《高电压技术第2版 吴广宁2.3》由会员分享，可在线阅读，更多相关《高电压技术第2版 吴广宁2.3（65页珍藏版）》请在金锄头文库上搜索。
1、当施加于电介质的电场增大到相当强时，电介质的电导就不服从欧姆定律了。 The dielectric conduction will not obey Ohms law if the electric field imposed on it is amplified quite strong.,2.3 固体电介质的击穿 2.3 Breakdown of solid dielectrics,实验表明，电介质在强电场下的电流密度按指数规律随电场强度增加而增加，当电场进一步增强到某个临界值时，电介质的电导突然剧增，电介质便由绝缘状态变为导电状态，这一跃变现象称为电介质的击穿。 Experiments
2、show that the current density of dielectric under strong field increases with an exponential law following the increase of field. Further, the conductivity will leap abruptly when field reach a critical value, and dielectric will change the insulation state to conducting state, this leap phenomenon
3、is called breakdown of dielectric.,介质发生击穿时，通过介质的电流剧烈地增加，通常以介质伏安特性斜率趋向于作为击穿发生的标志（见图2-21）。发生击穿时的临界电压称为电介质的击穿电压，相应的电场强度称为电介质的击穿场强。 With breakdown of dielectric, the current through it increases acutely, usually as the slope of dielectric voltammetry trend in a sign (as shown in fig 2-21). The critical
4、value lead to breakdown is called breakdown voltage of dielectric, and the corresponding electric field intensity breakdown field intensity of dielectric.,与气体、液体介质相比，固体介质的击穿场强较高，但固体介质击穿后材料中留下有不能恢复的痕迹，如烧焦或熔化的通道、裂缝等，即使去掉外施电压，也不象气体、液体介质那样能自行恢复绝缘性能。 Compared to gas and liquid, the solid media has a high
5、er breakdown field intensity, but there remain traces that can not be restored in material, such as channel, cracks due to char or melt, even if remove the voltage it can not restore the insulation performance by itself like gas and liquid media.,固体电介质的击穿中，常见的有热击穿、电击穿和不均匀介质局部放电引起击穿等形式。 The thermal b
6、reakdown, electrical breakdown and breakdown caused by PD in uneven media are common forms among the solid dielectric breakdown.,图2-22 固体电介质击穿场强与电压作用时间的关系,电介质击穿场强与电压作用时间的关系及不同击穿形式的范围示于图2-22。,The relationship between breakdown field intensity of solid dielectric and voltage action time and the range
7、of different breakdown forms are shown as fig 2-22.,Fig 2-22 relationship between breakdown field intensity of solid dielectric and voltage action time,热击穿 Thermal breakdown,热击穿是由于电介质内部热不稳定过程所造成的。当固体电介质加上电场时，电介质中发生的损耗将引起发热，使介质温度升高。 Thermal breakdown is caused by the thermal instability process insid
8、e the dielectric. With electric field on the solid dielectric, in which the wastage will cause heat, to rise the medium temperature.,电介质的热击穿不仅与材料的性能有关，还在很大程度上与绝缘结构（电极的配置与散热条件）及电压种类、环境温度等有关，因此热击穿强度不能看作是电介质材料的本征特性参数。 The thermal breakdown is related not only to the material performance, but also to th
9、e insulation structure (electrode configuration and thermal conditions), voltage type and environmental temperature, therefore it can not be regarded as the intrinsic parameter of dielectric material.,2. 电击穿 Electrical breakdown,电击穿是在较低温度下，采用了消除边缘效应的电极装置等严格控制的条件下，进行击穿试验时所观察到的一种击穿现象。电击穿的主要特征是：击穿场强高；在
10、一定温度范围内，击穿场强随温度升高而增大，或变化不大。 Electrical breakdown is a kind of breakdown phenomenon observed in breakdown test, which is under strict conditions with the electrode device to eliminate the edge effect in low temperature. The main features are: the breakdown field intensity is high; In a certain temper
11、ature range, the breakdown field intensity increase as the temperature rise, or change a little.,均匀电场中电击穿场强反映了固体介质耐受电场作用能力的最大限度，它仅与材料的化学组成及性质有关，是材料的特性参数之一，所以通常称之为耐电强度或电气强度。 In uniform field the electrical breakdown field intensity reflects the maximum capacity of solid medium tolerating the electric
12、 field, it relates only to the chemical composition and nature, and is one of the material parameters, called electrical resistance, or electrical intensity.,3. 不均匀电介质的击穿 The breakdown of inhomogeneous dielectric,不均匀电介质击穿是指包括固体、液体或气体组合构成的绝缘结构中的一种击穿形式。与单一均匀材料的击穿不同，击穿往往是从耐电强度低的气体开始，表现为局部放电，然后或快或慢地随时间发
13、展至固体介质劣化损伤逐步扩大，致使介质击穿。 The breakdown of inhomogeneous dielectric is a breakdown form in insulation structure including the composition of solid, liquid or gas. Different from the single uniform material, breakdown often started from the gas with low electric resistance, shown as PD, and then grows t
14、o the gradually expand of deterioration injury sooner or later, and lead to breakdown at last.,由于实际固体介质击穿还伴随有机械的、热的、化学的等复杂过程，因而至今还没有建立起可以满意地解释所有击穿现象的理论，但是已经有了一些能够较好说明部分现象的理论，以下将分别加以讨论。 Because of the complicated process of mechanical, thermal and chemical together, it still have not established a sa
15、tisfactory theory that could explain all the breakdown phenomenon so far. However, there have been theories to describe some phenomenon already, which will be introduced below.,2.3.1 固体电介质的热击穿 2.3.1 The thermal breakdown of solid dielectric 2.3.2 固体电介质的电击穿 2.3.2 The electrical breakdown of solid die
16、lectric 2.3.3 不均匀电介质的击穿 2.3.3 The breakdown of inhomogeneous dielectric,本节内容 Contents in this section,2.3.1 固体电介质的热击穿 2.3.1 The thermal breakdown of solid dielectric,瓦格纳的热击穿模型如图2-23所示。假设固体介质置于平板电极a、b之间，该介质有一处或几处的电阻比其周围小得多，构成电介质中的低阻导电通道。 The model of Wagner thermal breakdown theory is shown as fig 2-23. It is supposed the solid medium is placed between the parallel flat electrode, and there are one or more resistances in this medium much smaller than its surrounding, to make a low resistan
