• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.8
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• pp.329-333
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• 2006

We investigated the quench characteristics of a flux-lock type superconducting fault current limiter (SFCL) depending on the number of the serial connection between the superconducting elements at the subtractive polarity winding of a transformer. The flux-lock type SFCL consists of two coils. The primary coil is wound in parallel to the secondary coil through an iron core, and the secondary coil is connected to the superconducting elements in series. The operation of the flux-lock type SFCL can be divided into the subtractive and the additive polarity windings depending on the winding directions between the primary and secondary coils. In this paper, the analyses of voltage, current, and resistance of superconducting elements in serial connection were performed to increase the power capacity of flux-lock type SFCL. The power burden was reduced through the simultaneous quenching between the superconducting elements. This enabled the flux-lock type SFCL to be easy to increase the capacity of power system.

• Transactions on Electrical and Electronic Materials
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• v.6 no.5
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• pp.193-197
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• 2005

We investigated fault current limiting characteristics of the flux-lock type superconducting fault current limiter (SFCL), which consisted of a primary winding and several secondary windings connected in series between $high-T_C$ superconducting (HTSC) thin films. Each YBCO thin film has a 2 mm wide and 42 cm long meander line with 14 stripes of different length. The power imbalance due to the slight difference of Ie between YBCO current limiting elements causes the significant power burden on YBCO element with lower $I_C$. We confirmed from our experiments that the mutual coupling between the primary winding and secondary windings of the flux-lock type SFCL reduced the power imbalance between YBCO current limiting elements compared with the resistive type SFCL connected in series.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.1
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• pp.33-39
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• 2005

Comparing with the conventional transformer without the air gap, a contactless transformer with the large air gap between the long primary winding and the secondary winding has increased leakage inductance and reduced magnetizing inductance. For transferring the primary power to the secondary one, the high frequency series resonant converter has been widely used for the contactless power supply system with the large air gap and the increased leakage inductance of the contactless transformer However, the high frequency series resonant converter has the disadvantages of the low efficiency and high voltage gain characteristics in the overall load range due to the large air gap and the circulating magnetizing current. In this paper, the characteristics of the high efficiency and unit voltage gain are revealed in the proposed three-level series-parallel resonant converter. The results are verified on the simulation based on the theoretical analysis and the 5kW experimental prototype.

• 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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2078-2083
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• 2007

We have analyzed operating characteristics of transformer-type superconducting fault current limiter (SFCL) according to the serial or parallel connections of secondary coils with $YBa_2Cu_3O_7$ (YBCO) thin films. The turn ratio between the primary and secondary coils was 63:21. Transformer-type SFCL using a transformer with secondary winding of serial or parallel coils could reduce the unbalanced quench caused by differences of the critical current density between YBCO thin films. We found that transformer-type SFCL having serial or parallel connections induced simultaneous quench between the superconducting units. The limiting current in the transformer-type SFCL with a parallel connection was lowered to 30 % compared to the SFCL with a serial connection. In the meantime, when the currents generated in the superconducting units were similar, the voltage value in the parallel connection was 60 % as low as that in the serial connection. However, the voltage generated in the primary winding was some higher. In conclusion, we found that transformer-type SFCL with parallel connection of secondary coils was more effective in fault current limiting characteristics and in the reduction of the consumption power for superconducting units compared to those of the transformer-type SFCL with serial connection of secondary coils.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.15-17
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• 2002

Leakage inductance and temperature rise are two of the more impotent problems facing the magnetic core technology of today's high frequency transformers. Excessive leakage inductance increases the stress on the switching transistors and limits the duty-cycle, and excessive temperature rise can lead the design limitation of high frequency transformer with high current. The flat transformer technology provides a very good solution to the problems of leakage inductance and thermal management for high frequency power. The critical magnetic components and windings are optimized and packaged within a completely assembled module. The turns ratio in a flat transformer is determined as the product of the number of elements or modules times the number of primary turns. The leakage inductance increase proportionately to the number of elements, but since it is reduced as the square of the turns, the net reduction can be very significant. The flat transformer modules use cores which have no gap. This eliminates fringing fluxes and stray flux outside of the core. The secondary windings are formed of flat metal and are bonded to the inside surface of the core. The secondary winding thus surrounds the primary winding, so nearly all of the flux is captured.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.336-344
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• 2017

This paper presents the three-port DC-DC converter modeling and controller design procedure, which is part of the solid-state transformer (SST) to interface medium voltage AC grid to bipolar DC distribution network. Due to the high primary side DC link voltage, the proposed converter employs the three-level neutral point clamped (NPC) topology at the primary side and 2-two level half bridge circuits for each DC distribution network. For the proposed converter particular structure, this paper conducts modeling the three winding transformer and the power transfer between each port. A decoupling method is adopted to simplify the power transfer model. The voltage controller design procedure is presented. In addition, the output current sharing controller is employed for current balancing between the parallel-connected secondary output ports. The proposed circuit and controller performance are verified by experimental results using a 30 kW prototype SST system.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.5 no.4
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• pp.211-215
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• 2012

Surgery equipment in operating room is very important at treatment procedure of patients. In this circuit of large equipment, a sudden change of current make big problem such as short circuit. when the current is converted suddenly, the current converter becomes in saturate and it caused by the induction curve of the inductor. in this case, the rates of the primary and secondary winding are broken and it becomes a open circuit. in this paper, we will look around the current transform of the primary and secondary winding when current converter becomes in saturate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.587-590
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• 2003

The first attention in designing a transformer for low temperature rise should be to reduce losses. Leakage inductance and temperature rise are two of the more impotent problems facing the magnetic core technology of today's high frequency transformers. Excessive leakage inductance increases the stress on the switching transistors and limits the duty-cycle, and excessive temperature rise can lead the design limitation of high frequency transformer with high current. The flat transformer technology provides a very good solution to the problems of leakage inductance and thermal management for high frequency power. The critical magnetic components and windings are optimized and packaged within a completely assembled module. The turns ratio in a flat transformer is determined as the product of the number of elements or modules times the number of primary turns. The leakage inductance increase proportionately to the number of elements, but since it is reduced as the square of the turns, the net reduction can be very significant. The flat transformer modules use cores which have no gap. This eliminates fringing fluxes and stray flux outside of the core. The secondary windings are formed of flat metal and are bonded to the inside surface of the core. The secondary winding thus surrounds the primary winding, so nearly all of the flux is captured.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.2
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• pp.54-58
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• 2004

This paper presents the iron core design method of a high temperature superconducting (HTS) transformer considering voltages per turn (V/T). In this research, solenoid type HTS coils were selected for low voltage (LV) winding and double pancake coils for high voltage (HV) winding, just as in conventional large power transformers. V/T is one of the most fundamental elements used in designing transformers, as it decides the core cross sectional area and the number of primary and secondary winding turns. By controlling the V/T, the core dimension and core loss can be changed diversely. The leakage flux is another serious consideration in core design. The magnetic field perpendicular to the HTS wire causes its critical current to fall rapidly as the magnitude of the field increases slowly. Therefore in the design of iron core as well as superconducting windings, contemplation of leakage flux should be preceded. In this paper, the relationship between the V/T and core loss was observed and also, through computational calculations, the leakage magnetic fields perpendicular to the windings were found and their critical current decrement effects were considered in relation to the core design. The ％ impedance was calculated by way of the numerical method. Finally, various models were suggested.