• Journal of Magnetics
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• v.22 no.2
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• pp.196-202
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• 2017

The occurrence of ferroresonance in electrical systems including nonlinear inductors such as transformers will bring a lot of malicious damages. The intense ferromagnetic saturation of the iron core is the most influential factor in ferroresonance that makes nonsinusoidal current and voltage. So the nonlinear behavior modeling of the magnetic core is the most important challenge in the study of ferroresonance. In this paper, the ferroresonance phenomenon is investigated in a single phase transformer using the finite element method and considering the hysteresis loop. Jiles-Atherton (JA) inverse vector model is used for modeling the hysteresis loop, which provides the accurate nonlinear model of the transformer core. The steady-state analysis of ferroresonance is done while considering different capacitors in series with the no-load transformer. The accurate results from copper losses and iron losses are extracted as the most important specifications of transformers. The validity of the simulation results is confirmed by the corresponding experimental measurements.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.143-145
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• 1996

This paper presents the hybrid type based expert system for fault diagnosis in transformers. The proposed system uses the novel fault diagnostic technique based on dissolved gas analysis(DGA) in oil-immersed transformers. The uncertainty of key gas analysis, norm threshold, and gas ratio boundaries are managed by using a fuzzy set. Also, the uncertainty of the fault diagnostic rules are handled by using fuzzy measures. Finally, kohnen's feature map performs fault classification in transformers. To verify the effectiveness of the proposed diagnosis technique, the hybrid type based expert system for fault diagnosis has been tested by using KEPCO's transformer gas records.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.760-761
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• 2007

Instrument transformers provide the reproduction of the primary current or voltage to the measuring and protecting devices. The errors of an iron-cored transformer are caused by the difference between the primary and secondary currents due to the hysteresis characteristics of the iron-core. An error compensating algorithm for instrument transformer can improve the accuracy of conventional current and voltage transformers. This paper describes the performances of the electronic current and voltage transformers mounted an error compensating algorithm. The test results of the electronic transformers in Korea Electrotechnology Research Institute(KERI) are presented.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.449-452
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• 2004

The life of power transformer is basically dependent on the aging deterioration of insulating paper. Analysis of insulating paper for its DP value or tensile strength requires removal of a few strips of paper but direct measurement of this properties is not practical for in-service transformers. For this reason furfural analysis by HPLC has gained increasing favor as a means of estimating degradation of insulating papers in power transformers and this paper reports on the analysis of data on the concentration of furfural in oil samples from about 50 power transformers and the case study. The data showed that furfural content can estimate more accurately aging characteristics compared to concentration of CO, $CO_2$. We expect that these results can be useful to predict the aging characteristics and life diagnosis of power transformers and further the study must be continued.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.813-816
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• 2004

Unipoled piezoelectric transformers were designed with different input and output area ratios. The voltage step-up ratio increased proportionally with increasing the input area. The piezoelectric transformers operated in each transformer's resonance vibration mode. In this paper, ANSYS(FEM program) was used for analysing piezoelectric transformers. We compared with analysis and experimental results. The voltage step-up ratio showed maximum value in output area of small size. Output characteristics of piezoelectric transformers with various size were simulated. The result of analysis showed $2\sim7$ times higher voltage step-up ratio than a experiment result.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1163-1168
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• 2011

Most transformers use insulating and cooling fluids derived from petroleum crude oil, but mineral oil has some possibility of environmental pollution and fire with explosion. vegetable oil fluids extracted from seed has superior biodegradation and fire-resistant properties including an exceptionally high fire point enhancing fire safety. In this study, it is aimed at the practicality of substituting natural ester dielectric fluid for mineral oil in liquid insulation system of transformers. As a rise in coil winding temperature has a direct influence on transformer life time, it is important to evaluate the temperature rise of coil winding in vegetable oil in comparison with mineral oil. Four transformers for the test are designed with 10KVA, 13.2KV, one phase unit. The temperature are directly measured in insulating oil of these transformers with the two sorts of natural ester and mineral oil dielectric fluid respectively. Experiment for aging carry out two means. First means remained $120^{\circ}C$ that transformer of mineral oil were operated at 185% load. Second means is that insulating oils of two natural ester and mineral oil were aged by thermal cycles repeating from $30^{\circ}C$ to $120^{\circ}C$. For the heating, Transformers were operated at 185% load. For the cooling, cooling system was operated in the chamber. Samples were analyzed at 42, 63, 93, 143, 190, 240 300cycles. Analysis contents are dielectric strength, total acid value. Mineral oils compared results of first means with results of second means. And compared two sort natural esters respectively with mineral oil in second means.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.8
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• pp.110-115
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• 2009

Recently, there has been a growing global interest in environmental conservation, and the field of electric power equipment has been working to become more environment-friendly. Accordingly, the low noise cooling fan of power transformers was developed through the improvement of blade shape. These are expected to apply to existing power transformers and low noise transformers. It is essential for low noise fan to possess good cooling performance as well as low audible noises. But, there was not analysis on the audible noise level and the cooling performance for low noise cooling fans until present. In this paper, we measure the audible noise level and the flow rate of low noise cooling fans to inspect the performance, Also, we confirmed that the low noise cooling fan is available to apply to power transformers through temperature rise tests of power transformers.

• Journal of Power Electronics
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• v.16 no.2
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• pp.464-472
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• 2016

This study applies the selective harmonic elimination (SHE) technique to design and operate a regulated AC/DC/AC power supply suitable for maritime military applications and underground trains. The input is a single 50/60 Hz AC voltage, and the output is a 400 Hz regulated voltage. The switching angles for a multi-level inverter and transformer turns ratio are determined to operate with special connected transformers with equal power ratings and produce an almost sinusoidal current. As a result of its capability of directly controlling harmonics, the SHE technique is applicable to apparatus with congenital immunity to specific harmonics, such as series-connected transformers, which are specially designed to equally share the total load power. In the present work, a single-phase 50/60 Hz input source is rectified via a semi-controlled bridge rectifier to control DC voltage levels and thereby regulate the output load voltage at a constant level. The DC-rectified voltage then supplies six single-phase quazi-square H-bridge inverters, each of which supplies the primary of a single-phase transformer. The secondaries of the six transformers are connected in series. Through off-line calculation, the switching angles of the six inverters and the turns ratios of the six transformers are designed to ensure equal power distribution for the transformers. The SHE technique is also employed to eliminate the higher-order harmonics of the output voltage. A digital implementation is carried out to determine the switching angles. Theoretical results are demonstrated, and a scaled-down experimental 600 VA prototype is built to verify the validity of the proposed system.

• IEMEK Journal of Embedded Systems and Applications
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• v.18 no.3
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• pp.89-100
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• 2023

Recently, on-device artificial intelligence (AI) solutions using mobile devices and embedded edge devices have emerged in various fields, such as computer vision, to address network traffic burdens, low-energy operations, and security problems. Although vision transformer deep learning models have outperformed conventional convolutional neural network (CNN) models in computer vision, they require more computations and parameters than CNN models. Thus, they are not directly applicable to embedded edge devices with limited hardware resources. Many researchers have proposed various model compression methods or lightweight architectures for vision transformers; however, there are only a few studies evaluating the effects of model compression techniques of vision transformers on performance. Regarding this problem, this paper presents a performance evaluation of vision transformers on embedded platforms. We investigated the behaviors of three vision transformers: DeiT, LeViT, and MobileViT. Each model performance was evaluated by accuracy and inference time on edge devices using the ImageNet dataset. We assessed the effects of the quantization method applied to the models on latency enhancement and accuracy degradation by profiling the proportion of response time occupied by major operations. In addition, we evaluated the performance of each model on GPU and EdgeTPU-based edge devices. In our experimental results, LeViT showed the best performance in CPU-based edge devices, and DeiT-small showed the highest performance improvement in GPU-based edge devices. In addition, only MobileViT models showed performance improvement on EdgeTPU. Summarizing the analysis results through profiling, the degree of performance improvement of each vision transformer model was highly dependent on the proportion of parts that could be optimized in the target edge device. In summary, to apply vision transformers to on-device AI solutions, either proper operation composition and optimizations specific to target edge devices must be considered.

• Analytical Science and Technology
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• v.13 no.2
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• pp.166-172
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• 2000

The life expectation of power transformers is basically dependent on the aging deterioration of insulating paper which can not be obtained from operating transformers. Therefore, it will be very useful if we can manage transformers by indirect analysis of degradation products. "Furan derivatives" are known the decomposition products which are generated by the degradation of cellulose in insulating paper. We proved that 2-furfural is the only measurable product from our transformers, and determined easily the concentration of 2-furfural by HPLC without any specific pretreatments, Compared to concentration of $CO_2$ and CO by GC, the concentration of 2-furfural by HPLC can estimate more accurately aging characteristics of transformers. We expect that these results can be utilized to predict the aging characteristics and life diagnosis of power transformers.