• Progress in Superconductivity and Cryogenics
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• v.6 no.4
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• pp.37-40
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• 2004

A 1 MV A single phase high temperature superconducting (HTS) transformer was manufactured and tested. The rated voltages of primary and secondary of the HTS transformer are 22.9 kV and 6.6 kV respectively. BSCCO-2223 HTS tape was used for HTS windings of 1 MV A HTS transformer. In order to reduce AC loss generated in the HTS winding, the type of concentric arrangement winding was adopted to a 1 MV A HTS transformer. Single HTS tape for primary windings and 4 parallel HTS tapes for secondary windings were used considering the each rated current of the HTS transformer. A core of HTS transformer was fabricated as a shell type core made of laminated silicon steel plate. And a GFRP cryostat with a room temperature bore was also manufactured. The characteristic tests of 1 MV A HTS transformer were performed such as no load test, short circuit test and several insulation tests at 65 K using sub-cooled liquid nitrogen. From the results of tests, the validity of design of HTS transformer was ascertained.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.66-70
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• 2003

In a HTS transformer, the perpendicular component of magnetic flux density ($B_r$) applied to HTS tapes of pancake windings becomes larger than that of solenoid winding, thereby decreasing the critical current in the HTS tapes. This paper introduces several methods to reduce $B_r$ applied to the HTS tapes in the transformer with double pancake windings by changing winding arrangements and the relative permeability of flux diverters. We have conducted a winding design for a single-phase 1MVA 22.9kV/6.6kV HTS transformer. We observed a change of $B_r$ due to a variation of gap-length between the high voltage windings and the low voltage windings, reciprocal arrangement and an increase of the number of the high voltage pancake. We also observed a change of Br on the HTS tapes due to variation of the relative permeability of flux diverters placed between the high voltage winding and the low voltage winding. Finally, we have designed a 1MVA 22.9kV/6.6kV HTS transformer winding using suggested methods and calculated transformer parameters by the 3D finite element method.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.3
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• pp.173-178
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• 2003

This paper proposes a three-winding transformer protective relaying algorithm based on the ratio of the induced voltages (RIV). The RIV of the two windings is the same as the turn ratio for all operating conditions except an internal fault. For a single phase and a three-phase transformer containing the wye-connected windings, the induced voltages of the windings are estimated. For a three-phase transformer containing the delta-connected windings, the induced voltage differences are estimated using the line currents, because the winding currents are practically unavailable. The algorithm can identify the faulted phase and winding if a fault occurs on one phase of a winding. The test results clearly show that the algorithm successfully discriminates internal winding faults from magnetic inrush. The algorithm not only does not require hysteresis data but also can reduce the operating time of a relay.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.1
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• pp.17-21
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• 2005

AC loss is one of the important parameters in HTS (High Temperature Superconducting) AC devices. Among the HTS AC power devices, the transformer is the essential part in the electrical power system. But unfortunately, the transformer is the worst HTS device concerning AC loss because of very large magnetization loss due to high magnetic field applied to the HTS wire. We calculated the magnetization losses in HTS pancake windings for transformer according to the operating temperature. Two kinds of arrangement of HTS pancake windings were adopted for calculation of AC losses of a shell type transformer, and the analysis results were presented and discussed.

• Progress in Superconductivity and Cryogenics
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• v.2 no.2
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• pp.37-43
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• 2000

This paper describes the construction and test results of a 10kVA single phase HTS transformer. Double pancake windings with BSCCO-2223 HTS tape and G10-FRP cryostat with room temperature bore are used in the transformer. Two double pancake windings are connected in series to provide 188 turns and other two double pancake windings are connected in parallel to conduct the secondary current of 45.4[A]. Coefficients of the constructed transformer are obtained using the fundamental teats of the transformer. According to the test results, larger leakage reactance than expected is observed due to the bulky core which surrounds the sryostat.

• Proceedings of the KIEE Conference
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• 2000.11b
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• pp.321-323
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• 2000

This paper describes the construction and test results of a 10kVA single phase HTS transformer. Double pancake windings with BSCCO-2223 HTS tape and GFRP cryostat with room temperature bore are used in the transformer. Two double pancake windings are connected in series to provide 184 turns and two double pancake windings are connected in parallel to conduct the secondary current of 45.4A. Coefficients of the constructed transformer are obtained using the fundamental tests of the transformer. According to the test results, larger leakage reactance than expected is observed due to the bulky core which surrounded the cryostat.

• Progress in Superconductivity
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• v.4 no.1
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• pp.86-89
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• 2002

In this paper, the design of a IMVA single-phase high temperature superconducting(HTS) power transformer with BSCCO-2223 HTS tapes is presented. The rated voltages of each sides of the transformer are 22.9 ㎸ and 6.6 ㎸, respectively The winding of 1MVA HTS transformer is consisted of double pancake type HTS windings, which have advantages of insulation and distribution of high voltage, and are cooled by subcooled liquid nitrogen of 65K. Four HTS tapes were wound in parallel for the windings of low voltage side and the four parallel conductors are transposed. The design of 1MVA HTS transformer, a shell type core made of laminated silicon steel plate is chosen, and the core is separated with the windings by a cryostat with a room temperature bore. The cryostat made of non-magnetic and non-conducting material and a liquid nitrogen sub-cooling system is designed in order to maintain the coolant's temperature of 65K. For electromagnetic analysis of 1MVA HTS transformer, a finite element method of an axis of symmetry is used. The maximum perpendicular component of magnetic flux density of pancake windings is about 0.15T. And through analyzing the magnetic field distribution, an optimal winding arrangement of 1MVA HTS transformer is obtained.

• Journal of IKEEE
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• v.27 no.4
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• pp.587-600
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• 2023

This paper presents an optimal design of the slim type high frequency transformer used in the LLC DC to DC resonant converter for 65-inch UHD-TV with the rated power of 315W. This paper also performs an optimal design of the slim type high frequency through core loss analysis, AC winding loss analysis, and optimization design of the winding arrangement of the LLC resonant transformer. Particularly, the high-efficiency and slim type high frequency transformer based on the obtained results from theoretical analysis in this paper is constructed in the interleaved and vertical winding structures of its transformer to realize the winding method of automatic type and minimize AC winding loss. The primary and secondary windings of the slim type high frequency transformer the vertical winding structure proposed in this paper used the Litz-wire windings, PCB and copper plate windings, respectively. Finally, an optimal design of the slim type high frequency transformer proposed in this paper was carried out through the experimental results to confirm the validity of theoretical analysis based on the simulation results using Maxwell 2D and 3D tool.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.1
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• pp.23-26
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• 2003

This paper presents conceptual design and 3-D electromagnetic analysis of IMVA transformer with BSCCO-2223 High Tc Superconducting (HTS) tapes. The rated voltages of each sides of the transformer are 22.9 kV and 6.6 kV, and double pancake windings were adopted. High voltage and Low voltage sides were composed of several double pancake windings. Four HTS tapes were wound in parallel for the windings of low voltage side and were transposed in order to distribute the currents equally in each conductor The transformer core was designed as a shell type core made of laminated silicon steel plates and the core is separated with the windings by a cryostat with Fiberglass Reinforced Plastics(FRP). A sub-cooling system using L$N_2$ were designed to maintain the coolant temperature 65K. Finally perpendicular components of magnetic field applied to tapes were calculated 0.247 in the rated operation using 3-D analysis. A real 1MVA HTS transformer will be manufactured in near future based on the design parameters presented in this paper.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.885-886
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• 2006

We have proposed a 100 MVA, 3 phases, 154 kV class HTS transformer which will substitute for 60 MVA conventional transformer. In this paper, we designed conceptually the structure of the superconducting windings of a single phase 33 MVA transformer. The power transformer of 154 kV class has a tertiary winding besides primary and secondary windings. So the HTS transformer should have the 3rd superconducting winding, it makes the cost of the HTS transformer high and the efficiency low. Further more we considered On Load Tap Changer (OLTC) in HTS power transformer. OLTC equipment is required for fitting to a power transformer by which the voltage ratio between the windings can be varied while the transformer is on load. We analyzed the electrical characteristics of the HTS transformer such as magnetic stress and AC loss.