• 전기의세계
• /
• 제27권1호
• /
• pp.56-63
• /
• 1978

A new method is suggested for the bus active power vs. line power flow sensibility bector, applying the Optimally-Ordered Triangular Factorization Technique, and new algorithms are derived for the optimum measures against overloaded lines and transformers resulting from contingency analysis. According to the algorithms an online-purpose FORTRAN computer program package is developed and tested or the actual 48-bus, 91-line power system with good results.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1989년도 하계종합학술대회 논문집
• /
• pp.411-414
• /
• 1989

It is well known that switching overvoltages in the electric power system can damage electric power apparatus. To investigate switching overvoltages, electric power system has been modeled using mathematical equal ions. Using developed model, switching overvoltages in the transformer terminal have been computed and analysed.

• 전기학회논문지
• /
• 제63권10호
• /
• pp.1328-1336
• /
• 2014

This paper proposes Power System Health Index(PSHI) newly. The paper describes several kind of power system health indices based on two main categories, which are adequacy and security. In adequacy, four kinds of health indices of Frequency, Voltage, Reserve(Operating Reserve Power and Frequency Regulation Reserve Power) and Overload of lines and transformers are proposed. In security, four kinds of health indices of Voltage(154kV, 345kV and 765kV), Overload of lines and transformers, Power flow constraint among areas and SPS are proposed. All indices are mapped with three domains, which are indicated as Health, Margin and Risk, defined with expert interview. While domains of health, margin and risk is defined similar with the conventional well being analysis of power system. The criterion of the domains is proposed using an interview with expert operators and practical reliability codes in Korea. The several kinds of health index functions, which are linear ratio, piecewise linear ration and reverse ratio function etc. are developed in this paper. It will be expected that the developed health indices can help operators to control power system more successfully and also prevent power system from accident as like as black out in future because operator can make a decision immediately based on more easily visual information of system conditions from too much indices acquisition of complex power system.

• 한국소음진동공학회논문집
• /
• 제20권5호
• /
• pp.486-491
• /
• 2010

In this paper, it is identified that high-level vibration of the single phase main power transformers shut down due to the mechanical fault. vibration sources of the SPR in the transformer's are identified and the SPR vibrations are reduced by structural modification. For vibration characteristic identification, vibration signals were measured with an accelerometer when the transformer is driving. These signals are presented in a FFT analysis in order to find the dependency of frequency components on the transformer. From finite element analyses and some experiments, it is also found that resonances occur because the natural frequencies of the SPR exist in usual driving range. To shift the natural frequencies outside the driving range, the SPR is modified by increasing stiffness. It is verified that considerable amounts of vibration are reduced by the structural modification.

• Journal of Power Electronics
• /
• 제3권2호
• /
• pp.139-144
• /
• 2003

In this paper, 11 and 13 layered step-down piezoelectric transformers were fabricated and their electrical characteristics have been analyzed for AC-adapter. When the voltage is applied to the driving piezoelectric vibrator polarized in the longitudinal direction, the output voltage is generated at the generating piezoelectric vibrator polarized in the thickness direction due to the piezoelectric effects. From the piezoelectric direct and converse effects, symbolic expressions between the electric inputs and outputs of the step-down piezoelectric transformer are derived with an equivalent circuit model. With those expressions, load and frequency characteristics are discussed through the simulations. Output voltage and current from a 11-layered and a 13-layered piezoelectric transformers were measured under the different load and frequency conditions. First we measured resonant frequency from impedance curve and got equivalent impedance value of the piezoelectric transformer from admittance plot. It was shown from experiments that output voltage increase s and resonant frequency changes according to the various resistor loads. Output current decreases inversely proportional to the change of loads. Moreover, the measured output voltage and current are well matched with the simulated results obtained from the proposed equivalent circuit model. Furthermore, a new step-down piezoelectric transformer has been suggested to Increase the output power based on a simulation result having a driving piezoelectric vibrator polarized thickness direction.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 연구회
• /
• pp.135-139
• /
• 2001

Contour vibration mode piezoelectric transformers were designed and fabricated to the square plate with size of $27.5{\times}27.5{\times}2.5(2.6,\;3.0)mm^3$ using PNW-PMN-PZT ceramics. Electrical characteristics of the piezoelectric transformer were investigated for fluorescent lamp ballast application. The electrical properties and characteristic temperature rise were measured using oscilloscope and infrared temperature sensor. A 28W fluorescent lamp was successfully driven by the fabricated transformers. After driving the lamp using Power Amplifier for 24 min, the output power, efficiency and characteristic temperature rise of PT2 piezoelectric transformer showed the appropriate values of 28.01 W, 99.43% and $11^{\circ}C$, respectively. The electronic ballast using PT2 piezoelectric transformer showed an excellent output power of 28.85 W and efficiency of 86.3%, respetively.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2000년도 하계학술대회 논문집
• /
• pp.852-856
• /
• 2000

In this paper, we investigated the output power, step-up ratio and efficiency properties of piezoelectric transformer with dielectric and piezoelectric characteristics of manufactured ceramics. The piezoelectric transformers with $2.0$\times$10$\times$48[$mm^3$] size were fabricated and its electrical properties were measured. When output power of 6W was constantly maintained, T2 piezoelectric transformer showed the minimum temperature rise of $9(^{\circ}C)$ at $150(K\Omega)$ load resistance. However, T1 piezoelecric transformer showed the temperature rise of $7.2(^{\circ}C)$ at $200(K\Omega)$ load resistance. The 6[w] CCFL (Cold Cathode Fluorescent Lamp) was successfully driven by T1 and T2 piezoelectric transformer but, its temperature rise $\Delta$T[$^{\circ}C)$] was generated more than $20(^{\circ}C)$. It is concluded that we have to design the piezoelectric transformers so that its output impedance correspond to the load impeadance, including any stray capacitance.

• Journal of Power Electronics
• /
• 제12권6호
• /
• pp.960-973
• /
• 2012

The winding loss analysis of a flyback transformer is difficult and ambiguous because the primary side current and the secondary side current differs both in shape and phase, especially for DCM (Discontinuous Conduction Mode) operation. Meanwhile, the fringing field caused by the air gaps further makes the traditional 1-D loss analysis model not directly applicable. The paper gives a thorough investigation into the phase shift of winding currents, which indicates that the phase shift of the high order harmonics is still close to $180^{\circ}$ out-of-phase. Based on the analysis, a simplified 2-D winding loss analytical model for flyback transformers considering the effects of low order harmonics is proposed. By neglecting the y components of the fringing field, the proposed model has an acceptable accuracy and a simple form that is similar to the conventional 1-D model. The power loss calculated with the proposed analysis model is verified by FEA (Finite Element Analysis) simulations and experimental results.

• Journal of Electrical Engineering and Technology
• /
• 제6권5호
• /
• pp.671-676
• /
• 2011

A multilayer square-type piezoelectric transformer with a hole at the center was investigated in this paper. Temperature distribution at the center was improved by using this construction, therefore increasing input voltage and output power. This model was simulated and investigated successfully by applying a finite element method (FEM) in ATILA software. An optimized structure was then fabricated, examined, and compared to the simulation results. Electrical characteristics, including output voltage and output power, were measured at different load resistances. The temperature distribution was also monitored using an infrared camera. The piezoelectric transformer operated at first radial vibration mode and a frequency area of 70 kHz. The 16 W output power was achieved in a three-layer transformer with 96% efficiency and $20^{\circ}C$ temperature rise from room temperature under 115 V driving voltage, 100 ${\Omega}$ matching load, $28{\times}28{\times}1.8mm$ size, and 2 mm hole diameter. With these square-type multilayer piezoelectric transformers, the temperature was concentrated around the hole and lower than in piezoelectric transformers without a hole.

• 동력기계공학회지
• /
• 제10권4호
• /
• pp.78-82
• /
• 2006

Recently, The demands for the reduction of noise generated by transformers have been increasing. Almost all of the noise generated by transformers is a result of magnetostricitive vibration in the core. The noise radiates into the atmosphere from the tank through the insulation oil. As the noise of transformer irritates residents, needs for decreasing the noise of transformer have been arised. One method of reduction such a noise is to build a free-standing enclosure of concrete and steel plates around the transformer. However, this method has some disadvantages. Another method of noise reduction is to mount a close-fitting sound insulation panel on the side of a transformer tank. Side plate vibrations of transformer are transmitted to such a sound insulation panel along two paths. In one case, they are transmitted through air by sound pressure and in the other through supporting structures. In the paper, the vibration and noise effect which is transferred from reinforce channel to insulation panel generated by transformer have been identified for the several kinds of insulation panel and damping sheet analytically and experimetally.