US-12626836-B2 - Electrical insulation paper

US12626836B2US 12626836 B2US12626836 B2US 12626836B2US-12626836-B2

Abstract

This disclosure relates to an electrical insulation paper comprising at least 25% content by weight of cellulose fibers based on the total weight of the electrical insulation paper, 8% content by weight of synthetic fibers based on the total weight of the electrical insulation paper, and a thermal stabilizer comprising nitrogen, wherein a content by weight of the nitrogen constitutes between 1% and 4% of the content by weight of the cellulose fibers.

Inventors

Lucie BOIRON
Thierry Mayade

Assignees

AHLSTROM OYJ

Dates

Publication Date: 20260512
Application Date: 20230818
Priority Date: 20220819

Claims (16)

1 . An electrical insulation paper comprising: at least 25% content by weight of cellulose fibers based on the total weight of the electrical insulation paper; at least 5% content by weight of synthetic fibers based on the total weight of the electrical insulation paper, the synthetic fibers comprising aliphatic polyamide fibers and/or glass fibers; and a thermal stabilizer comprising nitrogen, wherein a content by weight of the nitrogen constitutes between 1% and 4% of the content by weight of the cellulose fibers.
2 . The electrical insulation paper of claim 1 , comprising: at least 50% content by weight of cellulose fibers based on the total weight of the electrical insulation paper; and 7 to 35% content by weight of synthetic fibers based on the total weight of the electrical insulation paper, said synthetic fibers being polyamide fibers and glass fibers.
3 . The electrical insulation paper of claim 1 , comprising: at least 45% content by weight of cellulose fibers based on the total weight of the electrical insulation paper; and 5 to 55% content by weight of synthetic fibers based on the total weight of the electrical insulation paper, said synthetic fibers being glass fibers, or a blend of glass fibers and polyamide fibers.
4 . The electrical insulation paper according to claim 1 , wherein the thermal stabilizer comprising nitrogen is selected from dicyandiamide, urea, melamine, polyacrylamide, or a mixture thereof.
5 . The electrical insulation paper of claim 1 , further comprising a binder in an amount of 5 to 20% content by weight based on the total weight of the electrical insulation paper, said binder being selected from thermofusible fibers, resin, or mixtures thereof.
6 . The electrical insulation paper of claim 5 , wherein the binder is a resin, and optionally the resin comprises the thermal stabilizer comprising nitrogen.
7 . The electrical insulation paper of claim 6 wherein the resin comprises a polyvinyl alcohol.
8 . A transformer comprising the electrical insulation paper of claim 1 wherein the transformer is selected from high voltage liquid immersed transformer, dry transformer, or traction transformer.
9 . The electrical insulation paper of claim 1 wherein the thermal stabilizer consists essentially of dicyandiamide.
10 . A method of manufacturing an electrical insulation paper, comprising the steps of: providing cellulose fibers and synthetic fibers; manufacturing a base paper from the cellulose fibers and synthetic fibers on a paper machine, with at least 25% content by weight of the cellulose fibers based on the total weight of the electrical insulation paper, and at least 5% content by weight of the synthetic fibers based on the total weight of the electrical insulation paper, the synthetic fibers comprising aliphatic polyamide fibers and/or glass fibers; wherein the method further comprises adding a thermal stabilizer comprising nitrogen, wherein a content by weight of the nitrogen constitutes between 1% and 4% of the content by weight of the cellulose fibers.
11 . The method of claim 10 , further comprising adding a binder in an amount of 5 to 20% by weight based on the total weight of the electrical insulation paper, said binder being selected from thermofusible fibers, resin, or mixtures thereof.
12 . The method of claim 11 , wherein the binder is a resin, said resin being coated on the base paper after the addition of the thermal stabilizer comprising nitrogen.
13 . The method of claim 11 , wherein the binder is a resin, said resin being coated on the base paper just after the step of manufacturing the base paper and before the addition of the thermal stabilizer comprising nitrogen.
14 . The method of claim 11 , wherein the binder is thermofusible fibers, said thermofusible fibers being mixed with the cellulosic and synthetic fibers before the manufacturing step of the base paper.
15 . The method of claim 11 , wherein the binder is a resin, said resin also comprising the thermal stabilizer comprising nitrogen, said resin being coated on the base paper just after the manufacturing step of said base paper.
16 . The method of manufacturing an electrical insulation paper of claim 14 , comprising a step, prior to the step of adding the thermal stabilizer comprising nitrogen or of coating the base paper with the resin, of hot calendaring the base paper at a temperature in a range of 120° C. to 160° C. and with a pressure in a range of 800 daN to 1200 daN.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a National Stage application of PCT/IB2023/058290, filed Aug. 18, 2023, which claims priority to European Patent Application Number 22306242.3, filed Aug. 19, 2022, both of which are incorporated herein in their entirety. TECHNICAL FIELD The present disclosure relates to an electrical insulation paper. The present disclosure further concerns a method for its manufacture and cables, transformers, capacitors, and/or other items of electrical equipment that are equipped with such an electrical insulation paper. TECHNICAL BACKGROUND The invention relates to an electrical insulation paper. The invention further concerns a method for its manufacture and cables, transformers, capacitors, and/or other items of electrical equipment that are equipped with such an electrical insulation paper. Electrical insulation papers are used for electrical insulation in a variety of apparatuses, such as, for example, transformers, cables and capacitors, and in particular in liquid-filled transformers, cables and capacitors. There is a particular interest in materials with good mechanical and electrical properties that can be produced at low cost in comparison with Nomex® based paper. Electrical insulation papers comprising cellulose have become known and play an important role in the field of electrical insulation. Cellulose-based insulation papers combine good electrical insulation with good mechanical properties, and they can be produced cheaply. However, for example in liquid immersed transformers, insulation papers are exposed to various thermal, chemical, and/or oxidant stresses which may cause rapid ageing of the cellulose. The ageing shows in the form of a loss of tensile strength and is prone to cause a failure of the transformer. It would be desirable to be able to provide smaller transformers and other electrical equipment, without compromising on the electrical insulation, and the operation temperature and/or runtime limits of known devices are not always satisfying. It would also be desirable to provide transformers having the same size as the existing ones but able to run at higher temperatures. It is an object of the present disclosure to address at least one of the shortcomings of the state of the art. SUMMARY Aspects of the above-mentioned object are achieved by an electrical insulation paper in accordance with the present disclosure. One aspect of the present disclosure relates to an electrical insulation paper. The electrical insulation paper comprises at least 25% content by weight of cellulose fibers based on the total weight of the electrical insulation paper, at least 5% content by weight of synthetic fibers based on the total weight of the electrical insulation paper, a thermal stabilizer comprising nitrogen, wherein a content by weight of the nitrogen constitutes between 1% and 4% of the content by weight of the cellulose fibers. The synthetic fibers comprise aliphatic polyamide fibers and/or glass fibers. Another aspect of the present disclosure relates to a method of manufacturing an electrical insulation paper. The method comprises the steps of providing cellulose fibers and synthetic fibers and of manufacturing a base paper from the cellulose fibers and synthetic fibers on a paper machine, with at least 25% content by weight of the cellulose fibers based on the total weight of the electrical insulation paper, and at least 5% content by weight of the synthetic fibers based on the total weight of the electrical insulation paper. Another aspect of the present disclosure is an electrical insulation paper comprising at least one layer made by the method described herein. Another aspect of the present disclosure is the use of the electrical insulation disclosed herein for insulating wires of high-voltage liquid-immersed transformers or dry transformers, or for insulating of wires used in traction transformers or for a low voltage foil winding in distribution transformers. Phrase alternatively, another aspect is a transformer comprising wires insulated with the electrical insulation paper described herein or a transformer comprising a low voltage foil winding comprising the electrical insulation paper as described herein. BRIEF DESCRIPTION OF FIGURES FIG. 1 is a chart of the conductivity of examples of electrical insulation paper. FIG. 2 is a chart of the initial tensile index of examples of electrical insulation paper. FIG. 3 is a chart of tensile index retention after ageing of examples of electrical insulation paper. FIG. 4 is a chart of tensile index retention after ageing of examples of electrical insulation paper. FIG. 5 is a chart of the conductivity of examples of electrical insulation paper. FIG. 6 is a chart of the initial tensile index of examples of electrical insulation paper. FIG. 7 is a chart of tensile index retention after ageing of examples of electrical insulation paper. DETAILED DESCRIPTION The Electrical Insulation Paper The elec