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集装箱式储能安全设计
在国家“双碳”战略下,以光伏、风电为代表的新能源蓬勃发展,随着光伏、风电大量的接入,电网的调频、调峰资源需求急剧上升, 储能系统在解决新能源消纳、增强电网稳定性、提高配电系统利用效率等方面发挥的作用日益重要。电化学储能锂离子系统,由于部署环境要求低,适用场景多,其应用规模正在快速增长,在大规模应用的同时,储能电站的安全问题也引起人们的普遍关注。

新能源电源侧储能、电网侧储能、大型离网和微网储能电站,常采用集装箱式储能,数万支电芯通过串/并联的方式,安装在集装箱内,锂离子电池正负极之间只有一层很薄的隔膜绝缘,电气隔离主要依赖绝缘材料和电气开关,绝缘材料在高温下有可能碳化,变成导电材料,隔离开关在高压下也可能击穿,功率器件开关管,在反向高压,浪涌冲击下,也有可能非正常导通。在长期数千次的充放电循环中,尤其是过充过放过温状态下,有可能造成电芯短路故障,局部失控,其中任何一个电芯出现安全问题,如果没有严密的安全防护措施提前应对,都可能引起系统的连锁反应,造成爆炸事故。

增加绝缘材料和强度,构建储能电站的铜墙铁壁,有可能解决储能电站的安全问题,但会增加电站的成本,不利于储能的大规模推广应用。集装箱式储能的安全问题,需要从系统方案、材料选型、安防设计等多方面着手,才能综合兼顾安全和成本两个重要指标。目前储能电站采取的主要安全技术和措施有:新型模块化储能技术,气凝胶隔热绝缘材料,传统的电气保护、热管理和高效消防安全系统等。

1、模块化储能技术

第一代锂电将电池PACK简单串联成簇,第二代锂电在一代锂电的基础上增加了部分智能电池管理单元。然而锂电系统的直流母线高压与电池绝缘风险、簇间放电不均流、梯次电池无法混用等一系列问题无法彻底解决,给锂电的安全稳定应用打上了问号。新型模块化储能,每一个电池模组对应一个BMS电池管理系统,配备的电气物理双隔离、故障模块自动退出、电池绝缘失效预警等多重功能,保障了锂电池的安全性和可靠性,模块自适应主动均流,支持梯次电池混用和不同品牌电池混用,分期扩容及分钟级维护,一举解决了锂电池诸多应用难题。

2、气凝胶(Aerogel)

气凝胶是一种具有纳米多孔网络结构、并在孔隙中充满气态分散介质的固体材料,是世界上最轻的固体。气凝胶被公认为是世界上已知的质量最轻的固体材料,是新一代高效节能绝热材料。气凝胶兼具阻燃性能高、体积轻及用量少的特点,成为动力电池电芯隔热材料的最佳选择,目前已经被电池企业和新能源汽车厂家所采用。在电芯之间以及模组、PACK的上盖采用气凝胶防火隔热材料。模组层面的安全设计主要是隔离,也就是通过隔离对问题单体“分而治之”,这就是模组的隔热隔火设计。模组热失控管理主要依靠单体电池之间的气凝胶实现。气凝胶通过PET封装,整体导热系数小,可以很好的延缓单体之间的热量传递,通过将个别出现问题的电芯隔离,杜绝影响给其他单体电芯,从而保障了电池模组层级的安全。

3、储能电站电气保护

储能电站的保护分区:直流侧分为直流储能单元保护区、直流连接单元保护区和汇流区;交流侧分为交流滤波保护区和变压器保护区。相邻保护区之间存在相互重叠的部分,保证了所有电气设备均在保护范围内。保护区的划分与继电保护的配置密切相关,一方面保护区内电气设备的类型不同,发生故障后的电气量及非电气量的特征不同;另一方面,相邻保护区间配合随着保护区划分的不同也存在巨大的差异。因此,储能电站保护的配置及配合都建立在保护分区的基础上。

直流储能单元保护配置:过欠压保护、热保护及过流保护、电压电流变化速率保护、充电保护;直流连接单元保护配置:配置熔断器、低压直流断路器、低压直流隔离开关及中跨电池保护,对于多储能单元,直流连接单元尽量分开连接,避免发生故障时损失更多的供电容量;双向变流器(PCS)保护配置:输入及输出侧过欠压保护、过频及欠频保护、相序检测与保护、防孤岛保护、过热保护、过载及短路保护。

兴储世纪工作人员在项目投运前对储能设备进行调试

4、锂电池热管理

为了满足项目现场地环境条件及系统运行工况下,电池组及配套设备的正常使用,集装箱通过以下几个方面进行热管理控制,主要含空调、热管理设计、保温层等方面,热管理系统使集装箱内的温度能保证电池组及配套电气设备的正常运行。

集装箱内的温度控制方案如下:通过温度探头实时监测集装箱内各设定点的温度,当设定点的温度高于空调的设定启动温度时,空调运行制冷功能,并通过特制的风道对集装箱内部进行降温,温度达到设定值的下限时,空调停止工作。当设定点的温度低于空调的设定启动温度时,空调运行制热功能,并通过特制的风道对集装箱内部进行升温,温度达到15℃,空调停止工作。

锂电池在运行过程中由于内部电化学反应存在和环境温度升高的影响,会提升电池的内腔温度而使反应加剧;而在高寒地区,由于环境低温的影响,也会降低电池内的反应速度。前者可能导致热失控而使电池提早失效并产生安全问题,后者也会降低电池的充放电能力和效率。

5、集装箱消防安全

相较铅酸电池,同体积的锂电池密度更大,储存能量更多,爆燃起火后,其火焰成喷射状,火源温度也更高,同时还会释放大量有毒有害气体,因此安全隐患更大。扑救锂电池火灾时,一要及时扑灭明火,避免火灾快速蔓延;二要降低热失控反应速率,使锂电池内部热失控反应产生的热量有序释放 ;三要持续降低锂电池温度,避免锂电池火灾发生复燃和快速蔓延。

集装箱内集成消防装置,多采用不低于三级的架构,包括预警、告警和动作,消防系统的装置,包含探测控制器,消防控制箱、声光报警铃/灯、温度及盐雾传感器、全氟己酮气体灭火装置。探测控制器的安装原则应选择靠近电池组位置,结合实际机架的结构,可以选择电池柜上顶部空间进行安装。灭火器装置采用柜式七氟丙烷灭火器和气溶胶灭火装置。其中,柜式全氟己酮安装在电池室内,气溶胶自动灭火系列装置安装在电器室内。

集装箱内配置全氟己酮消防装置,烟雾传感器、温度传感器一旦检测到高温火灾故障信号,集装箱可通过声光报警和远程通信的方式通知用户,同时,切掉正在运行的锂电池成套设备。30S后消防装置释放全氟己酮气体灭火。集装箱内逃生门上需要显著的指示:消防警示信号响起后请30S内离开集装箱。

气溶胶自动灭火系列装置是一种新型热气溶胶灭火装置,是一类具有超高灭火效能和可靠性的消防领域突破性产品。火灾发生时,及安盾消防热气溶胶自动灭火装置通过电启动或感温启动方式引发灭火药剂发生作用,迅速产生大量亚纳米级固相微粒和惰性气体混合物,以高浓度烟气状立体全淹没式作用于火灾发生的每个角落,通过化学抑制、物理降温、稀释氧气多重作用,快速高效扑灭火灾,对环境及人员无毒害。

气溶胶还能够做到三级防火保护,以电池簇为防护单元,采用集中式气体探测采样分析,通过预设在每个PACK箱内的探测器,实时探测锂电池内部化学成分的变化,由芯片对各种参数的变动情况进行分析计算,对电池箱内的电芯进行有效的火灾较早期抑制防控,以阻止锂电池热失控扩展及储能柜爆炸。一是电池模组消防:根据电池模组尺寸和电芯容量,将气溶胶安装于电池模组,可有效扑灭电芯第一次着火(第一级防护),电池从内而外灭火是最有效的灭火方法,可以令热失控损失减至最低;二是电池机柜消防:将气溶胶安装于电池柜,防护空间3m,可有效扑灭电池柜内第二次复燃或电气起火(第二级防护);三是储能集装箱消防:集装箱内可以安装气溶胶组来作为全体防护,作为整箱火情的抑制(第三极防护)。有了第一级和第二级防护,第三极防护启动机会大幅减低,提高整体消防安全性。

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.

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