Performance of Insulation of DC/DC Converter Transformer for Offshore Wind Power Applications

Green Solution for Insulation System of a Medium Frequency High Voltage Transformer for an Offshore Wind Farm

“…The new design uses biodegradable insulation materials instead of mineral oil, which is undesirable from an environmental point of view, especially for offshore applications. The electrical conductivities of mineral oil and OIP insulation materials were measured previously by the authors and reported in [16]. In this work, the properties of the biodegradable dielectric oil and OIP are measured under an extensive effort and presented, and the results are used for the insulation design of an MFT introduced in the paper.…”

“…But at the final steady state, in which the conductivity of materials determines the stress; a material with greater conductivity will take less field intensity, and vice versa [8]. For example, since the ratio of the mineral oil/OIP conductivities may vary from 2 to 1000 [16,28], the paper will be more stressed than the oil at steady state. Therefore, the conductivity plays a crucial role in an insulation system which is stressed by a DC voltage.…”

“…It is known that the electrical conductivity of dielectrics depends on temperature and electric field intensity [16,[30][31][32]. Therefore, the LMW model is not fully suitable for determining the electrical stress distribution in the transformer's dielectric structure under very high DC voltage application.…”

“…The conductivity of OIP is also dependent on the cellulose fiber density and properties of the oil used for the impregnation [34]. Studies show that the standard production and treatment methods do not guarantee reproducible and comparable measurements results under an HVDC test or service conditions [16]. Furthermore, parameters such as temperature, field strength, pre-stressing and duration of stress bear a direct effect on the conductivity values under high DC stress [35].…”

“…The method of conductivity measurements including the procedures for preparation of the test samples, the design and setup of the measuring equipment, and methods of treating the measurement data are presented by the authors in their previously published works [5,16]. To achieve reliable results, the following activities should be carefully planned and implemented: the test cell design and temperature chamber preparation, the preparation of oil and solid insulation samples as well as the high voltage supply system and its safety circuit design, the current measuring system and its protection circuit design and the mitigation of noises.…”