• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.307-309
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• 2008

This study suggests a modeling of grid-connected wind turbine generation system that has induction generator, and aims to perform simulations for outputs by the variation of actual wind speed and for fault current of wind generation system by the transformer winding connection. This study is implemented by matlab&simulink. The simulation shall be performed by assuming single line to ground fault generated in the system. Generator power, generator rotor speed, generator terminal current and fault current shall be observed following the performance of simulation. The fault current change will be dealt through the simulation results for fault current of wind generation system following the grid-connected transformer winding connection and the simulation result by the transformer neutral ground method.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.951-953
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• 2005

The current transformer is used for the insulation of measuring instrument, enlargement of measurement scope, standardization of measuring instrument, control of protective device. It's required various performance as the intention of service, site of establishment, insulation. especailly, current transformer has small ratio errors. if current transformer has large ratio error, it's caused a electricity failure. so in this paper, we examine the theory of current transformer, major factor of errors, output performance on over-current.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1765-1768
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• 1996

It is well known that the degradation transformer oil is mainly effected to the failure of transformer. In this paper it is discussed the characteristics of the degradation sensor checking transformer oil condition in live line. The degadation sensor composed with base ring, electrodes and porous ceramic passed through the transformer oil and checked the transformer oil condition with sensor's leakage current. It is important to minimize the leakage current of base ring and connection parts. To investigate the leakage current of base ring and connection parts it is examined the characteristics of V-T-I and DC 2 KV and other examinations. It is verified that ionized transformer caused by the expansion of oil temperature increase in the leakage current of porous ceramic sensor. It is certificated that the leakage current of other parts of porous ceramic is very small (about 2 %) than the porous ceramic and it is confirmed that the leakage current in porous ceramic is changed sensitively according to the new oil(NO) and and the degradation oil(DO).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.2
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• pp.184-189
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• 2022

In this paper, the fault current limiting operations of three-phase transformer type superconducting fault current limiter (SFCL) using double quench, which consisted of E-I iron core with three legs wound by primary and secondary windings and two superconducting modules (SCMs), were analyzed according to three-phase ground fault types. To verify the effective operation of the three-phase transformer type SFCL using double quench, the test circuit for three-phase ground faults was constructed, and the fault current tests were carried out. Through analysis on the fault current test results, the different fault current limiting characteristics of three-phase transformer type SFCL using double quench from three-phase transformer type SFCL using three SCMs were discussed.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.1
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• pp.79-84
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• 2009

In order to increase the capacity of the superconducting fault current limiter(SFCL), the current and voltage grades of the SFCL must be increased. As a method for the increase of the current and voltage grades of the SFCL, we compared the various characteristics between the flux-lock type SFCL "With three superconducting units connected in series and the transformer type SFCL using the transformer with three secondary circuits. One of three superconducting units had not quenched in the flux-lock type SFCL. Therefore, the unbalanced power burden happened because of the voltage difference generated by unbalanced quenching between the superconducting units. In the meantime, the three superconducting units were all quenched in the transformer type SFCL using the transformer, and the voltage difference generated between the superconducting units was decreased. Therefore, the difference of critical characteristics was complemented by distribution of fault current in accordance with the turn's ratio between primary and secondary windings. The unbalanced power burden of the superconducting units was reduced due to flux-share between the superconducting units in the transformer. In conclusion, the capacity increment of the SFCL using a transformer was easier due to equal distribution of voltages generated by simultaneous quench of the superconducting units. We think that the characteristics is improved more because of the decrease of saturation in the iron core if the secondary winding is increased in the SFCL using the transformer.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.27-30
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• 1991

With the recent development of high performance AC superconducting wire of very small ac loss and large current carrying capacity, the possibility of superconducting air core transformer is being studied. The air core transformer has merits of no iron loss, no insulation to the core and no harmonics. But the air core transformer has large exciting current and low magnetic coupling factor. To increase the coupling factor, the transformer of toroidal shape is proposed and designed. (10KVA, 110/220V) Compared with air core transformer of solenoidal shape, the performance is improved. The exciting current occupies about 22% of the rated current.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.3
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• pp.236-243
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• 2008

This paper analyses magnetic flux saturation of matching transformer considering characteristic of dynamic voltage restorer(DVR) system to solve voltage sags which are considered the dominant disturbances affecting power quality. This DVR consist of PWM inverter to inject arbitrary voltage, LC low pass filter and matching transformer for isolation and grid connection. However, the matching transformer has an excess of inrush current by magnetic flux saturation in the core of transformer. Due to this inrush current, the rating of matching transformers is double for needed nominal rating for protection of DVR. Therefore, in this paper, an advanced modeling method of magnetic flux saturation is used to analyze a magnitude and characteristic of magnetizing current. Simulation and experimental results considering characteristic of DVR system are provided to demonstrate the validity of the proposed analysis method.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.10
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• pp.683-692
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• 2000

A new primary-side-assisted zero-voltage and zero-current switching full bridge DC-DC converter with transformer isolation is proposed. The auxiliary circuit adopted to assist ZCS for the leading leg is composed of only one small transformer and two diodes. It has a simple and robust structure, and load current control capability even in short circuit conditions. Possibility of magnetic saturation due to asymmetricity of circuits or transient phenomena is greatly reduced, which is a very attractive feature in DC/DC converters with transformer isolation. The power rating of the auxiliary transformer is about 10% of that of the main transformer. Operation of a 12.5KW prototype designed for welding application was verified by experiments.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.239_240
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• 2009

This paper presents the brief analytical study on 돋 effects of higher impedance transformer(HIT) to reduce distribution system fault current. With the increase of source and load capacity of power system, fault current of D/L is much more increased and, conventional protection equipment-such as sectionalizer and recloser, have to be replaced higher switching capacity. However, this replacements needs a lot of budget to utility. Increase of transformer impedance is can be a countermeasure in practical basis. This paper compares the voltage and fault current magnitude of both cases -%Zt=20% and %Zt2=33.3%(transformer capacity is 75/100MVA). The simulation results show that the steady state voltage of HIT is dropped 5~6% more in peak load, and fault current was decreased about 5kA by high impedance on transformer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.8
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• pp.1479-1484
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• 2009

The introduction of the large transformer due to the large power demand has increased the fault current in power distribution system. The increased fault current can exceed the cut-off ratings of the circuit breaker. As the methods to solve this problem, the superconducting fault current limiter(SFCL) has been notified. However, the limited fault current by SFCL affects the operational characteristics of the protective device such as overcurrent relay. Therefore, the selection of the proper impedance for the SFCL is required to keep overcurrent relay's protective coordination with the SFCL when a large transformer is introduced into the distribution system. In this paper, the SFCL's impedance for protective coordination was investigates in that a large transformer is introduced.