Thermal shrinkage tube insulated cable shielding layer analysis is as follows:

The performance of the semi-conductive shielding layer inside and outside the heat shrinkable tube insulated cable plays an extremely important role in the performance of the XLPE insulated cable, and its development and transformation is also a symbol of the continuous improvement and development of the cross-linked cable, which will play a key role in our understanding and understanding of the whole structure of the XLPE insulated cable.

Thermal shrinkage casing insulation shielding layer is composed of semiconductor materials, it is squeezed between the metal wire core and the insulating layer or between the insulation and metal shielding layer, respectively, called insulation internal shielding and external shielding. Their function is to prevent partial discharge by uniform electric field. If the semiconductor shielding layer itself can not guarantee smooth electrical (rough surface, even sharp protrusion), there are uneven four pits or cracks, fracture and insulation according to poor and other defects, it is difficult to play the role of uniform electric field, and may even cause serious electric field concentration, leading to partial discharge or insulation breakdown.

The internal and external semiconductor layer is composed of polar polymers such as PE, EPM or EVA and selected high-conductivity carbon black. The most commonly used high-conductivity carbon black average granularity in (200~400) x10-9 square mm. The X LPE power cable below kV can be shielded by a stripping semiconductor mixture containing polar materials, and the cable of the 1l grade of the above kV and above should be shielded from the internal and external shielding by cross-linked semiconductors (see later semiconductor shielding design).

The contact surface of the inner shielding and insulating layer is the place with the highest cable field strength, and any defects in contact are easy to cause the electric field height concentration. The United States standard AELCNo S, if there is a specific shielding cylindrical protruding or uneven more than 0 mm of the cable, is not qualified. The main reason for the internal shielding protrusion is that the semiconductor "secretion" affixed to the extrusion die, the surface of the shielding layer, the so-called "mold" (DieBleed), the second is the semiconductor surface of the carbon black agglomeration, normal extrusion, because the inner diameter of the mold sleeve is generally larger than the outer diameter of the inner shielding layer (large 0.5-0.9 mm) Therefore, the carbon black agglomeration of 0 m M is easy to pass through the mold hole. Uneven surface or hemp pits on semiconductors can also lead to the concentration of electric fields. On the surface of rough semiconductor layers, carbon black particles are often embedded in insulators, which become hidden protruding objects.

The high field strength caused by semiconductor protrusion or embedding will also promote the electronic cold injection of carbon black particles, that is, at high field strength, the electron escape conductor of motion A, into the medium. In this way, it can lead to more severe partial discharge.

热缩管绝缘电缆半导电屏蔽层性能

热缩管绝缘电缆屏蔽层分析如下：

热缩管绝缘电缆内外半导电屏蔽层性能的优劣，对XLPE绝缘电缆的性能起极极其重要的作用，同时，它的发展和变革也是交联电缆不断完善和发展的象征，研究它对于我们认识和理解XLPE绝缘电缆的整个结构将起着关键作用。

热缩套管绝缘屏蔽层是由半导体材料组成，它挤在金属线芯与绝缘层之间或绝缘与金属屏蔽层之间，分别称为绝缘的内屏蔽和外屏蔽。它们的作用是均匀电场防止局部放电。如果半导体屏蔽层自身不能保证电性光滑(表面粗糙，甚至有尖锐的突出)，存有不平的四坑或有裂缝，断口与绝缘按触不良等缺陷，就难以起到均匀电场的作用，甚至有可能引起严重的电场集中，导致局部放电或绝缘击穿。

内、外半导体层是由PE, EPM或EVA等极性聚合物和特选的高导碳黑混成。最常用的高导碳黑平均粒度在(200~400) ×10的-9次方mm。 20 kV以下的X LPE电力电缆可以用含有极性材料的可剥离半导体混合物作外屏蔽,24 kV及以上电1l等级的电缆要用交联性半导体作内外屏蔽(见后文半导体屏蔽设计)。

内屏蔽和绝缘层的接触面是电缆场强最高的地方，接触上的任何缺陷都易引起电场高度集中。美国标准AELCNo S中规定，如有比内屏蔽圆柱突出或高低不平大于 0 25 mm的电缆，属于不合格。造成内屏蔽突出的主要原因一是贴在挤出模口的半导体“分泌物”脱逸出来，赫着在内屏蔽层表面，即所谓“模泌”( DieBleed)，二是半导体表层的碳黑结块，正常挤出时，因模套内径一般比内屏蔽层外径大些(大0.5-0.9 mm),所以0 25 m m的碳黑结块很易通过模孔。半导体表面不平或有麻坑等也能导致电场集中。在粗糙的半导体层表面上往往有碳黑颗粒嵌在绝缘物中，成为隐蔽突出物。

半导体突起或嵌入所引起的高场强还会促使碳黑颗粒的电子冷射，即在高场强下，运动A的电子逸出导体，射入介质。这样，会导致更严重的局部放电。