The causes of insulation aging can be attributed to mechanical force, thermal effect, electric action, chemical action and humidity.
Mechanical force action:
Mechanical aging will destroy mechanical strength and reduce mechanical strength when mechanical load, self weight, vibration, impact and short circuit current are applied. For example, the insulation at the notch is easy to crack and layering due to long-term vibration and high temperature.
The effect of heat:
During the operation of thermal aging power equipment insulation, the insulation temperature rises because of the high ambient temperature or the heating of the power equipment itself. Under the action of high temperature, the mechanical strength of the insulation is reduced and the structure is deformed. The material loses elasticity because of oxidation and polymerization, or the insulation breakdown is caused by the cracking of the material, and the voltage is reduced. The outdoor electric equipment will be damaged by heat expansion and cold contraction and water intrusion into insulation. Or because the thermal expansion coefficient of porcelain insulation and metal parts is different, the porcelain insulation breaks when the temperature changes violently.
The insulation of power equipment will be affected by working voltage and working current during operation. Under long-term operating voltage, insulation breakdown will cause partial damage to insulation materials. If the insulation structure is too large, the insulation will be damaged due to overheating under the long-term working voltage. Under the action of lightning overvoltage and operating overvoltage, partial damage may occur in insulation. When the voltage is applied again, the damage gradually expands and eventually leads to complete breakdown.
The relative humidity in the humidity aging environment has an influence on the performance of the insulation material to withstand surface discharge. If the water invades the insulation, the dielectric loss will increase or the breakdown voltage will decrease.