Mechanical Strength of Insulating Crepe Paper
- By : Insulation Materials
The most important factors for oil-immersed transformer to choose insulated corrugated paper tube materials include not only fiber composition, density, permeability and uniformity, but also mechanical strength requirements, including tensile strength, stamping strength, tearing strength and toughness.
1) Tensile Strength: Paper fibers are required to have the maximum stress that can be tolerated without breaking under tensile load.
2) Stamping Strength: A measure of the ability of paper fibers to withstand pressure without being broken.
3) Tearing strength: The force required for the tearing of paper fibers meets the corresponding standards.
4) Toughness: The strength of paper folding or cardboard bending can meet the corresponding requirements.
To judge the performance of solid insulation, we can try to measure the degree of polymerization of paper or cardboard by sampling or the content of furfural in oil by means of high performance liquid chromatography, so as to facilitate the analysis of whether solid insulation is involved or whether there is low-temperature overheating which causes the partial aging of coil insulation or whether there is solid insulation when there is a fault in transformer. Aging degree. In the operation and maintenance of paper fiber insulation material, attention should be paid to controlling the rated load of transformer, requiring good air circulation and heat dissipation conditions in the operating environment to prevent the temperature rise of transformer exceeding the standard and oil shortage in the box. It is also necessary to prevent the accelerated aging of fibers caused by oil pollution and deterioration, which will damage the insulation performance, service life and safe operation of transformers.
Deterioration of paper fiber materials. It mainly includes three aspects:
1) brittle fracture. When excessive heating separates moisture from the fibrous material, it accelerates the embrittlement of the fibrous material. Due to the brittleness and peeling of paper, electrical accidents may occur due to the impact of mechanical vibration, electric stress and operation wave.
2) The mechanical strength of fibre material decreases. The mechanical strength of fiber material decreases with the prolongation of heating time. When the moisture of insulation material is discharged again due to the heat of transformer, the value of insulation resistance may increase, but its mechanical strength will be greatly reduced. Insulating paper material will not be able to withstand the influence of mechanical forces such as short circuit current or impact load.
3) The shrinkage of the fibre material itself. The shrinkage of fibre material after embrittlement reduces the clamping force, which may cause shrinkage movement and damage insulation by shifting and friction of transformer windings under electromagnetic vibration or impulse voltage.
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