Shulou(Shulou.com)05/31 Report--

Data center communicates the problem of UPS battery pack security application. In view of this problem, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible method.

In the data center, the AC UPS system is a very important key infrastructure, which provides uninterrupted power supply for the load and ensures the smooth flow of the network and the normal operation of the equipment. Among them, the battery as the storage of electric energy must be an important part of the AC UPS system. However, due to the characteristics of the battery itself and various reasons, there are more or less misunderstandings in the understanding of the battery used in AC UPS system, and its application is not satisfactory. In practical application, many accidents or failures of AC UPS systems are caused by batteries. Therefore, it is necessary to strengthen the understanding of the application requirements and characteristics of batteries in AC UPS system, and to select and use batteries correctly to ensure that they can fully play their due role.

1. The function and significance of Battery in UPS Power supply system

The main function of battery in AC UPS system is to store electric energy. When the municipal power is supplied normally, the battery stores electric energy through the rectifier-charging circuit of the AC UPS system, smoothly filters the DC circuit, and acts as a buffer when the inverter is overloaded. Once the city power is accidentally fluctuated or even interrupted, the AC UPS system is supplied by the battery discharge to the inverter, and the inverter converts the direct current released by the battery into sinusoidal AC power to maintain the power output of the UPS. In other words, in the case of abnormal input, the AC UPS system depends on the battery to replenish the electric energy in time to ensure that the power supply is not interrupted.

Its function should mainly include two aspects:

The continuity of power supply is realized when the power supply of city electricity and oil engine fluctuates, instantly breaks or even interrupts. In the process of seamless switching of the power supply, ensure that the power supply of the equipment will not be interrupted greater than 10ms, and that the equipment will not lose power.

After the power supply of city electricity and oil engine is interrupted, it can be used as a backup energy for a limited time to ensure that the load uses electricity normally within a certain period of time. It is the maximum energy guarantee for emergency power supply to AC UPS system, and its role mainly depends on the discharge current and capacity of the battery.

Therefore, the battery pack is equivalent to the fire brigade and fire engine in the AC UPS system. "keep troops for a thousand days, use troops for a while", usually or even for a long time, but they can only rely on it completely in case of emergency.

The quality of its products and the quality of operation and maintenance will be directly related to the security and availability of the power supply of information and communication network equipment.

On the other hand, restricted by various factors, the valve-controlled sealed lead-acid battery is the weak link in the AC UPS system which is most prone to problems and the problems are not easy to be found in advance.

Therefore, it is necessary to establish such a concept: the focus of the application of battery pack in AC UPS system (including design, procurement, operation and maintenance) is its reliability and availability, rather than saving money, saving energy, reducing emissions or extending service life!

two。 Design life and effective service life of lead-acid battery

According to records, the application of lead-acid batteries in China's communications sector began in the 1930s, from the earliest open-ended lead-acid batteries to the acid-proof lead-acid batteries in the 1960s. Since 1980s, valve-regulated sealed lead-acid battery (VRLA) has become the mainstream product and has been used all the time as a replacement product. As the energy storage component of AC UPS, valve-regulated sealed lead-acid battery (VRLA) is still the main battery.

The service life of valve-regulated sealed lead-acid battery is mainly divided into two types: cycle life and floating charge life.

Cycle life refers to each charge and discharge of the battery, which is called a charge-discharge cycle. The number of charge-discharge cycles that the battery can carry out while maintaining a certain output capacity is called the cycle life of the battery.

The floating charge life refers to the operating time of the battery at the end of its available life under the specified floating charge voltage and ambient temperature. The end-of-life condition is set at 80% of the rated capacity at a rate of less than 10 hours.

From the theoretical analysis, the design life of valve-regulated sealed lead-acid battery (VRLA) can reach 15 to 20 years, which is based on it in practical use. For example, in the communication industry standard YD/T799-2002 "Valve-regulated sealed lead-acid Battery for Communication", the life of the battery is stipulated as follows: "the equivalent floating charge life of 2V series batteries is not less than 8 years." the equivalent floating charge life of batteries above 6V series is not less than 8 years. " In the newly revised YD/T799-2010, the life of the battery is further refined and standardized from the point of view of testing, as shown in Table 1.

To sum up, and combined with the analysis of the actual use, the provisions on the life of the battery in the current standards are appropriate and feasible. At present, the reason why the service life of valve-regulated sealed lead-acid battery (VRLA) used in AC UPS can not meet the requirements is not the problem of technical principle and production level.

3. Long delay battery and high rate battery

The batteries used in data centers can be divided into three types according to the discharge types, namely, "instantaneous high current discharge" used in oil generator sets, "long delay and low current discharge" used in communication power supply system, and "high rate discharge" used in AC UPS system.

In the power supply of traditional communication network equipment, the backup time of communication power supply system is basically designed and configured according to several hours of design load. For example, 10 h, 8 h, and at least 3-5 h. The battery group is basically in the working state of "long delay and low current" charge and discharge, and the nominal capacity of the battery is also calibrated by the capacity at the discharge rate of 10 h, such as 100Ah/12V, 200Ah/6V, 1000Ah/2V and so on. The electric energy that can be released by the discharge current of 10 h is 100Ah, 200Ah and 1000Ah respectively.

For high-power AC UPS systems, 6V or 12V batteries are mostly selected because of the high voltage. Due to the limitations of battery capacity, number of parallel units and investment cost, the backup time is even only 15min. In other words, the discharge rate of the battery is much less than the 10h rate, and the actual discharge current of the battery is much larger than the 10h rate discharge current. The discharge mode of the battery has been changed to the "high rate" discharge mode between the traditional backup battery for communication "long delay and small current" and the "instantaneous high current discharge" of the start-up battery. According to the current technology and process structure of valve-controlled sealed lead-acid battery, the communication backup battery designed and produced according to "long delay and low current" can not fully meet the requirements of this application.

Therefore, the choices of lead-acid batteries with the same 12V or 6V monomer are completely different in different applications. When used in traditional communication stations and base stations, the traditional lead-acid batteries with "low current and long delay" should continue to be selected, while the batteries used in AC UPS systems in data centers should choose "high rate" batteries suitable for high current discharge. The two should not be confused and abused.

4. The harm of short-circuit fault in DC circuit and the necessity of installing over-current protection at the near end of battery pack

The power supply system in the data center can be divided into AC and DC circuits. Compared with the AC circuit, the impact of DC circuit failure will be greater.

The main reasons are as follows:

The main results are as follows: (1) the harm of short circuit of storage battery is greater than that of AC, in general, the first measure of electrical short circuit fire is to cut off the power supply. For the AC power supply, because the electric energy comes from the municipal power grid or diesel generator set from top to bottom, when the electrical short-circuit fault occurs, there will always be a primary protection device to cut off the short-circuit electrical circuit in time. When the battery pack is located at the end of the power supply system, the power is provided from the bottom up, as long as it passes the protection fuse of the DC main distribution screen or the protection circuit breaker of the battery pack, there will be no other protection. When a short-circuit fault occurs, it is often impossible to effectively cut off the short-circuit electrical circuit. In addition, unlike the AC sine wave, the instantaneous EMF is zero when there is no zero crossing, and it is easy to spread in the event of an electrical short circuit. The impedance after short-circuit only depends on the wire resistance and the internal resistance of the battery, and the short-circuit current is basically infinite. Therefore, the harm of DC short-circuit is much greater than that of AC short-circuit.

(2) cause network outage accident

The DC power supply system in the communication power supply is the core system to ensure the uninterrupted power supply of the communication network equipment, and the backup battery is the emergency power supply of the communication network. For the DC power supply system, the battery pack is directly connected in parallel in the DC power supply circuit at the output end of the rectifier. It is precisely because of the existence of the backup battery pack that the power outage or the electrical short circuit interruption on the AC side will not directly lead to the interruption of the power supply of the communication network. Similarly, for AC UPS systems, as long as the inverter and subsequent circuits work properly, the backup battery can play a role. However, if the electrical short circuit occurs in the DC power supply system, especially in the battery pack, it will inevitably cause the output voltage of the DC power supply system to drop instantly, cause the load equipment to lose power, cause the network interruption fault, and seriously affect the smooth flow of information communication.

(3) cause fire in the computer room

After the occurrence of the battery electrical short circuit, if the circuit can not be found and cut off in time, it will inevitably cause fire. The better the quality of the battery pack is and the more sufficient the electricity is, the greater the harm is.

Therefore, the overcurrent protection of the DC circuit, especially the battery pack, is particularly important in the AC UPS system of the data center. In particular, it should be noted that the battery protection box must be arranged near the battery group, and its built-in switch should be a DC type (or AC / DC dual-purpose) circuit breaker or fuse. If multiple groups of batteries are used in parallel, the main output switch should be set up. And set switches for each group of batteries to protect and operate separately.

5. Analysis and detection of electrical short circuit fault and liquid leakage of lead-acid battery

In the cause of electrical short circuit of battery pack in AC UPS system, the leakage of battery causes short circuit or insulation decrease to the battery rack, resulting in indirect short circuit of positive and negative electrodes through the battery rack, which has always been a difficult fault with high probability and the most difficult to judge and find, but the consequences are very serious.

At present, the preventive measures against this kind of hidden trouble are more or less inadequate:

A tray is added to the bottom of the battery, and the tray is flammable

The addition of bakelite gasket to the battery rack can not avoid the diffusion of electrolyte.

The battery rack is insulated to the electrical ground & mdash, which is not easy to implement and does not comply with the safety specification.

The battery room is equipped with a very early smoke warning system, which is not timely.

The current DC power supply systems in use which are higher than the safe voltage (such as power operating power supply, 240V DC power supply system for communication, etc.) all require the DC loop-to-ground suspension mode, and equipped with insulation monitoring (Insulation Monitoring) function system.

The so-called insulation monitoring refers to the detection of the insulation performance of the DC output and the ground in the DC power supply system to determine whether there is a grounding fault or the insulation performance is reduced. Give an alarm when there is a grounding fault or insulation performance deterioration.

The insulation monitoring function mainly realizes the detection of the insulation resistance to the ground by detecting the voltage and current in the DC power supply circuit. Among them, the voltage detection technology is mainly by insulation monitoring to monitor the positive and negative DC bus voltage to the ground in real time, and calculate the positive and negative bus-to-ground insulation resistance through the ground voltage. When the insulation resistance is lower than the set alarm value, an alarm signal is sent.

In essence, the electrical short circuit of the battery pack is also an extreme form of decreasing insulation between the positive and negative electrodes, while for the electrical short circuit caused by the battery leakage, it must be the decrease of the insulation between the positive and negative electrodes or to the battery rack (grounding).

From the working principle of insulation monitoring, it can be known that as long as the battery is suspended to the ground, the positive and negative circuits (including charge and discharge circuits) of the battery are not grounded. The phenomenon of battery leakage or the decrease of insulation to the ground can be detected by balancing the bridge resistance. Because the measurement object of this detection method is the positive and negative pole-to-ground voltage of the battery pack, regardless of the grounding fault or the decrease of insulation at any point in the battery pack, it will cause the change of positive pole-to-ground voltage U1 or negative pole-to-ground voltage U2, and can be quickly reflected in the insulation monitoring system. Therefore, with the help of the detection principle of insulation monitoring, the detection of battery leakage can be realized.

This is the answer to the question about the safe application of UPS battery pack in the data center. I hope the above content can be of some help to you. If you still have a lot of doubts to be solved, you can follow the industry information channel for more related knowledge.

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