• 대한조선학회논문집
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• 제41권6호
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• pp.65-74
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• 2004

The inherent strain method is known to be very efficient in predicting the deformation of steel plate by line heating. However, in the actual line heating process in shipyard, the rapid quenching changes the phase of steel. In this study, In order to consider additional effects under phase transformation, inherent strain regions were assumed to expand. Also, when calculating inherent strain, material properties of steel in heating and cooling are applied differently considering phase transformation. In this process, a new method which can reflect thermal volume expansion of martensite is suggested.8y the suggested method, it was possible to predict the plate deformations by line heating more precisely.

• 조명전기설비학회논문지
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• 제29권12호
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• pp.83-87
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• 2015

This paper presents a simple notch filter, which is so suitable for three-phase unbalanced and distorted power line. In the d-q synchronous transformation, three-phase unbalanced and distorted voltages generate lots of ripple voltages on d-q axes. The ripples make disturbances on controllers such as PLL of phase tracking. Unbalanced state makes ripple of double the frequency of power line. Odd harmonics 5th and 7th on the line make even 4th and 6th ripples on d-q axes due to the rotating reference frame, respectively. Cascaded two comb filters, delay lines 1/4T and 1/8T, are adopted for the ripple rejection. The filter rejects harmonics 2nd, 4th, 6th, 10th and so on. They are very effective to remove the ripples of both unbalance and distortion. The filter, implemented by two FIFOs on an experimental system, is adopted on a PLL controller of power line phase tracking. Through the simulation and experimental results, performance of the proposed comb filter has been validated.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.119-121
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• 2001

This paper presents steady state analysis of single-phase line-start motor. 2-phase motor transformation is performed to consider the different specifications between main and auxiliary windings. The symmetrical coordinates transformation is applied to solve the unbalanced magnetic field. The validity of analysis method is verified by comparing to experiments.

• Journal of Welding and Joining
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• 제16권3호
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• pp.74-84
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• 1998

The microstructures of the HAZ (Heat Affected Zone) are generally different from the base metal due to rapid thermal cycle during welding process. Particuraly, CGHAZ (Coarsened Grain Heat Affected Zone) near the fusion line is the most concerned region in which many metallurgical and mechanical discontinuities have been normally generated. A computer program by the numerical formularization of phase transformation during cooling with different rates was developed to generate the CCT diagram, and to predict microstructural (phase) changes in the CGHAZ. In order to verify simulated results, isothermal and continuous cooling transformation experiments were conducted. The simulated and experimental results showed that the developed computer model could successfully predict the room temperature microstructural changes (changes in volume fraction of phases) under various welding conditions (heat input & cooling rate $(Δt_{8/5})$).

• KIEE International Transactions on Power Engineering
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• 제3A권2호
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• pp.79-84
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• 2003

Unbalanced systems, such as distribution systems, have difficulties in fault locations due to single-phase laterals and loads. This paper proposes new fault locations developed by the direct three-phase circuit analysis algorithms using matrix inverse lemma for the line-to-ground fault case and the line-to-line fault case in unbalanced systems. The fault location for balanced systems has been studied using the current distribution factor, by a conventional symmetrical transformation, but that for unbalanced systems has not been investigated due to their high complexity. The proposed algorithms overcome the limit of the conventional algorithm using the conventional symmetrical transformation, which requires the balanced system and are applicable to any power system but are particularly useful for unbalanced distribution systems. Their effectiveness has been proven through many EMTP simulations.

• 대한전기학회논문지:전력기술부문A
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• 제51권8호
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• pp.409-416
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• 2002

This paper presents a fault location algorithm using direct 3-phase circuit analysis for distribution power networks. The unbalanced feature of distribution networks due to single phase loads or asymmetric operation prohibits us from using the conventional symmetrical component transformation. Even though the symmetrical component transformation provides us with a very easy tool in three phase network analysis, it is limited to balanced systems in utilizing its strong point, which is not suitable for distribution networks. In this paper, a fault location algorithm using direct 3-phase circuit analysis is developed. The algorithm is derived and it Is shown that the proposed method if we use matrix inverse lemma, is not more difficult then the conventional methods using symmetrical component transformation. Since the symmetrical component transformation is not used in the suggested method, unbalanced networks also can be handled with the same difficulty as balanced networks. The case study results show the correctness and effectiveness of the proposed algorithm.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1754-1763
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• 2017

This paper analyses the characteristics of incomplete-journey double-circuit transmission lines on the same tower formed by single-circuit lines and double-circuit lines, and then presents a fault location algorithm based on identification of fault branch. With the relationship between the three-phase system and the double-circuit line system, a phase-mode transformation matrix for double-circuit lines can be derived. Based on the derived matrix, the double-circuit lines with faults can be decoupled, and then the fault location for an incomplete-journey double-circuit line is achieved by using modal components in the mode domain. The algorithm is divided into two steps. Firstly, the fault branch is identified by comparing the relationships of voltage amplitudes at the bonding point. Then the fault location, on the basis of the identification result, is calculated by using a two-terminal method, and only the fault distance of the actual fault branch can be obtained. There is no limit on synchronization of each terminal sampling data. The results of ATP-EMTP simulation show that the proposed algorithm can be applied within the entire line and can accurately locate faults in different fault types, fault resistances, and fault distances.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권12호
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• pp.592-600
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• 2001

This Paper presents the transient analysis of the single-phase line-start permanent magnet synchronous motor. To analyse the starting characteristics, the dynamic equation which is combined electric dynamic equations with mechanical dynamic equation is used. The electric dynamics are derived from the d-q axis voltages of stator and rotor respectively. Especially, symmetrical components transformation is used to consider unbalanced magnetic field which is produced by single-phase input. Non-linear d-q axis inductances according to current amplitude and current phase angle are calculated by Finite Element Method and applied to lumped parameter circuit. The analysis methods are validated by comparing simulated and experimental results.

• International Journal of Ocean System Engineering
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• 제1권1호
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• pp.46-51
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• 2011

In a line heating process for hull forming, the phase of the steel transforms from austenite to martensite, bainite, ferrite, or pearlite depending on the actual speed of cooling following line heating. In order to simulate the water cooling process widely used in shipyards, a heat transfer analysis on the effects of impinging water jet, film boiling, and radiation was performed. From the above simulation it was possible to obtain the actual speed of cooling and volume percentage of each phase in the inherent strain region of a line heated steel plate. Based on the material properties calculated from the volume percentage of each phase, it should be possible to predict the plate deformations due to line heating with better precision. Compared to the line heating experimental results, the simulated water cooling process method was verified to improve the predictability of the plate deformation due to line heating.

• 대한조선학회논문집
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• 제39권1호
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• pp.82-89
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• 2002

선상가열에 의한 판 변형 예측은 고유변형도법에 의해 효율적으로 예측할 수 있다. 종래의 용접에서의 고유변형도 결정 방법은 용접 실험을 통하여 온도분포와 강의 상변태 영역(Ac3)을 시편을 절단하여 계측하고 이를 고유변형도 영역으로 간주하는 것이었다. 선상가열의 현상은 용접과 유사하므로, 용접과 같은 조건 하에서 얻어진 결과를 그대로 선상가열 해석에 이용하여 왔으나 이 결과는 가열 패턴이나 판 두께에 제한을 가지고 있다. 또한 현장에서는 선상가열 후 수냉 처리하는데 그 과정에서 강이 원래의 상으로 돌아가지 않고 마르텐사이트가 되면서 전단 소성 변화를 일으킨다는 점에 착안하여, 본 연구에서는 종래에 시편의 온도계측과 상변태 영역을 직접 계측하는 파괴검사법을 FEM을 이용한 이론해석으로 대체하였다. 즉 임의의 적절한 열속 모델에 대한 온도 분포를 얻고, 조직변화에 따라 추가적으로 발생하는 소성 영역을 고려하기 위하여 공석 온도 영역까지 포함시켜 온도계측과 파괴실험 없이 순수한 이론만으로 고유변형도 영역을 결정하는 새로운 방법을 제안하였다. 이 방법으로 결정한 영역을 이용하여 판의 변형을 예측하고 실험 결과와 비교하여 잘 일치함으로써 본 논문에서 제안한 방법의 유효성을 입증하였다.