Leakage hazards and preventive measures of high-power lead-acid batteries used in data centers
Time of issue:2023-01-30
In the data center, the AC UPS system is a very important key infrastructure, providing uninterrupted power supply for the load, ensuring the smooth flow of the network and the normal operation of the equipment. Among them, the storage battery as electric energy storage 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 about the battery used in AC UPS systems, and the 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 battery application requirements and battery characteristics in AC UPS systems, and correctly select and use batteries to ensure that they can fully play their due role.
Long time delay battery and high rate battery
Batteries used in data centers can generally be divided into three categories according to the type of discharge, namely, "instantaneous high current discharge" for diesel generator sets, "long delay, small current discharge" for communication power systems, and "discharge for AC UPS systems". High rate discharge".
In the power supply of traditional communication network equipment, the backup time of the communication power system is basically designed and configured according to several hours of the design load. Such as 10h, 8h, at least 3 ~ 5h. The battery pack is basically in the charging and discharging working state of "long delay, low current". According to the discharge current of 10h rate, the electric energy that can be released is 100Ah, 200Ah and 1000Ah respectively.
For high-power AC UPS systems, due to the high voltage, 6V or 12V batteries are often used. Restricted by battery capacity, number of parallel groups, and investment costs, the backup time is as low as 15 minutes. That is to say, the discharge rate of the battery pack is already much lower than the 10h rate, and the actual discharge current of the battery pack is much greater than the 10h rate discharge current. The discharge method of the storage battery has been transformed into a "high rate" discharge method between the "long time delay and low current" of the traditional backup battery for communication and the "instantaneous high current discharge" of the start-up battery. From the perspective of the current technology and process structure of the valve-regulated sealed lead-acid battery, the communication backup battery designed and produced according to "long delay, low current" cannot fully meet the application requirements.
An engineer from Guangdong Inventec Electronics Co., Ltd. said that the same 12V or 6V single lead-acid battery has completely different choices for different usage occasions. When used in traditional communication stations, wireless base stations, etc., the traditional "small current, long delay" communication lead-acid battery should continue to be used; while the battery pack used in the AC UPS system of the data center should be selected for large Current discharge "high rate" battery pack. The two should not be confused and abused.
Harm of DC circuit short circuit fault
The power supply system in the data center can be divided into two circuits: AC and DC. Compared with the AC circuit, the influence of the failure of the DC circuit will be greater.
The main reasons are as follows:
The short circuit of the battery pack is more harmful than the alternating current. Under normal circumstances, the primary measure for fire caused by an electrical short circuit is to cut off the power supply. For AC power supply, since the electric energy comes from the mains grid or diesel generator set from top to bottom, when an electrical short circuit fault occurs, there will always be a primary protection device that will act to cut off the short circuit electrical circuit in time. And when the battery pack is located at the end of the power supply system, the electric energy is provided from bottom to top, as long as the protective fuse of the DC power distribution panel or the protective circuit breaker of the battery pack are crossed, there will be no other protection. When a short-circuit fault occurs, it is often impossible to effectively cut off the short-circuited electrical circuit. In addition, the DC current is not like the AC sine wave, and the instantaneous electromotive force is zero when there is no zero crossing point. Once an electrical short circuit occurs, it is easy to cause spread. However, the impedance after a short circuit only depends on the wire resistance and the internal resistance of the battery pack, and the short circuit current is basically approximately infinite.
2. Cause network outages
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 pack is the emergency power supply source 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 failure of the mains or the interruption of the electrical short circuit on the AC side will not directly lead to the interruption of the power supply of the communication network. . Similarly, for the AC UPS system, as long as the inverter and subsequent circuits work normally, the backup battery pack can play a role. However, if the DC power system, especially the battery pack, has an electrical short circuit, it will inevitably cause the output voltage of the DC power system to drop instantaneously, causing power failure of the load equipment, resulting in network interruption, and seriously affecting the smooth flow of information communication.
3. Fire in the computer room
After the electrical short circuit of the battery pack occurs, if the circuit cannot be found and cut off in time, it will inevitably cause a fire. The better the quality of the battery pack and the more power it has, the greater the damage.
Therefore, the overcurrent protection of the DC circuit in the AC UPS system of the data center, especially the battery pack, is particularly important. Special attention must be paid to the battery protection box near the side of the battery pack, and the built-in switch should be a DC (or AC and DC) circuit breaker or fuse. If multiple sets of batteries are used in parallel, a general output switch should be set, and the Each group of storage batteries is provided with switches for protection and operation.
Analysis and detection of battery short circuit fault and liquid leakage
Among the causes of electrical short circuit in battery packs in AC UPS systems, battery leakage causes a short circuit to the battery frame or a decrease in insulation, resulting in an indirect short circuit between the positive and negative electrodes through the battery frame. But a very serious problem.
Leak detection and preventive measures
(1) Choose regular, big brand batteries
At present, there are a lot of counterfeit and refurbished batteries on the market. The biggest advantage of this kind of battery is that it is cheap, but it is extremely risky; and the shell material may be made of secondary materials, which are relatively brittle, hard, and easy to break, resulting in leakage; even cut corners, Reduce the investment, the thickness of the shell is not enough, and it cannot withstand the normal pressure or collision generated during use.
Therefore, fundamentally, it is necessary to ensure that the purchased battery products are batteries from regular sources and big brands. In the current domestic market, Inventec high-power batteries are widely used in the industry.
(2) Select qualified engineering installation personnel
The installation link is an extremely important process. During installation, the battery packaging must be removed, and the battery case will directly contact the battery rack/cabinet, plus the weight of the battery, it is easy to cause bumps. If you want to handle it with care, you need great physical strength, professionalism and sense of responsibility, otherwise the result will be very unsatisfactory; and the rupture of the battery case caused by the installation will not be visible at the time of acceptance, which will bury hidden dangers for the later stage .
It is recommended to choose professional construction personnel with qualifications, strict management, excellent technology and guaranteed after-sales to ensure that the entire construction process is controlled and guaranteed.
(3) Physical isolation method
Only by eliminating all possible risks and taking precautions can we ensure the reliable operation of products and equipment and reduce risk discovery. Isolating the battery from the rack/cabinet is an effective solution. A non-conductive plastic tray (see Figure 2) is used between the battery and the frame. When there is liquid leakage, the acid will remain in the tray to avoid forming a live body with the battery frame, which can effectively avoid electric shock.
(4) Battery real-time monitoring method
Principle: When liquid leaks, with the loss of acid, the battery's ability to transmit current decreases, and the internal impedance increases. The final performance is the increase in the internal resistance of the battery and the change in voltage. By judging the change of battery internal resistance and voltage, it can be judged that the battery is abnormal. Method: Select a suitable battery monitor system, detect the voltage, temperature, and internal resistance of each battery in real time, set the alarm value, and provide sound and light alarms when there is an abnormality, so that maintenance personnel can find and deal with it immediately , to avoid the risk.
The device can continuously detect 24 hours, know the battery parameters in time, and analyze the change trend of the battery according to the historical data of the battery, grasp the life and status of the battery in time, and prevent problems before they happen.
(5) Insulation resistance monitoring method
Principle: In the case of isolation between the battery circuit and the AC circuit, when the liquid leaks, the battery acid will be in contact with the battery rack/cabinet. Due to the conductive effect of the electrolyte, at this time, the impedance between the positive and negative electrodes of the battery and the battery rack will be reduced. If it becomes smaller, if it is smaller than a certain value, there will be a risk of electric shock. Method: Choose a suitable DC insulation impedance monitor, detect the impedance of the positive/polarity of the battery and the battery rack/cabinet in real time, set the alarm value, and provide an audible and visual alarm when there is an abnormality, so that the maintenance personnel can find out immediately, deal with and avoid risks. At present, domestic manufacturers already have corresponding mature technologies, which can detect accurately, without false positives, and at low cost.
(6) Regular inspection method
Carry out maintenance, dust removal, observation, impedance test, etc. once every three months or half a year, and carry out corresponding inspections and records according to the listed inspection list to ensure that the inspection work is effectively implemented. This work can be arranged by the user himself, or can be entrusted to the professional after-sales service personnel of the power supply manufacturer or a third-party company.
There are various methods, and the key is early prevention and regular inspection. The above methods can be used in combination (note: 3 and 5 cannot be used at the same time), which will reduce the probability of risk occurrence by multiple orders of magnitude or even eliminate it completely.