| 1. |
- Abbasi, A, et al.
(författare)
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Progress on Partial Discharge Detectionunder DC Voltage Stress
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Detection and evaluation of partial discharges (PD) is important for quality assurance and diagnosis ofelectrical insulation systems. With increasing use of DC voltages in electrical transmission and distributionsystems, the field of PD under DC voltage stress needs to be further investigated.CIGRE Working Group D1.63 was approved for start in May 2015, where available knowledge and experiencein particular concerning the field distribution in insulation systems used in DC voltage systems, and thephysical processes of the PD phenomena under DC voltage stress should be reviewed. In order of guidingto meaningful procedures for DC PD measurements of HV equipment thorough understanding of i) thedifferences of PD behaviour between AC and DC with respect to the physical process and ii) influencingfactors of operating conditions (as e.g. polarization, temperature etc.) of different insulation systems underDC stress and respective effects on PD phenomena had to be examined.
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| 2. |
- Alikhanzadehalamdari, Babak, 1993, et al.
(författare)
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Optimum Leakage Inductance Determination for a Q2L-Operating MMC-DAB with Different Transformer Winding Configurations
- 2019
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Ingår i: 20th IEEE International Symposium on Power Electronics (Ee). - 9781728150673
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Konferensbidrag (refereegranskat)abstract
- This paper discusses the procedure for the determination of the optimum leakage inductance of a medium frequency transformer (MFT) for a quasi-two-level (Q2L) operating three-phase modular multilevel converter dual-active bridge (MMC-DAB) considering the effects of the MFT winding configuration. Three different winding configurations-namely, Y-Y, D-D, and Y-D-are considered for the connection of the MFT windings. The optimum leakage inductance requirement of the MFT, the currents total harmonic distortion (THD), and the transformer utilization factor (TUF) are compared for the three winding configurations. It is found that the Y-Y and the D-D configurations have similar optimum leakage inductance patterns, which are different from the Y-D configuration. Furthermore, it is established that an optimized leakage inductance value for a conventional DAB, can be utilized for the Q2L-operating MMC-DAB for a wide range of transition time with the Y-Y and the D-D winding configurations if less than a 5% error could be tolerated in its value. A comparison with respect to the TUF and the currents THD revealed that the Y-Y and the D-D configurations result in a higher TUF compared to the Y-D configuration; However, the Y-D configuration has approximately two times lower currents THD compared to the other two configurations.
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| 3. |
- Bahmani, Amin, 1985, et al.
(författare)
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Design Methodology and Optimization of a Medium Frequency Transformer for High Power DC-DC Applications
- 2015
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Ingår i: Applied Power Electronics Conference APEC. ; , s. 2532-2539, s. 2532-2539
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The high power medium frequency transformer (HPMFT) is one of the key elements of an isolated, bi-directional DC-DC converters in applications such as future all-DC offshore wind farms, traction and solid state transformers. This paper describes a design methodology taking into account the loss calculation, isolation requirements and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a design example to find the highest power density while the efficiency, isolation, thermal and leakage inductance requirements are all met.
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| 4. |
- Bahmani, Amin, 1985, et al.
(författare)
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Design methodology and optimization of a medium-frequency transformer for high-power DC-DC applications
- 2016
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Ingår i: IEEE transactions on industry applications. - : Institute of Electrical and Electronics Engineers Inc.. - 0093-9994 .- 1939-9367. ; 52:5, s. 4225-4233
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Tidskriftsartikel (refereegranskat)abstract
- The medium-frequency power transformer (MFPT) is one of the key elements of an isolated bi-directional dc-dc converters in applications such as future all-dc offshore wind farms, traction, and solid state transformers. This paper describes a design methodology taking into account loss calculation, isolation requirements, and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a design example to find the highest power density while the efficiency, isolation, thermal, and leakage inductance requirements are all met.
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| 5. |
- Bahmani, Amin, 1985, et al.
(författare)
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Optimization and Experimental Validation of Medium-Frequency High Power Transformers in Solid-State Transformer Applications
- 2016
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Ingår i: 2016 IEEE Applied Power Electronics Conference and Exposition (APEC). - 9781467383936 - 9781467395502 ; , s. 3043-3050
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High power isolated DC-DC converters are likely to provide solutions for many technical challenges associated with power density, efficiency and reliability in potential applications such as offshore wind farms, inter-connection of DC grids, MVDC in data centers and in future solid state transformer applications. The high power medium frequency transformer (HPMFT) is one of the key elements of such a converter to realize the voltage adaption, isolation requirements, as well as high power density. This paper describes a design and optimization methodology taking into account the loss calculation, isolation requirements and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a 50 kW, 1 / 3 kV, 5 kHz transformer to find the highest power density while the efficiency, isolation, thermal and leakage inductance requirements are all met. The optimized transformers are then manufactured and will be presented in this paper.
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| 6. |
- Elg, Alf Peter, et al.
(författare)
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Characterization of dielectric properties of insulating materials for use in an HVDC reference divider
- 2012
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Ingår i: CPEM Digest (Conference on Precision Electromagnetic Measurements). - 9781467304399 ; , s. 80-81
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Konferensbidrag (refereegranskat)abstract
- Dielectric properties of polyethylene (PE), polyoxymethylene (POM) and ceramic glass (MACOR) are compared. Their suitability to act as a support for a resistor chain in a wideband HVDC reference divider is characterized. The support material forms a parallel capacitance to the resistive resistor chain, and a bandwidth of more than 100 kHz is needed. The frequency dependence of dielectric constant has been measured in the range 20 - 100 kHz. The depolarization current of these materials was measured to be at least 6 orders of magnitude lower than the current through the resistive chain. Neither MACOR nor PE does build up space charge which POM does. Possessing the highest dielectric constant makes MACOR well suited for the application.
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| 7. |
- Elg, Alf Peter, et al.
(författare)
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Traceability and characterization of a 1000 kV HVDC reference divider
- 2014
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Ingår i: CPEM Digest (Conference on Precision Electromagnetic Measurements). - 9781479952052 ; , s. 780-781
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Konferensbidrag (refereegranskat)abstract
- This paper presents the characterization of a resistive HVDC reference divider and methods to establish a traceability. The divider is designed for use as a laboratory reference for calibration of HVDC measuring systems up to 1000 kV. Targeting a measurement uncertainty of 20 ppm at full voltage has put a focus on the temperature coefficients of the resistors, elimination of humidity dependence and control of leakage currents in the high voltage arm.
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| 8. |
- Elg, Alf Peter, et al.
(författare)
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Traceability and Characterization of a 1000 kV HVDC Reference Divider
- 2015
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 64:6, s. 1709-1715
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the characterization of a resistive high-voltage dc (HVDC) reference divider and methods to establish traceability. The divider is designed for use as a laboratory reference for calibration of HVDC measuring systems up to 1000 kV. Targeting a measurement uncertainty of 20 μV/V at full voltage has put a focus on the temperature coefficients of the resistors, elimination of humidity dependence, and control of leakage currents in the high-voltage arm. A scale factor calibration against a 50 kV divider at 10 kV leads to an expanded uncertainty of 15 μV/V.
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| 9. |
- Eslamian, Morteza, et al.
(författare)
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An Accurate Analytical Method for Leakage Inductance Calculation of Shell-type Transformers with Rectangular Windings
- 2021
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Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers Inc.. - 2169-3536. ; 9, s. 72647-72660
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Tidskriftsartikel (refereegranskat)abstract
- 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. CCBYNCND
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| 10. |
- Eslamian, Morteza, et al.
(författare)
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An Accurate Method for Leakage Inductance Calculation of Shell-Type Multi Core-Segment Transformers With Circular Windings
- 2021
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Ingår i: IEEE Access. - 2169-3536. ; 9, s. 111417-111431
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Tidskriftsartikel (refereegranskat)abstract
- 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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