Insulation Design of a Medium Frequency Power Transformer for a Cost-Effective Series High Voltage DC Collection Network of an Offshore Wind Farm

Kharezy, Mohammad; Eslamian, Morteza; Thiringer, Torbjörn

doi:10.1007/978-3-030-31680-8_134

Cited by 8 publications

(11 citation statements)

References 6 publications

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“…According to the Linear MW model (LMW) after applying a step DC voltage to the oil/paper dielectrics, the initial electric field distribution is based on material dielectric constants ratios (2.2 for oil and 4.4 for paper for example), and therefore the electric field intensity in the oil has a value nearly twice its value inside the paper. But at the final steady state, which may last up to several hours, it is the conductivity of materials that determines stress; a material with greater conductivity will take larger field intensity, and vice versa [66]. Since the ratio of the oil to paper conductivity may vary from 10 to 1000 or higher [67] and [52], the paper will be more stressed than the oil at steady state.…”

Section: Linear Maxwell-wagner Methodsmentioning

confidence: 99%

“…For an oil paper insulation system, the low permittivity oil which experiences a high voltage potential difference under AC will take less voltage drop then under DC due to the lower conductivity compared with solid paper or pressboard insulation. When a DC voltage is applied to the transformer, first it is the permittivity values which determine the voltage distribution and at the steady state condition, the distribution is based on conductivity values [66].…”

Section: Transformer Insulation Under Ac Stressmentioning

confidence: 99%

“…On the interface of the transformer board with the oil, the maximum permissible creepage strength is 30% lower than the permissible strength for an oil gap of the same length [65]. [66]. The study shows that for a dry-type MFT this is difficult to accomplish with a relatively high voltage to ground insulation.…”

Section: Ac Design Creepage Distancesmentioning

confidence: 99%

“…The dynamic behaviour is characterized by the time constants τOil=εOil/σOil and τOIP=εOIP/σOIP. The relative dielectric permittivity of the materials can be assumed to be constant at the operational conditions of the transformer and equal to typical values of 2.2 and 4.4 for oil and OIP, respectively [66]. In contrast, the electric conductivities depend on temperature and electric stress as demonstrated in this work.…”

Section: Prototype Insulation Designmentioning

confidence: 99%

See 3 more Smart Citations

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

Kharezy

Mirzaei

Serdyuk

et al. 2021

IEEE Trans. Power Delivery

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Section: Linear Maxwell-wagner Methodsmentioning

confidence: 99%

Section: Transformer Insulation Under Ac Stressmentioning

confidence: 99%

Section: Ac Design Creepage Distancesmentioning

confidence: 99%

Section: Prototype Insulation Designmentioning

confidence: 99%

See 2 more Smart Citations

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

Kharezy

Mirzaei

Serdyuk

et al. 2021

IEEE Trans. Power Delivery

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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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Design and electric field analysis of novel winding structures with fillets for medium frequency transformers

Wang

Yuan

2021

IET Electric Power Appl

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The medium frequency transformer (MFT) has a significant role in large-capacity DC-DC convertors, whereas the design of insulation under compact structures remains a critical challenge. Generally, the electric field strength near the winding edges is much larger than other positions. To fulfil insulation requirements, the distance between windings and the magnetic core needs to be enlarged, which also expands the window area of the core and the total volume of the MFT. A series of winding structures with fillets is proposed, including constructing winding fillets with reshaped foil and adopting different techniques to fillet the foil. The finite-element method is used to analyse the insulation effects of various winding structures with fillets, conducted under diverse voltage levels and insulation materials commonly used in MFTs. The structures can substantially reduce the local electric field strength, further compressing the volume of the MFT.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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Insulation Design of a Medium Frequency Power Transformer for a Cost-Effective Series High Voltage DC Collection Network of an Offshore Wind Farm

Cited by 8 publications

References 6 publications

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

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

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

Design and electric field analysis of novel winding structures with fillets for medium frequency transformers

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