• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.635-640
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• 2016

This paper dealt with the deterioration characteristics and an on-line diagnosis equipment for SPDs (surge protective devices). An accelerated aging test was carried out using a $8/20{\mu}s$ standard lightning impulse current to analyze the changes of electrical characteristics and to propose the diagnostic parameters and the criterion for deterioration of ZnO varistor which is the core component of SPDs. Based on the experimental results, an on-line diagnosis equipment for SPD was fabricated, which can measure the total leakage current, reference and clamping voltage. The leakage current measurement circuit was designed using a low-noise amplifier and a clamp type ZCT. A linear controller, the leakage current measurement part and a HVDC were used in the measurement of reference voltage. The measurement circuit of clamping voltage consisted of a surge generator and a coupling circuit. In a calibration process, measurement error of the prototype equipment was less than 3%.

• Korean Journal of Materials Research
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• v.5 no.8
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• pp.1020-1025
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• 1995

The Schottky barrier hieght(SBH) of Au/n-Si(100) were investigated by current-voltage(I-V) and capacitance voltage(C-V) measurement within a temperature range of l00K∼300K. The values of SBH at room temperature obtained from these two measurements were (0.79${\pm}$0.02)eV. The SBH obtained from the C-V measurement was temperature independent, while that obtained from the I-V measurement decreased linearly with decreasing temperature. This indicates that the Schottky diode has deviated from the thermionic emission theory at low-temperature, Thus, other current transport processes were considered and the contribution of recombination current was dominant at low temperature. We found that it leads to a lower SBH value. Thus, the conflicating results between C-V and I-V measurement were explained, C-V measurement is believed to yield mare reliable SBH values in present study since it is not affected by the current transport uncertainties.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.7
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• pp.1551-1557
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• 2013

A current velocity measurement radar estimates Doppler frequencies to extract the corresponding surface velocity information. Therefore, it is required to maintain the high degree of reliability and accuracy of Doppler frequency estimates. However, Doppler spectra of water surface return echoes can have very widely varying shapes according to measurement environments and weather conditions. Therefore, serious problems may arise in maintaining the reliability and accuracy of conventional velocity estimating algorithm in a radar sensor. Therefore, in this paper, a newly suggested algorithm is proposed for improvement using estimation of peak Doppler frequencies. The proposed method shows that the more accurate velocity measurement can be possible comparing with the conventional one.

• Progress in Superconductivity and Cryogenics
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• v.12 no.3
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• pp.16-20
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• 2010

For large scale power applications of HTS conductor, it is getting more important to have a stacked HTS coated conductor with low loss and large current capacity. But it was not easy to measure some electric properties. Stabilizer free YBCO CC for striated/ stacked conductors is easily burned out during the measurement of the critical current density because it has no stabilizer and it is difficult to set-up the current lead and voltage taps because it has many pieces of YBCO CC in a conductor. Instead of direct measuring the critical current of a stacked HTS coated conductor, indirect estimation from measuring a magnetization loss of HTS coated conductor could be useful for practical estimation of the critical current. The magnetization loss of a superconductor is supposed to be affected by a full penetrating magnetic field, and it tends to show an inflection point at the full penetrating magnetic field when we generate the graph of magnetization loss vs. external magnetic field. The full penetrating magnetic field depends on the shape of the conductor and its critical current density, so we can estimate the effective critical current density from measuring the magnetization loss. In this paper, to prove the effectiveness of this indirect estimation of the critical current, we prepared several different kinds of YBCO CC(coated conductor) including a stacked conductor short samples and measured the magnetization losses and the critical currents of each sample by using linked pick up coils and direct voltage measurement with transport current respectively.

• Journal of the Korean Society of Safety
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• v.22 no.4
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• pp.20-25
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• 2007

Instrument transformers are a safe measurement device designed to measure high voltage and large current. A current transformer(CT) is a type of instrument transformer designed to provide a current in its secondary winding proportional to the current flowing in its primary. It is commonly used in metering and protective relaying in the electrical power industry where it facilitates the safe measurement of large current. But, care must be taken that the secondary of a current transformer is not disconnected from its load while current is flowing in the primary, as this will produce a dangerously high voltage across the open secondary, and may permanently affect the accuracy of the transformer. Especially, industrial disaster such as an electric shock and/or a burn accident occurs occasionally by disregard of warning or attention. In this paper, we developed the detector for open of current transformer secondary terminal, and which was tested by the Korea Electrotechnology Research Institute. Test results show that Current Transformer secondary Open Detector(CTOD) interrupted within one second electronically when the 2nd terminal of current transformer opened.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.5
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• pp.761-766
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• 2008

This paper describes a compensation algorithm for a measurement voltage transformer (VT) based on the hysteresis characteristics of the core. The error of the VT is caused by the voltages across the primary and secondary windings. The latter depends on the secondary current whilst the former depends on the primary current, i.e. the sum of the exciting current and the secondary current. The proposed algorithm calculates the voltages across the primary and secondary windings and add them to the measured secondary voltage for compensation. To do this, the primary and secondary currents should be estimated. The secondary current is obtained directly from the secondary voltage and used to calculate the voltage across the secondary winding. For the primary current, in this paper, the exciting current is decomposed into the two currents, i.e. the core-loss current and the magnetizing current. The core-loss current is obtained by dividing the primary induced voltage by the core-loss resistance. The magnetizing current is obtained by inserting the flux into the flux-magnetizing current curve. The calculated voltages across the primary and secondary windings are added to the measured secondary current for compensation. The proposed compensation algorithm improves the error of the VT significantly.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.2
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• pp.468-473
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• 2017

This paper presents an in-process measurement system for shaft radius measurement during grinding process. This system does not require to stop the grinding process, which can enhance productivity and quality. In order to measure the radius, the system employs an eddy current sensor that can measure without any contact with the shaft. This type of sensor is very appropriate because it is insensitive to interference such as cutting fluid, coolant, contact pressure, and wear. For data analysis, the measurement system is modeled as a linearized discrete form where the states with noise are estimated by an extended Kalman filter. This system has been validated through simulations and experiments.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.3 s.96
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• pp.136-144
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• 1999

This paper presents an in-process measurement system for shaft radius measurement during grinding process. This system does not require to stop the grinding process, which can enhance productivity and quality. In order to measure the radius, the system employs an eddy current sensor that can measure without any contact with the shaft. This type of sensor is very appropriate because it is insensitive to interference such as cutting fluid, coolant, contact pressure, and wear. For data analysis, the measurement system is modeled as a linearized discrete form where the states with noise are estimated by an extended Kalman filter. This system has been validated through simulations and experiments.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.4
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• pp.78-87
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• 1997

In machine tools, frictional force exists between the table and the guideways, and in ballscrews. In this paper, feed motor current measured by a hall sensor is used to calculate the motor torque. Some frictional phenomena are studied in feed drive systems, such as the relationship between feedrate and frictional torque, and chip cover effects on frictional torque. Considering frictional phenomena, the relation- ship between the feed froce and the feed motor current id obtained. Feed force can be well estimated by feed motor current measurement considering frictional behavior. The relationship between the cutting force and the feed motor current is slightly different between up milling and down milling due to the effect of y direc- tional cutting force on frictional torque.

• Journal of Welding and Joining
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• v.33 no.4
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• pp.24-29
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• 2015

The current waveform was analysed to monitor the weld quality in real time process. The acquired current waveform was discretely analysed for the top and bottom limits of peaks as well as the pulse frequency measurement. Fast Fourier Transform was implemented in the program to monitor the pulse frequency in real time. The developed algorithm or program was tested for the validation purpose. The cross-section of weld profile was compared to the current waveform profile to correlate the monitored signal and the actual parts. Pulse frequency was also used as auxiliary tool for the quality monitoring. Based on the results, it was possible to evaluate the quality of welding by measure the current waveform profile and frequency measurement.