• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2007년도 추계학술대회 논문집
• /
• pp.377-378
• /
• 2007

In this paper, we were confirmed the optical characteristics of LED module by changing ambient temperature and driving current. When we supplied same driving current, the brightness quality drops due to an increased ambient temperature. The difference of brightness properties came out more large according to an increased driving current. Moreover, peak wavelength become shifted by long wavelength and declined output power by increasing driving current.

• Bulletin of the Korean Chemical Society
• /
• 제10권5호
• /
• pp.414-418
• /
• 1989

The electrochemical behavior of cadmium(Ⅱ) in tartrate solution has been studied over the pH range of 6 to 13.6 in order to explain the phenomena of the changes in limiting current depending on the pH. The polarographic limiting current showed a constant value up to pH of 7.8, after which it decreased sharply to show a minimum at pH between 11 and 12. The limiting current, then, increased again with increasing pH. The number of peaks in cyclic voltammogram was 1 to 3 depending on the pH of the solution. Two other voltammetric peaks could be observed when the main reduction peak diminished. The decrease of limiting current at 7.5$Cd(C_4H_3O_6)^-$. The increase of limiting current at strong alkaline solution, however, was due to the complex $Cd(Tart)_2(OH)_2^{4-}$.

• 한국산업융합학회 논문집
• /
• 제25권1호
• /
• pp.47-53
• /
• 2022

This paper proposes a method for selecting the capacitance of DC-link capacitors of inverters. In general, the DC-link capacitance of the inverter system must be considered for DC-link voltage, ripple current, switching frequency, ripple voltage, and pulse-width modulation techniques. Therefore, the appropriate capacitance can be determined by finding the rms and peak values of the ripple current of the capacitor. In this paper, the process of extracting the ripple current of DC-link capacitor is described in detail. In addition, the simple method for finding DC-link capacitor capacitance using the result value is presented through the simulations.

• 전력전자학회논문지
• /
• 제27권4호
• /
• pp.339-347
• /
• 2022

This study proposes the mitigation method for overcurrent and oscillation motor current in an active short-circuit operation. This operation is attracting attention as the safe state of electric vehicle traction inverters. However, the active short-circuit operation generates oscillation and overcurrent of motor currents during a transient state. The proposed method uses two different safe states in PMSM, such as active short circuit and freewheeling. The active short circuit is used for safe state in a steady state. To reduce the overshoot and oscillation, a freewheeling state is injected between active short-circuit operation by comparing the motor phase current with an analytically calculated steady-state motor current. Freewheeling state is only used in a transient state. The performance is demonstrated through simulations and experimental results. The peak current of the motor was reduced from 52 A to 40 A, and oscillation time was reduced.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제48권7호
• /
• pp.550-555
• /
• 1999

This paper deals with the effect of lightning impulse current on electrical characteristics of ZnO blocks used in distribution lightning arrester. The electrical characteristics of ZnO blocks are degraded by overtime impulse current, and the degraded ZnO block is brought to a thermal runaway and finally destroyed. It is therefore important to estimate the change of electrical characteristics of ZnO blocks. In this study, an impulse current generator which can produce 8/20$[\mus]$, 3[㎄] and 4/10$[\mus]$, 5[㎄] waveform is designed and fabricated to simulate the lightning impulse current of power systems. Total energy applied to the ZnO blocks at each time is 739[J] in 8/20$[\mus]$, and 523[J] in 4/10$[\mus]$, impulse current, respectively. From the experimental results, the 3rd harmonic of the leakage current increases continuously with the number of applied impulse current, but no significant changes in residual voltage and in reference voltage are observed until the ZnO block is destroyed. Also, it is confirmed that the main factor on degradation of ZnO blocks is rather the total energy applied to ZnO blocks than the peak value of the impulse current.

• E2M - 전기 전자와 첨단 소재
• /
• 제9권7호
• /
• pp.674-679
• /
• 1996

Using the home made Kuhn type LB (Langmuir - Blodgett) film's deposition apparatus, We measured the displacement current of monolayer film on the water surface. The obtained displacement current had each different pattern by the kind of solution while varying pressure of the monolayer. Solution of 4 - octyl - 4' - (5 - carboxyl - pentamethyleneoxy ) - azobenzene (8A5H) and stearic acid (CH$_{3}$(CH$_{2}$)$_{16}$COOH) (C18) were spreaded at the air water interface respectively, and the current induced by the dynamic behavior of molecules were pressed by barrier. Displacement current of 8A5H measured small current than C18 at same condition and it was positive direction when increasing pressure but it was negative direction when decreasing pressure. Also, Two patterns of displacement current were symmetrical form and appeared repeatedly. The C18 has unsymmetrical form of displacement current and weak current when decreasing pressure (expansion). The C18 molecules have two distinct peak values of displacement current that show that the orientations of molecules were changed largely at this points. From these results, we obtained that the 8A5H has more elasticity than the C18.8.C18.

• 전력전자학회논문지
• /
• 제18권3호
• /
• pp.270-278
• /
• 2013

This paper proposes a control method for high voltage direct current(HVDC) with modular multilevel converter (MMC) under unbalanced voltage conditions considering the submodule(SM)'s current capacity and circulating current. It is aimed to propose a control method in which the current peak value does not exceed the maximum value of HVDC-MMC by considering the current capacity of the SM under unbalance voltage conditions. And it analyzes the effect of the unbalanced voltage on circulating currents in MMC and then proposes a control method considering each component of circulating currents under unbalanced voltages. The effectiveness of the proposed controlling method is verified through simulation results using PSCAD/EMTDC.

• 조명전기설비학회논문지
• /
• 제28권10호
• /
• pp.56-62
• /
• 2014

When fault currents contain decaying DC offset, the peak value of the fault current in the first cycle of the fault period is higher than the fault current during the steady-state period. To reduce the asymmetric fault current, this paper proposes an operation scheme using the series connection of two hybrid type Superconducting Fault Current Limiters (SFCLs) : an auxiliary SFCL and a main SFCL. The proposed method calculates the fault angle by comparing the zero-crossing time with fault detection time. According to the fault angle calculated, an auxiliary SFCL operates to reduce an asymmetric fault current during half a cycle after fault occurrence. After this process, the fault current is limited by a main SFCL. To confirm the usefulness of the proposed method, case studies using Electro-Magnetic Transients Program (EMTP)/Alternative Transient Program (ATP) Draw are perfomed.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제50권5호
• /
• pp.238-245
• /
• 2001

During an AC motor's start-up accelerating period, a large amount of current is required to reach to the rating speed. This is called in-rush current. This peak in-rush current can be more than about several times the operating or steady-state current in the full load rating of the motor. In-rush current is present in both and electronic ballasts. The main area of concern is the tripping of circuit breaker and fuses which can affect electrical system components From this, we can see that the electrical power controllers will be rather concerned, since they have to supply the actual current necessary to start the motor. This paper presents a new method to reducing in-rush current and energy saving of the single-phase induction motor used in air-conditioner. It can be obtained that proposed system is low cost and small size as compared with other controller. Experiments are focused on a capacitor starting single-phase induction motor. The optimal power saving and in-rush current limiting by phase angle control are verified by experimental results. Also, auxiliary winding was controlled by electronic starting switch.

• 대한화학회지
• /
• 제21권4호
• /
• pp.276-283
• /
• 1977

산성용액중에서 백금음극을 사용하여 중크롬산이온의 환원을 전위주사법 및 정전위전해에 의하여 검토하였다. 지지전해질로서 황산나트륨(pH 1.5∼4.0)을 사용한 비완충용액중의 중크롬산칼륨의 분극곡선은 3단파가 생기며 첫째파 및 둘째파의 파고는 각각 크롬(Ⅵ)농도 및 수소이온의 활동도에 비례하나 셋째파는 어느 것에도 비례하지 않았다. 첫째 및 둘째 peak이 전류는 전위주사속도(${\nu}$)에 비례하나 셋째 peak는 50mV/sec이하의 늦은 주사속도에서 ${\nu}^{1/2}$에 비례하였다. 정전위전해에 의하면, 크롬(Ⅵ)의 환원은 셋째 peak보다 더 base이고 초기 pH가 약 2.3 이상이 되면 완전히 억제되었다. 그러므로 이 세 peak는 각각 $Cr_2O_7^{\to}Cr^{3+},\;2H^+{\to}H_2$ 및 음극피막의 형성으로 간주하였다.