• Journal of Welding and Joining
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• 제13권4호
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• pp.85-102
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• 1995

Weld quality of GMA welding processes is closely related to arc stability. Although many researches on arc stability have been performed, real-time estimation of arc stability has not been attempted. For instance, Mita proposed a off-line statistical method in which short circuiting and arcing time, and voltage and current wave forms were sampled to assess arc stability. But this method is not suitable to assess arc stability for GMA welder which employ inverter power source due to its controlled current and voltage wave forms. In this paper, the relationship between are stability and wire feed rate fluctuation is analyzed to propose new criterion for inverter power source. When arc voltage and arc current and arcing time are analyzed, we can assess arc stability only for short circuit transfer mode. When wire feed rate is analyzed, we can estimate arc stability udner the condition of spray transfer mode as well. Hence, the wire feed rate is chosen for monitoring process variable to cover possible metal transfer modes in GMAW. Through this research, it has been identified that arc stability in GMA welding processes is closely related to wire fed rate. When inverter power source is used, conventional statistical method of estimating arc stability, such as Mita index, is no longer valid due to its controlled voltage and current wave forms. Arc stability has been also examined in phase plane diagram.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.87-89
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• 2002

This paper presents a new approach using an Improved branch exchange (IBE) technique to maximize the voltage stability as well as loss minimization in radial power systems. A suitable voltage stability index (VSI) for optimal routing algorithm is developed using novel methods both a critical transmission path based on a voltage phasor approach and an equivalent impedance method. Furthermore, the proposed algorithm can automatically detect the critical transmission path to be reached to a critical load faced with voltage collapse due to additional real or reactive leading. To develop an effective optimization technique, we also have applied a branch exchange algorithm based on a newly derived index of loss change. The proposed IBE algorithm for VSI maximization can effectively search the optimal topological structures of distribution feeders by changing the open/closed states of the sectionalizing and tie switches. The proposed algorithm has been tested with the various radial power systems to show its favorable performance.

• 조명전기설비학회논문지
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• 제18권5호
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• pp.169-173
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• 2004

본 논문은 전력계통의 전압 안정도 제약 문제를 해결하는데 고온 초전도 케이블을 적용하기 위한 기법을 제시하였다. 대전력계통의 유효 송전용량은 종종 전압 안정도 제약에 의해 결정된다. 기존의 초전도 케이블 응용 연구는 주로 도심지역의 고밀도 전력 수송 문제를 해결하는 대안으로 연구의 초점을 두어왔지만, 고온 초전도 케이블의 선로정수 개선효과를 이용하면 전압 안정도로 제약된 계통의 송전용량을 증가시킬 수 있어 그 응용 범위가 확대될 수 있다. 전압 안정도에 의한 최대 수송전력을 결정하는 데는 IPLAN에 의한 P-V곡선을 이용하였고, 대체 대상선로는 부하 증가시 무효전력 손실감도가 가장 큰 선로로 하였다. 결과의 타당성을 검증하기 위해 IEEE 14모선 계통을 사용하였으며, 적용결과 Case II는 70[%], Case III에서는 160[%]의 추가 수송 능력 증가를 가져올 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.77-79
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• 1996

This paper presents an integrated stability analysis by the direct energy function method based on Equivalent Mechanical Model(EMM) which reflects the system behavior related to both angle and voltage stabilities. Actually, angle and voltage stability are intimately related in power system, so complete decoupling of these stability analysis is not possible in general, particularly in stressed power systems. In this paper, it is shown that a identical energy function can be used for angle and voltage stability analysis. The proposed energy function reflects the line resistances and reactive powers under the constraints of the same R/X ratio. The energy margin between UEP and SEP presents a good collapse proximity index in both types of stability analysis.

• 조명전기설비학회논문지
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• 제24권4호
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• pp.17-24
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• 2010

송변전설비들이 점점 중부하로 운용되어짐에 따라 송전용량이 전력회사에서 중요한 문제로 부각되어 왔다. 한전 시스템의 경우 전체송전용량은 주로 전압 안정도에 의해 제한을 받고 있으며, 이의 향상을 위한 연구들이 계속하여 수행되어 오고 있다. 본 논문에서는 전압안정도 관점에서의 전체송전용량을 향상시키기 위하여 STATCOM 설비를 설치하는 위치를 효과적으로 선택하기 위한 송전용량지수가 제시된다. 이 지수를 소규모 전력시스템인 IEEE 39모선 시스템에 적용하여 제시된 지수의 효과를 보여준다. 그리고, 이 소규모 시스템을 활용하여 부하가 증가할 때 전체송전용량에 전압안정도뿐 만이 아니라 과도안정도가 미치는 영향을 분석한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 A
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• pp.145-148
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• 1992

The best index should show the margins to the operating limit at the present operating point without much efforts. Such voltage collapse proximity index has been proposed in this study. Differently from the normal procedure in which every bus load is increased at the same propotion, bus load increase toward the direction of T/L loss increase has been applied in this study. Sample studies show the usefulness and the practical applicability in voltage stability analysis.

• 대한전기학회논문지
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• 제45권1호
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• pp.1-8
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• 1996

Recently, much attention has been paid to problems which is concerned with voltage instability phenomena and much works on these phenomena have been made. In this paper, by substituting d $P_{k}$ d $e_{k}$ ( $v^{\rarw}$= e +j f) for $P_{k}$ in conventional load flow, direct method for finging the limit of voltage stability is proposed. Here, by using the fact that taylor se- ries expansion in .DELTA. $P_{k}$ and .DELTA. $Q_{k}$ is terminated at the second-order terms, constraint equation (d $P_{k}$ d $e_{k}$ =0) and power flow equations are formulated with new variables .DSLTA. e and .DELTA.f, so partial differentiations for constraint equation are precisely calculated. The fact that iteratively calculated equations are reformulated with new variables .DELTA.e and .DELTA.f means that limit of voltage stability can be traced precisely through recalculation of jacobian matrix at e+.DELTA.e and f+.DELTA.f state. Then, during iterative process divergence may be avoid. Also, as elements of Hessian mat rix are constant, its computations are required only once during iterative process. Results of application of the proposed method to sample systems are presented. (author). 13 refs., 11 figs., 4 tab.

• 전기학회논문지
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• 제59권8호
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• pp.1366-1373
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• 2010

Purpose of the electric power system planning and operation is to supply the electric energy to customers continuously and economically. With the mutual exclusive laws of nature between reliability and economic, finding the meeting point is very important but not easy. Commonly the probabilistic reliability indices of the electric power systems are represented with negatively. And the effectiveness of FACTS on the probabilistic reliability could not be reflected with common methods. In this paper, a method to evaluate the probabilistic arrival power at each load point is presented. With this new proposed method, probabilistic reserve margin at load points can be calculated and which can be used with positive reliability index also. Using the P-V analysis, the voltage stability is considered in reliability evaluation. It is expected that the proposed method will be useful expecially in reliability evaluation of electric power system which has voltage restriction.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.914-919
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• 1998

A Capacitor Commutated Converter (CCC) has less difficulty of commutation failure in comparison to the conventional line commutated converter. This paper proposes the Ar1R control of the CCC in the inverter operation, which deserves as the Ar1R of the conventional converter. The CCC can be operated in high power factor area by using the proposing Ar1R control. The voltage stability at an AC bus connected the CCC inverter is investigated and estimated its ability of preventing the AC voltage collapse. To estimate the voltage stability, this paper developed the simplified converter mathematical model and led the VSF index. The results shows that the AC voltage stability is guaranteed and enables the interconnection to an weak AC system, when compensation factor of the compensation capacitor is higher than 200%.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1400-1407
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• 2015

This paper deals with methodology to control an automatic substation system. The control system can predict the power system condition by a voltage stability index (VSI). The strategies in this paper is called as Voltage-Reactive Power Control (VRPC), which regulates an abnormal voltage of a target substation by using coordination between tap changers and shunt capacitor/reactor. This method is efficient for better voltage profile. The monitoring substation includes whole of substations around the contingency event. The control quantities of the monitoring substations are decided by the calculation of the VSI, called as a Z-index. Case studies with BC Hydro-Quebec system are presented to illustrate this approach using real-time simulator.