Sang- Yun

An evaluation method of voltage sag using a risk assessment model in power distribution systems

Abstract In this paper we explore a new method for evaluating the impact of voltage sags in the power distribution systems. The proposed method incorporates the generalization of the evaluation method as well as the effects of voltage sags on customers. To generalize the evaluation method, historical reliability data will be used. We take into account the impact of voltage sags on customers using a representative power acceptability curve and a fuzzy model. The final result of the evaluation model yields on a yearly basis the magnitude of customers’ risk caused by voltage sags. The evaluation methodology is divided into the analytic and probabilistic method. The time sequential Monte Carlo simulation is used as probabilistic method. The proposed method is tested using the modified Roy Billinton Test System (RBTS) form and the reliability data of Korea Electric Power Corporation (KEPCO) system. Through the case study, we verify that the proposed method evaluate the actual impact of voltage sags and can be effectively applied to the real system using the historical reliability data as the conventional reliability indices in power distribution systems.

Mitigation of voltage sag using feeder transfer in power distribution system

This paper presents a mitigation method of voltage sag using feeder transfer in power distribution systems. The proposed method is carried out using the switching for the sectionalizing points of distribution networks. It consists of two main sequences. First, the authors find the weakness points for voltage sags. Second, they transfer the customers of weakness points to other sources during the fault currents existence. A reliability evaluation using a risk assessment model of voltage sagging was performed for case studies. The Monte Carlo method and the historical reliability data of KEPCC (Korea Electric Power Corporation) were used for simulations.

Quantitative Evaluation of the Impact of Repetitive Voltage Sags on Low-Voltage Loads

Automatic reclosing is a typical protection method to clear temporary faults in power distribution systems. However, it has a weakness in regards to voltage sags because it produces repetitive voltage sags. In this paper, we explored the repetitive impacts of voltage sags due to the automatic reclosing of power distribution systems. The actual tests of low voltage loads were carried out for obtaining the susceptibility of voltage sags. The final results of the tests yielded the power acceptability curves of voltage sag, and the curves was transformed the 3-D Computer Business Equipment Manufacturer Association (CBEMA) format. For the quantitative evaluation of the impact of repetitive voltage sags, an assessment formulation using the voltage sag contour was proposed. The proposed formulation was tested by using the voltage sag contour data of IEEE standard and the results of the test. Through the case studies, we verified that the proposed method can be effectively used to evaluate the actual impact of repetitive voltage sags.

Application of Ant Colony Algorithm for Network Reconfiguration in Distribution Systems

Abstract This paper presents an efficient algorithm for the loss minimization by automatic sectionalizing switch operation in distribution systems. Ant colony algorithm is a multi-agent system in which the behaviour of each single agent, called artificial ant, is inspired by the behaviour of real ants. Ant colony algorithm is suitable for combinatorial optimization. The proposed methodology with some modification to the ant colony algorithm improves the computation time and convergence property. Numerical examples demonstrate the validity and effectiveness of the proposed methodology on a 32 bus system and a KEPCO 148 bus system.

Peak load estimation of pole-transformer using load regression equation and assumption of cooling load for customer

Abstract This paper summarizes the results of the research for load management of pole-transformers done in 1997–1999 in Korea. The purpose of the research is to enhance the peak load estimation of pole-transformers. For this purpose, we concentrate on two parts. One is to modify the load regression equation for load management of pole-transformers. The other is to estimate the cooling load possessions of customers and reduce estimation errors of the peak load for pole-transformers in the summer season. To do this, we propose indices of cooling load estimation using the increment of electric energy from spring to summer. Case studies for sample pole-transformers show that the proposed peak load estimation method could reduce estimating error of the peak load in the summer season, compared with the conventional method in Korea.

Particular characteristics associated with temporary and permanent fault on the multi-shot reclosing scheme

This paper presents the characteristics associated with temporary and permanent faults on the multi-shot reclosing scheme which is employed in a power distribution system. In order to extract the characteristics of temporary and permanent faults, we utilize the fault currents that have been measured in the field for 4 years. We have measured them by means of fault recorders which have been installed at the secondary side of the substation transformer in the KEPCO system. After the waveforms are analyzed by using the Fourier transform, the magnitude spectrum and total harmonic distortion are calculated.

Evaluation of Reliability Worth Considering Sustained Interruptions and Voltage Sags

Power quality problems such as momentary interruptions and voltage sags do not great influence on loads at past. However, the interests in power quality problems increase as the use of sensitive loads with microprocessor like computers increases recently. Accordingly, power system reliability research focusing to sustained interruption and momentary interruption partially needs more accurate evaluation methods including momentary and instantaneous problems. That is, many sensitive loads being tripped by voltage sags result in interruption costs. In this paper, new reliability worth evaluation method is presented considering voltage sags. We calculated the magnitude of voltage sags using fault studies and the duration of voltage sags using the trip time of protective relays for each fault. Moreover, we includes the customer interruption cost resulted from sensitive load trip by voltage sags. Through case studies, we evaluate the effects of voltage sags for permanent faults.

Evaluation method of transformer damage from auto-reclosing scheme in power distribution system

This paper presents how to evaluate the transformer damage caused by an auto-reclosing scheme in a power distribution system. We describe a quantitative relationship between the reclosing scheme and the number of fault currents flowing through a transformer using the probability of a reclosing success/failure. The transformer damage from the reclosing scheme is formulated as an index that forms a weight function and a damage function. This index is associated with the number of reclosing attempts, a reclosing deadtime and a transformer functional life. In the case studies, the transformer damage is simulated for the probability of a reclosing success. We carried out an evaluation of transformer damage using KEPCOs operation data.

Overload criterions of mineral-oil-immersed distribution transformer rated 100 kVA and less using the characteristics of top-oil temperature rising

This paper presents the general recommendations for the overload criteria of mineral-oil-immersed distribution transformers rated 100 kVA and less in Korea. For this purpose, the experiments are performed to analyze the characteristics of top-oil temperature rising for distribution transformer at KERI (Korea Electrical Research Institute) from December 2000 to May 2001. Twenty pole transformers are used for the test samples and they are supplied from KEPCO (Korea Electric Power Corporation). The experiment results are represented by the critical time of overload for each transformer capacity. Finally, the authors present the overload criteria of distribution transformers for summer and winter seasons, respectively.