• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.830-839
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• 2017

Support vector machine (SVM) is introduced as an effective fault diagnosis technique based on dissolved gases analysis (DGA) for oil-immersed transformers with maximum generalization ability; however, the applicability of the SVM is highly affected due to the difficulty of selecting the SVM parameters appropriately. Therefore, a novel approach combing SVM with improved imperialist competitive algorithm (IICA) for fault diagnosis of oil-immersed transformers was proposed in the paper. The improved ICA, which is proved to be an effective optimization approach, is employed to optimize the parameters of SVM. Cross validation and normalizations were applied in the training processes of SVM and the trained SVM model with the optimized parameters was established for fault diagnosis of oil-immersed transformers. Three classification benchmark sets were studied based on particle swarm optimization SVM (PSOSVM) and IICASVM with four multiple classification schemes to select the best scheme for transformer fault diagnosis. The results show that the proposed model can obtain higher diagnosis accuracy than other methods. The comparisons confirm that the proposed model is an effective approach for classification problems.

• 전기학회논문지
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• 제58권9호
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• pp.1784-1789
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• 2009

This paper describes the measurement technology of the dissolved hydrogen gas due to partial discharge in oil using gas sensor. For higher resolution and less error in measurement of the dissolved hydrogen gas in oil, the sensor outputs with ambient temperature which affect the sensor output characteristics should be considered. The sensor output trends with ambient temperature and the properties of the dissolved hydrogen gas in oil with partial discharge characteristic were analyzed through the test results. It was indicated that the sensor peak and the base voltage with measuring time were affected by ambient temperature and the measurement errors of the sensor output by temperature were reduced by using the difference between the peak and the base voltage rather than just the peak voltage. In addition, the hydrogen gas sensor outputs were increased with the increase of partial discharge energy.

• 조명전기설비학회논문지
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• 제21권9호
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• pp.87-94
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• 2007

This paper presents new criteria for DGA(Dissolved Gases Analysis) using CDF(Cumulative Distribution Function) obtained from the data from the diagnosis of transformers operated in KEPCO over a period of 16 years. Because of differences in operating environments, construction type, oil volume, and other factors, the interpretative criteria of DGA at KEPCO differs from other standards such as IEC-60599, or Rogers and Doernenburg. To suggest the most appropriate criteria, the DGA data from transformers under normal conditions as well as from developing fault transformers were collected. Using these data, this study suggests the limitative gas level of transformers under normal operating conditions and verifies the suitability of the criteria. Because the application of this new criterion to transformers at KEPCO increases the detectable ratio of incipient faults and reduces unnecessary follow-up sampling and analysis, the new criteria yields a more reliable prediction of transformer condition.

• 전기학회논문지
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• 제59권10호
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• pp.1741-1747
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• 2010

The development of overload management systems for distribution transformers offers new opportunities for improving the reliability of distribution systems. It allows network planners to optimize the system resource utilization and investment cost. Such an improvement in the flexibility of the distribution network is only possible if the operator has more accurate knowledge of the realtime conditions of distribution transformers. In this paper, we present an improved overload decision system for distribution transformers using realtime monitoring data. Our study can be categorized into two parts: (a) improvement in the criteria for judging the overload conditions of distribution transformers and (b) development of an overload evaluation system using realtime monitoring data. In order to determine the overload criteria, overload experiments are performed on sample transformers; the results of these experiments are used to define the relationship between the transformer overload and the increase in the top-oil temperature. To verify the accuracy of the experimental results, field tests are performed using specially manufactured transformers, the loads and top-oil temperatures of which can be measured. For arriving at online overload decisions, we propose methods whereby the measured load curve can be converted into an overload characteristic curve and the overload time can be calculated for any load condition. The developed system is able to evaluate the overload for individual distribution transformers and calculate the losses using realtime monitoring data.

• 전기의세계
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• 제26권6호
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• pp.78-85
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• 1977

This paper studies flashover voltage and surface corona loss of A.C and D.C in the mixed gas of air and SF$_{6}$ for solid insulators P.V.C, arcylic, glass and bakelite in two cases. In one case, those solids are covered with transformer oil and the other case, those solids are not covered with it. 1) The flashover voltage for each solids in SF$_{6}$ is more than three times compared with that in the air. The flashover voltage for P.V.C is the highest and then arcylic, glass, bakelite in a decreasing order. 2) The more the amount of SF$_{6}$ in the mixing ratio, the less corona loss. The P.V.C shows the least amount of corona loss and the bakelite the largest. 3) Compared with the corona loss of positive polarity and the negative polarity, the former has less corona loss than the latter. 4) The more the number of flashover discharge, the less insulation of each solids, but in case of bakelite, insulation almost vanishes after a couple of discharge. 5) When each insulator is covered with transformer oil, the flashover voltage generally increases and the corona loss decreases.eases.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권10호
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• pp.485-491
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• 2006

This paper describes that the distribution of electromagnetic field occurred by PD(Partial Discharge) pulse was calculated with simulation program and characteristics of calibration and PD pulses measured with folded dipole types sensors were analyzed. As the distribution of electromagnetic field in simulation was very random the wide band measuring methods were good. Therefore three folded dipole antenna types sensors which had different their widths were designed and made. The signal according to direction and distance between sensor and pulse source in these sensor was measured and the spectrum of surface PD were acquired in the experiment of model transformer. In this result the characteristics of sensor which had middle width was better than others and the main spectrum of PD signals in surface discharge were existed in around 220MHz, 320MHz and from 450MHz to 750MHz.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.1558-1560
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• 2004

Liquid-immersed pole transformers have utilized an insulation system consisting of natural cellulose-based materials and mineral oil for many years. If the transformers are installed with the abruptly changing load over limitation, its insulation materials are apt to unexpected aging with high temperature. Therefore we have been conscious of developing a transformer that is more thermally stable then conventional types. To measure temperature distribution in the winding of conventional and newly designed transformers, temperature sensors were installed fordirect reading of oil and conductor temperatures at transformers. And we conducted accelerating aging test for these transformers. The measuring data had made use of the design to hybrid insulation system. Also we could find the possibility of this insulation system to apply in pole mounted transformers.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1453-1458
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• 2011

This paper dealt with the measurement and analysis of electromagnetic waves generated by partial discharges in insulation oil to develop insulation diagnostic techniques for power transformer. Two types of narrow-band monopole antennas with the resonant frequency of 500 MHz and 1 GHz were designed and fabricated. We simulated defects which consist of a needle electrode with curvature radius of 10 ${\mu}m$ and a plane electrode with diameter of 60 mm in insulation oil. From the experiment, the maximum output voltage of the fabricated antennas was measured; 620 $mV_{max}$ for 500 MHz resonant frequency and 920 $mV_{max}$ for 1 GHz resonant frequency.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2004년도 춘계학술대회 논문집
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• pp.298-303
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• 2004

It is well known that a discharge in oil is the source of various physical phenomena. Ultrasonic-wave detection is a useful method to the diagnosis of the transformer-insulation condition. Conventionally, ultrasonic waves are detected by Piezo-electric transducer, and we use optical method that has many advantages. In this paper, we constructed a Mach-Zehnder interferometer with optical fiber and investigated the principle of operation. Test arrangement is based rut the needle-plane electrode system in oil and applied AC high voltage Ultrasonic waves were detected and showed signal- analysis results with wavelet transform.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1609-1611
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• 2003

This paper presents the results on the development of capacitive sensor for the diagnosis of electrical insulating oil, widely used for power transformer. To survey the dielectric properties of the new and used mineral insulating oil, we utilized the highly precise measuring system of KRISS. And the results were used to determine the design factors of the sensor. To evaluate the operational and the hysteresis characteristics of the sensor, we constructed a test chamber, including dielectric property measuring system. Through the results we could confirm the superior characteristics of the newly developed sensor.