Challenges of Prototyping in the NOVUM project
New manufacturing technologies and the materials associated with them must result in high quality of transformer insulation. This refers to dimensional stability, mechanical performance, electrical withstand, as well as good behavior at oil environment at elevated temperatures exposure for many years.
Materials used inside power transformer tanks that will come in contact with transformer oil must be compatible with the oil, i.e. the material must neither adversely affect the properties of the oil nor be degraded by the oil. Most of the materials developed and tested in frame of the NOVUM project have been characterized by good oil compatibility, but in some cases even short exposure to oil resulted in deformations of the material disqualifying its usage in industrial conditions (Figure 1).
Figure 1. Deformations of the material after immersion in transformer oil
Another challenge, when developing the suitable material and doing prototyping is related with aging in oil at elevated temperatures. Some of the materials after oil ageing have showed a tendency to undergo changes in material structure (swelling, delamination, voids – Figure 2), leading to a very high brittleness of the samples and their easy cracking. As a consequence of such behaviour, in some cases, it was not possible to perform tensile and compression mechanical tests (Figure 3).
Figure 2. Changes in internal material structure after ageing in oil
Figure 3. Samples prepared for compression tests deformed after oil ageing
Also very important properties of the transformer insulation are related with electrical performance, and such properties as dielectric constant ε, dielectric loss tanδ, as well as electrical breakdown strength must be assured when developing and prototyping new materials. And still so far it is a huge challenge for a whole NOVUM team to formulate the material fulfilling all parameters defined in technical requirement specification. At that stage of the project, most of the testing and prototyping have been done on flat material samples, and the real applicability of new materials and technologies will be verified as soon as benchmark transformer components (three-dimensional structures) will be manufactured.