• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2305-2307
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• 1999

Partial discharge measurement using a ultrasonic technique allows us to detect degradation of the electrical insulation in a power transformer. However, The ultrasonic measurement studies don't offer a good solution in operating conditions. In this paper, we investigated characteristics of ultrasonic noise caused by a 345kV power transformer under operating conditions. The ultrasonic noises generated by corona in air, vibration of core, pump and fan, etc. An ultrasonic frequency caused by corona in air was appeared 9 and 18[MHz] at the outside wall of the transformer. And a spectra of core vibration was detected below 2.5[kHz]. These spectrum were compared with 20 $\sim$ 200[kHz] of the internal partial discharge in the model transformer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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• pp.1106-1113
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• 2001

This paper presents experimental works on the ultrasonic influence during melting of ice and paraffin and compared the paraffin's result with ice's results. The experiments was carried out under two setting conditions.: 1) Heater without ultrasonic vibration, 2) heater with ultrasonic vibration. Experimental observations show that the ultrasonic vibration enhances significantly the phase-change process (melting) so that the melting time is reduced about 16∼25% compared to those of molting process without ultrasonics in the melting of both ice and paraffin. But the influence of ultrasonics was not significant to affect the reduction of the power consumption. In the case of paraffin, the reduction rate of power consumption was about 20%, but the reduction of the power consumption was increased about 0∼12%.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.142-148
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• 2013

High-power ultrasonic promotes a chemical reaction by its own energy, thus it has been used for sonochemistry applications. For example, it has been mostly used for mixing, reaction catalyst, dispersion and disintegration. High-power ultrasonic transducer is made with structure based on a Bolt-clamped Langevin type Transducer (BLT), But it has difficulty in the development because degradation of piezoelectric ceramic by the heat generation of BLT. In this study, for a development of the transducer of 25 kHz and 1000 W used in sonochemistry and industrial cleaning, BLT with a hole in its center and tubular type waveguide of the transducer were designed based on finite element method (FEM). The transducer was fabricated based on the design parameter, and the impedance characteristics are measured experimentally and compared with the numerical results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.7
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• pp.583-589
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• 2008

For the purpose of monitoring by ultrasonic test of the ball bearing conditions in rotating machinery, a system for their diagnosis was developed. ultrasonic technique is used to detect abnormal conditions in the bearing system. And various data such as frequency spectrum, energy and amplitude of ultrasonic signals, and ultrasonic parameters were acquired during experiments with the simulated ball bearing system. Based on the above results and practical application for power plant, algorithms and judgement criteria for diagnosis system was established. Bearing diagnosis system is composed of four parts as follows : sensing part for ultrasonic sensor and preamplifier, signal processing part for measuring frequency spectrum, energy and amplitude, interface part for connecting ultrasonic signal to PC using A/D converter, graphic display and software part for display of bearing condition and for managing of diagnosis program.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.106-111
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• 2021

In this study, an ultrasound-assisted micellar extraction process was developed to efficiently purify the anticancer substance paclitaxel from the plant cell Taxus chinensis. The problem of many extraction steps and long phase separation time in the traditional micellar process could be dramatically improved. The highest paclitaxel yield (~96%, extracted twice) was obtained at 180 W of ultrasonic power and 1.5 h of ultrasonic irradiation time, which was 24.7% higher than that of the traditional method. In addition, the partition coefficient (K) showed a maximum value (24.0) at 180 W of ultrasonic power and 1.5 h of irradiation time. There was no significant difference in the purity of paclitaxel, and the purity of initial paclitaxel (6.81%) increased to 22.0% after purification. Compared to the traditional method, the phase separation time of the back extraction decreased by 40.7-56.2% (ultrasonic power 80 W), 46.3-67.6% (ultrasonic power 180 W), and 51.9-67.6% (ultrasonic power 250 W), respectively. The phase separation time decreased as the ultrasonic power (80-250 W) and irradiation time (0.5-2.5 h) increased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.6
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• pp.591-598
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• 2006

The research was tried to investigate the hydrogen generation from water by the pulsed power plasma process. Hydrogen was generated by way of the electrical pulse power discharge process with the ultrasonic wave. The yield on the hydrogen generation was also studied with and without operating the ultrasonic generator, in which the applied high voltage was varied from 10 kV to 15 kV. Nitrogen and argon gases were used as working gases. As the results, the generation yield using the pure nitrogen gas is better than argon and mixed gases such as argon and nitrogen. Hydrogen concentration are significantly increased when the ultrasonic generator was operated with the electrical discharge simultaneously. It is increased with increasing the applied ultrasonic level as well.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.3
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• pp.383-390
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• 2018

Piezoelectric micro-machined ultrasonic transducers for highly directional speaker need DC bias voltage. Most existing power amplifiers are not suitable for use in highly directional transducers because they are based on AC. In addition, since the piezoelectric micro-machined ultrasonic transducer has a large capacitive reactance, the power efficiency of the power amplifier is very low. Thus this paper proposes a new high efficiency power amplifier with DC bias voltage. In addition, by designing a matching circuit to compensate the capacitive reactance of the micro-machined ultrasonic transducer, the power efficiency of the power amplifier increases. The operating characteristics of the proposed power amplifier was verified by an experimental prototype. The proposed power amplifier is expected to be widely used in designing and implementing other related power amplifiers.

• Journal of the Korea Society of Computer and Information
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• v.7 no.3
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• pp.36-41
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• 2002

This study was carried out develope a ultrasonic transducer displacement generator through 26KHz and 38KHz of the frequency phase modulation on the ultrasonic transducer. This system was producted a power output generation such as 100W, 300W, 400W and 600W. Ultrasonic power output had a change of time. We made use of a Thiram hydration and detected it measurement by the ACAO method. It was to decide the result of ultrasonic power supply for time duration and the result of comparison in the 26KHz & 38KHz by UV/VIS spectrophotometer.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.631-636
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• 1987

The design of ultrasonic transducer energy processing systems requires highly reliable command featuring mechanical frequency tracking and constant velocity control of the ultrasonic transducer with an acoustic load. This paper presents a new conceptional instantaneous current resultant control base high-frequency inverter using self turn-off devices driving an electrostrictive ultrasonic transducer system and its optimum control technique, which is implemented by feed-back of the ultrasonic transducer applied voltage and instantaneous velocity of the transducer vibrating system through a Phase-Locked-Loop control scheme. The feedback voltage corresponding to instantaneous velocity is averaged over a half-period with respect to constant amplitude/constant velocity control strategy. Described are the theory of this signal detection technique and the experimental set-up.

• Journal of Microbiology and Biotechnology
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• v.9 no.3
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• pp.243-248
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• 1999

Ultrasonic wave technology was employed to improve filtration performance and ethanol production in a bioreactor equipped with an internal ceramic-membrane filter module. The filtration performance was found to depend on the power and the pattern of ultrasonic wave irradiation. Under the optimized conditions (irradiation time: 25 see, period: 5 min, and ultrasonic power: 60 W), the flux was improved with the periodic-pause method by 200-700％ compared with the control (with no irradiation), while the improvement was only 30 to 90％ without the periodic-pause method. The final ethanol concentration also increased slightly. However, in a more severe condition (irradiation time: 2.5 min, period: 5 min, and ultrasonic power: 110 W), the irradiation of ultrasonic waves was observed to disturb cell integrity and viability, and thus to decrease ethanol production.