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The fundamental cause of the break of strut insulator and the brief description of strut insulator

30 Jul 2019

strut insulator

1. Overview of strut insulators

The knife gate stanchion insulator is an important component of substation operation and plays the role of supporting conductor and insulation.Prevent post insulator rupture accident is the key work over the years I plant, power grid to avoid post insulator rupture accident also put forward higher requirements, power grid caused by post insulator rupture failure occurs frequently, the widely effective, loss is big, our factory have occurred several post insulator rupture accident, breaker great threat to the safe operation, the fracture reason is mainly due to the post insulator aging root mechanical intensity is abate, and post insulator breaker broken accident after local damage caused.Ultrasonic flaw detection technology for strut insulator is a new technology developed in recent years. The introduction of this technology can find local damage of strut insulator as early as possible, which is of great significance to prevent sudden fracture of strut insulator during operation, and is a practical and feasible method to eliminate the hidden danger of strut insulator fracture.

2. Reasons for fracture of strut insulator

Prop insulators are mainly made up of clay, feldspar quartz and other aluminosilicate elements. After being processed into a certain shape, the inorganic insulation material is baked at high temperature. The surface of the insulator is covered with a smooth thin layer of vitreous glaze.The deterioration of prop insulators is influenced by many factors, which are not only related to the material, formula and technological process selected by the manufacturer, but also related to the operating environment and the load resistance and even the external force.If the strut insulator is improperly formulated in the production process, the raw materials are not evenly mixed in the technological process, and the roasting firepower is insufficient, then the strut insulator is easy to form moisture absorption pores.The unreasonable structure, or the mistake in forming and uneven force, will also cause internal stress inside the pillar insulator, which will lead to crack, air gap and even deterioration of the pillar insulator.Prop insulators are usually made by molding and sintering the powder.The strut insulators made by these processes are composed of polycrystals with many microcrystals, which inevitably leads to the existence of grain boundary.Grain boundaries not only play an important role in the sintering process of strut insulators, but also have a great influence on the physical and chemical properties of sintered bodies.The microstructure of strut insulator is composed of microcrystals, grain boundaries, precipitates in grain boundaries, pores in grain boundaries, precipitates in grain grains, and pores in grain grains.The microcrystalline size of the main component of the strut insulator generally ranges from 1 micron to dozens of microns, and the crystal setting axis is arbitrary. The microcrystalline diameter is related to the raw material particle diameter, impurities and sintering conditions.There are lattice defects and lattice distortions in ceramic grain boundary such as errors, empty holes and so on.Thus, impurities tend to be concentrated and form crystalline boundary segregation layer and lamellar precipitates.Generally, the layer formed by the impurities at the grain boundary is called the grain boundary segregation layer. The thickness of the grain boundary segregation layer ranges from 20 angstroms to 1 micron.The post insulator is usually made of cement.After the cement absorbs water and CO2, its volume will increase. After the cement absorbs water, it will repeatedly freeze and melt, which will promote the deterioration of the prop insulator.And cement drying, condensation, not only will form a hygroscopic pores, and will produce a lot of cracks.

When the ambient temperature suddenly changes, the strut insulator will face a great test.For example, when the hot summer sun and a sudden rainstorm occur, all parts of the strut insulator cannot expand and contract at the same time, and the local position of the strut insulator (such as the head) will bear great mechanical stress, and even cause porcelain parts to crack.At this point, if the size of the strut insulator is larger and the structure is more complex, the possibility and severity of cracking will be greater.Long-term operation experience shows that the deterioration rate of the pillar insulator with poor quality is often several times higher than that in winter, especially in summer when the sun is hot and the rain falls suddenly.Similarly, the upper porcelain skirt and head of the multi-layer pin post insulators that are exposed to sunlight and rain, as well as the glue fitting parts of the post insulators, all have high degradation rates.There are many factors that cause the damage and fracture of the strut insulator, mainly including: the product quality is not high, the defective product leaves the factory.Some of them are even inferior or use old products to replace new ones, which can't get any quality guarantee at all.Specifically, cracks, slag inclusion, interlayer, pores, etc. generate cracks and expand under the action of internal stress with greater concealment.Damage caused by packing, transportation and installation.When the strut insulator operates in harsh environment, there are differences in expansion coefficients among the electric porcelain, cement and cast iron flanges, as well as temperature differences, which lead to cracking.Excessive stress and mounting stress and frequent operation lead to the fracture of the strut insulator.

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