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This paper compares the differences in economic feasibility and dynamic characteristics between underground (U/G) cable and overhead (O/H) line for low-voltage direct current (LVDC) distribution. Numerous low loaded long-distance distribution networks served by medium-voltage alternative current (MVAC) distribution lines exist in the Korean distribution network. This is an unavoidable choice to compensate voltage drop, therefore, excessive cost is expended for the amount of electrical power load. The Korean Electric Power Corporation (KEPCO) is consequently seeking a solution to replace the MVAC distribution line with a LVDC distribution line, reducing costs and providing better quality direct current (DC) electricity. A LVDC distribution network can be installed with U/G cables or O/H lines. In this paper, a realistic MVAC distribution network in a mountainous area was selected as the target model to replace with LVDC. A 30 year net present value (NPV) analysis of the economic feasibility was conducted to compare the cost of the two types of distribution line. A simulation study compared the results of the DC line fault with the power system computer aided design/electro-magnetic transient direct current (PSCAD/EMTDC). The economic feasibility evaluation and simulation study results will be used to select the applicable type of LVDC distribution network.

With power systems switching to smart grids, real-time and on-line monitoring technologies for underground distribution power cables have become a priority. Most distribution components have been developed with self-diagnostic sensors to realize self-healing, one of the smart grid functions in a distribution network. Nonetheless, implementing a real-time and on-line monitoring system for underground distribution cables has been difficult because of high cost and low sensitivity. Nowadays, optical fiber composite power cables (OFCPCs) are being considered for communication and power delivery to cope with the increasing communication load in a distribution network. Therefore, the application of distributed temperature sensing (DTS) technology on OFCPCs used as underground distribution lines is studied for the real-time and on-line monitoring of the underground distribution power cables. Faults can be reduced and operating ampacity of the underground distribution system can be increased. This paper presents the development and improvement of an intelligent cable monitoring system for the underground distribution power system, using DTS technology and OFCPCs as the underground distribution lines in the field.

To save on the island area's power supply cost and protect the clean environment, the Isolated MicroGrid is being duly considered. Consisting of the Wind Turbine Generator (WT), photovoltaic generator, battery system, back-up diesel generator, etc., Isolated MicroGrid, which usually uses the inverter to maintain voltage and frequency of the system, is very weak in terms of voltage and frequency stability compared to the large-scale electrical power system. If wind turbine generator is applied to this weak power system, it could experience many problems in terms of maintaining its voltage and frequency. In this paper, the measurement result of voltage and frequency is presented for MicroGrid, which consists of the Wind Turbine Generator adopting the induction generator and the battery system. MicroGrid’s voltage waveform distortion and Wind Turbine Generator’s output oscillation problems are analyzed using PSCAD/EMTDC. Based on the analyzed result, the importance of type and capacity choice has been suggested in case the Wind Turbine Generator is applied to the Isolated MicroGrid.

All feasible local minima of the neutral taurine (2-aminoethanesulfonic acid) in the gas phase and its zwitterionic form in water are explored using a density functional (M06-2X) that provides an accurate treatment of medium-range correlation energy and the recently improved solvation model SMD with the larger basis set (cc-pVTZ). In the gas phase, the conformer gtGg (II1) with the gauche− conformation around the N CH2 CH2 S sequence and the hydrogen bond between the sulfonic O H and the amine NH2 is found to be most preferred, which can be ascribed to the favored hyperconjugative n → σ* interaction between the lone electron pair of the amine nitrogen and the antibonding O H orbital of the sulfonic moiety. The calculated rotational constants of the conformer gtGg are consistent with the values obtained from LA-MB-FTMW experiments. In addition, the feasible structures of taurine± · (H2O)n complexes with a small number of water molecules (n = 0, 1, 2, and 4) were investigated in the implicit SMD aqueous medium. The calculated results of taurine± with four water molecules support that taurine exists as a mixture of gauche and trans conformers in aqueous solution. Its gauche population is calculated to be 71%, which is in good agreement with the observed value of 67% from 1H NMR experiments in D2O. It is known that the increased population of the trans conformer for the taurine± · (H2O)4 complex is ascribed to the preferred solvation by the interactions between the solute and the discrete water molecules in the complex and by the polarization of the continuum water due to the complex.

A distribution system was designed and operated by considering unidirectional power flow from a utility source to end-use loads. The large penetrations of distributed generation (DG) into the existing distribution system causes a variety of technical problems, such as frequent tap changing problems of the on-load tap changer (OLTC) transformer, local voltage rise, protection coordination, exceeding short-circuit capacity, and harmonic distortion. In view of voltage regulation, the intermittent fluctuation of the DG output power results in frequent tap changing operations of the OLTC transformer. Thus, many utilities limit the penetration level of DG and are eager to find the reasonable penetration limits of DG in the distribution system. To overcome this technical problem, utilities have developed a new voltage regulation method in the distribution system with a large DG penetration level. In this paper, the impact of DG on the OLTC operations controlled by the line drop compensation (LDC) method is analyzed. In addition, a generalized determination methodology for the DG penetration limits in a distribution substation transformer is proposed. The proposed DG penetration limits could be adopted for a simplified interconnection process in DG interconnection guidelines.

Various DSM (Demand Side Management) programs have been developed and carried out to use the limited energy resources of human-beings reasonably. LED lighting is one of essential DSM programs and the development of technologies is ongoing vigorously. Recently, one-person households have been increased and the electricity consumption pattern is different with conventional households because residents live as a single. On the other hand, owners of the one-person households tend to not prefer to install high efficient appliances due to the cost increasement. Therefore, the existing DSM subsidy programs should be revaluated so that the owners decide to install high efficient appliances.

The integration of Distributed Energy Resources (DERs) into the future Smart Distribution Network (SDN) has challenging issues regarding the successful development of smart grids. The SDN offers new opportunities in the improvement of the efficiency of power distribution networks. The DERs will be distributed in the existing distribution networks, interconnected in customer areas and operated on its own schedule without communication to the control center of the existing distribution system. The DER units have both positive and negative effects regarding SDN operations. With the appropriate operation of the DER units in the SDN, losses can be reduced during normal operations and they can support local loads during abnormal conditions. Thus, the positive effects of the DER units need to be enabled in the SDN by adopting advanced operation schemes. In this paper, the smart control functions for the DER units in the SDN are defined and classified. In addition, the integration schemes for the SDN with DER units are introduced. The proposed operation strategies will be implemented into the Korean Smart Distribution Management System (KSDMS) as operation schemes used for loss reduction and service restoration. A sample case study shows the effectiveness of the proposed operation schemes to achieve smart operation functions for the SDN with DER units.

The Development of smart grids offers new opportunities to improve the efficiency of operating and controlling distribution systems. It allows network operators to optimize the use of dispersed generation resources and enables real-time communication between customers and utility service providers to allow optimization and balancing of energy usage. Such an improvement in the flexibility and control of the distribution network is only possible if the control center operator has more accurate knowledge of the real-time situation of the network. The Korean Smart Distribution Management System (KSDMS) project was started in 2009 to achieve advanced distribution operation for potential smart grid systems in Korea. In this paper, we summarize two KSDMS design strategies for situational awareness in real-time distribution operation. One is the preparation of standardized data acquisition networks. In the KSDMS, numerous data related to the voltage, current, faults, power quality and load profiles of the network are gathered using a standardized communication method based on IEC 61850. The other is a real-time security analysis tools for smart distribution systems, designed to provide the distribution operator with accurate real-time situational information and predictive operation. We present a database design which can be used commonly for all security analysis programs in KSDMS.

In this paper, we present an improved overload decision system for oil-immersed distribution transformers under 100 kVA using load monitoring data. Our study can be categorized into two parts: (a) improvement in the criteria for judging the overload conditions of distribution transformers and (b) development of an overload evaluation system using load monitoring data. In order to determine the overload criteria, overload experiments are performed on sample transformers; the results of these experiments are used to define the relationship between the transformer overload and the increase in the top-oil temperature. To verify the accuracy of the experimental results, field tests are performed using specially manufactured transformers, the loads and top-oil temperatures of which can be measured. For arriving at online overload decisions, we propose methods whereby the measured load curve can be converted into an overload characteristic curve and the overload time can be calculated for any load condition. The developed system is able to evaluate the overload for individual distribution transformers using load monitoring data.

The hybrid superconducting fault current limiter (SFCL) is now at the stage of practical use in a power grid in Korea. A cryogenic cooling system was designed, fabricated, and successfully tested for a prototype of 22.9 kV/630 A SFCL. The operation scheme of cryogenic system has been investigated in preparation for temporary loss of cryocooler power in hybrid SFCL (in Kim et al., IEEE Trans. Appl. Supercond. 21(3):1284–1287, 2011). In this paper, we investigated the empirical modeling of cryogenic cooling system for SFCL using principal components and auto-associative support vector regression (PCSVR) for the prediction and fault detection of the cryogenic cooling system. For empirical model, data were acquired during a blackout test of cryogenic cooling system. Blackout times of the test were 1 hour and 4 hours at two operation current levels. Three set of data were used for training and optimization of the model and the rest set of data was used for verification. Signals for the model are temperatures measured at copper band and cold head of cryocooler, system pressure and liquid temperatures measured at two locations in liquid-nitrogen pool. For optimization of the SVR parameters, the response surface method (RSM) and particle swarm optimization (PSO) were adopted in this paper. After developing the empirical model we analyzed the accuracy of the model. Also, these results were compared with that of auto-associative neural networks (AANN). RSM and PSO gave almost the same optimum point. PCSVR showed much better performance than AANN in accuracy aspects. Moreover, this model can be used for the prognosis of cryogenic cooling system for SFCL.

The conformational study of γ-aminobutyric acid (GABA) has been carried out at the M06-2X/cc-pVTZ level of theory in the gas phase and the SMD M06-2X/cc-pVTZ level of theory in water. In the gas phase, the folded conformation gG1 with gauche− and gauche+ conformations for the Cβ Cα and Cγ Cβ bonds, respectively, is found to be lowest in energy and enthalpy, which can be ascribed to the favored hyperconjugative n → π* interaction between the lone electron pair of the amine nitrogen atom and the C O bond of the carboxylic group and the favored antiparallel dipole–dipole interaction between the N H bond and the C O bond. In addition, the intramolecular hydrogen bonds between the carboxylic group and the amine N H group have contributed to stabilize some low-energy conformers. However, the most preferred conformation is found to be tG1 and more stable by 0.4 kcal/mol in ΔG than the conformer gG1, in which the favored entropic term due to the conformational flexibility and the other favored n → σ*, σ → σ*, and π → σ* interactions seem to play a role. The conformational preferences of the neutral GABA calculated by ΔG’s are reasonably consistent with the populations deduced from FT microwave spectroscopy in supersonic jets combined with laser ablation. In water, the two folded conformers Gg and gG of the zwitterionic GABA are dominantly populated, each of which has the population of 47%, and the hydrogen bond between the ammonium N H group and the lone electron pair of the C O− group seems to be crucial in stabilizing these conformers. Our calculated result that the folded conformers preferentially exist in water is consistent with the 1H NMR experiments in D2O.

The Load Tap Changing (LTC) transformer and Shunt Capacitor (SC) bank are major devices for voltage and reactive power control in a distribution substation. Thus, the coordination operation of a LTC transformer and a SC bank is required to achieve better voltage and reactive power compensation at a distribution substation in the same time. This paper proposes coordinate control method of LTC transformer and SC bank to achieve better voltage and reactive power compensation and operation times of these two devices in the same time. The mathematical formulations of the proposed coordinate control method are introduced. Sample case studies are shown to verify the effectiveness of the proposed coordinate control method.

MG(Microgrid) is a small power supply system located on-site that can supply both the electricity and the hot-water simultaneously. Engineering S/W is requested to construct Microgrids economically. We developed Engineering S/W that can combine DERs (Distributed Energy Resources) most economically using the linear programming and estimate of the economic. Developed S/W was programed using GAMS(General Algebraic Modeling System) and it is composed of the optimal DER combination module and forecasting module of renewable energy`s output. We embody it based on MS Excel considering the user`s convenience and we show its validity through a case study. We think that developed S/W will be very useful for planning MGs and energy supply.

Fractal mathematics is being highlighted as a research method for classification of image. But the application of Fractal dimension(FD) has been requited the complicated calculation method because of its complex repetition progressing. In this paper, it has been developed the new approach method to express the Fractal Dimension(FD) for aging level calculation and estimation system of outside insulator using special image processing algorithm. As a result after FD testing, the recognized aging estimation of FD has a very characteristics compared to the conventional visual inspection.

Temperature rise characteristics of medium voltage class transformers and dielectric characteristics of its insulation oil according to the loading rate were investigated using the transformer that has thermocouples embedded in the windings. The hottest-spot of the transformer locates at about 2/3 height of the windings where they adjoin each other among the 3 phase windings. The temperature difference between the hottest-spot and top-oil is about and the value keeps uniformly in short time after changing the loading rate. Capacitance of the oil varies in inverse proportion to temperature and the inclination rate is about -0.0106 that is not dependent on the aging rate. On the other hand the capacitance is increased depending on the aging rate, so the capacitance characteristics of the oil could be applied to the diagnostic technique.

In this study we developed accelerated aging test cycle and equipment which can simulate domestic weather condition. And we proposed long term reliability assessment method for polymer housed distribution surge arresters. We carried out electrical and chemical analysis of the arresters which are used for accelerated aging test and outdoor exposure test. Through the analysis we verified the capability of the proposed method and we presented characteristic data for maintenance of domestic arresters.

This paper introduces the development and actual test results of the Korean Smart Distribution Management System (KSDMS). The KSDMS has been designed and developed to cope with the lack of interconnection capability of the Dispersed Energy Resource (DER), to provide standardization and compatibility, and to implement automatic processing of service restoration, in the existing Distribution Automation System (DAS) in Korea. First, real-time system analysis and control application programs were developed, to solve the problems of the existing DAS; and the Distribution Management System (DMS) platform was developed, to run the developed application programs. Second, international standard-based communication, platform, and database structures were adopted, for standardization and compatibility. Third, a platform and application program functions were developed to process faults automatically; and a communication device and an intelligent electronic device (IED) were developed to automate fault restoration, through communication between devices. The KSDMS was evaluated by three tests: unit function test, platform and application program integration test, and empirical test. The first two were conducted on both small and large demonstration systems. The empirical test was performed at the Power Testing Center (PTC) in Gochang, and on a real system, at the Korea Electric Power Corporation (KEPCO), on Jeju Island. The test results verified that the KSDMS can actively resolve the problems of the existing DAS.

This paper is a summary of the development and demonstration of an optimization program, voltage VAR optimization (VVO), in the Korean Smart Distribution Management System (KSDMS). KSDMS was developed to address the lack of receptivity of distributed generators (DGs), standardization and compatibility, and manual failure recovery in the existing Korean automated distribution system. Focusing on the lack of receptivity of DGs, we developed a real-time system analysis and control program. The KSDMS VVO enhances manual system operation of the existing distribution system and provides a solution with all control equipment operated at a system level. The developed VVO is an optimal power flow (OPF) method that resolves violations, minimizes switching costs, and minimizes loss, and its function can vary depending on the operator’s command. The sequential mixed integer linear programming (SMILP) method was adopted to find the solution of the OPF. We tested the precision of the proposed VVO on selected simulated systems and its applicability to actual systems at two substations on the Jeju Island. Running the KSDMS VVO on a regular basis improved system stability, and it also raised no issues regarding its applicability to actual systems.

In this paper, we summarize the development and test for the Korean Smart Distribution Management System (KSDMS). To overcome the challenges faced by the Korean distribution automation system (KDAS), we propose three types solutions-real time, study and event-driven mode. For the architectural designs of KSDMS, we propose a communication system using the IEC 61850 and DNP3 protocols, feeder IEDs, and CIM-based middleware and server systems. We propose a database model that all KSDMS application programs will commonly use. The functions of FRTU and FIED are tested, and the test results of base platform are monitored through various HMIs. Through the integration test in Gochang power test center (PTC) between the base platform and the application program, we verify the performance of KSDMS. (4 pages)

This paper introduces a prototype volt/var optimization (VVO) method for the Korean smart distribution management system (K-SDMS) considering control of distributed generations (DGs) and a looped distribution topology. The main function of the VVO is to determine the references of volt/var control devices, including DGs to eliminate violations, to minimize the switching operation of the on-load tap changer (OLTC), the step voltage regulator (SVR), and capacitors, and to minimize the active power loss of the distribution network. The effectiveness of the VVO is presented with case studies using the K-SDMS simulator. (4 pages)

In this paper, we develop the simulation platform of the distribution systems with distributed generations (DGs). The detailed simulation models of a DG and a step voltage regulator (SVR) are developed as PSCAD user defined model (UDM). The control schemes of SVR and DGs to regulate the local voltages are proposed and implemented as a function block in the PSCAD platform. Some case studies to verify the effectiveness of the control schemes are performed in the developed simulation platform.

The interconnection standards/guidelines have been designed to prevent unfavourable interconnection problems of the DG (Dispersed Generations). Therefore, in practice, unit or cumulative interconnection capacity for particular voltage levels have been be limited to maintain admissible power quality and reliability. Recently, the interconnection standard/guidelines in South Korea are revised at Feb. 2012. In this paper, we briefly introduce the revised version of the DG interconnection standard/guidelines in South Korea and technical solutions/recommendations for large penetration of DG in the KEPCO (Korea Electric Power Company) distribution network. (4 pages)

In this paper, we propose a reduction method of distribution network for Korean Smart Distribution Management System (KSDMS). For this, we propose the network reduction rules and the application common database structure. The basic concept of reduction rules are the electrical unification of successive line section which has not lateral branches and the removal of simple lateral branches which has not devices and other laterals. The branch impedances and section loads of reduced network are recalculated. The application software is performed using the database links and parameters between original network and reduced network tables. The network reduction rate, on the average, is about 40% in case studies and the performance of application software (for calculation time) is significantly enhanced than the conventional network. (4 pages)

The smart grid offers new opportunities to improve the efficiency of operating and controlling distribution systems through the accurate information of the realtime situation of the network. And also, it is possible to automatically protect the network by using the communication infrastructure. The Korean Smart Distribution Management System (KSDMS) project launched at 2009 to achieve advanced distribution operation for potential smart grid systems in Korea. The KSDMS allows the optimization for operating and controlling the network, whose circumstance is hourly changed by the energy supply(depending on Distributed Generator(DG)) and consumption(depending on Load), by using the various analysis and control software. And also, in KSDMS, the energy security is highly considered by using the protection estimation method which automatically changes the setting value of protection coordination under the circumstance. In this paper, an adoptive algorithm for change and estimation of the protection coordination setting is proposed, and the protection coordination scheme designed in KSDMS is briefly introduced.

Penetration level of distributed generation (DG) on the grid is increasing worldwide. For the connection of new DG to the distribution network, various factors are considered including technical requirements that ensure the DG does not adversely affect the operation and safety of the network. Distribution system operators (DSO) have to perform impact studies of DG but these studies need cumbersome modeling and simulating of the target distribution network whenever DG is connected and the long time required for technical review. Therefore, utility engineers need the screening methods that can straightforwardly indentify cases with no impact on distribution system or those applications requiring detail studies. This paper presents the screening process and evaluation methods with simple rule on bank level and feeder level, respectively.

Conformational preferences and prolyl cis-trans isomerizations of the X-Pro motifs (Ac-X-Pro-NHMe, X = Ala and Aib) are explored using the meta-hybrid functional M06-2X and the double-hybrid functional B2PLYP-D with empirical dispersion corrections in the gas phase and in water, where solvation free energies were calculated using the implicit SMD model. Ac-Ala-Pro-NHMe favors the type VI β-turns in the gas phase and the open conformations in water. The populations of type VI β-turns decrease from 71% in the gas phase to 21% in water, which is reasonably consistent with IR and NMR experimental results on tBoc-Ala-Pro-NHMe. However, Ac-Aib-Pro-NHMe prefers the type I β-turns with α-helical structures for both residues in the gas phase and in water, whose populations are estimated to be 66% in both phases. These calculated results may rationalize why most of the peptaibiotics containing the Aib-Pro sequence have a regular α-helical conformation at the N- or C-terminus but a kinked α-helical structure in the middle of the helix. The cis-trans isomerizations of the Ala-Pro and Aib-Pro peptide bonds proceed via the clockwise rotation with the different backbone conformations. The rotational barriers to cis-to-trans isomerization are estimated to be 19.73 kcal/mol for the Ala-Pro tripeptide and 16.64 kcal/mol for the Aib-Pro tripeptide in water, which indicates that the rotational barrier becomes lower by ~3 kcal/mol for the Aib-Pro peptide bond. The calculated rotational barrier for Ac-Ala-Pro-NHMe is consistent with the observed value of 19.3 kcal/mol for Suc-Ala-Ala-Pro-Phe-pNA from NMR experiments in a buffered solution.

The purpose of this paper is to verify the aging characteristics of domestic polymer housed distribution surge arresters. In this study accelerated aging test equipment was developed to simulate field condition of the distribution polymer housed surge arresters. Polymeric housing of distribution surge arresters should be degraded by environmental stress and the interface between housing and inner module can be affected by moisture ingress. This moisture absorption should increase leakage current and make tracking damage at the interface. Proposed aging test equipment can simulate UV, temperature, humidity, voltage, salt fog and rain and it can monitor total and resistive leakage current of arresters. In addition we carried out field exposure test at the outdoor test yard and characteristic analysis of field operated arresters. And then electrical performance of arresters, insulation condition of housing material and surface condition of the housing were compared.

Because of environmental friendly and higher fire point, Natural ester fluids are widely used for transformer cooling materials. Natural ester has higher viscosity than that mineral oil. Top oil temperature and hottest temperature will be warmer when using natural ester fluid in transformers designed for conventional transformer oil. Although natural ester has less influence on deterioration of cellulose paper than mineral oil, an increased hottest temperature might have an effect on the aging of insulating paper in coil winding. When comparing natural ester with mineral oil at the same designed transformers up to 500 kVA. The deviation of hottest temperature between the two is increased with load. For preventing additional aging of insulation paper, design changes are required when substituting natural ester for conventional transformer oil.

Recent R&D progress on condition monitoring and diagnosis for power apparatus such as substation equipments including GIS and main transformer, rotating machineries including hydro-generator, turbo-generator, and HV motor, and power distribution equipments including power cable, overhead line system and lightning arrester, and so on in Korea are investigated in this paper. The fields experiences on the CMD carried out by KEPCO are also introduced.

Since 1998, Korea Electric Power Corporation (KEPCO) 's distribution automation system (DAS) has been deployed and now operated in whole 190 branch offices in KEPCO. From 2005, research project has been carried on, which titled with "Development of Intelligent Distribution Automation System (IDAS)" to give DAS more intelligence. The project is consisted of 4 sub projects in which high level master station for IDAS, intelligent multifunctional remote terminal unit, sensor and intelligent distribution facilities with diagnosis are being developed to improve the power quality and reliability of the distribution networks and test bed for distribution generation is being established. The high level management systems and intelligent RTUs and distribution facilities has already developed and will be integrated and tested in the field next year. From 2008, KEPCO will launch new research project for Smart Distribution Grid. In this project, distribution automation system will be transformed into the smart multi-agent, self diagnostic and fault anticipatable system with fully integrated with Distributed Energy Resources and with conformance to IEC 61850. And new DC (direct current) power distribution network configuration and operating technology will also be developed using DC microgrid and customer storage system. After completion of this future projects, the power distribution architecture for next grid will be developed, through products of that revolutionary improvement for power network in terms of integrated operation, reliability and utilization will be accomplished. (4 pages)

The puckering transition of 4-substituted proline residues by electron-withdrawing groups, i.e., 4(R)-hydroxy-L-proline (Hyp) and 4(R)-fluoro-L-proline (Flp) residues, with trans and cis prolyl peptide bonds was studied by adiabatic optimizations along the torsion angle chi1 of the prolyl ring at the HF/6-31+G(d) level. By analyzing the potential energy surface and local minima, it is observed that the puckering transition of the prolyl ring for Hyp and Flp residues proceeds from a down-puckered conformation to an up-puckered one through the transition state with an envelope form having the N atom at the top of envelope and not a planar one for both trans and cis conformers, which is the same as found for the unsubstituted proline residue. At HF/6-31+G(d) and B3LYP/6-311++G(d,p) levels, the structures of the backbone and prolyl ring for local minima of Ac-Hyp-NHMe and Ac-Flp-NHMe are quite similar to those of Ac-Pro-NHMe. However, the relative stability of the up-puckered conformation to the down-puckered one is increased for Ac-Hyp-NHMe with the cis imide bond and for Ac-Flp-NHMe with the trans and cis imide bonds. In particular, the 4(R)-substitution by hydroxy and fluorine groups has brought some structural changes in the prolyl ring of the transition states and the changes in barriers for the puckering transition. The puckering transitions for Ac-Hyp-NHMe and Ac-Flp-NHMe are proven to be predominantly electronically driven by analyzing the electronic and enthalpic contributions to the barriers, as seen for Ac-Pro-NHMe.

We report here the conformational preference and prolyl cis-trans isomerization of 4(R)-substituted proline dipeptides, N-acetyl-N'-methylamides of 4(R)-hydroxy-L-proline and 4(R)-fluoro-L-proline (Ac-Hyp-NHMe and Ac-Flp-NHMe, respectively), studied at the HF/6-31+G(d), B3LYP/6-31+G(d), and B3LYP/6-311++G(d,p) levels of theory. The 4(R)-substitution by electron-withdrawing groups did not result in significant changes in backbone torsion angles as well as endocyclic torsion angles of the prolyl ring. However, the small changes in backbone torsion angles phi and psi and the decrease of bond lengths r(Cbeta-Cgamma) or r(Cgamma-Cdelta) appear to induce the increase of the relative stability of the trans up-puckered conformation and to alter the relative stabilities of transition states for prolyl cis-trans isomerization. Solvation free energies of local minima and transition states in chloroform and water were calculated using the conductor-like polarizable continuum model at the HF/6-31+G(d) level of theory. The population of trans up-puckered conformations increases in the order Ac-Pro-NHMeAc-Hyp-NHMeAc-Flp-NHMe in chloroform and water. The increase in population for trans up-puckered conformations in solution is attributed to the increase in population for the polyproline-II-like conformations with up puckering. The barriers DeltaGct++ to prolyl cis-to-trans isomerization for Ac-Hyp-NHMe and Ac-Flp-NHMe increase as the solvent polarity increases, as seen for Ac-Pro-NHMe. In particular, it was identified that the cis-trans isomerization proceeds through the clockwise rotation about the prolyl peptide bond for Ac-Hyp-NHMe and Ac-Flp-NHMe in chloroform and water, as seen for Ac-Pro-NHMe.

The root causes of underground distribution medium voltage cable faults are water penetration into insulation layer and stress enhancement on semi-conductive layers. Accordingly, it is needed to improve the waterproof performance of jacket materials and the structure of power cables for extending lifetime and preventing failure. We uses non-flaming polyethylene materials instead of PVC(polyvinyl chloride) as a outer jacket material and encapsulating structure. We also use super smooth class material as a inner semi-conductive layer. The newly developed cables have improved in AC breakdown voltage after ageing tests.

Pole transformers of MV class have utilized an insulation system consisting of natural cellulose-based materials and mineral oil for many years. If transformers are subjected to rapidly changing overload conditions, insulation materials can see high temperatures leading to unexpected aging. Therefore, we have been conscious of developing a transformer that is more thermally stable than conventional types. To measure temperature distribution in the winding of conventional and newly designed transformers, temperature sensors were installed for direct reading of the transformer oil and conductor temperatures of transformers. We also conducted accelerated aging tests for these transformers. The measurement data was utilized in the design of the hybrid insulation system. Also, we found the possibility of applying this insulation system in 13.2 kV pole mounted transformers.

This paper describes the thermal characteristics of varnish treated Kraft and aramid papers in order to understand the effect of the varnish concentration on the heat flow pattern. The insulating papers were impregnated by the varnish diluted with solvent and then dried completely. The heat flow of the specimens was obtained using a differential scanning calorimeter (DSC) and analyzed. As a result, the heat flow curves of varnish and varnish treated insulating paper linearly changed with the varnish concentration and it was confirmed that the varnish concentration could be determined by comparing with the changing patterns in heat flow of the varnish treated insulating papers with temperature.

Liquid-immersed pole transformers have utilized an insulation system consisting of natural cellulose-based materials and mineral oil for many years. If the transformers are installed with the abruptly changing load over limitation, its insulation materials are apt to unexpected aging with high temperature. Therefore we have been conscious of developing a transformer that is more thermally stable then conventional types. To measure temperature distribution in the winding of conventional and newly designed transformers, temperature sensors were installed for direct reading of oil and conductor temperatures at transformers. And we conducted accelerating aging test for these transformers. The measuring data had made use of the design to hybrid insulation system. Also we could find the possibility of this insulation system to apply in pole mounted transformers.

To understand the electrical characteristics of water tree aged XLPE, artificially aged XLPE specimens of which the water tree with uniform length grew on the large area have been fabricated. The AC breakdown strength of the specimens has been reduced as the growth length increased and the trend of the reduction has been similar to that of water tree growth rate. Space charge distributions in the virgin and aged specimens have been measured by the PEA method and, as a result, it has been shown that the homo-charge is heavily concentrated at the tip of the water tree path while a little hetero-charge is gathered in front of electrode contacted to the water tree. Through the electric field calculation using the charge distribution, the local field enhancement at the tip of water tree path was also verified. Based on the experimental results and analysis, it can be said that the water tree reduces the breakdown strength of XLPE because of the homo-charge concentration at the tip of water tree path, which results in the reduction of effective insulating thickness.

In this study, experimental investigation has been carried out for the defect detecting capability of two different way of the OW (oscillating wave) voltage test, such as with-cable-charging and without-cable-charging method. For this purpose, two types of OW voltage tests have been performed at the laboratory on the 22.9 kV CN/CV cables in which artificial needle-type and knifecut-type defects were well integrated. Based on the test results, it could be remarked that the with-cable-charging method is more appropriate to the after laying test due to its consistency of the test condition regardless of the cable length under testing.

In this study, the effects of cracks on the electrical breakdown of line post insulators were investigated by comparing a new insulator, manufactured in 1996, with service-aged insulators which has been used in areas of severe contamination, heavy dust contamination and mild contamination. These insulators were tested to the ES and IEC specifications and especially analyzed using HRB tests, material characterization and SEM.

Partial discharge (PD) signals in various polyethylenes such as low density polyethylene (LDPE), crosslinked polyethylenes (XLPE) and chemically modified polyethylenes are measured by an ultrasonic signal detection systems, and their characteristics are analyzed. The PD characteristics of commercial XLPEs are different from sample to sample. PD activities in XLPE are more extensive than those in LDPE, which depends on the type of polyethylene. PD activities are suppressed in the tree-retardant XLPEs as compared to the conventional XLPEs. A chemical modification of LDPE using an acrylic acid suppresses PD activities in LDPE. Details of these results are described.