Raw materials used in NOVUM. Reasons behind the decision of the materials chosen
Power transformer is a key element of the power grid infrastructure and its reliability, safety and lifetime is strongly affected by the insulation system used, namely oil and cellulosic insulation.
Cellulose is a common raw material for the insulation components due to its high purity, excellent dielectric strength (dielectric constant ε and dielectric loss tanδ, as well as proper breakdown strength), good mechanical strength (comprising compression strength in static and dynamic conditions during short circuits), ability to be impregnated with oil thus avoiding partial discharges and long lifetime at operating temperature (up to 30 years life-time).
Cellulose is usually applied as wet sheets of electrotechnical paper (pressboard or press pan). Superior mechanical strength of cellulose insulation is obtained with unbleached sulphate pulp made mostly from spruce and pine trees. The pulp is dispersed in clean water and refined to a suitable fibre length, composition and bonding ability. And such material can be easily used in currently used forming process of transformer insulation components where the wet cellulose sheets are then prepared, formed, compressed and dried to obtain the final insulation product.
Having in mind all mentioned benefits of cellulosic materials used as the transformer insulation, it is foreseen that the cellulose (or nanocellulose) will still play essential role and will be the main component in the materials being under development within NOVUM project for new processes as 3D printing or thermoforming. This is not only due to its material properties but also resulting from cost advantage, as well as environmental impact.
Author : ABB Poland