Several considerations in power supply construction and maintenance

　　In the communications industry, people often compare power supply equipment to the "heart" of the communications system , which fully proves the importance of the position of communications power supply in the communications system. The operation quality of the communications power supply system is directly related to the operation quality and communication security of the communications network. With the improvement of the overall level of the communications network, the communications power supply system has also developed by leaps and bounds. How to ensure the safe and reliable operation of the communications power supply system is the basis for ensuring the normal operation of our communications network. Let's discuss it from the application of several various power supply systems.

　　1. About the matching of switching power supply and generator set (when generating electricity for main base stations)

　　Problem 1: The mismatch between the generator set and the switching power supply may cause the generator output voltage to be unstable and the vibration to increase. For example, the no-load voltage of the generator is 230V, and the output voltage may increase to 250V after adding the switching power supply load. Our maintenance personnel may go to the generator set to find the cause. The cause of this situation is mostly caused by the mismatch between the load and the generator set.

　　The rectifier modules of the high-frequency switching power supply system are all capacitive loads. The so-called capacitive load means that the load current leads the load voltage (power factor leads). When this current is added to the excitation current vector of the generator's excitation system, the excitation current of the generator increases. The magnetic assist effect it produces causes the generator output voltage to rise. The larger the load current, the higher the voltage rise and the greater the generator vibration.

　　Problem 2: The generator output power is insufficient. For example, a 50A module

The calculation is based on 60V*50A=3000VA. If a base station has two such modules, a generator set with a rated power of 6000VA is required to carry the load. This calculation method will cause the problem of insufficient output power.

　　The particularity of the switching power supply (itself is a capacitive load) requires a large redundancy in the power supply. For example, in the instructions of a switching power supply manufacturer: "The capacity of the rectifier module should not exceed 30% of the capacity of the generator set, otherwise the high-order harmonic current generated by the rectifier will flow through the stator winding of the synchronous generator set, and the voltage waveform will be seriously distorted, which will cause unstable operation and mechanical vibration of the generator set on the one hand, and harmonic current will cause the generator to overheat and accelerate the insulation aging of the motor on the other hand." Since the rectifier modules are of different brands, it is best to calculate the generator capacity according to 1:2. For example, a 6000VA generator set is best to carry a 3000VA switching power supply (capacitive load), and the remaining capacity of the generator can carry an inductive load or a resistive load, so that the output characteristics of the generator will be greatly improved.

　　The solution to the above problem is to first increase the capacity of the generator. A smaller engine can be used to drive a larger generator, which can meet the rectifier module's requirements for the generator capacity and improve the engine's utilization efficiency.

　　The second is to reduce the speed of the generator. A small generator with inductance and capacitance phase excitation is used. The speed of the generator is proportional to the voltage. Reducing the speed will reduce the no-load voltage. When a pure capacitive load such as a switching power supply is loaded, the output voltage will rise, provided that the capacity ratio of the load and the generator is 1:2. Only by this ratio can the speed be reduced, and the output power of the generator will not be affected.

　　2. Comparison of dual power supply configuration and single power supply configuration of DC switching power supply

　　1. Discussion on the dual system power supply problem

　　All DC equipment in our company's existing core network room is powered by a power supply system. The so-called dual-circuit power supply is just two different fuses connected on a power supply system. This has a great hidden danger, that is, the power supply system is a bottleneck. If there is a problem with the power supply system, all loads on it will be paralyzed. The circuit connection diagram is shown in Figure 1.

　

　
Figure 1

　　In order to improve the quality of power supply, we can use another dual-circuit power supply method to improve the reliability of the existing power grid. The DC cabinet of the main equipment can be connected to the power supply from two sets of DC panels of different power supply systems. This can solve the power supply bottleneck problem of the DC power supply system and realize dual power supply from beginning to end. The power supply system diagram is shown in Figure 2

　

　
Figure 2

　　From the diagram, it is obvious that the second power supply method is more reliable than the first. Let's analyze the advantages and disadvantages of the two power supply methods below.

　　Disadvantages of method 1: As mentioned above, it cannot form a true dual-circuit power supply and has a single-point bottleneck problem. (With monitoring and guaranteed repair of faults, the reliability is still very high)

　　Disadvantages of method 2: When both sets of power supply equipment are working normally, there can be current in both circuits. We must consider the configuration of the power supply according to the extreme situation, that is, the load capacity of each system cannot exceed 50% of its design current. It must be satisfied that when a system has a problem, all the loads can be transferred to another system. The first problem is the increase in investment, and the load of each set is smaller. The total number of power supplies increases, and a larger power room is required. In the core network room of Hebei Mobile, the power room has always been relatively tight. There are two aspects to pay attention to when considering this power supply mode.
　　
        The advantage of method 2 compared to method 1 is that the reliability of power supply is greatly improved.

　　For a parallel power supply system consisting of two subsystems, as long as one system can work, the entire power supply system can work normally, or in other words, the power supply system will not work normally until all subsystems fail.

　　For parallel systems:
        MTBF system = MTBF subsystem (1 + 1/2 + 1/3 + ... 1/m)
        where MTBF system represents the reliability of the system, MTBF subsystem represents the reliability of the subsystem, and m is the number of parallel subsystems.

        For a parallel system consisting of two subsystems, MTBF system = MTBF subsystem (1 + 1/2) = 3/2 MTBF subsystem. Therefore, the MTBF of the dual power supply system is 1.5 times that of the single power supply system.

　　In fact, under the condition of monitoring, timely repair of the faulty power supply system can greatly reduce the failure rate of the entire system. The reliability level of the dual power supply system is much higher than the above value.

　　When the power supply is in the second mode, it is best to use a high-impedance power distribution cabinet for the main equipment:
　　
        because two power supply systems are connected to the same load. If a single load short-circuits, it will affect the output of the two power supplies, causing all loads to lose power instantly. Therefore, in order to ensure that the power supply of other loads is not affected when one load shorts, the power distribution cabinet should adopt a high-impedance distribution mode. (Whether to use a high-impedance power distribution cabinet depends on the manufacturer of the main equipment. Currently, the manufacturers that use this type of power distribution cabinet are mainly Ericsson, and other manufacturers are rare).

　　3. Investment issues of dual power supply systems

　　Each power supply configuration in the dual power supply system must meet the power supply requirements of two sets of communication equipment at the same time.
　　
Assume that the actual load of the communication station is 500A. Using a single power supply solution, the backup time is 2 hours. The same system uses dual power supply. Due to the improved reliability of the power supply system, consider reducing the battery backup time to 1 hour. According to the above requirements, the configuration table of the power supply system required for each communication equipment is listed:

　　
        

        The percentage increase in investment is around 50%.

　　4. Summary of the above issues
        a) With dual network element power supply, the power supply reliability rate increases by 50%.
        b) With dual network element power supply, the investment will increase by about 50%; the occupied area of ​​the power room will increase by 80%; and the wiring in the room will not increase.
        c) For the core of the core network room, such as the power distribution method for inter-provincial signaling or provincial transmission, this power supply method can be used. For ordinary switching network elements, if there are monitoring and maintenance personnel who can handle faults in time, the reliability of the existing power supply method is already relatively high.
        d) The advantages of dual network element power supply outweigh the disadvantages.

　　3. About the configuration plan of UPS in IDC computer room

　　In the existing IDC computer room, the main equipment is powered by dual power redundant power supply mode. For this solution, we cannot just use a parallel or dual bus system. Different power supply construction solutions are used for different design schemes of the main equipment.
　　
        1. When the main equipment adopts dual system backup, the best solution should be to use different UPS power supply systems to power the dual systems of the main equipment. Each power supply system adopts 1+1 parallel or single machine dual bus connection.

　　

Figure 4A Schematic diagram of power supply for a single machine dual bus system

　　

Figure 4B Schematic diagram of power supply for parallel system　

        By using the mutual backup of the main equipment in business, two power supply systems are used to supply power, which can double the reliability of the main equipment in terms of power supply. If one of the power supplies has a problem, it will not affect the business of the entire main equipment. Another advantage of these two power supply systems is that the two power supply systems are unrelated and will not affect the single UPS.

In the supporting power supply of Hebei Mobile's BOSS disaster recovery room under construction, we use the connection method shown in Figure 4B.

　　The advantages and disadvantages of the above two networking structures are as follows: The advantage of the networking method in Figure 4A is that it is convenient to adjust the three-phase imbalance of the UPS system. The disadvantage is that when a single UPS has a problem, the power supply of the main equipment it provides is directly supplied by the mains, and there will be an impact of the mains harmonic current on the load.
　
        The advantage of the networking method in Figure 4A is that it reduces the impact of the mains harmonic when one UPS has a problem, but the parallel connection method is not conducive to adjusting the three-phase imbalance of the UPS.

　　Which structure to use depends on the level of data security requirements of the host device.

　　Note: If there are three power loads, use the connection method of Figure 4A and add LBS and STS.

　　2. When the business systems of the main equipment are not backed up, it is best to use the "1+1" parallel system + UPS dual total output connection method in the power supply system. The power supply system is shown in Figure 5:

　　

        Because the main equipment has no backup, we need to find ways to improve the reliability of the power supply system in all aspects. The biggest advantage of this networking structure is that it eliminates the possibility of switching to AC bypass mains, ensuring that the main equipment always works with a stable current after passing through the UPS, and reducing the damage of mains harmonics to the main equipment, because the impact of harmonics may cause the main equipment to freeze or increase the bit error rate. It is also conducive to the parallel operation of the UPS system.

　　If there is no triple-power load, cancel LBS and STS during design.

　　Note: LBS load synchronization controller, the main device is generally a dual-power load.