The battery is widely used in power systems, factories and mines, communication rooms and other fields. In the power supply system, the DC screen provides switch operation and protection control power, accident lighting, etc., and the UPS power supply in the branch provides backup power for control systems such as PCL and DCS. If the battery is faulty, it will cause the switch to refuse, the monitoring system, the automatic control system, etc., causing different degrees of impact and loss. Therefore, it is of great significance to maintain the battery.
1 Battery basics
A battery is an electrical storage device. When two metals (usually metals with different properties) are immersed in the electrolyte, they can conduct electricity and generate a certain electromotive force between the "plates." The magnitude (or voltage) of the electromotive force is related to the metal used, and the electromotive force of different types of batteries is also different. A lead-acid battery refers to a battery using lead dioxide as a positive electrode, active lead as a negative electrode, and dilute sulfuric acid as an electrolyte. It consists of a battery case, a positive and negative plate, an electrolyte, a separator, and the like. The chemical reaction of the lead-acid battery during charging and discharging is as follows:
Discharge charging
PbO2+2H2SO4+Pb≒2PbSO4+2H2O
The reversible equation of charge and discharge above expresses the characteristics of charge storage and discharge of lead-acid batteries, each of which has a 2V electromotive force. In use, the batteries can be connected in series to obtain the required higher voltage, or the batteries can be connected in parallel to obtain the larger capacity required.
According to the way of electrolyte in lead-acid batteries, lead-acid batteries are divided into open-type (rich liquid) lead-acid batteries and valve-regulated (lean-liquid) sealed lead-acid batteries. The working principle of the valve-regulated lead-acid battery is: gas recombination, that is, the oxygen generated by the positive electrode, reacts with the negative electrode active material and dilute sulfuric acid through the pores in the AGM separator (or the crack of the colloid), and then synthesizes the water, and simultaneously synthesizes the water. A part of the negative electrode plate is placed in a discharged state, thereby suppressing generation of hydrogen gas. As long as the oxygen generation rate of the positive electrode plate does not exceed the absorption rate of oxygen by the negative electrode plate, no excess gas is generated in the battery, and the water in the battery is not lost, so that the sealing can be achieved. In the actual use of the battery, there is always a small amount of gas that cannot be recombined. To prevent the internal pressure of the battery from being too large, a check valve is installed on the battery cover to remove excess gas inside the battery. This is called valve control.
Valve-regulated sealed lead-acid batteries have low maintenance characteristics, so valve-regulated sealed lead-acid batteries are commonly used in DC systems and UPS.
The basic parameters of the battery include: battery electromotive force, open circuit voltage, termination voltage, working voltage, discharge current, capacity, specific energy, battery internal resistance, storage performance, service life (floating charge and discharge cycle life, etc.); performance indicators include: maximum discharge Current, overcharge resistance, capacity retention rate, sealing reaction performance, safety valve action, explosion-proof performance, anti-acid mist performance, etc.
2 Basic requirements for battery use
(1) Environmental requirements
The battery must be used within the specified ambient temperature range. The temperature must be lower than the specified temperature range. The battery should be installed in a space with relative humidity ≤70%, ventilation, heat dissipation, no acid, alkali or other corrosive gases. Installation is strictly prohibited. In a completely sealed environment.
(2) Installation requirements
Installation location: When installing the battery, it should be separated from other parts of the device as much as possible. Try to avoid direct connection with the printed circuit board. When the two requirements cannot be met due to design, space restrictions or any other reason, at least the battery should be placed in the device or single. The lowermost end of the board to prevent the battery from leaking and corroding equipment parts or boards in case of accident;
(3) Space size: The space for installing the battery should be able to meet the maximum external dimensions of the battery and have a certain margin to facilitate the installation of the battery, while considering the compatibility of the dimensions;
Connection: The length of the connection between the battery and the equipment or the board should be as small as possible to reduce the voltage drop; the cross-sectional area of ​​the connector is based on the principle of long-term battery charging or current twice the operating current.
(4) Storage requirements
The battery should be stored in a dry, clean and cool environment under fully charged conditions; if the battery is stored for 6 months or longer, the battery should be recharged regularly; the storage temperature of the battery should be kept at 30. Below °C.
(5) Selection of battery
At present, there are many brands of batteries. Domestic and foreign brands must choose brands that are more cost-effective according to the actual use environment. It is imperative to choose small brand manufacturers or even counterfeit products for a short time. Fully conduct brand investigation before purchasing. Understand brand awareness, performance and after-sales service, etc., through the shop around, finally choose the most cost-effective products.
3 battery operation and maintenance
(1) Maintenance-free is not maintenance
Valve-regulated sealed lead-acid batteries have been widely used in various industries. The understanding of the maintenance technology of valve-regulated sealed lead-acid batteries is also constantly deepening and improving. From the initial maintenance-free to less maintenance, and finally to the maintenance under the current monitoring conditions.
At present, the functions of monitoring and detecting means reliability, measurement accuracy, and battery charging control mode are not completely consistent with the actual use requirements of the battery. It is not possible to rely entirely on the results of monitoring data as a criterion for judging the actual operating conditions of the battery, and it is possible to find hidden dangers in the current operation of the battery.
The actual condition of the battery will be very different from the data from our monitoring test. The more correct method is to strengthen the regular maintenance of the valve-regulated sealed lead-acid battery in addition to the daily monitoring test. Correctly find the difference between the operating parameter settings of the intelligent charging device and the actual application parameters of the battery. Make corrections so that the battery system can always operate in a safe and reliable working condition. The biggest advantage of VRLA batteries compared to open batteries is the reduced labor intensity for battery maintenance. But daily charging and maintenance work is still indispensable.
(1) New battery use
After the new battery is put into use, it must first be recharged (ie, charged). The voltage value is 2.35 V / monomer ± 0.02 V at 25 ° C. The charging time is about 16 to 20 hours. If it is not at the standard temperature, its charging voltage should be corrected. The verification capacity test can only be carried out when the battery is fully charged, and should be carried out according to the battery charge and discharge standard, that is, the initial capacity is checked by 95%.
It should be noted that since it takes a certain time for the battery plate active material to undergo a sufficient chemical reaction from the surface to the inside, it is recommended that the charge and discharge time interval be greater than 10 days (in the case of deep discharge). The longer the charging time, the deeper the discharge depth.
(2) Floating charge
The float voltage of the valve-regulated sealed lead-acid battery is 2.25V ± 0.02 / monomer at 25 ° C. It is recommended to take the 2.25V ~ 2.26V / monomer, which is slightly higher than the center value.
The standard for selecting the float voltage is: in addition to the energy required for self-discharge and oxygen recombination when the battery is charged, it must be fully charged after short-term discharge of the battery. Otherwise, the battery will be undercharged when it is floating for a long time. Insufficient capacity is caused during discharge.
When the battery of the same brand is used under different environments and different maintenance conditions, the actual service life will vary greatly. The most influential factor is the float voltage value when the battery is not noticed for a long time.
Therefore, it is necessary for maintenance personnel to understand the degree of influence of the charging method on the service life of the battery and how to adjust the charging parameters of the battery to the battery in time according to the actual use of the battery.
(3) Regular charging
The average charging voltage is 2.35V/cell ± 0.02V. It should be charged every three months to six months, and the charging time is generally 8 to 12 hours.
The purpose of periodic charging is to eliminate the temperature change without correcting the effect of the floating charging voltage change; the battery pack is often discharged but the floating charging voltage cannot be fully charged within the specified time; the floating charging voltage value is obtained due to the device voltage limitation. When the time is low; the unattended machine room does not often detect the change of the floating charge voltage; the individual cell voltage in the battery system is ≤ 2.20V; the battery storage period is more than 6 months.
(4) Regular therapeutic or nuclear discharge test
When the battery system is in the floating charge for a long time, due to the excessive design of the negative active material and the presence of oxygen compounding, the negative electrode plate always has a part of the active material in a state of insufficient charging, and the long-term floating charge flow value is small enough to make the plate The internal active material is sufficiently electrochemically reacted to cause sulfation of the active material inside the electrode plate, thereby reducing the capacity of the negative electrode plate and affecting the service life of the battery. In order to avoid the above phenomenon, the battery system for long-term floating charging operation should be subjected to a therapeutic discharge test every 6 months or 12 months depending on the working state. When the discharge is performed once every 6 months, the depth of discharge may be shallower. It should be about 30% to 40%. If the discharge test is carried out for 12 months, it may be appropriately deepened, preferably 50% to 60%. After deepening, the battery will be easily found. A faulty single cell that appears in the group.
If it is found through the discharge test that there are backward cells in the battery pack, the battery pack can be remedied by charging and discharging or monomer activation to ensure safe and reliable operation of the battery pack.
4 Conclusion
Strengthen the scientific use and maintenance management of the battery, so that the DC and UPS power supply systems of the power industrial and mining enterprises work normally, not only can ensure the normal power supply of the DC power supply and the UPS, but also play its due role in the event of an accident power outage. At the same time, it can extend the service life of the battery and reduce the investment cost. The unit has achieved the purpose of saving and increasing efficiency.
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