Analysis of the Causes of Cable Insulator Heating

Power cables generate heat when passing a certain load current.
The maximum permissible temperature for cross-linked polyethylene insulated cables is 90°C.
If it has been higher or exceeded the maximum allowable continuous working temperature of the cable, the cable will be hot for a long time.
If you do not find the cause of timely troubleshooting, the cable continues to run continuously energized will produce an insulation thermal breakdown phenomenon, resulting in a phase-to-phase short circuit tripping phenomenon of the cable, and a serious fire may cause.

Heat during operation may be caused by the following:

1 Conductor DC Resistance does not meet the Requirements
Cause the cable in the operation of the heating phenomenon.

2 Improper Cable Selection
The conductor cross-section of the cable is too small, resulting in overload in operation, and after a long time, the heat generation and heat dissipation of the cable is not balanced, resulting in heat generation.

3 Cable Arrangement is too Dense
This will lead to poor ventilation and heat dissipation, or the cable is too close to other heat sources, affecting the normal heat dissipation of the cable, and may also cause the cable the operation the phenomenon of heat generation.

4 Bad Joint Manufacturing Technology
The contact resistance at the joints is too large due to the joints not being crimped tightly, which may also cause the cable to generate heat.

5 Interphase Insulation Performance is not good
This causes the insulation resistance to be small, the operation will also produce a heat phenomenon

6 Armored Cable Local Sheath Broken
Once the water into the insulation performance caused by the slow destruction of the role, resulting in insulation resistance gradually reduced, will also cause the cable in operation to generate heat phenomenon.

Analysis of the causes of insulator heating

Research shows that the heat generation of power line insulators consists of three parts.

One is the heat generated by the polarization effect of the dielectric excited under the action of the working frequency voltage.

Second is the internal penetrating leakage current heat generation.

The third is the surface creepage leakage current heat generation.

When the insulator is in good operating condition, heat generation is of primary importance.
When the porcelain insulator performance deteriorates, or the porcelain cracks or the surface of the porcelain plate is dirty, it will make the second or third leakage current increase, and heat generation increases, leading to the insulator temperature rise.
There are 3 main reasons for insulator deterioration considered so far:
1 Improper control of the manufacturing process
2 Internal defects
3 The influence of changes in the operating environment.

Due to the manufacturing process and formulation, microcracks and hygroscopic pores tend to form inside the ceramic and may lead to uneven internal stresses.
Local stress concentration increases microcracking, water passes through the cracks and enters the porcelain body through pores, and hygroscopic pores provide space for water molecules to reside.
The corresponding force between water and glass induces a chemical reaction, which induces a slow crack expansion.
In the working frequency voltage conditions, water molecules in the process of repolarization friction with each other, and molecular movement of intense regional heat generated will make the insulator's local temperature rise significantly.

In power systems, rod-shaped porcelain column insulators are widely used in busbars and disconnecting barriers.
During long-term operation, the combined effects of mechanical, thermal, electrical, and environmental factors make various physical and chemical changes inevitable. 

Therefore, the electrical properties and mechanical strength of insulators will gradually decrease with the increase in working time.