At present, in 110 kV and 35 kV middle and low voltage substations, the equipment equipped with batteries is mainly dc screen and communication device. This paper discusses the service life of dc battery.

1 The operation requirement of the dc system in the station

As the standby power supply for the dc system in the station, the battery is required to be kept at a certain charging level at ordinary times, so that when the high-frequency switching power supply of the dc screen or the silicon rectifying device loses power and fails to output the dc power supply due to failure, the battery can be put into operation in time, so as not to affect the normal operation of the dc equipment and dc circuit in the station. Therefore, the performance of the battery itself should be able to meet its capacity, voltage in a certain period of time (including dc power supply device maintenance period), maintain at a high level. Only in this way can the safe and reliable operation of the dc system in the station be guaranteed.

2 Current status of battery operation

With the popularization of unattended substation, maintenance-free lead-acid battery is gradually adopted in the dc system of substation. Some substation operation, maintenance personnel understand "maintenance free" as "no maintenance", the actual operation of the station battery is often not satisfactory.

Take the 35 kV XX substation and 35 kVYY substation under the jurisdiction of XXX company as an example. The maintenance-free lead-acid batteries are replaced at the same time at the two stations. During the two-year operation, the batteries are only deeply activated once a year. However, in the third year, the voltage of some batteries in XX substation began to decrease. By the end of the third year, the voltage of most batteries dropped below the standard value, and that of some batteries dropped below 8 V. At the beginning of the fourth year, the battery can not be charged to float, its performance indicators can not meet the operating requirements, had to replace a new battery.


3 Cause analysis of shortening battery life
 

1. Follow manufacturer's advice and customary practice

Because of the maintenance-free battery, and the dc system for automatic control charging mode, the operation is more reliable, according to the manufacturer's recommendations, only once a year for activation. As the first two years of good operating conditions, immediately approved the battery management mode. Because of the potential problems with the battery, the first two years of operation did not show up, and after many years of operation, the battery capacity dropped significantly.
 

      2. The degree of battery aging varies with the operating state

The substations of XX and YY under the jurisdiction of XXX company are 35 kV substations. They are at the end of the substations with a single operation mode and few operation opportunities. And 110 kVXX substation is the hub substation, the operation mode is changeable, the operation is frequent, the battery often discharges, and the discharge is very big, the activation frequency is high, the capacity is easy to maintain at a high level.

3. Lack of understanding of battery performance, improper management of daily operation and maintenance

According to the requirements of anti-accident measures in the dc system, the floating charging operation of the battery bank, except for the special provisions of the manufacturer, should use the constant voltage floating charging. During floating charging, the upper and lower limits of floating charging voltage of single battery should be strictly controlled to prevent the battery from being damaged due to too high or too low charging voltage, that is, to avoid long-term overcharging or undercharging. Taking the valvy-controlled sealed lead-acid battery commonly used now as an example, the practice has proved that the service life will be shortened by half when the difference between the actual floating charging pressure and the specified floating charging pressure is 5%.

The floating charging voltage of the battery is generally set according to U(25) = E + 0.1 (E is the rated voltage of the single battery). If the manufacturer has instructions, it shall be set according to the instructions. The average current limiting current can be set as I = (0.1 ~ 0.125)C10 (C10 is the discharge current of the battery at a rate of 10 hours), and the rated charging current cannot exceed 1.5c10. But in the daily maintenance often ignore this detail, can not according to different models, manufacturers of the battery to the specific requirements of different charging parameters, but the use of uniform uniform, floating charging parameters, or even set the charging parameters, eventually led to the destruction of the battery performance.

In addition, to prevent overdischarge. Setting of overdischarge voltage: take 2 V battery as an example, the discharge time of valve-controlled sealed lead-acid battery is 10 h, and the discharge voltage is 1.8 ~ 1.9 V.

4.Storage battery installation is not standard, storage and transportation of the battery damage and storage battery working environment temperature, ventilation conditions do not meet the requirements will also have a negative impact on the performance and life of the battery. The imperfect monitoring system under unattended condition is also an important reason for shortening the service life.