• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1621-1625
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• 2015

Power quality has always been a concern of power engineers. Certainly an argument can be successfully made that most parts of power engineering have the ultimate objective to improve power quality. AC motors were widely used in industrial and domestic applications. Generally, AC motors were of two types: Induction and Synchronous motors. In motor many parameters like different load cycling, switching, working in hot weather and unbalances creates harmonics which creates major reasons for temperature rise of the motors. Due to high peak value of voltage, harmonics can weaken insulation in cables, windings and capacitors and different electronic components. Higher value of harmonics increase the motor current and decrease the power factor which will reduce the life time of the motor and increase the overall rating of all electrical equipments. Harmonics reduction of all the motors in India will save more power. Coating of windings of the motor with nano fillers will reduce the amount of harmonics in the motor. Based on the previous project works, actions were taken to use the enamel filled with various nano fillers for the coating of the windings of the different AC motors. Ball mill method was used to convert the micro particles of Al₂O₃, SiO₂, TiO₂, ZrO₂ and ZnO into nano particles. SEM, TEM and XRD were used to augment the particle size of the powder. The synthesized nano powders were mixed with the enamel by using ultrasonic vibrator. Then the enamel mixed with the nano fillers was coated to the windings of the several AC motors. Harmonics were measured in terms of various indices like THD, VHD, CHD and DIN by using Harmonic analyzer. There are many other measures and indices to describe power quality, but none is applicable in all cases and in many instances, these indices may hide more than they show. Sometimes power quality indices were used as a basis of comparison and standardization. The efficiency of the motors was increased by 5 – 10 %. The thermal withstanding capacity of the motor was increased by 5º to 15º C. The harmonics of the motors were reduced by 10 – 50%.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.421-432
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• 2020

This paper proposes a 2-kW solid-state power amplifier (SSPA) developed by employing power amplifier pallets designed using gallium-nitride high electron mobility transistors, which is used in S-band military radars and to replace existing traveling-wave tube amplifier (TWTA). The SSPA consists of a high-power amplifier module, which combines eight power amplifier pallets, a drive amplifier module, a digital control module, and a power supply unit. First, the amplifier module and component were integrated into a small package to account for space limitations; next, an on-board harmonic filter was fabricated to reject spurious components; and finally, an auto gain control system was designed for various duty ratios because recent military radar systems are all active phase radars using the pulse operation mode. The developed SSPA exhibited a max gain of 48 dB and an output power ranging between 63-63.6 dBm at a frequency band of 3.1 to 3.5 GHz. The auto gain control function showed that the output power is regulated around 63 dBm despite the fluctuation of the input power from 15-20 dBm. Finally, reliability of the developed system was verified through a temperature environment test for nine hours at high (55 ℃) / low (-40℃) temperature profile in accordance with military standard 810. The developed SSPA show better performance such as light weight, high output, high gain, various safety function, low repair cost and short repair time than existing TWTA.

• 한국해양학회지
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• v.2 no.1_2
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• pp.24-33
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• 1967

The variations of monthly mean sea levels along the coast of Korea anre studied graphic and harmonic methods with the data from 9 tides stations and compared with the variations of atmospheric pressure and the changes in density of sea water measured near some of the stations. The monthly mean sea level generally rises in Summer to Autumn, and falls in Winter to Spring and its range is from 20 cm to 50 cm. The variation of monthly mean sea level is of annual type, having one maximum and one minimum. The semi-range of annual components is 10.5 cm at Pusan and increases to the north in the west coast, to 20.8 cm at Inchon. It's phase is, on the whole, similar for the entire coast with about 210 (middle of August), except at Inchon, 200 . The variation of monthly mean sea level is mainly isostatic, or caused by those of sea water density and atmospheric pressure. Especially, the steric effect is predominant on the south- east coast around Pusan. However, in shallow long bays and estuaries on the west coast, the river runoff effect as well as local wind effect is also considerable. Magnitudes of annual variations at each stations are not constant, but widely variable from year to year. On the east and south coast, especially at Ulneungdo and Pusan the variations are large, which seem to be connected with the shifting of main current axes or current patterns in the offing.

• Journal of Physiology & Pathology in Korean Medicine
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• v.26 no.6
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• pp.970-975
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• 2012

In Sasang constitutional medicine, doctors diagnose and treat patients according to their Sasang consitutition (SC) type. In this work, by a clinical test with a radial pulse tonometer, we investigated radial pulse properties which were significant in distinguishing unhealthy subjects from healthy subjects for each SC type. We measured radial pulse properties on left and right Gwan locations with a pulse tonometer for 299 elderly female subjects of age of 50 years old or above. We used a newly developed SCAT system to determine subjects' SC types. Subjects' health levels of either healthy or unhealthy were determined independently by two Korean medical doctors. To investigate the statistical differences, we used either of Student's t-test or Mann-Whitney U test depending on the normality of distribution of test statistic. For TE type, unhealthy subjects were characterized with significant increases in heart rate, systolic to diastolic period, pulse depth, while they showed significant decreases in width of pulse in normal direction, pulse area in diastolic period, and high harmonic components (6th, 7th) of power spectral density. For SE type, unhealthy subjects were characterized with significant increases in pulse pressure and pulse depth, while no significant differences were found for SY type. We investigated the characteristic differences in radial pulse properties due to change in health levels on each SC type for elderly females. Pulse variables which were significantly different between healthy subjects and unhealthy subjects were found to vary between SC types. For TE type subjects, many variables were found significant at the left Gwan location, which is in support of the theory of hyperactive liver functioning for TE type. Irrespective of the constitution, the related changes in the pulse properties due to worsened health level were in support of elevated blood flow amount in compensation with weakened blood circulatory function.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.11
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• pp.63-70
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• 2001

We demonstrate the MMIC (monolithic microwave integrated circuit) frequency doublers generating stable and low-cost 29 GHz local oscillator signals from 14.5 GHz input signals. These devices were designed and fabricated by using the M MIC integration process of $0.1\;{\mu}m$ gate-length PHEMTs (pseudomorphic high electron mobility transistors) and passive components. The measurements showed S11 or -9.2 dB at 145 GHz, S22 of -18.6 dG at 29 GHz and a minimum conversion loss of 18.2 dB at 14.5 GHz with an input power or 6 dBm. Fundamental signal of 14.5 GHz were suppressed below 15.2 dBe compared to the second harmonic signal at the output port, and the isolation characteristics of fundamental signal between the input and the output port were maintained above :i0 dB in the frequency range 10.5 GHz to 18.5 GHz. The chip size of the fabricated MMIC frequency doubler is $1.5{\times}2.2\;mm^2$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.12 s.115
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• pp.1156-1163
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• 2006

This paper presents an ultra wideband(UWB) direct conversion mixer for IEEE 802.15.3a applications with simulation and measurement results. Since the direct conversion mixing causes dc-offset and even-order distortion, the proposed mixer adopts an anti-parallel diode pairs(APDPs) to solve these problems. The proposed mixer consists of an in-phase wilkinson power divider over $3.1{\sim}4.8GHz$, a wideband $45^{\circ}$ power divider over $1.5{\sim}2.4GHz$, and miniatured band pass filters(BPFs) for RF-LO isolations. The conversion loss is optimized with impedance matchings between APDPs and wideband components. The measured mixer shows the conversion loss of 13.5 dB, input third-order intercept-point($IIP_3$) of 7 dBm, and 1-dB gam compression point($P_{1dB}$) of -4 dBm. Quadrature(I/Q) outputs have the magnitude difference of about 1 dB and phase difference of ${\pm}3^{\circ}$.

• 한국해양학회지
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• v.30 no.4
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• pp.237-249
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• 1995

To understand the cross-sectional structures of temperature, salinity and current across the Korea Strait, field measurements were carried out for the period of May 2 to 20, 1994. Using the R/V Tam Yang, detailed CTD profiles and ADCP records were obtained and used to examine the mean and variability field on two time scales (15 days and 25 hours). A sharp coastal front in the middle of the Korea Strait exists across which two different water masses, i.e., warm and saline water in the eastern side and cold and less saline water in the western side are neighboring. We observed highly variable field of T and S apparently caused by the westward movement of warm and saline water mass. Short-term fluctuations of T and S in the middle layer are remarkable and their importance was analysed as the first Eigen mode accounting for more than 50% of total variances. The currents in th Korea Strait are strongly influenced by tidal currents with spring and neap variation whose maximum speed ranges 80-90 and 60-70 cm/s respectively near the central portion of the channel. Strong southward tidal current could even mask the Tsushima Current completely. Results of harmonic analysis show that the magnitudes of semidiurnal, diurnal and mean components of currents are comparable to each other at spring and neap tide conditions. The volume transport across the western channel of the Korea Strait were estimated to be 2.1 Sv at neap tide condition and 3.4 Sv at spring tide condition.

• Journal of the Korean GEO-environmental Society
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• v.16 no.9
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• pp.43-51
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• 2015

In this paper, a 3D shell-spring model that can perform time history analysis of buried pipelines is used to evaluate the effect of the incident direction of the earthquake motion. When applying harmonic motions, it is shown that the period of vibration has pronounced influence on the response of buried pipelines. With decrease in the period, the curvature of the pipeline and corresponding response are shown to increase. To evaluate the effect of the incident angle, the motions are applied in the direction of the pipleline, horizontal, and vertical planes. When the motion is applied parallel to the direction of the pipeline, it only induces bending strains and therefore, the response is the lowest. Under motions subjected in horizontal and vertical planes at an angle of $45^{\circ}$ from the longitudinal axis of the buried pipeline, the axial deformation is shown to contribute greatly to the response of the pipelines. When imposing two-components simultaneously, the calculated response is similar to the case where only single-component is imposed. It is because one component only induces bending strain, resulting in very small increase in the response. The trend of the response is shown to be quite similar for recorded motions. Therefore, it is concluded that use of a single-component is sufficient for estimation of the longitudinal response of buried pipelines.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.4
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• pp.257-268
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• 2012

The EFDC model with find grid resolution system connecting the Gyeong-Gi bay and Han River estuary was constructed to study on spring-neap variability of net volume transport at each channel of the Han River estuary. The simulation time of numerical model is 124 days from May to August, 2009 with freshwater discharge at Han, Imjin and Yeseong River. The calibration and verification of model results was confirmed using harmonic components of water level and tidal current. The net volume transport was calculated during 30 days with normal freshwater conditions at Seokmo channel and Yeomha channel around Ganghwado. The ebbing net volume transport of 44% and 56% is drained into Gyeong-Gi bay through Yeomha and Seokmo channel, respectively. The ebbing net volume transport nearby Seodo at Yeomha channel convergence flooding net volume transport at Incheon harbor, and drain (westward direction) through channel of tidal flat between Ganghwado and Yeongjongdo to the Gyeong-Gi bay. The averaged net volume transport during 4 tidal cycles was compared to variation of spring-neap periods of the Yeomha channel. The convergence position is moved up- and down-ward according to spring-neap variability. The movement of the convergence zone is appeared because 1) increasing of discharged rate tidal flat channel between Ganghwado and Yeongjongdo at the spring period, 2) The growth of barotropic forcing with downward direction at the spring tide, and 3) The strength of the baroclinic pressure gradient is greater than spring with mixing processes.