• The Journal of the Acoustical Society of Korea
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• v.33 no.2
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• pp.111-117
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• 2014

In this paper, the structure-borne noise reduction on electrical equipment is discussed by the experimental analysis. The water cooling system in electrical equipment is the only noise source, so the mock-up was made to measure noise characteristics. Effects of power supply, stiffness, isolation of noise source and natural frequency determined by resilient mounts are investigated using the mock-up. The console prototype was made referring to noise reduction technique by the mock-up. The structure-borne noise level of a console prototype was measured and some experiments to reduce the noise was undertaken. The $1^{st}$ and $4^{th}$ harmonics of operating frequency of cooling fans causes highest structure-borne noise levels. The control of operating speeds of several DC cooling fan groups was tried. Also types and installation layouts of resilient mounts were investigated. To reduce structure-borne noise, followings can be applied: increase of stiffness, isolation of source, decrease of natural frequency of mount, combination of operating speed of fans, selection of mounts, and so on.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.5
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• pp.163-168
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• 2019

In this paper, We investigated the effects of the transparency variations from 0% to 90.7% on meshed SF-MPAA(Series Fed Microstrip Patch Array Antenna). For this, we designed SF-MPAA in 3 cases that is meshed radiation patches, meshed GND, and meshed radiation patches plus GND. And we investigated the characteristics of SF-MPAA depend on the variations of transparency in each case. In the case of meshed radiation patches, the gain decreased by 18.8% and the operating frequency is lower by 5.5%. In the case of meshed GND, the gain decreased by 15.4% and the operating frequency is lower by 5.56%. In the case of meshed radiation patches plus GND, the gain decreased by 31.94% and the operating frequency is lower by 7.6%. However, the bandwidth and the SLL(Side Lobe Level) did not show apparent tendency on the the variations of transparency.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.439-446
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• 2011

Frequency is an important operating parameter for the protection, control, and stability of a power system. Thus, it must be maintained very close to its nominal frequency. Due to the sudden change in generation and loads or faults in a power system, however, frequency deviates from its nominal value. An accurate monitoring of the power frequency is essential for optimum operation and prevention of wide area blackout. Most conventional frequency estimation schemes are based on the DFT filter. In these schemes, the gain error could cause defects when the frequency deviates from the nominal value. We present an advanced frequency estimation technique using gain compensation to enhance the DFT filter-based technique. The proposed technique can reduce the gain error caused when the frequency deviates from the nominal value. Simulation studies are performed using both the data from EMTP-RV software and the user-defined arbitrary signals to demonstrate the effectiveness of the proposed algorithm. Results show that the proposed algorithm achieves good performance under both steady state tests and dynamic conditions.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.12
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• pp.622-626
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• 2001

HID(high intensity discharge)lamps are high pressure mercury lamp, high pressure sodium lamp and metalhalide lamp. metalhalide lamp among these lamps has considered to be one of the most effective artificial light sources and this lamp has good efficiency, good color rendition and good focusing capability, But the shortcorning of metalhalide lamp is known as acoustic resonance phenomena in the discharge tube when lighted by electronic ballast and then acoustic resonance cause various problems such as the arc instability, light output fluctuations. In this paper, to reduce the acoustic resonence phenomena, the electronic ballast was designed by three methods for high frequency operation wish frequency-modulated sinusodial waves in acoustic resonance frequency band. These frequency-modulated methods are resonance frequency and resonance frequency, resonance frequency and non-resonance frequency non-resonance frequency and non-resonance frequency Experiment results could't show the Presence of acoustic resonance visually and it proved that the resonance-generating conditions can be avoided by continuously changing the two operating frequencies in acoustic resonance band (20.59kHz∼94.2kHz).

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.4
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• pp.143-148
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• 2020

In the case of a system that detects and controls the phase of an alternating voltage, the analog control method compensates the phase offset part by filtering for the detected phase and applies it to the control. However, in the digital control method, precise control cannot be achieved due to an error between the operating frequency of the microprocessor or the microcontroller and the input phase time when controlled using such phase detection. In general, when the method used is a certain time, the accumulated error is compensated and adjusted at random. To solve this problem, a method of detecting a zero point in real time and compensating for the operating frequency of the microprocessor is needed. Therefore, the research to be performed in this paper to reduce these errors and apply them to precise digital control is as follows. 1) Research on how to implement Zero Crossing Detection algorithm through simulation modeling to compensate the zero point to match the operating frequency through detection. 2) A study on the method of detecting zero points in real time through the Zero Crossing Detection design using a microcontroller and compensating for the operating frequency of the microprocessor. 3) A study on the estimation of the rotor position of BLDC motors using the Zero Crossing Detection circuit.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.9
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• pp.2744-2751
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• 1996

In case of limited power supply, a rotating shaft system may not reach its operating speed that is greater than its critical speed, but the speed oscillates with small ampllitude near critical speed. As a result, it is considered that the operating mode plays an important role in the smooth start of machines. In order to investigate the dynamic behaviors of the rotating shaft system at the beginning stage, one has derived the equations of motion whose degrees of freedom is three, two translations and one rotation. The simultaneous differential equations are numerically solved by using runge-Kutta method, and thus the small time step length could be required corresponding to the stability of solution. Three types of operating modes dependent upon the driving torque rate have been numerically investigated according to the maximum displacement of shaft center. The first type of relation is linear, the second type is composed of two linear curves recommended by machine manufacturer, and the last one is the proposed torque curve reflecting the frequency response curve of one degree of freedom system. For the second type of modes, it is found that the optimal range of intermediate speed to the critical speed lies between 0.8 and 0.9. In addition to that, the maximum displacement can be reduced more if the third type of mode is utilized.

• Journal of the Korean Society of Safety
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• v.37 no.2
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• pp.43-53
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• 2022

This paper describes an attempt to improve and optimize the operational safety level of a domestic research reactor by conducting a probabilistic safety assessment (PSA) under full-power operating conditions. The PSA was undertaken to assess the level of safety at an operating research reactor in Korea, to evaluate whether it is probabilistically safe and reliable to operate, and to obtain insights regarding the requisite procedural and design improvements for achieving safer operation. The technical objectives were to use the PSA to identify the accident sequences leading to core damage, and to conduct sensitivity analyses based thereon to derive insights regarding potential design and procedural improvements. Based on the dominant accident sequences identified by the PSA, eight types of sensitivity analysis were performed, and relevant insights for achieving safer operation were derived. When these insights were applied to the reactor design and operating procedure, the risk was found to be reduced by approximately ten times, and the safety was significantly improved. The results demonstrate that the PSA methodology is very effective for improving reactor safety in the full-power operating phase. In particular, it is a highly suitable approach for identifying the deficiencies of a reactor operating at full power, and for improving the reactor safety by overcoming those deficiencies.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.2
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• pp.173-178
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• 2010

Frequency is an important operating parameter of a power system. Due to the sudden change in generation and loads or faults in power system, the frequency is supposed to deviate from its nominal value. It is essential that the frequency of a power system be maintained very close to its nominal frequency. And monitoring and an accurate estimation of the power frequency by timing synchronized signal provided by FDR is essential to optimum operation and prevention for wide area blackout. As most conventional frequency estimation schemes are based on DFT filter, it has been pointed out that the gain error by change in magnitude could cause the defects when the power frequency is deviated from nominal value. In this paper, an advanced frequency estimation scheme using gain compensation for fault disturbance recorders (FDR) is presented. The proposed scheme can reduce the gain error caused when the power frequency is deviated from nominal value. Various simulation using both the data from EMTP package and user's defined arbitrary signals are performed to demonstrate the effectiveness of the proposed scheme. The simulation results show that the proposed scheme can provide better accuracy and higher robustness to harmonics and noise under both steady state tests and dynamic conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.6419-6424
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• 2015

Recently, high-cost energy storage systems are applying to hybrid generation systems with wind turbine and diesel generator in island areas for stable operation. But, this paper proposes an operating algorithm and modeling method of an islanding microgrid that is composed of PMSG(Permanent Magnet Synchronous Generator) and Diesel Generator applied in island areas without such energy storage system. Initially, the operating algorithm was proposed for frequency and voltage to be maintained within the proper ranges for the load and weather change. And then the modeling method were proposed for PMSG, WT-side AC/DC converter and Grid-side DC/AC converter. The proposed operating algorithm and modeling method were applied to a typical islanded microgrid with PMSG wind turbine and diesel generator. The frequency and voltage was kept within the permissible ranges and the proposed method was proven to be appropriate through simulations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.3
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• pp.311-320
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• 2008

In this paper, a new variable active inductor using a conventional grounded active inductor with feedback variable LC-resonator is proposed. The grounded active inductor is realized by the gyrator-C topology and the variable LC-resonator is realized by the low-Q spiral inductor and varactor. This variable LC-resonator can compensate the degradation of Q-factor due to parasitic capacitance of a transistor, and the frequency range with high Q-factor is adjustable by resonance frequency adjustment of LC-resonator. The fabricated variable active inductor with Magnachip $0.18{\mu}m$ CMOS process shows that high-Q frequency range can be adjusted according to varactor control voltage from 4.66 GHz to 5.45 GHz and Q-factor is higher than 50 in the operating frequency ranges. The measured inductance at 4.9GHz can be controlled from 4.12 nH to 5.97 nH by control voltage.