaction. Therefore, the integrated solution reduces the TCO (Total Cost of Ownership) for operators while improving the service life of the battery.
Application examples and user value
The integrated solution has been put into practical use in Pakistan. In mid-May 2010, the TEC battery cabinet arrived at an outdoor base station of a carrier in Pakistan, and the DC power supply system of the station was retrofitted with an integrated solution. After the TEC battery cabinet is put into use, its refrigeration capacity is tested. The temperature trend curve generated based on the field test data is shown in Figure 2. T2 is the internal temperature of the TEC battery cabinet, Tc is the outdoor ambient temperature (measured in the shade under the awning), and ΔT is the temperature difference between the ambient temperature and the temperature inside the cabinet.
Figure 2 TEC battery cabinet temperature trend curve
From the test results, the outdoor ambient temperature is relatively high between 12:00 and 5:00 pm, and the TEC battery cabinet can achieve a cooling effect of 15 °C between the inside and the outside when the temperature reaches 45 °C. The internal temperature of the battery cabinet can be controlled between 25 °C and 30 °C to meet the optimal operating temperature range of the battery.
Through the on-site transformation of the DC power supply system of an operator's outdoor station in Pakistan, the user fully recognizes the comprehensive solution of ZTE, and believes that the comprehensive solution can greatly improve the survivability of the battery in the harsh application environment and significantly reduce the maintenance workload of the battery. , can effectively reduce the comprehensive TCO of the outdoor station DC power system.
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