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Analysis of Causes of Operation Failure of High-Voltage Insulators



Analysis of the operating status of the high-voltage insulator

The performance of high-voltage insulators is mainly determined by electrical properties, mechanical properties, thermal properties and anti-aging properties.

The electrical properties of high-voltage insulators mainly include: high-voltage insulator flashover characteristics, electrical properties under various overvoltages, pollution flashover characteristics of high-voltage insulators, and power frequency breakdown voltage characteristics in oil;

The mechanical properties of high-voltage insulators mainly include: bending strength; the thermal properties of high-voltage insulators mainly include its hot and cold performance.

The "Regulations" stipulate that when measuring the insulation resistance with a 2500V megohmmeter, the insulation resistance of the multi-element pillar insulator and each suspension insulator shall not be less than 300M, and the insulation resistance of the 500kV suspension insulator shall not be less than 500M.

1. Cracking
When a high-voltage insulator is found to be cracked, it is dangerous in terms of electrical and mechanical properties and must be replaced as soon as possible. Partial skirt defect or flange defect may not necessarily cause an accident, but because it will expand into cracks, it should be replaced as soon as possible.

For high-voltage insulators made of polymer materials, the reasons for cracks are as follows:

(1) Causes of cracks in high-voltage porcelain insulators
A. There are small defects on the surface and inside of the porcelain piece during the manufacturing process. Due to the repeated bearing of external forces, it is subjected to mechanical stress, and then cracks and skirt breaks develop.
B. Flashover caused by overvoltage or fouling can cause damage to porcelain parts by arc and local overheating.
C. High-voltage insulators are coated with silicone grease, which is generally used as an anti-fouling measure. When the silicone grease is not reapplied for a long time and continues to be used, leakage current and partial discharge will occur due to the aging of the silicone grease, as well as peeling of the glaze on the surface of the high-voltage insulator, skirt defects and cracks.
D. Due to the over-tightening of the fastening hardware, some parts of the porcelain are subjected to excessive stress.
E. Due to negligence during the operation, the high-voltage insulator is damaged by accidental external force or damage caused by external force such as stone throwing.
F. The porcelain sleeve used on the equipment, if the internal equipment is not well matched, sometimes it will cause indirect damage to the porcelain sleeve.

(2) Causes of cracks in high-voltage polymer insulators
A. The residual internal stress generated when the material is cured and contracted during the manufacturing process will cause cracks.
B. The thermal cycle caused by the repeated operation and shutdown of the equipment will cause the product to be subjected to cyclic thermal stress due to the difference in the thermal expansion coefficient of different materials, which will cause the metal embedded in the resin to peel off and crack.
C. Due to the decrease of the mechanical strength of the insulating material during long-term operation or the fatigue caused by repeated stress, cracks will also occur.
D. The fastening parts of the high-voltage insulators are over-tightened, resulting in excessive mechanical stress and cracks.

2. Creepage traces
When the surface of the organic insulating material is contaminated and wet, the leakage current flowing through the surface will form a local dry zone with high insulation resistance, which will increase the voltage applied to this part, thereby generating a small discharge. As a result, the insulating surface is carbonized to form a conductive path, which is the creepage trace. If the high-voltage insulator that has produced creepage traces is left as it is, it will gradually develop and eventually cause a ground short-circuit accident due to flashover.

While replacing high-voltage insulators with traces of creepage, it is necessary to strengthen the management of problems such as contamination and moisture, and try to use materials that are resistant to traces of creepage and excellent performance to prevent the recurrence of traces of creepage.