Discussion on the technology of battery life extension in transformer substation

1 The introduction

With the power grid companies to ensure the safe and reliable supply of power, deepen lean management and the goal of potential efficiency, the safety and stability of transformer substation DC power supply system has become a subject of concern, and the DC power supply matching battery is particularly important in the performance of DC power supply. At present, transformer substation DC power system matching battery, mostly using glass fiber (AGM) separator, grid type plate valve control lead acid battery, this kind of battery has mature technology, low price and many manufacturers. But this kind of battery quality is uneven, some brand service life can be up to 10 years, some brands may use only 2 to 3 years, There are even some illegal vendors to shoddy, in the battery inside mixed with broken glass, cement and other attempts to get through, it also reflects the current user for storage battery lack of easy to operate effective detection means, Then for the power grid company's battery procurement, incoming material inspection and other work increased the difficulty.

Battery usage, also has close relationship with the battery working environment, in some countries it has large substation coverage, using the environment difference is big, such as environmental temperature of the transformer substation, There are huge differences for different places, Temperatures also vary greatly from season to season, And the use of the battery is very sensitive to the ambient temperature, so even a brand of the same specifications of the battery, the use condition varies from place to place.

For the above situation, The market demand for products with good environmental adaptability, long life and good stability is increasing. Domestic battery manufacturers are also doing research and development of different technical routes for the above situation and thinking, such as lead carbon technologies, increasing positive plate, tubular positive plate and so on, also including the lithium iron phosphate, ternary lithium and other lithium battery of new technology to explore and try. Aiming at the above market conditions, some battery companies improves the traditional valve-controlled maintenance-free battery from the aspect of improving the lead-containing purity of the battery positive plate, and improves the overall battery life through the corrosion resistance of the high-purity grid plate, in order to develop a model with high life and high stability. And has good high-temperature performance and high-rate discharge ability of pure lead battery new products.

Compared with the traditional lead-acid battery, the grid of pure lead battery is composed of purity up to 99.99% or more pure lead. It is extremely corrosion resistant and has longer service life. It can operate in a high temperature environment of 30~35℃, which can greatly save air conditioning investment and energy consumption cost. At the same time, the thin plate design makes there are more plates in the battery, with a larger chemical reaction area, brings excellent high-current discharge performance, more suitable for substation short-time high-current backup demand.

2 The feasibility of pure lead battery for the current DC power supply in the substation

Batteries operating at higher temperatures (such as 30~35℃, rather than the traditional 20~25℃) can effectively save air conditioning construction investment and energy costs in the operation process; In addition, the use of long-life batteries can reduce the frequency of battery failure replacement and save the replacement investment. The use of high temperature resistant and long life pure lead battery makes it possible to improve the quality and efficiency of substation operation.

Will raising the temperature of the substation room cause unmeasurable consequences to the equipment in the substation room? Where is the bottleneck of high temperature substation?

The analysis of working temperature of various equipment in substation room is as follows:

（1） DC equipment: Many DC equipment itself can operate at high temperatures.
High temperature sensitivity:：★★☆☆☆

（2） Air conditioning equipment: most air conditioning equipment can have an operating temperature of up to 50℃.
High temperature sensitivity：★☆☆☆☆

（3） Power supply and distribution equipment, lighting and other: Power supply and distribution devices such as the DC host, switching power supply, and AC distribution box do not have high requirements on the ambient temperature. They can run normally when the temperature is lower than 40℃. Lighting and other equipment are not sensitive to temperature.
High temperature sensitivity：★☆☆☆☆

（4） Battery: Lead acid battery with lower cost and higher safety is mainly used in the substation. The best working temperature of lead-acid battery is 20~25℃; Every 10℃ increase in operating temperature, the life of lead-acid battery is halved; At the same time, lead-acid batteries will also face water loss, positive plate corrosion, negative sulphuric acid, battery container bulging and other problems at high temperature, resulting in battery capacity reduction, failure and even safety accidents.
High temperature sensitivity：★★★★★

From the above analysis, it can be seen that the sensitivity of the battery to high temperature is the main bottleneck restricting the improvement of the working temperature of the battery room. The selection of batteries that can work at high temperature can effectively improve the operating temperature of the battery room, reduce air conditioning energy consumption, and achieve energy saving and consumption reduction in the substation.

3 Introduction of pure lead battery

The basic chemical reaction of lead-acid battery is the conversion and electron exchange process of positive plate (PbO₂), negative plate (Pb) and sulfuric acid electrolyte (H₂SO₄) during the charging and discharging process.

Figure 1 Basic chemical reaction of lead-acid batteries

The basic structure of the lead-acid battery is shown in Figure 2 below, mainly including:

n Components that generate current, key components that affect battery life and performance:

– Positive active substance (positive plate)

– Negative active material (negative plate)

– Electrolyte (sulfuric acid)

n Conductive components, important components affecting battery life and performance:

n Other key components that affect battery life and performance:

– Separator: (1) separate positive and negative plates to avoid short circuit; (2) There are enough pores to ensure the passage of carrier ions

– Battery case and cover: ensure the safety of the battery internal structure and avoid battery damage; The connection of battery case and cover should ensure air tightness; Flame retardant materials can be selected to avoid fire combustion.

– Safety valve (valvle-controlled sealed battery) : (1) retaining valve , normally closed to prevent electrolyte evaporation and prevent external air from entering, to avoid battery drying up; (2) Keep the battery at a certain internal pressure to improve the sealing reaction efficiency;   (3) When the pressure inside the battery is too high, excess gas is discharged to prevent explosion

Figure 2 Basic structure of lead-acid batteries

In the basic structure of the lead-acid battery, positive and negative plate and electrolyte are the direct substances involved in the reaction, and its performance directly affects the capacity, performance and life of the battery; The grid in the plate plays a key role in supporting and conducting, and is an important component affecting the performance and life. Positive plate corrosion is one of the most common failure modes of the battery, this is because the positive plate is the main part to provide energy, usually the capacity of lead-acid battery is controlled by the positive electrode capacity; The positive plate is in the state of oxidation in the reversible reaction of the battery. The corrosion speed (corrosion resistance) of the positive plate grid as the skeleton determines the sustainable time of its support and conductive ability of the plate, that is, determines the life of the battery.

Therefore, the positive plate of lead-acid battery is usually thicker than the negative plate, and it is generally believed that the thicker the positive plate, the longer the battery life. Plate thickness is positively correlated with battery life to some extent, but it is not the only necessary condition. The thicker the positive plate, the more difficult it is to contact with sulfuric acid electrolyte in the middle of the positive plate grid, the more difficult to be corroded, so the life can be extended; But the positive plate in the middle part of the positive active material is difficult to contact with the electrolyte, can not get the reaction, the utilization rate of positive active material is low, low energy, high current discharge performance is not good.

As the conductive carrier of the plate and the supporting part of the active material, the corrosion resistance of the alloy material plays a crucial role in the cycle life of the battery. The direct consequence of grid corrosion failure is that the battery internal resistance is too large or disconnection, it is difficult to carry out or completely can not conduct electricity, leading to the phenomenon that even if the active material is not failed, the battery can not be normally charged and discharged.

Common grid include:

– Early pure lead grid: the earliest grid is made of pure lead, pure lead positive grid corrosion resistance and high hydrogen evolution of the negative electrode overpotential makes it has very good characteristics in floating charging applications; But because lead is soft, there are some problems such as poor castability and mechanical properties of pure lead grid. At present, due to the needs of manufacturing technology and discharge performance, and the improvement of people's understanding of the performance of lead alloy, other metal components with different contents are added to the grid, resulting in the difference of corrosion resistance.

– Lead antimony Pb-Sb alloy: the main advantages are tensile strength, ductility, hardness better than pure lead, the main disadvantages are high resistance, make water more easily decomposed (battery drying up).

– Lead calcium Pb-Ca alloy: the main advantages are small resistance, high hydrogen evolution superpotential, so less water decomposition; The main disadvantage is the poor creep resistance, that is, the positive plate grows up seriously.

– Lead-calcium-tin-aluminum Pb-Ca-Sn-Al alloy: improved the poor creep resistance of Pb-Ca alloy, but still could not overcome the lack of charge and discharge cycle performance of maintenance-free valve-controlled sealed battery

– New pure lead thin grid: Taking the HPPL pure lead grid as an example, we can understand the unique technology and advantages of pure lead battery. The next generation of high-performance lead-acid battery with HPPL (High Performance Pure Lead) technology will adopt high-purity Lead (> 99.99%) as raw material and form a very dense corrosion resistant crystal structure through multi-stage strong roller pressing. This dense crystal structure, The contact of lead particles in the grid is more compact, the surface is more flat, and there are fewer pores in the structure. Overcome the soft weakness of pure lead, strengthen mechanical structure strength; It effectively prevents sulfuric acid from corroding the material inside the grid and improves the corrosion resistance of the grid, so that the battery has a higher life; Even under the condition of intensified molecular movement at high temperature, the corrosion of sulfuric acid on the material inside the grid can be greatly slowed down, so it has the performance of high temperature resistance. At the same time, as a new generation of products, ESS (Extended Stability Standard) technology can still be introduced into the production process of pure lead battery, so that the long life and high reliability in the use of further enhanced.

4 Summary

Through the selection of pure lead plate technology, not only can improve the current substation battery life cycle, but also can further reduce the risk of failure; Moreover, through the efficient use of raw materials, prolong the battery replacement cycle, reduce the consumption of resources, is conducive to energy conservation and environmental protection. For battery used in substation, pure lead technology is an innovative product, which is a targeted technical breakthrough; For the traditional valve-controlled lead-acid battery industry, it is a fruitful technical innovation; It is significant to improve the quality and efficiency of DC power supply in substation, energy saving and environmental protection.