• The Journal of Korean Academy of Prosthodontics
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• v.28 no.1
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• pp.165-191
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• 1990

Although a number of studies have been performed to assure that residual stress caused by a mismatch of alloy porcelain thermal expansion can contribute to clinical failure of a ceramometal restoration, the interactive influence of cooling rate on the magnitude of thermal expansion difference and on bond strength between them have not been extensively analyzed. The objective of this study was to determine the influence of cooling rate and the number of firing cycles on the expansion mismatch and the flexural failure resistance of metal porcelain strip. Tested alloys included one Pd-Ag alloy, one Ni-Cr-Be alloy with two kinds of porcelain, Vita and Ceramco. Metal specimens were cast into rods with a height of 13mm and a diameter of 5mm. Subsequently, the castings were subjected to scheduled firing cycles without porcelain. And the porcelain specimens after being fired were trimmed into a bar with a final dimension of $5{\times}5{\times}25mm$. Thermal expansions of the alloys and porcelains were measured by using a push rod or a differential dialometer respecitvely. Porcelain glass transition temperatures and expansion values were derived alloy-porcelain pairs were assessed by comparing expansion values of the components at a porcelain glass transition temperature. Calculations were made using combinations of a Ni-Cr alloy or Pd-Ag alloy with each of two porcelain products. Metal-porcelain strip specimens were subjected to four point loading in an Instron testing machine until crack occured at the metal-cramic interface at the time of sharp decrease of load on recorder. On the basis of this study, the following conclusions may be stated: 1. Regardless of the kinds of ceramometal combinations, both of calculated and experimental data revealed that the double fired specimens exhibited a significantly lower flexural strength. 2. By the rise of the amount of mismatch, bond strength were decreased. 3. Thermal expansion value of Pd-Ag alloys were higher than that of Ni-Cr alloys. 4. Expansion curves of metal were proportional to the increase of temperature and were not affected by the experimental conditions, however porcelains did not show the same magnitude of metal, and a shift of the glass transition temperature to higher temperatures was observed when cooled rapidly 5. Alloy-porcelain thermal compatibility appeared more dependent on the porcelain than the alloy.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.1
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• pp.111-137
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• 1991

Although a number of studies have been performed to assure that residual stress caused by a mismatch of alloy porcelain thermal expansion can contribute to clinical failure of a ceramometal restoratoin, the interactive influence of cooling rate on the magnitude of thermal expansion difference and on bond strength between them have not been extensively analyzed. The objective of this study was to determine the influence of cooling rate and the number of firing cycles on the expansion mismatch and the flexural failure resistance of metal porcelain strip. Tested alloys included one Pd-Ag alloy, one Ni-Cr-Be alloy with two kinds of porcelain, Vita and Ceramco. Metal specimens were cast into rods with a height of 13mm and a diameter of 5mm. Subsequently, the castings were subjected to scheduled firing cycles without porcelain. And the porcelain specimens after being fired were trimmed into a bar with a final dimension of 5 x 5 x 25mm. Thermal expansions of the alloys and porcelains were measured by using a push rod or a differential dialometer respectively. Porcelain glass transition temperatures and expansion values were derived alloy- porcelain pairs were assessed by comparing expansion values of the components at a porcelain glass transition temperature. Calculations were made using combinations of a Ni-Cr alloy or Pd-Ag alloy with each of two porcelain products. Metal- porcelain strip specimens were subjected to four point loading in an Instron testing machine until crack occured at the metal-cramic interface at the time of sharp decrease of load on recorder. On the basis of this study, the following conclusions may be stated : 1. Regardless of the kinds of ceramometal combinations, both of calculated and experimental data revealed that the double fired specimens exhibited a significantly lower flexural strength. 2. By the rise of the amount of mismatch, bond strength were decreased. 3. Thermal expansion value of Pd-Ag alloys were higher than of Ni-Cr alloys. 4. Expansion curves of metal were proportional to the increase of temperature and were not affected by the experimental conditions, however porcelains did not show the same magnitude of metal, and a shift of the glass transition temperature to higher temperatures was observed when cooled rapidly. 5. Alloy- porcelain thermal compatibility appeared more dependent on the porcelain than the alloy.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.10
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• pp.798-803
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• 2010

This paper describes the characteristics of electromagnetic wave propagation in power transformer. A transformer which is similar to 154 kV single phase on-site transformer unit was provided for the purpose of the experiment. The 12 dielectric windows on the transformer enclosure to install UHF (ultra high frequency) sensors and the full scale mock ups of winding and the core were also equipped in the transformer. Every sensors to be installed to the transformer was tested and verified whether they show same characteristics or not before the experiment. A discharge gap which was used as a PD (partial discharge) source moved to several necessary locations in the transformer to simulate dielectric defects. Propagation times of electromagnetic wave signal from PD source to sensors decided by the routes of both reflection phenomenon and diffraction phenomenon were compared each other. The experimental results showed propagation route of the PD signal makes an effect on the frequency spectrum of front part of the signal and the magnitude of the signal and propagation time of the signal when the signal is captured on the sensor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.124-124
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• 2010

Diagnostic tests were performed on six high voltage motors. These tests included ac current, dissipation factor(tan6) and partial discharge(PD) magnitude. The rewind of motor stator insulation at rated voltage is assessed by the results of these tests. After completing the diagnostic tests, the stator windings of motors were subjected to gradually increasing ac voltage, until the insulation punctured. No. 1 and No.2 motors(4.16 kV) failed near rated voltage of 12.3 kV and 14.2 kV, respectively. The breakdown voltage of No.3 and No.4 motors(6.6 kV) was 17.6 kV and 17.8 kV, respectively. These motors are higher that expected for good quality coils in 6.6 kV class motors.

• Journal of Industrial Technology
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• v.19
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• pp.351-359
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• 1999

If the tactile sense is introduced to engineering and industries, it may provide more realistic virtual tactile sensing to human and it is possible to develop product that satisfy various consumer's taste. This paper presents a compliance emulator system as a new concept of tactile reproduction simulator which uses magnetic levitation in order to minimize friction and emulates compliance only along the vertical direction. Compliance is one of the important mechanical properties of the object related to tactile sensing of the human. The implemented system equipped with an analog LVDT sensor for a position sensor and employs a PD control with gravity compensation to emulate the specified compliance. To compensate the limited range of the system, the method of attaching the spring with various magnitude of stiffness to the system is adopted and its preliminary test is performed to confirm the validity of the method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.285-288
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• 1998

Ultrasonic signal characteristics related with the growth of electrical trees in epoxy resin are examined under 67[Hz] ac voltage application along with a CCD camera and PD current method. The ultrasonic sensor with a resonant frequency of 200[Hz] supported by a mechanical spring is attached directly to the lower-side of plane electrode. The magnitude of Partial discharge and count rate of ultrasonic signals have been measured according to the tree growth from a needle tip in an epoxy sample.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1659-1661
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• 2003

Recently, diagnostic techniques have been investigated to defect a partial discharge in high voltage electrical equipment. We have studied the characteristics of the acoustic partial discharge originating from the electrical defects in cubicle GIS(C-GIS). An acoustic emission(AE) sensor is used on the enclosure to detect partial discharge source because the sensor is sensitive to stress waves in its frequency range that may not be from a partial discharge source. AE signal is analyzed with phase-magnitude-frequency number(${\Phi}$-V-n) and pulse per second(PPS). Experience result has shown that the omitted acoustic signal has phase dependency and phase shift characteristic according to increase with applied voltage. These result will be helpful to the pattern recognition of the acoustic partial discharge in a C-GIS.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.237-238
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• 2008

Electrical properties of Pd/Zn/Pd/Au contacts to p-InP were investigated as function of the V/III ratio of p-InP. P-type InP was made by the Zn diffusion into InP and activation process with rapid thermal annealing (RTA) measurement. After activation, the hole concentration was two orders of magnitude higher than that of the sample having only diffusion process. According to transmission line method (TLM) results, the specific contact resistance of p-InP was lower as used InP having the lower V/III ratio. The experimental results represent that the diffusion of Zn in undoped InP deeply related to the equilibrium between interstitials and substitutional Zn is established via indium interstitials.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.4
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• pp.542-548
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• 2012

This study presents a new method of system modeling by using the Discrete Fourier Transform for the position control system of DC Motor. And the proposed method is similar to the method of System Identification by analysis of correlation of the measured input-output data. The measured output signals are transformed to the frequency domain using DFT. The Fourier Spectrum of the transformed signals is used for knowing to the feature of having an important effect on the system. And transfer function of the second order system is estimated by the dominant parameter which is computed in the magnitude and the phase of Fourier spectrum of the transformed signals. In addition, the output signal includes the unique feature of system. So, although the basic parameter of the system is unknown for us, the proposed method has an advantage to system modeling. And the controller is easily designed by the estimated transfer function. Thus, in this paper, the proposed method is applied to the system modeling for the position control system of DC Motor and the PD-controller is designed by the estimated model. And the efficiency and the reliability of the proposed method are verified by the experimental result.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.1
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• pp.75-81
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• 2018

In this study, the simulation of partial discharge pulse waveform have been performed for the typical joints such as EBA and PMJ in the HV underground transmission XLPE cable system in order to improve the understanding of partial discharge pulse waveform and the on-site measurement accuracy of partial discharges. FDTD simulation technique was adopted for the simulation and has been shown to be suitable for partial discharge simulation of power cables in terms of pulse propagation characteristics and waveform formation. The simulation results for the EBA showed that the second not-so-large opposite polarity peak appeared after the first negative polarity peak and the measurement sensitivity was the highest near the bottom of the EBA copper box. In the analysis results for PMJ, the magnitude of the second opposite polarity peak was large enough to compare with the first peak, and the measurement sensitivity at the end of the PMJ copper box was the highest. These simulation results show considerable similarity with the on-site measurement, and it would be very useful for the partial discharge measurement of HV XLPE cable systems.