• Proceedings of the KIEE Conference
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• 2000.11a
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• pp.171-173
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• 2000

This paper presents a discriminating algorithm between magnetizing inrush and internal faults of transformers using difference of a differential current. Incase of inrush, change of magnetizing inductance repeats. Thus, second difference of differential current periodically shows pulse while periodic pulse is not represented in case of internal winding fault. The proposed algorithm is suitable irrespective of the amount of remanent flux.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.3
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• pp.201-207
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• 2020

With the expansion in the use of DC power systems and increased need for system maintenance, the development of measurement devices for maintenance requires high stability. Of the different kinds of DC current measurement devices, the single-shot measurement device causes the input signal of the current measuring unit to initially generate a high inrush current. The high inrush current flows into the signal processor of the meter, shortening the life of the internal fuses and causing failure. Therefore, in this study, the I²t value for increasing the durability of the fuse is designed using the available wire diameter. Operating characteristics for 210~400% over-current of the rated current, which is relatively low over-current, are realized by the plating of low melting tin metal. As a result, a method of designing a fuse element for a DC power supply, which improves the safety of the DC current measurement device by blocking the failure caused by the inrush current, is presented.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.5
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• pp.61-67
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• 2001

Magnetic flux saturation dependent on phase of initial input power to high voltage transformer used in Micro wave oven. To limit inrush current high voltage transformer the relay contact should be ˝ON˝ when the lowest point of input voltage phase. The improved circuit is form compensating interrupt signal Micom input so the relay contact can be ˝ON˝ when the inrush current is lower. Test results are presented that improved circuit satisfies the limit 50[A] of requirement for input voltage variation mode. And the result verified by statistical method.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.3
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• pp.138-142
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• 2014

In general, the voltage stability of induction generator is lower than synchronous generator. However, induction generator has many advantages rather than a synchronous generator in terms of price and maintenance. So Induction generator is used little by little in small hydroelectric power station rather than 1000kW recently. Squirrel cage induction generator generates a high inrush current at the grid-connection. This high inrush current causes a voltage drop on the grid. In order to increase the penetration of the induction generator, it is necessary to present a method of reducing inrush current. In this study, we suggested that it is possible to present a reactor startup method, by applying the parameter to reduce the voltage drop.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.340-348
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• 2006

This paper proposes an inrush current control technique of matching transformer for configuration of dynamic voltage restorer(DVR). The DVR system consist of PWM inverter to inject arbitrary voltage, LC low pass filter as harmonic eliminator and matching transformer for isolation. However, the matching transformer has an excess of inrush current by magnetic flux saturation in the core. Due to this inrush current, the rating of matching transformers is double for needed nominal rating for protection of DVR. Therefore, in this paper, the modeling method of magnetic flux saturation is used to analyze a magnitude of inrush current, and additional current controller is used for PWM inverter output regulation. Simulation and experimental results are provided to demonstrate the validity of the proposed control method.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.675-682
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• 2016

Sudden voltage drops and outages frequently disturb the operation of sensitive loads for domestic, commercial, and industrial use. In some cases, these events may even impair the functioning of relevant equipment. To maintain power under such conditions, a UPS system is usually installed. Once a disturbance happens at the grid side, the line-interactive UPS system takes over the load to prevent an interruption. But, due to magnetic saturation of the transformer, a significant inrush current may occur for the transformer-coupled loads during this transition. The generation of such transient currents may in turn decrease the line voltage and activates over-current protecting devices of the system. In this work, a cost-effective, line-interactive UPS system is proposed that eliminates the inrush current phenomenon associated with transformer-coupled loads. The strategy was implemented by connecting a standard current-regulated voltage source inverter (CRVSI) to the secondary winding of the load transformer. During any transient condition at the grid side, the load current is monitored and regulated to achieve either seamless compensation of the load current or complete transferal of load from grid to the inverter. Experimental results were obtained for a prototype under all possible operating conditions so as to validate the performance of the proposed topology.

• KIEE International Transactions on Power Engineering
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• v.5A no.1
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• pp.1-8
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• 2005

During magnetic inrush or over-excitation, saturation of the core in a transformer draws a significant exciting current, which can cause malfunction of a current-differential relay. This paper proposes a modified-current-differential relay for transformer protection. The relay calculates the core-loss current from the induced voltage and the core-loss resistance as well as the magnetizing current from the core flux and the magnetization curve. Finally, the relay obtains the modified differential current by subtracting the core-loss and the magnetizing currents from the conventional differential current. A comparative study of the conventional differential relay with harmonic blocking is presented. The proposed relay not only discriminates magnetic inrush and over-excitation from an internal fault, but also improves the relay speed.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.2
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• pp.80-86
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• 2004

During magnetic inrush or over-excitation, saturation of the core in a transformer draws a large exciting current, which can cause mal-operation of a differential relay. This paper proposes a modified current differential relay for transformer protection. The relay calculates core-loss current from the induced voltage and the core-loss resistance; the relay calculates the magnetizing current from the core flux and the magnetization curve. Finally, the relay obtains the modified differential current by subtracting the core-loss and the magnetizing currents from the conventional differential current. Comparison study with the conventional differential relay with harmonic blocking is also shown. The proposed technique not only discriminates magnetic inrush and over-excitation from an internal fault, but also improves the speed of the conventional relay.

• Geomechanics and Engineering
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• v.28 no.6
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• pp.573-584
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• 2022

Water inrush may occur during seaside urban tunnel excavation. Various factors affect the water inrush, and the water inrush mechanism is complex. In this study, nine evaluation indices having potential effects on water inrush were analysed. Specifically, the geographic and geomorphic conditions, unfavourable geology, distance from the tunnel to sea, strength of the surrounding rock, groundwater level, tidal action, cyclical footage, grouting pressure, and grouting reinforced region were analysed. Furthermore, a two-step interval risk assessment method for water inrush management during seaside urban tunnel excavation was developed by a multi-index system and interval risk assessment comprised of an interval analytic hierarchy process, fuzzy comprehensive evaluation, and relative superiority analysis. The novel assessment method was applied to the Haicang Tunnel successfully. A preliminary interval risk assessment method for water inrush was performed based on engineering geological conditions. As a result, the risk level fell into a risk level IV, which represents a section with high risk. Subsequently, a secondary interval risk assessment method was performed based on engineering geological conditions and construction conditions. The risk level of water inrush is reduced to a risk level II. The results agreed with the current tunnel situation, which verified the reliability of this approach.

• Proceedings of the KIEE Conference
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• 2008.11a
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• pp.37-39
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• 2008

This paper suggests a decision scheme for optimal insertion resistance in an Superconducting Fault Current Limiter (SFCL) application to reduce the transformer inrush current. This scheme and the SFCL model are implemented using Electromagnetic Transient Program (EMTP). We determine the optimal SFCL resistance by EMTP simulation, and this value is applied to model the SFCL by EMTP. The simulation results show the validity and effectiveness of the suggested scheme and the ability of a SFCL to reduce the inrush current.