Measures to improve the service life of valve regu

Measures to improve the service life of valve regulated lead-acid batteries in substations

1. Preface

with the popularity of high-frequency switching power supply, valve regulated lead-acid batteries have been widely used in power systems. Because it is fully sealed and does not need to be maintained with water, it was once called "maintenance free" battery. Due to the misleading word "maintenance free", users relaxed the daily maintenance and management of valve regulated lead-acid batteries, resulting in the early capacity reduction and damage of batteries. Accidents in substations and power plants caused by insufficient or invalid battery capacity have been common. Therefore, it is of great significance to correctly use and maintain valve regulated lead-acid batteries and improve their service life

2. Main factors affecting the service life of valve regulated lead-acid batteries

the normal service life of valve regulated lead-acid batteries is more than 10 years, theoretically up to 20 years, but in practical use, there are often insufficient capacity or early failure. There are many factors that affect the service life of valve regulated lead-acid batteries, mainly including:

2.1 the influence of ambient temperature

the battery can obtain a long service life at 25 ℃ [1]. When the temperature rises, the plate corrosion of the battery will intensify, and more water will be consumed at the same time. Most man-made materials are chemically very stable: they should be decomposed into the original components, so as to shorten the battery life. If the long-term operating temperature rises by 10 ℃, the service life will be reduced by about half. The capacity of valve regulated lead-acid battery changes with the change of temperature. The capacity of battery at 25 ℃ is 100%; When the temperature is above 25 ℃, the capacity of the battery will be reduced by half for every 10 ℃ increase

therefore, we must carefully adjust the discharge current of the battery according to the change of the actual temperature, and control the temperature of the battery room to keep it within 22 ℃ ~ 25 ℃

2.2 effect of overcharge

under the long-term overcharge state, the positive electrode is consumed due to oxygen evolution reaction, and H + increases, resulting in increased acidity near the positive electrode, accelerated grid corrosion, thinning the grid, accelerated battery corrosion, and reduced battery capacity; At the same time, due to the aggravation of water loss, the battery will be in danger of drying up, thus affecting the service life of the battery

2.3 impact of excessive discharge

excessive discharge of battery mainly occurs after AC power failure, and the battery supplies power to the load for a long time. When the battery is over discharged to a low or even zero voltage, a large amount of lead sulfate inside the battery will be adsorbed to the cathode surface of the battery, causing "sulfation" at the cathode of the battery. Lead sulfate is an insulator, and its formation will have a great negative impact on the charge and discharge performance of the battery. Therefore, the more sulfate formed on the cathode, the greater the internal resistance of the battery, the worse the charge and discharge performance of the battery, and the shorter the service life of the battery

2.4 influence of low current discharge conditions

the size of lead sulfate particles formed under low current discharge is much larger than that under high current discharge, that is to say, the maximum static load of crystal shape under high current condition is 5kn, and the speed of formation is slower than that under low current condition. The crystal is oxidized and reduced quickly before it has time to grow, so the particles are relatively small, while under low current condition, the larger lead sulfate crystals are not easy to be reduced. If the lead sulfate crystal cannot be cleaned for a long time, it will inevitably affect the capacity and service life of the battery. Therefore, there should be an accurate calculation of the capacity of the battery under the actual discharge current

2.5 effect of unbalanced charge and discharge

the relevant research results show that the distribution of alloy composition and structure in different parts of the grid is different, which will lead to the imbalance of electrochemical performance of the grid [2], which will make the voltage difference between floating charge and charge and discharge, and will increase with the cycle of charge and discharge, Form the so-called "backward battery (battery failure)". At present, domestic standards require that the difference of the maximum floating charge voltage in a group of batteries should be ≤ 50mV, while the standard of developed countries is ≤ 20mV, so we should pay attention to and reduce the difference of battery operating voltage under floating charge

2.6 thermal runaway phenomenon

due to the lean solution design of valve regulated lead-acid battery, the electrolyte filled in the battery is adsorbed on the fiberglass board. When the charging current increases, it is necessary to release gas through the safety valve, which results in the loss of water, increase of internal resistance, capacity attenuation and large amount of heat generated in the process of charging and discharging. These heat can be divided into two cases: (1) the coaxiality of force is 5%; (2) If the geometric coaxiality is 0.2mm and the temperature increases sharply due to diffusion, thermal runaway will be formed. The causes of thermal runaway include the failure to reduce the floating charge voltage in time, the lax safety valve or the low valve opening pressure, etc. in the case of serious thermal runaway, if the discharge, it may cause the instantaneous voltage drop of the battery and the temperature of the battery shell to rise to 70 ℃ ~ 80 ℃. Therefore, great attention must be paid to the problem of thermal runaway

2.7 impact of long-term floating charge

in the long-term floating charge state, the battery is only charged without discharging, which is bound to lead to the passivation of the anode plate of the battery, increase the internal resistance of the battery, greatly reduce the capacity, and thus shorten the service life of the battery

3. Measures to improve the service life of valve regulated lead-acid batteries through the analysis of the above factors affecting the service life of valve regulated lead-acid batteries, in order to improve the service life of valve regulated lead-acid batteries, we must do:

3.1 strictly control the ordering quality of batteries. In the process of battery selection and procurement, we should fully understand the manufacturer's production process, manufacturing process, quality control means, as well as technical characteristics. If necessary, we can require the first capacity test in the manufacturer to screen batteries with small differences

reasonably select charging equipment. As the switching power supply has the functions of real-time monitoring and intelligent management, it can make the sealed battery work in the best state at all times, so it is necessary to choose high-quality switching power supply as the charging equipment. The high-frequency switching power supply system should adopt modular design. When the module fails, it should be able to immediately exit the operation without affecting the normal operation of other modules. The standby module should be able to automatically put into operation to ensure that the battery will not be over discharged due to module failure

3.2 pay attention to the installation quality. Installation quality includes storage, installation, capacity test and other aspects. Therefore, attention should be paid to avoid collision during transportation and storage