• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.12
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• pp.685-690
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• 2000

Multiple-lightning impulse currents are a general feature of the lightning ground f=flash. It is therefore necessary for lightning arresters used in power systems to be estimated by applying not only a single-lightning impulse current but also a multiple-lightning impulse currents. This paper presents the effects of multiple-lightning impulse currents on deterioration of ZnO arrester blocks. The multiple-lightning impulse generator which can produce quadruple 8/20$[\mus]$ 5[kA] with separation time of 30~120[ms] is designed and fabricated. The total energy applied to the arrester block at each impulse is about 1,200[J]. In experiment, various parameters such as leakage current component, reference voltage, and temperature are measured with the number of applied impulse current. Also, micro-structure changes of the ZnO blocks after applying the single and the multiple-lightning impulse currents of 200 times are compared. The experimental results indicate that the types of arrester blocks are more vulnerable to deterioration or damage by multiple-lightning impulse currents.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.10
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• pp.82-88
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• 2014

This paper presents the results of model tests for the attachment process of lightning leader to ground which is one of poorly understood processes of cloud-to-ground lightning discharges. In order to simulate the attachment process of lightning leader to ground, we investigated the discharge characteristics of air gap between the tip of needle-shaped electrode and the soil surface as a parameter of moisture content in soils when the positive and negative $1.2/50{\mu}s$ lightning impulse voltages are applied. The breakdown voltage and the discharge light were observed. As a result, the attachment processes of lightning leader to ground are strongly dependent on the grain size and the moisture content of soils. The time to breakdown was shortened with increasing the magnitude of incident impulse voltages. The delay time from application of the highest voltage to breakdown in sand is shortened with increasing the moisture content. The delay time from application of the voltage to breakdown in gravel varied from about $0.5{\mu}s$ to several ${\mu}s$. As the moisture content in soil increases, the breakdown voltages are decreased and the breakdown voltage versus time to breakdown curves are shifted toward the lower side. The results obtained in this work are similar to those for non-uniform air gap stressed by lightning impulse voltages.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1368-1370
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• 1995

Lightning impulse voltage is essential to evaluate the insulation performance of electric power apparatus. Recently international standard(IEC-60) on high voltage measurement techniques are being revised. In the draft of this standard, a new calibration method is introduced and the accuracy of most industrial measuring systems is maintained by means of comparison test against the reference measuring systems. Intercomparison tests of dividers for lightning impulse measurement were carried out by KERI. The shielded resisitive divider with 700kV rating developed by KERI were done comparison test with PTB divider with 300kV rating which have the similar charateristics as that were circulated among the laboratories. This paper reports on the comparison test results with full lightning impulse voltages from 126kV to 240kV. It is demonstrated that KERI are capable of realizing the idea in the revision of the IEC standand, that is, to establish traceability.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1549-1551
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• 2001

Cyclic aging for 14 days is performed to remove a large amount of the volatiles found in freshly manufactured cable. In this paper, we examined lightning impulse characteristics of 22.9 kV CV power cable before and after cyclic aging for 14days. As the result, the breakdown voltage after aging under normal temperature was lower than that before aging, and the breakdown voltage after aging under hot temperature was lower than that before aging. We found that the dispersion of lightning impulse breakdown voltage before 14 cyclic aging test were reduced rather than those after 14 cyclic aging test.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.8
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• pp.142-149
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• 2010

This paper describes dielectric characteristics of $SF_6$ and dry-air gases under lightning impulse voltages in a quasi-uniform electric field. In order to simulate to a quasi-uniform electric field, electric field utilization factor of the used sphere-plane electrode is 71[%]. The gas pressure of $SF_6$ ranges from 0.1 to 0.2[MPa] and that of dry-air ranges from 0.2 to 0.6[MPa]. Electrical breakdown voltages of $SF_6$ and dry-air gases are measured and analyzed as functions of the polarity of lightning impulse voltage and gas pressure. As a result, the electrical breakdown voltage of both gases under the positive lightning impulse voltage is higher than that under the negative one. The electrical breakdown voltage in $SF_6$ is almost higher than 2.67 times compared to dry-air. The results presented in this paper can be used as a useful information to evaluate the capability of alternative insulation gases for $SF_6$ in power distribution equipment with prominent ability against lightning surge.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.212-216
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• 2000

ZnO varistors for distribution surge arrester (18kV, 5kA) were developed and tested microstructure and electrical characteristics. Microstructure of ZnO varistor was consisted of ZnO grain, spinel phase and Bi-rich phase. Average grain size of ZnO varistor was $\mu\textrm{m}$ Reference voltage and lightning impulse residual voltage of ZnO varistor exhibited a good haracteristics above 5.5kV and below 11.56kV, respectively. Consequently, discharge capacity which is the most important characteristics of ZnO varistor for surge arrester exhibited excellent properties above 70kA at twice high-current impulse test. Moreover, variation rate of reference voltage and lightning impulse residual voltage showed below 5% and 2% after high-current impulse test, respectively. Leakage current and watt loss of ZnO varistor will not increase during accelerated aging test at stress condition, such as 3.213kV/$115^{\circ}C$/1000h.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.491-492
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• 2008

This paper describes the series-gap characteristics of transmission line arrester with switching and lightning impulse flashover test. The transmission line arrester exhibited external gap because it is must not flashover with switching impulse on the other hand it is must flashover with lightning impulse. In accordance, minimum and maximum length of series-gap was determinated with these tests. As gap length is increased flashover voltage was increased in the range of 315.4 kV~496.3 kV and negative polarity exhibited a high voltage. As a result, It was thought tat the series-gap length of transmission line arrester exhibited in the range of 580 mm~1100 mm.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.1005-1010
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• 2011

The accidents caused by dielectric instability have been increasing in power grid. It is important to enhance the dielectric reliability of a high voltage apparatus to reduce the damage from electrical hazards. To develop an electrically reliable high voltage apparatus, the experimental study on the electrical breakdown field strength is indispensable, as well as theoretical approach. In this paper, the lightning impulse breakdown characteristics considering utilization factors are studied for the establishment of insulation design criteria of an high voltage apparatus. The utilization factors are represented as the ratio of mean electric field to maximum electric field. Dielectric experiments are performed by using several kinds of sphere-plane electrode systems made of stainless steel. As a result, it is found that dielectric characteristics are affected by not only maximum electric field intensity but also utilization factors of electrode systems. The results are expected to be applicable to designing the air-insulated high voltage apparatuses.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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• pp.1326-1336
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• 2018

This paper proposes a numerical approach to predict the critical flashover voltages of air gaps under lightning impulses. For an air gap, the impulse voltage waveform features and electric field features are defined to characterize its energy storage status before the initiation of breakdown. These features are taken as the input parameters of the predictive model established by support vector machine (SVM). Given an applied voltage range, the golden section search method is used to compute the prediction results efficiently. This method was applied to predict the critical flashover voltages of rod-rod, rod-plane and sphere-plane gaps over a wide range of gap lengths and impulse voltage waveshapes. The predicted results coincide well with the experimental data, with the same trends and acceptable errors. The mean absolute percentage errors of 6 groups of test samples are within 4.6%, which demonstrates the validity and accuracy of the predictive model. This method provides an effectual way to obtain the critical flashover voltage and might be helpful to estimate the safe clearances of air gaps for insulation design.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.61-62
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• 2009

This paper describes the characteristics of lightning impulse current of ZnO block for transmission line arrester with external gap. The ageing parameters of lightning arresters ate impulse current, moisture ingress, temperature ageing and so on. Especially it is important to estimate the change of electrical characteristics by impulse current. Total energy applied to the ZnO arrester each time is $4/10{\mu}s$, 30kA and $2/20{\mu}s$, 10kA impulse current. Before and After the test, the residual voltage variation of varistors passed was below 5%. According to the test, it is thought that the ZnO arrester shows good stability with impulse current test.