Electrical insulation papers are

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distribu ...

types that are used as electrical insulation in many applications due to pure

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wa ...

having outstanding electrical properties. Cellulose is a good insulator and is also

polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the cli ...

, having a

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the ma ...

constant significantly greater than one. 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 Paperboard is a thick paper-based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker (usually over 0.30 mm, 0.012 in, or 12 points) than paper and has certain superior attribute ...

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. In 1970, a branch of Weidmann Electrical Industries centered in St. Johnsbury, Vermont produced the largest Transformerboard ever measuring 12'5" by 21'8". At the time, the

Vermont Vermont () is a U.S. state, state in the northeast New England region of the United States. Vermont is bordered by the states of Massachusetts to the south, New Hampshire to the east, and New York (state), New York to the west, and the Provin ...

-based company was named EHV Industries.

Production

The more demanding application the cleaner the

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

distilled Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the hea ...

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 electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

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. In order to not become excessively thick 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 or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...

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 A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

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 paper pulp on a paper machine. Tissue paper is very versatile, and different kinds of tissue are made to best serve these purposes, w ...

(normally 6-12 g/m²) that is super

calender A calender is a series of hard pressure rollers used to finish or smooth 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 cal ...

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