In the current 110kV and 35kV medium and low voltage substations, the devices equipped with batteries are mainly DC screens and communication devices. A simple discussion is made on the service life of the DC screen backup battery.
First, the operating requirements of the DC system on the battery in the station
The storage battery serves as a standby power source for the DC system in the station, and it is required to maintain a certain level of charge at all times so that the AC screen loses power when the high-frequency switching power supply or the silicon rectifier device fails. When a fault occurs and the DC power source cannot be output, the storage battery can be timely input so as not to affect the battery. The normal operation of the DC equipment and DC loop in the station. Therefore, the performance of the battery itself should be able to maintain its capacity and voltage at a relatively high level within a certain period of time (including the maintenance of the DC power supply unit). Only in this way can the safe and reliable operation of the DC system in the station be guaranteed.
Second, the battery operating status
With the popularity of unattended substations, substation DC systems are gradually adopting maintenance-free lead-acid batteries. Some substation operation and maintenance personnel understand “free maintenance” as “non-maintenance” and the actual operation of the storage battery inside the station is often unsatisfactory.
Taking the 35kV Taishan substation and 35kV Gaodu substation under the jurisdiction of Mengyin County Company as an example, two stations replaced the maintenance-free lead-acid battery at the same time. During the two years of operation, the battery is only activated once a year. The battery operating status is mostly float state. The maintenance volume is really small, and the battery parameters meet the requirements of the regulations. However, by the third year, part of the battery voltage at Taishan substation began to decrease. By the end of the third year, most battery voltages fell below the standard value, and individual batteries dropped below 8V. At the beginning of the fourth year, the storage battery charge could not be converted to floating charge, and its performance indicators could not meet the operational requirements, and only a new set of batteries had to be replaced.
The same problems exist in the batteries of the high substations. The battery life of Taishan Substation and Gaodu substation is within three years, which is far short of the five-year limit of the manufacturer's design and directly reduces the lifespan by 40%.
Third, lead to shorten the battery life analysis
1. Follow the manufacturer's recommendations and customary practices
Because it is a maintenance-free battery, and the DC system is automatically controlled charging mode, the operation is more reliable, according to the manufacturer's recommendations, only one activation per year. Due to the good performance in the previous two years, this kind of management mode for batteries has been approved. Due to potential battery problems, the first two years did not appear in operation, after many years of operation, the battery capacity dropped significantly.
2. The difference in operating conditions, the degree of battery aging is also different
The Taishan and Gaodu substations under the jurisdiction of Mengyin County Company are 35kV substations. They are at the end of the substation and have a single operating mode with very few operating opportunities. The discharge capacity of the battery is very low, almost no activation, and the capacity is reduced quickly; while 110kV Mengyin Substations are hub substations, and their operation modes are changeable. The operation is frequent, the batteries are often discharged, and the discharge capacity is large. The activation frequency is high and the capacity is easily maintained at a relatively high level.
3. The lack of understanding of battery performance, improper daily operation and maintenance
According to the DC system anti-accident measures, the battery operated by floating charge shall be charged by means of a constant voltage method except for special provisions by the manufacturer. When float charging, the float charge voltage and the lower limit of the single battery should be strictly controlled to prevent the battery from being damaged due to the charging voltage being too high or too low, that is, to avoid long-term overcharge or undercharge. Taking valve-regulated sealed lead-acid batteries, which are now commonly used, as an example, it has been proved that when the actual floating charging voltage differs from the specified floating charging voltage by 5%, its service life will be shortened by half.
The battery float voltage is generally set by U(25)=E+0.1 (E is the rated voltage of the single cell). If the manufacturer has stated it, it should be set according to the instructions. Charge current limit current can be set according to I = (0.1 ~ 0.125) C10 (C10 is the battery discharge rate of 10 hours), the maximum charging current can not exceed 1.5C10. In routine maintenance, this detail is often overlooked. Different types and manufacturers of batteries can not be treated differently according to the specific requirements of the charging parameters. Instead, unified uniform and floating charging parameters are used, and even charging parameters are randomly set. This eventually leads to the storage battery. Destruction of performance.
In addition, overdischarge should also be prevented. Over-discharge voltage setting: Take a 2V battery as an example, the discharge time of the valve-regulated sealed lead-acid battery is 10h, and the discharge voltage is 1.8 to 1.9V.
4. The change of system parameters reduces the frequency and depth of battery charge and discharge, accelerates the aging of the battery, and significantly reduces the capacity.
Some of the operating mechanisms of the circuit breaker are all electromagnetic type, and the closing current is large, and the indicating lamp is a large-current lamp, so that the discharge current of the battery is increased, and the number of charging cycles is all high, so that the battery can be frequently activated and the battery capacity can be increased. Always stay at a high level. As the operating mechanism of the circuit breaker is gradually replaced with a spring energy storage type, the closing current is very small, and the indicator light is also replaced with a small-current energy-saving light bulb, so that the discharge current of the battery is reduced, there is almost no equalizing opportunity, and only the operation is performed. In the floating state, the activation frequency of the battery is extremely low, and the active material of the battery plate gradually solidifies, so that the battery capacity gradually decreases until it falls below the standard value.
5. Influence of other factors
The installation of batteries is not standardized, and the damage to the batteries during storage and transportation and the working environment temperature and ventilation conditions of the batteries do not meet the requirements, which will also adversely affect the performance and life of the batteries. The unsound monitoring system under unattended conditions is also an important reason for shortening the service life.
The focus here is to analyze the effect of ambient temperature. Valve-regulated sealed lead-acid batteries have poor heat dissipation due to structural reasons (tight plate assembly, poor fluid design, and complete sealing), and their charge voltage is closely related to temperature. Specifically, the charge voltage of valve-regulated sealed lead-acid batteries has a negative temperature coefficient of -3 mV/°C. That is, for every 1°C increase in temperature, the individual battery charging voltage drops by 3mV. Otherwise, it is easy to cause thermal runaway (thermal runaway: when the battery is charged, the internal gas compound in the battery itself is an exothermic reaction, causing the internal temperature of the battery to rise. If the float charge voltage is constant, the charge current will increase and the gas release amount will increase, prompting the temperature. The temperature rises even higher, but it is not easy to dissipate heat due to structural reasons, which will cause thermal runaway, and if the temperature is too high, it will cause the active material of the plate to fall off, the plate deformation and corrosion, and the battery life will become shorter.So, it must be based on the ambient temperature. Changes in the float voltage compensation, there should also be anti-high temperature measures).
Fourth, related measures
According to the above analysis and on-site investigation and statistics, from the user's point of view, the main reasons for the shortened service life of the battery are the following points. Corresponding measures can be taken in response to these factors.
1. The depth of activation and the cycle are fixed. In response to this problem, it is possible to artificially shorten the activation cycle, for example, from once a year to quarterly, once a month; change the depth of activation, for example, a small-volume discharge (30% of the depth of discharge) per month; The capacity discharge (50% of the depth of discharge) is performed once a year for large-capacity discharge (100% of the depth of discharge, and the depth of discharge must be strictly controlled to prevent the battery from becoming defective).
2. The operating status is different. The related maintenance and management system can be improved, and the monitoring of the substation battery at the end of the grid can be increased to increase the number of inspections. In the maintenance and repair process, the performance difference of the battery pack is just like the short board effect of the barrel. The consistent performance is the most effective maintenance. The method of manual inspection is relatively backward, and the user can also install advanced battery on-line monitoring system to monitor its running status in real time and transmit it to the monitoring center through remote control. For example, the ABMS series of Changkai Electronic Technology Co., Ltd. has an independent management system with online management and automatic detection, which can help you better manage and maintain battery packs.