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The lightning impulse voltage test waveform of power equipment is prescribed in the IEC 60060-1 "High-voltage test techniques" revised in 2010. This revision introduced an evaluation method by k-factor function (test voltage function), which converts an overshoot waveform to a test voltage waveform. At present, the test standard for UHVclass equipment is being studied and the authors have experimentally acquired k-factor values for gas-insulated switchgears, oil-immersed transformers and air insulation using the largest possible model assuming an actual UHV-class equipment to date. This paper reports the experimental result on the breakdown characteristics of lightning impulse voltage test waveforms for the SF6 gas insulation model under a nonhomogeneous electric field. The k-factor value was calculated by measuring the breakdown voltage and time using the superimposed oscillation frequency and the overshoot rate as parameters. The change with respect to the superimposed frequency of this experiment was similar to that of the existing k-factor function, and the effectiveness of evaluation by the k-factor function was confirmed. [ABSTRACT FROM AUTHOR]

In IEC-60060-1 as revised in 2010, a conversion method for lightning impulse voltage test waveforms using the test voltage function (K-factor function) was adopted. Presently, studies are being conducted on the test standards for ultra-high voltage (UHV)-class equipment. Since the existing K-factor function was established based on the experimental results for more small models compared with the insulation structure of UHV-class equipment, the issue has arisen as to whether this K-factor function can also be applied for UHV-class equipment. The authors experimentally obtained K-factor values using the largest possible model assuming UHV-class equipment in the previous studies. This paper reports the K-factor values and the insulation characteristics with respect to the front time obtained for air insulation under a negative-polarity lightning impulse voltage. According to the results of this experiment, even though the K-factor values for an air gap were likely to be slightly lower than the existing K-factor function in the negative polarity, the tendency of the change with respect to the superimposed oscillation frequency was similar. Furthermore, it was found that even though the breakdown voltage for waveforms with an extended front time was likely to decrease further than that for the standard lightning impulse waveforms, the decline was about 3.1% even for a front time of 4.8 ~\mus. Consequently, it was indicated that a lightning impulse voltage test waveform with an extended front time may help properly verify the insulation performance of a UHV-class air bushing. [ABSTRACT FROM PUBLISHER]

The authors are conducting a study on the lightning impulse voltage test standard for UHV-class equipment, including the application of the evaluation method using the Kfactor (test voltage) function. Previously, the actual measurement results of K-factor values assuming UHV-class power transformers and UHV-class gas insulated switchgear were reported. The present paper reports the evaluation results of the influence of LI voltage test waveforms on the breakdown characteristics in the largest possible bushing model, assuming actual UHV-class air insulation. According to the test of the breakdown voltage characteristics with respect to the overshoot rate, it was indicated that the 50% breakdown voltage tended to rise with increasing overshoot. Subsequently, the evaluation using the K-factor function is considered useful for UHV-class air insulation. The evaluation result of the K-factor value based on the experimental results was lower in value than the present K-factor function and the result of the European Project, which is considered attributable to the significant formative time lag of a discharge in the long air insulation distance. Consequently, the K-factor function might be reviewed downward in these cases. Furthermore, according to the experimental results of the breakdown characteristics, when the front time is extended, its extension up to about 3.6 μ?s might possibly be allowed under a standard assuming UHV-class air insulation. [ABSTRACT FROM PUBLISHER]

The lightning impulse withstand voltage test waveform for electrical power equipment is specified in IEC 60060-1 ???High-voltage test techniques???. Now that ultrahigh voltage-class (UHV-class) electrical power equipment is being introduced and increasingly used, the electrical capacitance of equipment to be tested has increased, which has eventually hampered the test using the waveform that conforms to the previous standard. To address this issue, the IEC revised the IEC 60060-1 standard in 2010 and now is studying the standard for UHV-class electrical equipment. In this revision, an evaluation method using the k-factor function (test voltage function) was introduced, whereby the overshoot waveform was converted to a test voltage waveform. To date, concerning these k-factor values, measurement results based on experiments have been reported, but most were for small-scale insulation models with breakdown voltage levels mainly around 100 kV. This paper reports the experimental result of insulation breakdown characteristics for lightning impulse withstand voltage test waveforms in the model with the largest oil gap possible assuming an actual UHV-class oil-immersed transformer. Breakdown voltages and breakdown times were measured with the superimposed oscillation frequency, overshoot rate and front time as parameters. Consequently, it was indicated that, as the overshoot rate increased, the 50% breakdown voltage was inclined to increase. Subsequently, the evaluation using the k-factor function is considered to be useful for UHV-class oil immersed transformer. The result of evaluation of the k-factor value based on the experimental result was almost identical to the result of the European Project, which is the basic data of the existing k-factor function. As a result, it emerged that the existing k-factor function itself was most likely to be applicable to UHV-class oil-immersed transformers. Furthermore, since the extension of the front time up to about 3.6 ??s caused only a small change in insulation breakdown characteristics, the extension of the front time up to about 3.6 μs might possibly be allowed in the standard that assumes a UHV-class transformer. [ABSTRACT FROM PUBLISHER]