Under the national "double carbon" strategy, new energy represented by photovoltaic and wind power is booming. With the massive access of photovoltaic and wind power, the demand for frequency modulation and peak load regulation resources of the power
grid has risen sharply. The energy storage system plays an increasingly important role in solving the consumption of new energy, enhancing the stability of the power grid, and improving the utilization efficiency of the distribution system. Electrochemical
energy storage lithium-ion system, due to its low deployment environment requirements and many applicable scenarios, its application scale is growing rapidly. At the same time of large-scale application, the safety of energy storage power stations has
also attracted widespread attention.
New energy power side energy storage, grid side energy storage, large off grid and micro grid energy storage power stations often use container type energy storage. Tens of thousands of electric cells are installed in containers through series / parallel connection. There is only a thin layer of diaphragm insulation between the positive and negative electrodes of lithium-ion batteries. Electrical isolation mainly depends on insulating materials and electrical switches. Insulating materials may be carbonized and become conductive materials at high temperatures, The disconnector may also break down under high voltage, and the power device switch tube may also conduct abnormally under reverse high voltage and surge impact. During thousands of charging and discharging cycles for a long time, especially under the condition of overcharge, over discharge and over temperature, it is possible to cause short-circuit fault of the cell and local out of control. If any cell has a safety problem, if there is no strict safety protection measures to deal with it in advance, it may cause a chain reaction of the system and cause an explosion accident.
Increasing the insulating materials and strength and building an iron wall of the energy storage power station may solve the safety problems of the energy storage power station, but it will increase the cost of the power station and is not conducive to the large-scale promotion and application of energy storage. The safety of container type energy storage needs to start from the system scheme, material selection, security design and other aspects, so as to comprehensively take into account the two important indicators of safety and cost. At present, the main safety technologies and measures adopted by the energy storage power station include: new modular energy storage technology, aerogel gel thermal insulation materials, traditional electrical protection, thermal management and efficient fire safety systems, etc.
1. Modular energy storage technology
The first generation lithium battery simply connected the battery packs in series into clusters, and the second generation lithium battery added some intelligent battery management units on the basis of the first generation lithium battery. However, a series of problems, such as the risk of DC bus high voltage and battery insulation, uneven current discharge between clusters, and the inability to mix echelon batteries, cannot be completely solved in the lithium battery system, which has cast a question mark on the safe and stable application of lithium battery. New modular energy storage. Each battery module corresponds to a BMS battery management system. It is equipped with multiple functions such as electrical and physical double isolation, automatic exit of fault modules, early warning of battery insulation failure, etc., which ensure the safety and reliability of lithium batteries. The modules are self-adaptive and active current sharing, support the mixed use of echelon batteries and batteries of different brands, phased capacity expansion and minute maintenance, and solve many application problems of lithium batteries in one fell swoop.
2. Aerogel gel
Aerogel gel is a kind of solid material with nano porous network structure and filled with gaseous dispersion medium in the pores. It is the lightest solid in the world. Aerogel gel is recognized as the lightest solid material in the world, and it is a new generation of energy-efficient thermal insulation materials. Aerogel gel has the characteristics of high flame retardancy, light volume and low consumption. It has become the best choice of thermal insulation materials for power battery cells. At present, it has been adopted by battery enterprises and new energy vehicle manufacturers. Aerogel gel fireproof and thermal insulation materials are used between the cells and the upper covers of modules and packs. The safety design at the module level is mainly isolation, that is to divide and rule the problem unit through isolation, which is the thermal insulation and fire isolation design of the module. The thermal runaway management of the module mainly depends on the aerogel gel between the individual cells. The aerogel gel is encapsulated by pet, and the overall thermal conductivity is small, which can well delay the heat transfer between the cells. By isolating individual cells with problems, it can eliminate the impact on other single cells, thus ensuring the safety of the battery module level.
3. Electrical protection of energy storage power station
Protection zones of energy storage power station: DC side is divided into DC energy storage unit protection zone, DC connection unit protection zone and confluence zone; The AC side is divided into AC filter protection zone and transformer protection zone. There are overlapping parts between adjacent protected areas, ensuring that all electrical equipment is within the protection range. The division of the protection zone is closely related to the configuration of relay protection. On the one hand, the types of electrical equipment in the protection zone are different, and the characteristics of electrical quantity and non electrical quantity after fault are different; On the other hand, there are also great differences in the coordination of adjacent protection zones with the division of protection zones. Therefore, the configuration and coordination of the protection of the energy storage power station are based on the protection zoning.
DC energy storage unit protection configuration: over and under voltage protection, thermal protection and over-current protection, voltage and current change rate protection, charging protection; DC connection unit protection configuration: configure fuse, low-voltage DC circuit breaker, low-voltage DC disconnector and mid span battery protection. For multiple energy storage units, DC connection units shall be connected separately as far as possible to avoid loss of more power supply capacity in case of failure; Two way converter (PCS) protection configuration: input and output side overvoltage and undervoltage protection, over frequency and under frequency protection, phase sequence detection and protection, anti islanding protection, overheating protection, overload and short circuit protection.
The staff of xingchu century commissioned the energy storage equipment before the project was put into operation
4. Lithium battery thermal management
In order to meet the normal use of the battery pack and supporting equipment under the environmental conditions of the project site and the system operating conditions, the container carries out thermal management control through the following aspects, mainly including air conditioning, thermal management design, insulation layer, etc. the thermal management system enables the temperature in the container to ensure the normal operation of the battery pack and supporting electrical equipment.
The temperature control scheme in the container is as follows: the temperature at each set point in the container is monitored in real time through the temperature probe. When the temperature at the set point is higher than the set starting temperature of the air conditioner, the air conditioner operates the refrigeration function and cools the interior of the container through a special air duct. When the temperature reaches the lower limit of the set value, the air conditioner stops working. When the temperature at the set point is lower than the set starting temperature of the air conditioner, the air conditioner operates the heating function and heats up the interior of the container through a special air duct. When the temperature reaches 15 ℃, the air conditioner stops working.
During the operation of lithium battery, due to the existence of internal electrochemical reaction and the increase of ambient temperature, the inner cavity temperature of the battery will be increased and the reaction will be intensified; In high cold regions, the reaction speed in the battery will also be reduced due to the influence of low ambient temperature. The former may lead to thermal runaway and lead to early battery failure and safety problems. The latter will also reduce the charging and discharging capacity and efficiency of the battery.
5. Container fire safety
Compared with lead-acid batteries, lithium batteries with the same volume have higher density and store more energy. After deflagration and fire, the flame will form a jet, and the fire source temperature is also higher. At the same time, a large number of toxic and harmful gases will be released, so the potential safety hazard is greater. When putting out lithium battery fire, first, put out the open fire in time to avoid the rapid spread of the fire; Second, the rate of thermal runaway reaction should be reduced so that the heat generated by the thermal runaway reaction inside the lithium battery can be released orderly; Third, the temperature of lithium battery shall be continuously reduced to avoid the re ignition and rapid spread of lithium battery fire.
The integrated fire-fighting devices in the container mostly adopt a three-level structure, including early warning, alarm and action, devices of the fire-fighting system, including detection controller, fire control box, audible and visual alarm bell / lamp, temperature and salt mist sensor, and perfluorohexanone gas fire-extinguishing device. The detection controller shall be installed close to the battery pack in principle. Combined with the structure of the actual rack, the top space on the battery cabinet can be selected for installation. Cabinet type heptafluoropropane fire extinguishers and aerosol fire extinguishers are used. Among them, cabinet type perfluorohexanone is installed in the battery room, and aerosol automatic fire extinguishing series devices are installed in the electrical room.
The container is equipped with a perfluorohexanone fire-fighting device. Once the smoke sensor and temperature sensor detect a high-temperature fire fault signal, the container can notify the user through audible and visual alarm and remote communication. At the same time, cut off the running lithium battery equipment. After 30s, the fire-fighting device releases perfluorohexanone gas to extinguish the fire. Obvious instructions are required on the escape door in the container: please leave the container within 30s after the fire warning signal sounds.
Aerosol automatic fire extinguishing device is a new type of hot aerosol fire extinguishing device, which is a breakthrough product in the field of fire protection with ultra-high fire extinguishing efficiency and reliability. In case of fire, Andun fire control hot aerosol automatic fire extinguishing device will trigger the action of fire extinguishing agent through electric startup or temperature sensing startup, quickly produce a large number of sub nanometer solid particles and inert gas mixture, act on every corner of the fire in the form of high concentration flue gas, and quickly and efficiently extinguish the fire through multiple actions of chemical inhibition, physical cooling and oxygen dilution, without poisoning the environment and personnel.
Aerosol can also achieve three-level fire protection. Taking the battery cluster as the protection unit, the centralized gas detection sampling analysis is adopted. Through the detectors preset in each pack box, the changes in the internal chemical composition of the lithium battery are detected in real time. The chip analyzes and calculates the changes of various parameters, and effectively inhibits and prevents the early fire prevention and control of the cells in the battery box, so as to prevent the uncontrolled expansion of the lithium battery and the explosion of the energy storage cabinet. First, fire fighting of battery module: according to the size of battery module and the capacity of battery cell, installing aerosol in battery module can effectively extinguish the first fire of battery cell (first level protection). The most effective fire fighting method is to extinguish the fire from the inside out of battery, which can minimize the loss of heat out of control; Second, battery cabinet fire protection: install aerosol in the battery cabinet with a protective space of 3M, which can effectively extinguish the second re ignition or electrical fire in the battery cabinet (second level protection); Third, fire protection for energy storage containers: aerosol groups can be installed in the containers as overall protection and as the suppression of the whole container fire (the third pole protection). With the first and second level protection, the opportunity of starting the third pole protection is greatly reduced and the overall fire safety is improved.