Electrical insulation papers are specific types of

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses, Feces#Other uses, herbivore dung, or other vegetable sources in water. Once the water is dra ...

that are used as

electrical insulation Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

. They are used in many applications due to the outstanding electrical properties of pure

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

. Cellulose is a good insulator and is also polar, having a relative permittivity significantly greater than 1. Electrical paper products are classified by their thickness, with tissue considered papers less than 1.5 mils (0.0381 mm) thickness, and ''board'' considered more than 20 mils (0.508 mm) thickness.ASTM ''Paper and paperboard: characteristics, nomenclature, and significance of tests'', ASTM, 1951 page 26

History

The use of paper board as electrical insulation paper started in the early-mid 20th century. Since the need for high voltage electrical transformers, there has been a need for an insulating material that could withstand the high electrical and physical stresses experienced around a core and windings. Pressboard, a board made by compressing layers of paper together and drying them, has been used for installation purposes in many of the first electrical machines. However, as electrical technology increased, the need for a higher density material that was capable of insulating larger and higher voltage transformers grew. In the late 1920s, Hans Tschudi-Faude became the director of H. Weidmann Limited and began developing a type of pressboard that would meet the higher standards needed for the newer, more powerful transformers. Unlike older methods of pressboard production, Transformerboard was not based on used paper or cotton waste but was made with high-grade sulfate cellulose. The new product was made purely out of cellulose without a resin or binder, improving electrical insulation capabilities and could be completely dried, degassed, and oil impregnated. The new product became famous under the name Transformerboard. Throughout the 1930s, new methods of production and advances in understanding replaced almost all insulating parts of transformers with parts made from transformer board.

Production

The more demanding application the cleaner the

needs to be. Paper machines are run with deionised or even

distilled Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

process water when producing higher grades of electrical insulation paper. Electrical insulation papers are made from well delignified unbleached kraft pulp.

Applications

Cable paper

Electrical cables are categorized by the

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

and current used. Telephone cables have moderate voltage and current associated with cables leading moderate electric current or transmitting electrical signals. The telephone cables have a large number of conductors that are individually insulated. The paper needs to be thin (30-40 g/m²). A normal power cable needs more insulation and therefore paper with higher

paper density Paper density is a paper product's mass per unit volume. The density can be calculated by dividing the grammage of paper (in grams per square metre or "gsm") by its caliper (usually in micrometres, occasionally in mils). The "ISO 534:2011, ...

is used, normally 60-190 g/m². The paper needs to be strong, elastic, uniform and free of holes or debris. These applications are being replaced by

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

insulation.

High voltage power cable paper

Submarine power cable A submarine power cable is a transmission cable for carrying electric power below the surface of the water.capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

s and is an extremely clean and thin

tissue paper Tissue paper, or simply tissue, is a lightweight paper or light crêpe paper. Tissue can be made from recycled pulp (paper), paper pulp on a paper machine. Tissue paper is very versatile, and different kinds are made to best serve these purposes ...

(normally 6-12 g/m²) that is super

calender A calender is a series of hard pressure rollers used to finish a sheet of material such as paper, textiles, rubber, or plastics. Calender rolls are also used to form some types of plastic films and to apply coatings. Some calender rolls are ...

ed. The pulp is clean unbleached kraft pulp that is extremely refined. The paper is made on small paper machines with slow speeds because the stock has to be drained very slowly.

Transformer board

Transformer board is used mainly in oil-filled transformers where a solid insulating structure is needed. This is a pressboard up to 8 mm in thickness. The board is built up wet on forming cylinders and cut off when at the desired thickness. This makes a sheet with the size of the width and circumference of the drum. The wet sheets are hot- or cold-press dried and finished on separate machines.

References

{{Paper Dielectrics Paper