• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.390-393
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• 2007

The reliability as well as the power capability of the UPS system can be increased by replacing a single UPS unit with multiple small UPS units in parallel, resulting in a so-called module UPS. This module UPS system allows that a new module can be added or replaced while maintaining power to loads, which is a hot-swappable operation. In addition, it has desirable features such as ease of output power expandability, convenience of maintenance and repair, and high reliability. To realize the module UPS, load sharing without interconnection among parallel connecting modules as well as a small scale and lightweight topology is necessary. The frequency and voltage droop method is applied to parallel operation control to achieve load sharing. 5kVA modules are designed and implemented to confirm the effectiveness of the proposed approaches. Experimental results show that the module UPS system has a high power factor, a low distortion of output voltage and input current, hot-swappable operations and good load sharing characteristics.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.2
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• pp.227-232
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• 2016

To test the effectiveness of using an energy storage system for frequency regulation, the Energy New Business Laboratory at KEPCO Research Institute installed a 4 MW energy storage system (ESS) demonstration facility at the Jocheon Substation on Jeju Island. And after the successful completion of demonstration operations, a total of 52 MW ESS for frequency regulation was installed in Seo-Anseong (28 MW, governor-free control) and in Shin-Yongin (24 MW, automatic generation control). The control system used in these two sites was based on the control system developed for the 4 MW ESS demonstration facility. KEPCO recently finished the construction of 184 MW ESS for frequency regulation in 8 locations, (e.g. Shin-Gimjae substation, Shin-Gaeryong substation, etc.) and they are currently being tested for automatic operation. KEPCO plans to construct additional ESS facilities (up to a total of about 500 MW for frequency regulation by 2017), thus, various operational tests would first have to be conducted. The high-speed characteristic of ESS can negatively impact the power system in case the 500 MW ESS is not properly operated. At this stage we need to verify how effectively the 500 MW ESS can regulate frequency. In this paper, the effect of using ESS for frequency regulation on the power system of Korea was studied. Simulations were conducted to determine the effect of using a 524 MW ESS for frequency regulation. Models of the power grid and the ESS were developed to verify the performance of the operation system and its control system. When a high capacity power plant is tripped, a 24 MW ESS supplies power automatically and 4 units of 125MW ESS supply power manually. This study only focuses on transient state analysis. It was verified that 500 MW ESS can regulate system frequency faster and more effectively than conventional power plants. Also, it was verified that time-delayed high speed operations of multiple ESS facilities do not negatively impact power system operations. It is recommended that further testing be conducted for a fleet of multiple ESSs with different capacities distributed over multiple substations (e.g. 16, 24, 28, and 48 MW ESS distributed across 20 substations) because each ESS measures frequency individually. The operation of one ESS facility will differ from the other ESSs within the fleet, and may negatively impact the performance of the others. The following are also recommended: (a) studies wherein all ESSs should be operated in automatic mode; (b) studies on the improvement of individual ESS control; and (c) studies on the reapportionment of all ESS energies within the fleet.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.931-938
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• 2011

Nondestructive inspection(NDI) is a testing procedure used to easily inspect an object for internal defects, abnormalities, shape, and structure, etc. without destroying it. Typical candidates for NDI include buildings, railways, aircraft, bridges, underground pipelines and various types of factory equipment. Recent advances in nondestructive evaluation(NDE) technologies have led to improved methods for quality control and in-service inspection, and the development of new options for material diagnostics. Under frame side sill in rolling stocks is designed for preventing corrosion in order to meet mechanical requirements. However during long operation time, there are corrosion in the under frame side sill caused by environmental effect, vibration and etc. This paper introduces the methods of a survey and assessment on NDI applications in Electric Multiple Units(EMU). The main objective of this paper was to obtain information on various applications and evaluation of NDI technology in EMU.

• Journal of the Korean Operations Research and Management Science Society
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• v.18 no.3
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• pp.51-63
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• 1993

We consider a cyclid server system under N-policy. This system consists of multiple queues served in a cyclic order by a single server. In this paper, we consider the following control policy. Every time server polls one queue, the server inspects the state of the queue. If the total number of units is found to have reached or exceeded a pre-specified value, the server begins to serve the queue until it is empty. As soon as the queue becomes empty, the server polls next queue. An approximate analysis of this system is presented. Sever vacation model is used as an analytical tool. However, server vacation periods are considered to be dependent on the service times of respective queues. The results obtained from the approximate analysis are ompared with simulation results.

• Journal of the Korean Professional Engineers Association
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• v.38 no.4
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• pp.7-9
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• 2005

The recent speculation fever in Kangnam and its southern vicnity of Seoul resulted in surging apartment prices. The government is determined to employ more effective anti-speculation policy measures to control the property speculative demand. The Government plans to implement support measures to discourage people from owning multiple homes by reinforcing tax measures. To meet the increasing demand for more large-sized apartments in Seoul, the Government may allow to build more large sized units. By the end of August, 'a comprehensive package tool of real estate policy measures' ,as a real estate controlling guidelines, is scheduled to be presented by the Government. We hope that the package tool will stabilize housing market more effectively and enhance the national economy.

• Proceedings of the Membrane Society of Korea Conference
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• 1996.06a
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• pp.177-189
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• 1996

Raverase osmosis or ultrafiltration systems have generally been regarded as hard to validate about WFI production. Though the Japanese and US Pharmacopoeias have allowed distillation and RO to be applied to WFI production process, only water stills, especially multiple effects have practically been employed for parenteral water production. On the other hand, the latest analysis has shown that even distillate contains such volatile organic matters as trihalomethanes and traces of heavy metals at a little higher concentration than supposed. The JP requires TOC to be monitored in WFI process based on RO or UF systems to control the concentration below 300ppb, but very few monographs or papers have so far been published about the concentrations of organic volatile matters in distillate. (See table 1-1) Therefore, this paper proposes a new applicable WFI systems based on the result of purified water analysis with some membranes used in the process. A well combined membrane system with other units could be expected to provide less amount of impurities in membrane-treated water than in distillate.

• ETRI Journal
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• v.44 no.2
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• pp.194-207
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• 2022

In the last decade, substantial progress has been achieved in intelligent traffic control technologies to overcome consistent difficulties of traffic congestion and its adverse effect on smart cities. Edge computing is one such advanced progress facilitating real-time data transmission among vehicles and roadside units to mitigate congestion. An edge computing-based deep reinforcement learning system is demonstrated in this study that appropriately designs a multiobjective reward function for optimizing different objectives. The system seeks to overcome the challenge of evaluating actions with a simple numerical reward. The selection of reward functions has a significant impact on agents' ability to acquire the ideal behavior for managing multiple traffic signals in a large-scale road network. To ascertain effective reward functions, the agent is trained withusing the proximal policy optimization method in several deep neural network models, including the state-of-the-art transformer network. The system is verified using both hypothetical scenarios and real-world traffic maps. The comprehensive simulation outcomes demonstrate the potency of the suggested reward functions.

• Journal of Korean Academy of Nursing
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• v.31 no.2
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• pp.206-220
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• 2001

The purpose of this study was to investigate the impact of depression, discomfort, spirituality, physical care, and opioid use on pain with terminally ill cancer patients residing in hospice units. The convenient sample of this study consisted of 41 terminally ill cancer patients at three hospice units in university affiliated hospitals. Patients were interviewed with structured questionnaires three times at predetermined intervals: admission to the hospice unit (Time 1), one week later (Time 2), and two weeks later (Time 3). The data was collected from January 1998 to January 1999 and was analyzed using ANOVA, Pearson correlation coefficient, and multivariate multiple regression. 1. The mean age of the participants was approximately 55 years old. In terms of diagnosis, lung cancer showed the highest frequency (19.5%), followed by stomach cancer and rectal cancer (17.1%). The motive of seeking hospice unit admission was control (72. 2%), followed by spiritual care (50%), and symptom relief (38.9%). 2. Regarding the type of pain felt, the highest pain frequency the participants experienced was deep pain (55%), followed by multiple pain (25%), intestinal pain (10%), then superficial (5%) and neurogenic pain (5%). For the level of pain measured by VAS, there was no significant difference among the three time points; Time 1 (5.04$\pm$2.21), Time 2 (4.82$\pm$2.58) and Time 3(4.73$\pm$2.51). 3. There was significant change seen in spirituality and physical care in each time interval. Namely, the longer the length of admission at the hospice unit, the higher the importance of spirituality (p=0.0001) and the more the physical care the participants received (p=0.01). The opioid use at the three time points showed the following frequencies : Time 1 (75.6%), Time 2 (85.4%) and Time 3 (75.6%). 4. Regarding factors influencing pain, the pain level was significantly affected by the depression level (p〈0.01) and the opioid use (p〈0.1). These results were the most significant at the two time points (Time 1 and Time 2). At Time 3 (two weeks later), the pain level was significantly affected by the depression level (p〈0.05) and the amount of physical care the participants received (p〈0.1). In conclusion, the terminally ill cancer patients had moderate pain, were generally depressed, and were treated with opioid analgesics. As approaching death, the patients received more physical care due to increased physical symptoms experienced and they had a higher perception of the importance of spirituality. Thus, health care professionals need to provide continuous care for each of them to die comfortably physically, psycho- logically, and spiritually.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.65-72
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• 2020

The purpose of this descriptive research study was to identify the effects on job satisfaction of nurses working at comprehensive nursing care service units. The study was conducted in five hospitals, two of 250 beds or more in three cities and three of 800 beds. The study subjects were nurses working at comprehensive nursing care service units. A structured questionnaire of 150 questions was distributed to them and 146 were collected. The data collection period was from August 1, 2019 to November 15, 2019. The collected data were analyzed using the SPSS 22.0 program, using x²-test, t-test, ANOVA, Pearson correlation, and multiple linear regression. Emotional labor and toughness were negatively correlated (r=-.20, p=.018), and emotional labor and job satisfaction were positively correlated (r=.25, p=.004). The predictive variables affecting the job satisfaction of the subjects were the aptitude of the ward service (β=-.35, p=<.001) and hardness(β=.21, p=.009). The explanation of job satisfaction in the variables was 18.2% (F=3.54, p=.009). The study results revealed that the predictive variables affecting job satisfaction were the hardiness and aptitude of the ward service. Therefore, in order to increase the job satisfaction of ward nurses, it is necessary to provide administrative support to control the hardiness of the nurse and to allocate manpower in consideration of the aptitude in the hospital personnel system.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4111-4124
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• 2022

The control rod drive system is critical to the reactor's reliable operation. The performance of its control system and mechanical system will gradually deteriorate because of operational and environmental stresses, thus increasing the reactor's operational risk. Currently there are few researches on the aging-related degradation of the entire control rod drive system. Because it is difficult to quantify the effect of various environmental stresses and establish an accurate physical model when multiple mechanisms superimposed in the degradation process. Therefore, this paper investigates the aging-related degradation of a control rod drive system by integrating Dynamic Object-Oriented Bayesian Network and Hidden Markov Model. Uncertainties in the degradation of the control system and mechanical system are addressed by using fuzzy theory and the Hidden Markov Model respectively. A system which consists of eight control rod drive mechanisms divided into two groups is used to demonstrate the method. The aging-related degradation of the control rod drive system is analyzed by the Bayesian inference algorithm based on the accelerated life test data, and the impact of different operating schemes on the system performance is also investigated. Meanwhile, the components or units that have major impact on the system's performance are identified at different operational phases. Finally, several essential safety measures are suggested to mitigate the risk caused by the system degradation.