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文章采用工频耐压实验平台测量复合涂层样品的绝缘击穿场强(表征绝缘强度),该平台由工频变压器系统、耐压测试系统、控制和测量系统三大部分构成,其具体结构如图5所示。根据GB/T 1408.1-2016标准[27],对样品施加幅值可控的交流电压,为防止试验样品发生沿面闪络,“板−板电极”浸入矿物油中,电压升高速率1 kV/s,样品击穿后静置2 min,所有实验在室温25±5 ℃下进行[28-30]。
为减小偶然因素产生的试验误差,每组式样进行重复试验9次[31],对样品的击穿电压进行统计,以失效概率63.2%时击穿场强作为特征击穿场强,进行双参数Weibull分布参数计算如下:
$$ P(U) = 1 - \exp \left( { - {{\left( {\frac{U}{\eta }} \right)}^\beta }} \right) \times 100\text{%} $$ (1) 式中:
P(U)——累积概率值(%);
U ——击穿电压场强值(kV/mm);
η ——尺度参数,代表特征击穿场强值(kV/mm);
β ——形状参数,表征数据分散性。
经过耐压测试,掺杂不同质量分数热敏微胶囊的复合涂层的绝缘强度Weibull分布情况如下图6所示。由图6可知,随着热敏微胶囊的掺杂质量分数的增加,复合涂层的绝缘强度随之下降。相较于纯环氧树脂的击穿场强,掺杂质量分数为0.25%热敏微胶囊的复合涂层的击穿场强仅下降0.77%,绝缘强度几乎不变;而掺杂质量分数为1.00%热敏微胶囊的复合涂层的击穿场强下降了6.76%,绝缘强度显著下降。这可能是由于掺杂微胶囊质量分数较小时,微胶囊在环氧树脂基体中分散均匀,导致其MF外壳上的极性基团与环氧分子产生相互渗透的分子链,从而形成互穿网络[32-34],使得绝缘性能保持不变。随着掺杂微胶囊质量分数的增加,微胶囊会在基体中发生团聚情况,且交联过程中引入基体大量内部缺陷,导致复合涂层的整体绝缘击穿强度下降。
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文章采用Novocontrol Concept 80宽频介电谱仪分析复合材料的介电性能。采用标定转换模块进行校准,防止泄漏电流造成测量误差。实验频率设置为10−1~107 Hz,测试环境温度为(25±5) ℃,湿度为(60±3)%RH。测得掺杂微胶囊不同质量分数的复合涂层的相对介电常数和介电损耗角正切值Tanδ分别如图7、图8所示。在测试电压频率为50 Hz时,纯环氧树脂(EP)和掺杂质量分数为0.25%、0.50%、0.75%和1.00%热敏微胶囊的复合涂层的相对介电常数分别为4.210、4.251、4.342、4.448和4.527。
用介电损耗正切值表征介电损耗的大小,在测试电压频率<50 Hz时,随着热敏微胶囊掺杂质量分数的增加,复合涂层的介电损耗越大;在测试电压频率≥50 Hz时,纯环氧树脂(EP)和掺杂质量分数为0.25%、0.50%、0.75%和1.00%热敏微胶囊的复合涂层的介电损耗角的正切值近似一致。在工频50 Hz条件下,掺杂质量分数为0.25%热敏微胶囊的复合涂层介电损耗最小。图7、图8共同表明在微胶囊掺杂质量分数为0.25%时保持了环氧复合涂层的优良介电性能。
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图9、图10分别显示了掺杂质量分数为0.25%热敏微胶囊的复合涂层样品在升温和降温过程中的颜色变化。
图 9 0.25%质量分数的微胶囊样品升温变色过程
Figure 9. Ramp-up discoloration of microencapsulated samples with a mass fraction of 0.25%
图 10 0.25%质量分数的微胶囊样品降温变色过程
Figure 10. Cooling discoloration of microencapsulated samples with a mass fraction of 0.25%
从图9中可以看出,复合涂层升温变色过程。受热温度逐渐升高,涂层从红色逐渐变得白色透明,颜色的突变在60~65 ℃之间完成。从图10中可以看出,随着温度的降低,样品颜色逐渐恢复到红色,与加热前相比,颜色几乎没有差别,其颜色的突变同样在60~65 ℃之间完成。反复测试表明,即使在经过多次加热和冷却循环,该样品仍保持热敏变色的特性,即制备的复合涂层拥有可逆的变色能力。
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本节按照GB/T 11026.1-2016标准设计复合材料热老化试验,探索复合材料耐老化性能[35]。复合涂层样品尺寸为2.5 mm×2.5 mm×1 mm(长宽厚),样品的热敏微胶囊质量分数为0.25%。设置老化温度为超过变色温度约10 ℃、40 ℃,分别确定老化温度为70 ℃、100 ℃,热老化实验环境为电热干燥箱。设置老化时间周期设置为1天,3天,5天,···,15天,测量试验前后的质量损失率。为减小实验误差,每组7个样品取平均数。
在70 ℃、100 ℃两种不同的老化温度下,复合涂层的质量损失率如图11所示。复合涂层的质量损失率均随着老化时间的延长而逐渐增高,质量损失率仍然保持在0.20%以下。老化温度越高,复合涂层的质量损失率随之越高。这可能是因为人工模拟的老化在高温下进行,复合涂层内部的局部区域的分子链将会发生断裂、重排,导致试样的质量有所降低。由2.3可知热敏微胶囊外壳(三聚氰胺-甲醛树脂)热稳定性好,热分解温度为300 ℃左右。在老化实验时,热敏微胶囊内部尚处于熔融态,但由于老化温度远未达到胶囊外壳的热分解温度,微胶囊外壳仍呈现出致密坚固形态,进而保护内部热敏变色芯材。综上所述,复合涂层具有长期耐老化特性,可实际用于磷酸铁锂电池储能电站的状态监测与局部过热预警。
制备的热感知变色涂层材料是以环氧树脂为基体掺杂质量分数为0.25%热敏微胶囊构成的,材料本身的制备成本较为低廉。而且,在磷酸铁锂电池模组外绝缘层上再刷层较薄的热敏涂层后,在锂电池组模块外绝缘层达到60 ℃时立即发生颜色突变,不需要施加外界激励或传感器检测,即可实现对温度场的“无源”可视化表征,实时反馈温度场信息。文章提供了一种局部过热预警技术路线,相比于外施加制作成本和运维成本均高昂的传感器而言,可从材料本身性能出发,赋予电池模组温度感知特性,显著降低储能电站局部过热预警的技术成本。
Research on Thermosensitive Coatings for Thermal Runaway Warning in Energy Storage Power Station
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摘要:
目的 磷酸铁锂电池储能电站是新型电力系统消纳大规模新能源的重要基础,然而电池单元的热失控严重威胁储能电站的运行安全。对储能电站局部过热进行实时监测和科学预警具有重要意义。 方法 在此工作中,制备了一种具有感知过热温度并产生颜色变化的热敏微胶囊,将其适量添加到环氧树脂基体中构成具有感知外部过热温度场特性的复合绝缘材料。 结果 测试结果表明,所制备的热敏微胶囊/环氧树脂绝缘示温涂层的颜色可以灵敏地随外界温度变化而发生变化,在60 ℃左右时发生颜色突变。当热敏微胶囊的掺杂质量分数为0.25%时,复合涂层的绝缘强度、介电特性和纯环氧树脂材料相当,保持良好的本征电气性能。 结论 研究提出的热敏变色复合绝缘涂层可对外界局部过热状态的温度可视变化,为储能电站的热失控预警应用提供了一条新的技术路线,具有一定的工程应用价值。 Abstract:Introduction Lithium iron phosphate battery storage power plants are an important basis for new power systems to consume large-scale new energy, however, the thermal runaway of battery cells seriously threatens the operational safety of storage power plants. It is important to conduct real-time monitoring and scientific warning of local overheating in storage power plants. Method In this work, a thermal microcapsule with the ability to sense overheating temperature and produce colour changes was prepared and added in appropriate amounts to an epoxy resin matrix to form a composite insulating material with the characteristics of sensing external overheating temperature fields. Result Test results show that the colour of the prepared thermosensitive microcapsule/epoxy insulating temperature indication coating can change sensitively with external temperature changes, with a sudden colour change occurring at around 60 °C. When the doping mass fraction of the thermosensitive microcapsules is 0.25%, the insulation strength and dielectric properties of the composite coating are comparable to those of the pure epoxy resin material, maintaining good intrinsic electrical properties. Conclusion The thermosensitive colour-changing composite insulation coating proposed in the study can visibly change the temperature of the external local overheating state, providing a new technical route for the application of thermal runaway warning in energy storage power plants, which has certain engineering application value. -
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