A Novel Oil-Immersed Medium Frequency Transformer for Offshore HVDC Wind Farms

Kharezy, Mohammad; Mirzaei, Hassan Reza; Serdyuk, Yuriy V.; Thiringer, Torbjörn; Eslamian, Morteza

doi:10.1109/tpwrd.2020.3035718

Cited by 14 publications

(23 citation statements)

References 70 publications

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“…The results of that work were expected to be used by offshore windfarm integration-network designers and manufacturers of equipment for wind farms, as well as manufacturers of MFTs for insulated DC/DC converters. Furthermore, during the previous phases of the project, design and construction processes of prototype transformers that can withstand a high DC offset voltages were reported [5,6] and the challenges in designing such transformers were reviewed [7]. In the present paper, the next step of the project is reported, which focuses on implementation of an environmentally friendly solution of the insulation system of MFT, based on biodegradable transformer oil and Oil Impregnated Pressboard (OIP).…”

Section: Hvdc Cablementioning

confidence: 99%

“…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. Additionally, a 10 MVA HVDC MFT with an insulation system using biodegradable oil and OIP is designed based on the method developed previously and verified by experimental testing [5]. Consequently, the performance of the ester-based insulation system is analyzed and compared to the case when mineral oil is used.…”

Section: Hvdc Cablementioning

confidence: 99%

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

et al. 2022

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High Voltage Direct Current (HVDC) transmission represents the most efficient way for transporting produced electrical energy from remotely located offshore wind farms to the shore. Such systems are implemented today using very expensive and large power transformers and converter stations placed on dedicated platforms. The present study aims at elaborating a compact solution for an energy collections system. The solution allows for a minimum of total transformer weight in the wind turbine nacelle reducing or even eliminating the need for a sea-based platform(s). The heart of the project is a Medium Frequency Transformer (MFT) that has a high DC voltage insulation towards ground. The transformer is employed in a DC/DC converter that delivers the energy into a serial array without additional conversion units. The insulation design methodology of an environmentally friendly HV insulation system for an MFT, based on pressboard and biodegradable oil, is introduced. The measurement method and results of the measurements of electrical conductivities of the transformer oil and Oil Impregnated Pressboard (OIP) are reported. The measurements show that the biodegradable ester oil/OIP conductivities are generally higher than the mineral oil/OIP conductivities. Numerical simulations reveal that the performance of the insulation system is slightly better when ester oil is used. Additionally, a lower temperature dependency for ester oil/OIP conductivities is observed, with the result that the transformer filled with ester oil is less sensitive to temperature variations.

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Section: Hvdc Cablementioning

confidence: 99%

Section: Hvdc Cablementioning

confidence: 99%

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

et al. 2022

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“…Reducing the HV winding height is also done in order to keep the HV winding far from the core edges at the top and bottom. To minimize high electric stresses at the winding's sharp edges, the commonly used rectangularshaped windings [7] are replaced with circular windings which are more suitable for MFTs with high voltage applications. As a result of using circular windings, the core segments are also distributed along the circumference of the winding region.…”

Section: Test Object and Experimental Verificationmentioning

confidence: 99%

“…Also, in parallel-input series-output DC-DC converters in all-DC offshore wind farms [6], there is a high DC offset voltage between the primary and secondary windings inside MFT. This requires an appropriate insulation system which enforces further restrictions on reducing the distances between windings which is extensively investigated by the authors in their previously reported activity [7]. Recent studies show that, from a practical point of view, for achieving a certain power and specific voltage conditions in a high-power MFT, there is a specific range for the optimal operating frequency which is 6-20 kHz [8]- [10].…”

Section: Introductionmentioning

confidence: 99%

An Accurate Method for Leakage Inductance Calculation of Shell-Type Multi Core-Segment Transformers With Circular Windings

2021

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The leakage field in shell-type transformers is strongly affected by the boundary conditions introduced by the core walls and thus the effect of the core should be considered properly in the leakage inductance calculation. In this paper, a new method for accurate calculation of the leakage inductance of shell-type multi core-segment transformers with circular windings is presented. For this purpose, first, the expressions for self and mutual inductances are derived in cylindrical coordinates considering the core walls as the flux-normal boundary condition. Then, a new approach is proposed for calculating the leakage inductance considering the number and dimensions of the used core segments. The method is developed at first for single and double core-segment transformers (known also as E-core and U-core transformers) and then adopted for shell-type segmented-core transformers. The method is verified by 3-D FEM simulations. The comparisons with the previous analytical methods demonstrate the superiority of the proposed method. A transformer prototype has been built and verification tests have been conducted. The comparisons show that the leakage inductance can be estimated with an error less than 1%, demonstrating a very high accuracy with the proposed method.

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“…An insufficient leakage inductance can adversely affect the converter efficiency while higher values of leakage inductance can cause an unnecessary reactive power circulation within the converter [4]. Therefore, the design of an MFT should fulfill the criteria of having a determined leakage inductance in addition to meet the other design requirements such as the specified isolation, efficiency and the thermal requirements [3], [5], [6], [7].…”

Section: Introductionmentioning

confidence: 99%

An Accurate Analytical Method for Leakage Inductance Calculation of Shell-Type Transformers With Rectangular Windings

2021

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This paper presents an accurate analytical method for calculating the leakage inductance of shell-type E-core transformers with rectangular windings. For this purpose, first, an expression for calculating the leakage inductance per unit length inside the core window considering the core walls as the flux-normal boundary condition is derived. Then, a new accurate method for determining the Mean Length of Turns (MLT) based on the total stored energy is presented. The MLT is needed for the leakage inductance calculation using 2-D methods. By dividing the MLT into three partial lengths and calculating the corresponding leakage inductances using three different core window arrangements, the effect of core structure on the total leakage inductance is considered. The method is verified by 3-D FEM simulations as well as the leakage inductance measurements on two different fabricated transformer prototypes. The superiority of the method is also confirmed by comparisons with the previous analytical approaches. The proposed method enables the leakage inductance calculation with an error less than 1%, compared to the 3-D FEM results. Using the presented method, the leakage inductance calculations can be performed rapidly and accurately in the design stage without the need for time-consuming 3-D FEM simulations.

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A Novel Oil-Immersed Medium Frequency Transformer for Offshore HVDC Wind Farms

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Cited by 14 publications

References 70 publications

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

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

An Accurate Method for Leakage Inductance Calculation of Shell-Type Multi Core-Segment Transformers With Circular Windings

An Accurate Analytical Method for Leakage Inductance Calculation of Shell-Type Transformers With Rectangular Windings

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