Semi-conductive paper and its preparation method and overall shielding structure of multi-winding current transformer

Abstract

The invention belongs to the field of current transformers, and in particular relates to semiconducting paper and a preparation method thereof, and a bulk shielding structure for a multi-winding current transformer. The semiconducting paper comprises the following components in parts by weight: 65 to 100 parts of unbleached softwood kraft pulp, 15 to 25 parts of acetylene black, 2 to 4 parts of magnesium borate whiskers, 1 to 5 parts of modified anionic starch and 20 to 45 parts of an ethanol solution with the concentration of 5%. The semiconducting paper has an excellent electrical property, maintains high mechanical strength and achieves remarkable progress as compared with the control group. In addition, the invention also provides the bulk shielding structure for the multi-winding current transformer. Bubble gaps between secondary windings caused by the fact that epoxy resin cannot permeate completely during pouring can be effectively reduced, local discharging of the product is reduced and the quality of the product is improved.

Description

technical field [0001] The invention belongs to the field of current transformers, and in particular relates to a semiconductive paper, a preparation method and an overall shielding structure of a multi-winding current transformer. Background technique [0002] Existing shielding materials include metal foil, semiconductor rubber tape, and surface-type semiconductor materials. These materials all have shortcomings such as uneven coating to varying degrees, easy peeling off of the coating, and unstable resistance characteristics. [0003] Semi-conductive paper is a new type of electrical material, its conductivity is between the conductor and the semiconductor, and the resistance value is generally required to be between the conductor and the insulator (1×10 5 ~1×10 7 ohm cm). Semi-conductive paper is divided into two types: single-color and double-color, both of which are made of 100% unbleached kraft wood pulp and added an appropriate amount of conductive material. Sing...

AI Technical Summary

Problems solved by technology

However, it is found in actual production that the amount of cationic starch added has a significant relationship with the forming of paper. When the amount of cationic starch added reaches 0.08%, the slurry will undergo obvious flocculation. When the amount reaches 0.3%, the size of the slurry will Flocculation is very obvious, which seriously affects the forming of paper

Therefore, it is generally recommended that the dosage of cationic starch be around 0.08% in production, but on the other hand, if the dosage of cationic starch is reduced, the retention rate of carbon black will not meet the requirements.

[0006] On the other hand, there is still room for improvement in the relationship between paper strength and resistance. The addition of conductive substances such as carbon black fills the fibers with particles, which reduces the contact area of ​​fibers and hinders the combination of hydrogen bonds between fibers, resulting in paper decrease in physical strength

However, if the amount of conductive substance is reduced, it will affect the resistivity of the paper and it is difficult to meet the requirements.

In order to solve the problem that the relationship between paper strength and resistance is difficult to balance, in the prior art, a reinforcing agent is generally added in the late stage of beating for reinforcement, such as CMC. Layer shielding requires good oil permeability, so that the oil-impregnated material is easy to immerse into the internal gap of the insulation. Therefore, it is not advisable to use CMC for reinforcement.

[0007] In addition, there are gaps between multiple secondary windings in the existing current transformer, and the gaps cannot penetrate epoxy resin, and bubbles are formed during casting, and the product is prone to partial discharge

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