Transformerboard is a highly compressed electrical pressboard made from pure cellulose that forms the solid insulation inside an oil-filled transformer. It separates windings, guides the electric field lines and keeps the components apart. Because it forms a proven insulating system together with insulating oil, it has to be oil resistant, dimensionally stable and dielectrically clean. Common thicknesses range from about 0.5 to 8 millimetres, thicker boards are built by bonding several layers. GOBA cuts and stamps transformerboard into barriers, angles, spacers and cylinders to drawing.
What transformerboard is
Transformerboard, often also called electrical pressboard or insulating board, is a stiff, dense cellulose-based material for the solid insulation in a transformer. It sits in the oil between and around the windings and carries mechanical as well as electrical loads there. Unlike thin insulating papers, it is thick, dimensionally stable and can be formed into three-dimensional parts. Its role in the insulating system is described in the article on the electrical transformer.
Transformerboard from GOBA: supply forms, thicknesses and enquiry
GOBA supplies Transformerboard from a single piece, as material or as a finished part to your drawing.
- Supply forms
- Sheet and board, Cut-to-size, Die-cut part to drawing, Formed part (folded, embossed or bent)
- Thicknesses
- To your specification. GOBA processes materials from 7 µm to 3 mm.
- Versions
- Barriers, angles, spacers and cylinders for oil-filled transformers to your drawing.
- Die-cut and formed parts
- Material thickness 0.023 to 3.0 mm, dimensions up to 1,000 × 2,000 mm
- Quantity
- From 1 piece, from sample to series
- Lead time
- Two weeks at most when the material is in stock
What we need for your quotation
- Drawing or dimensions
- Quantity
- Material and thickness
Manufacture from pure cellulose
High-grade transformerboard consists of 100 percent unbleached, sulphate-cooked cellulose, without binders or fillers. The fibres are layered while wet and compressed under high pressure. This wet compression creates the high density, the mechanical strength and the uniform structure. Doing without additives is not a detail but the basis of oil resistance: foreign matter would age in hot oil and degrade the dielectric values. After compression the board is dried and cut to format.
Properties
Three groups of properties make transformerboard the standard material of solid transformer insulation.
- Oil resistance: the board absorbs insulating oil and forms a shared insulating system with it. It stays dimensionally stable in hot oil for decades.
- Mechanical strength: high density and compressive strength, so it takes up short-circuit forces and the weight of the windings.
- Dielectric values: high dielectric strength and low losses, clearly better oil-impregnated than dry.
The thermal classification follows the insulation material classes. Pure cellulose belongs classically to thermal class A, and in the oil system of the transformer it stays stable over long periods, as long as temperature and moisture are under control.
Difference from pressboard
The terms transformerboard, pressboard and electrical board are often mixed up in daily use. Technically they describe closely related cellulose materials that differ in density, thickness and purity. Transformerboard denotes the highly compressed, mostly single-layer wet-compressed grade for transformer insulation. Classic pressboard is the umbrella term for compressed cellulose boards and ranges from thin, calendered grades to thick, bonded panels. For the oil-filled power transformer the high density and purity of transformerboard count, for dry applications plain pressboard is often enough.
Applications in the transformer
In the transformer, transformerboard takes on the load-bearing solid insulation. Typical parts are made by cutting, stamping and forming.
- Barriers: flat panels between the windings that guide the field lines.
- Spacers and strips: keep clearances and channels for the oil flow open.
- Angle rings and angles: guide the field around the edge at the winding ends.
- Cylinders and tubes: enclose the winding, made from rolled and bonded layers.
- Caps and formed parts: shaped parts for bushings and leads.
The solid insulation from transformerboard and the liquid insulation from oil work together, often complemented by impregnating and casting compounds. Their role is described in the article on insulating resin. Where higher temperatures are required, aramid paper is used instead of cellulose.
Cutting and stamping at GOBA
Transformerboard comes as a panel or roll and only becomes a part through precise cutting. GOBA cuts and stamps boards from about 0.5 to 8 millimetres into barriers, angles, spacers and strips, to your drawing and with clean edges. We process the dense material so the cut face does not break out and the dimensional accuracy holds, because in the field every edge counts. We also make thicker, multi-layer bonded builds and milled contours. Since 1959 GOBA has cut and stamped electrical insulating materials, and cellulose materials have been part of that from the start.
GOBA Takeaway
Transformerboard is the solid insulation of the oil-filled transformer: pure cellulose, highly compressed, oil resistant and mechanically strong. For the power transformer the high-density board leads, for simpler dry applications pressboard is enough. GOBA supplies transformerboard and electrical pressboard as insulation materials and makes ready-to-fit insulation and molded parts from it. Send us a drawing, thickness and quantity, and you will receive a technical quote.
