Insulation Materials Main Performance
1, Insulation Materials the concept of aging: electrical equipment in the process of insulation, due to various factors in the long-term role, will occur a series of irreversible changes, resulting in their physical, chemical, electrical and mechanical properties such as deterioration, this irreversible change is commonly known as aging.
2, the main performance of polymer aging:
2.1 Apparent changes: material discoloration, viscosity, deformation, cracking, embrittlement
2.2 Physical and chemical properties change: Relative molecular weight, relative molecular mass distribution, melting point, solubility, heat resistance, Insulation Materials cold resistance, permeability, light transmittance, etc.;
2.3 Mechanical Properties: elasticity, hardness, strength, elongation, adhesion, wear resistance, etc.
2.4 Electrical Properties: insulation resistance, dielectric constant, Insulation Materials dielectric loss angle tangent, breakdown strength, etc.
3, the essence of polymer aging:
3.1 cross-linking: crosslinking to a certain extent can improve the physical and mechanical properties of polymers and heat-resistant properties, but with the increase of intermolecular cross-linking, gradually forming network structure, polymer into a hard, brittle, insoluble product;
3.2 Degradation: molecular weight reduction, resulting in mechanical properties and electrical properties of the lower, the emergence of sticky and powder.
3.3 Environmental Aging: acid, alkali, salt composition of the dust (or with rain, dew, frost, snow, combination) of the long-term role of insulation, it is obvious that the insulation (especially organic insulation) corrosion.
3.4 Environmental Aging Reasons:
The energy of sunlight ultraviolet rays is greater than that of most organic insulators, most organic insulators will gradually aging under ultraviolet light.
After absorbing ultraviolet energy, some molecules are stimulated, when oxygen or ozone is present, the oxidation and degradation reaction of polymers is also induced, Insulation Materials which is called photochemical reaction. Photo-oxidation reaction is one of the important processes in environmental aging.
4, Electrical Aging: insulation materials in the electric field for a long time, the physical and chemical changes in performance, resulting in the breakdown of the media, Insulation Materials this process is called electrical aging. There are three main types: ionization aging (alternating voltage), electrical conductivity aging (AC voltage), electrolytic aging (DC voltage)
5, Ionization Aging: (1) in insulating materials exist bubble or air gap (process defects, heat and cold shrinkage, material decomposition, material damp) (2) The dielectric constant of the gas medium is close to 1, which is much smaller than the dielectric constant of the solid medium, under field, Insulation Materials the field strength in the air gap is much stronger than the field in the neighboring solid medium, and its initial free field strength (atmospheric pressure) is usually much smaller than that of the solid medium, so the free radicals are most likely to occur in these gaps, in some air gaps, There may even be a steady spark discharge. (3) The free radicals of the air gap will cause
6, electrical conductivity Aging: In the insulating layer between the two electrodes (the most common is at the junction of the electrode and insulation), there are some liquid conductive substances (most commonly water)
When the field strength exceeds a certain value, these conductive substances will gradually infiltrate the insulating layer in the direction of the electric field, Insulation Materials forming an approximate tree-like mark into the water branch. The cumulative development of the water branch will eventually lead to the breakdown of the insulating layer.
The mechanism for producing water branches may be:
The ions in water or other electrolytes repeatedly impact the insulating material under field action, causing fatigue damage and chemical decomposition.
The electrolyte gradually penetrated and diffused into the depths, Insulation Materials forming a water branch.
The strength required to produce and develop a branch is much lower than the field strength required to produce and develop the branch.
7, electrolytic Aging: Under the long-term effect of DC voltage, Insulation Materials even if the voltage is much lower than the starting voltage of the local discharge, because the medium of the electrochemical process near the line, the media will gradually aging, resulting in breakdown.
8, thermal aging: At a higher temperature, thermal pyrolysis, oxidation decomposition, crosslinking, and the escape of low molecular volatile, resulting in the dielectric loss of elasticity, embrittlement, Insulation Materials cracking, mechanical strength, and some media as soft, sticky, loss of shape, Insulation Materials and dielectric properties deterioration. The degree of thermal aging depends mainly on temperature and thermal action time. Insulation Materials In addition, such as humidity in the air, pressure, oxygen content, Insulation Materials the flow of air and so on, the speed of heat aging has a certain impact。