Discharge Development and Characteristics of Oil-immersed Pressboard Surface with Different Moisture Contents
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摘要: 电力变压器内部水分增加将严重影响油纸绝缘性能，导致绝缘纸板表面更容易出现沿面放电故障. 为了研究交流电压下不同水分含量绝缘纸板的沿面放电特性，建立了典型的针板沿面放电模型. 基于脉冲电流法实时测量沿面放电模型的放电特征图谱，同时采用高速相机记录绝缘纸板上白斑形成和发展过程. 分析了不同水分含量纸板起始放电电压和闪络电压的变化趋势，以及沿面放电特征参数变化趋势. 分析结果表明：纸板含水量的增加导致起始放电电压显著降低；不同水分含量纸板的沿面放电和白斑形成发展过程均可划分为4个阶段，沿面放电过程和白斑形成发展的4个阶段存在一一对应关系；通过观察分析绝缘纸板微观结构，发现试验后的纸板纤维严重断裂，且纸板中水分含量越高，纸板表面受损害越严重，纸板含水量从小于0.5%增加到3.8%时，起始放电电压下降了61.3%.Abstract: The increase of moisture content in power transformer will seriously affect the insulation performance of oil-paper, more easily resulting in the surface discharge fault of insulated pressboard. In order to study the discharge characteristics of insulated pressboard with different moisture contents under AC condition, a typical model of needle board surface discharge was established. Based on the pulse current method, the characteristic charts of the surface discharge model were measured in real time, and a high-speed camera was used to record the formation and development of white mark on insulated pressboard. The variation trend of initial discharge voltage and flashover voltage under different moisture contents of pressboard was analyzed, and then that of the related discharge characteristic parameters was analyzed. The results show that the increase of moisture content in pressboard significantly reduces the onset voltage. The process of surface discharge and white mark formation and development on pressboard with different moisture contents can be divided into four stages. There is a one-to-one relationship between the four stages of surface discharge and white mark formation and development. By observing and analyzing the microstructure of insulated pressboard, it is found that the fibers of the pressboard were severely broken after tests. The higher the moisture content of the pressboard before tests, the more serious the damage to the surface of the pressboard. When the moisture content of pressboard increases from less than 0.5% to 3.8%, the initial discharge voltage decreases by 61.3%.
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Key words:
- surface discharge /
- moisture content /
- discharge characteristics /
- white mark /
- microstructure
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图 2 针板沿面放电模型结构图和实物图
Figure 2. Structure diagram and physical picture of needle board model
图 3 局部放电特征参数随电压变化情况
Figure 3. Relationship between partial discharge characteristics and supply voltage
图 4 针板沿面放电模型的局部放电四个阶段的PRPD图谱
Figure 4. PRPD patterns for four stages in needle board discharge model
图 5 绝缘纸板上白斑形成发展过程
Figure 5. Formation and development of white mark on pressboard surface
图 6 不同水分含量纸板试验后表面微观形貌（1 000倍放大）
Figure 6. Surface micrograph of pressboard with different water contents after tests (1 000 times)
表 1 处理后变压器油各项参数
Table 1. Parameters of transformer oil after filtering
属性 指标 实测值 试验标准 水分含量/
×10−6≤ 30 14 GB/T 7600—2014 击穿电压/kV ≥ 30 71 GB/T 507—2002 介质损耗 ≤ 0.005 0 0.000 8 GB/T 5654—2007 界面张力/
（mN•m−1）≥ 40 46 GB/T 6541—1986 酸值/（mg•g−1） ≤ 0.010 0 0.007 NB/SH/T 0836—2010 
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表 2 纸板水分含量对起始放电电压和闪络电压的影响
Table 2. Effect of moisture content in pressboard on initial discharge voltage and flashover voltage
水分含量/% 起始放电电压/kV 闪络电压/kV 平均值 标准差 平均值 标准差 < 0.5 31 1.91 63 0.48 1.1 28 1.41 61 0.98 1.5 23 2.33 59 0.33 1.9 17 1.77 58 0.47 2.4 14 1.64 57 0.28 3.8 12 2.63 57 0.44
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表 3 不同电压下纸板中水分含量对放电功率的影响
Table 3. Effect of moisture content in pressboard on discharge power under different voltages
电压/kV 水分含量/% 放电功率/nW 15 < 0.5 0 1.1 0 1.5 0 1.9 0 2.4 0 3.8 467 25 < 0.5 0 1.1 0 1.5 0 1.9 1 221 2.4 1 954 3.8 2 650 35 < 0.5 10 412 1.1 12 530 1.5 15 460 1.9 17 235 2.4 20 645 3.8 21 930
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