Effect of internal defects of heat shrinkable tube insulator on insulation performance of heat shrinkable tubing

The following are a variety of defects in heat shrinkable tube insulation:

1, heat shrinkable tube insulation in the contaminants (debris);

2, the heat shrinkage tube of the outer shielding protrusion;

3, electric branches;

4, Butterfly knot branches (water branches);

5, internal shielding protrusion;

6. Micropores (often annular);

7, poor contact with the inner wall;

8, voids;

9, the inner wall gap;

10, internal shielding break gap;

11, powder scattered antiaging Agent Regiment.

The above defects of heat shrinkable pipe insulation can generally lead to partial discharge of insulation and accelerate the electrical aging of insulation. The main defects are summed up in 11 kinds, which can be divided into two categories. One is to cause electric field concentration in insulation and improve local field strength. The protrusion of the semiconductor shielding layer into the insulation and the conductive impurities in the insulator belong to this category. The other is to weaken the local insulation strength in the insulation, in the insulator or in the shielding layer and insulator interface on the gap or air gap are part of this category of defects.

In the process of thermal shrinkage tube insulation extrusion, the heating medium into the insulating material can form countless small holes, the dielectric coefficient of the microporous is less than the insulating material, so under the action of the electric field, the microporous size is more and more large, prone to branch damage, so limiting the size and quantity of micropores in the insulation is the key to inhibit the dendritic. In the wet process used in cross-crosslinking in the past, water vapour will inevitably be residual in insulation, forming aqueous micropores, and the use of dry crosslinking, can reduce the microporous to less than 5µm. Therefore, in the future use of crosslinked polyethylene heat shrinkable pipe, in the cost acceptable range should be as far as possible to use dry cross-linked products, so as to ensure the safety of use.

热缩管绝缘体内部缺陷对热缩管绝缘性能的影响

热缩管绝缘内部缺陷或杂质对绝缘性能的影响

以下是热缩管绝缘中的各种缺陷：

1、热缩管绝缘中的污染物(杂物);

2、热缩管的外屏蔽突起;

3、电树枝;  

4、蝶结状树枝(水树枝);  

5、内屏蔽突起;

6、微孔(往往呈环状);  

7、内壁接触不良;  

8、空隙;  

9、内壁空隙;  

10、内屏蔽断隙;  

11、粉散防老剂团。

以上这些热缩管绝缘的缺陷一般都能导致绝缘局部放电，加速绝缘的电老化。主要缺陷归纳起来有11种，可分两大类。一类是在绝缘中导致电场集中，提高局部场强。半导体屏蔽层凸入绝缘中的突起物和在绝缘体中的导电杂质等属于此类。另一类是在绝缘中减弱局部绝缘强度，在绝缘体中或存在于屏蔽层和绝缘体界面上的空隙或气隙都属于这一类缺陷。

在热缩管绝缘挤塑过程中，加热介质进入绝缘材料可以形成无数的小孔洞，微孔的介电系数小于绝缘材料，因而在电场的作用下，微孔尺寸越来越大，容易发生树枝破坏，所以，限制绝缘中微孔的尺寸和数量，是抑制树枝化的关键。在过去交联使用的湿法过程中，水蒸汽不可避免地会在绝缘中残余，形成含水的微孔，而采用干法交联，可以使微孔降到5µm以下。因此今后使用交联聚乙烯热缩管时，在造价可接受的范围内应尽可能采用干法交联的产品，这样才能保证使用的安全性。