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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]

Since SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, an effective alternative is sought from an environmental perspective. The authors are focusing on CO2 gas as a potential alternative, given its relatively good insulation characteristics among gases with a low environmental impact (natural gases). The present study obtained and evaluated the insulation characteristics for complex waveforms, such as double-frequency oscillation waveforms, generated in an actual substation under a non-uniform electric field typically represented by metallic particle. Consequently, it was emerged that the breakdown voltage for a positive polarity waveform was 1.1 to 1.6 times higher than that for the standard lightning impulse waveform; even if parameters such as the frequency and damping rate were changed within the range assumed in the field. Furthermore, a study was conducted on a means of evaluating the insulation characteristics of the CO2 gas gap for non-standard lightning impulse waveforms via an approach involving comprehensive handling of various waveforms, as was applied to the experimental results accumulated to date. Consequently, using a parameter of so-called duration, the breakdown characteristics for various waveforms, including complex oscillation waveforms generated in actual systems, could be expressed using a single characteristic line. [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]

SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence the search for an effective alternative is required from an environmental perspective. The authors focus particularly on CO2 gas, which has a low global warming potential, as one of these potential alternatives. In order to apply this CO2 gas to actual equipment, the insulation characteristics for overvoltage waveforms generated in an actual field (called non-standard lightning impulse waveforms) must be obtained. The present study obtained and evaluated the insulation characteristics where a disconnector switching surge was superimposed over the residual dc component (bias voltage) caused by operating a switchgear under a non-uniform electric field, typically represented by metallic particles. Consequently, it was concluded that the breakdown voltage was lower for positive polarity under a non-uniform electric field in the presence of a bias voltage and that it was appropriate to conduct an experiment using a positive polarity waveform in the study of dielectric strength. Furthermore, it emerged that the breakdown voltage for a positive polarity waveform was 1.05 to 1.64 times higher than that for the standard lightning impulse waveform, even if the frequency and damping rate were changed. [ABSTRACT FROM AUTHOR]

SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence the search for an effective alternative is required from an environmental perspective. As one potential alternative, the authors are focusing on N2 gas, which has relatively good insulation characteristics among gases with a low environmental impact. To use this N2 gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (non-standard lightning impulse waveforms; non-standard-LIWs) must be obtained. The present study obtained and evaluated the insulation characteristics where a surge occurred in the presence of a bias voltage (dc component), which was considered realistic and severe under a non-uniform electric field typically represented by metallic particles. Consequently, it was concluded that the breakdown voltage was lower for positive polarity under a non-uniform electric field in the presence of a bias voltage and that it was appropriate to conduct an experiment using a positive polarity waveform when studying dielectric strength. Furthermore, it emerged that the breakdown voltage for a positive polarity waveform was 1.06 to 1.67 times higher than that for the standard lightning impulse waveform, even if the frequency and damping rate were changed. These results support the rationalization of insulation for actual surge waveforms under the quasi-uniform electric field. [ABSTRACT FROM AUTHOR]

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]

SF6 gas has been widely used in electrical power equipment such as gas insulated switchgear (GIS) due to its superior insulation and interruption characteristics. However, in 1997, SF6 gas has been designated a greenhouse gas subject to emission restrictions at COP3 (The 3rd session of the Conference Of the Parties to the United Nations Framework Convention on Climate Change). Therefore, it is important to study the possibility of using environmentally friendly gases as alternative insulation gases for practical gas-insulated apparatuses, such as GIS. In the selection of an alternative gas, it is thought that high-pressure natural gases, such as Air, N2, and CO2 are promising environmentally friendly candidates. The authors are focusing on N2 gas as one of its potential alternatives. In order to use this N2 gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (nonstandard lightning impulse waveforms; non-standard-LIWs) must be obtained. The present study, with single-frequency oscillation waveforms as a representative basis, experimentally obtained the insulation characteristics by changing the polarity, frequency, and damping rate of the applied voltage in the non-uniform electric field represented by the presence of metallic particle in the equipment. As a result, the breakdown voltage was lower for the positive polarity under the non-uniform electric field. In this polarity, the breakdown voltage was 1.06 to 1.74 higher than that by standard lightning impulse waveforms even if the frequency and damping rate were changed. These results support the rationalization of insulation for actual surge waveforms under the quasi-uniform electric field. [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]

SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence the search for an effective alternative is required from an environmental perspective. As one of its potential alternatives, the authors are focusing on N2 gas, which has relatively good insulation characteristics among natural gases and a low environmental impact. However, to use this N2 gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (non-standard lightning impulse waveforms; non-standard-LIWs) must be obtained. The present study, with single-frequency oscillation waveforms as a representative basis among non-standard LIWs, experimentally obtained the insulation characteristics of an N2 gas gap by changing the frequency and the damping factor. Consequently, the breakdown voltage (BDV) was lower for the negative polarity under a quasi-uniform electric field, hence the conclusion that it was reasonable to conduct experiments using negative polarity waveforms in order to discuss the dielectric strength. In addition, even if the frequency and damping factor changed, the BDV remained relatively constant, and that is consistently higher than that for the standard lightning impulse waveforms (standard-LIWs) at a level of 1.14 to 1.24 times. As a result, it was also confirmed for GIS using N2 gas that the insulation specification could be rationalized by about 20% by converting lightning impulse waveforms from non-standard to equivalent standard-LIWs of 1.2/50 μs. Furthermore, insulation characteristics were obtained under the pattern in which a disconnector switching surges are superposed on residual dc elements generated through the operation of disconnectors (bias voltages). Consequently, the bias voltage had only a minor influence on the insulation characteristics and it emerged that insulation characteristics were likely to be evaluated using a single polarity waveform. [ABSTRACT FROM AUTHOR]

The lightning impulse withstand voltage test waveform for electric power equipment is specified in IEC 60060-1 "High-voltage test techniques" as revised in 2010. At present, test standards for UHV-class equipment are under study. Increasing equipment capacity and the digitization of measuring equipment are mentioned as these backgrounds. Withstand voltage test by the standard waveform specified in the previous standard had been difficult (it eventually becomes an overshoot waveform) with increasing equipment capacitance. In response, an evaluation method using the kfactor function (test voltage function) was introduced, whereby the overshoot waveform was converted to the test voltage waveform. To date, concerning these kfactor values, measurement results based on experiments have been reported, but most were from small-scale insulation models with breakdown voltage levels mainly around 100 kV. The present study reports the experimental results of the insulation breakdown characteristics for the lightning impulse withstand voltage test waveform in the largest SF6 gas insulation model possible assuming actual UHV-class gas insulated switchgear. Breakdown voltage and breakdown time were measured with the superimposed oscillation frequency, overshoot rate, and front time as parameters. Following evaluation of the k-factor value based on these experimental results, the k-factor value with the overshoot rate of 10% was almost identical to that of the existing k-factor function. Consequently, evaluation using the existing k-factor function is considered appropriate. Subsequently, the existing k-factor function is most likely to be effective also for UHV-class equipment. In addition, it emerged that changes in the insulation breakdown characteristics due to the extension of the front time were small. It was considered that extending the front time, rather than allowing an excessive overshoot rate, would enable proper verification of the insulation performance as part of standard assuming UHV-class equipment. [ABSTRACT FROM AUTHOR]

SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence an effective alternative means is expected from the environmental perspective. The authors are focusing on CO2 gas, which has a lower global warming potential, as one of its potential alternatives. To use this CO2 gas for the actual GIS, the insulation characteristics for overvoltage waveforms generated in the actual fields (non-standard lightning impulse waveforms) must be obtained. For this purpose, the preceding study experimentally obtained and evaluated the insulation characteristics for various non-standard lightning impulse waveforms covering the surge waveforms generated in the actual field. In the present paper, the experimental results accumulated to date were comprehensively handled to conduct a study on the evaluation method of the insulation characteristics of the CO2 gas gap for non-standard lightning impulse waveforms. Consequently, similarly to the previous study using SF6 gas, the insulation characteristics could be expressed by one characteristic line using the duration as a parameter. Furthermore, after establishing an evaluation method of the insulation specification for generated waveforms based on the characteristic line and applying it to actual surge waveforms at substations as an example, it emerged that the insulation specification could potentially be reduced by about 10%. [ABSTRACT FROM AUTHOR]

In a lightning impulse withstand voltage test for large-sized electric power equipment, voltage waveforms sometimes contain overshoot due to the capacitance of the test equipment and the residual inductance of the test circuit including the power source. The authors have been studying fitting methods for extracting a reasonable base curve from this overshoot waveform. In the previous study, each of the fitting methods was applied to the overshoot waveform simulated using a mathematical equation to evaluate the respective merits and demerits. As the test waveform, the present paper used the overshoot waveform actually generated using a large-scale test circuit. This actual waveform was determined as one over which an oscillation waveform of several hundred kHz, which was actually at issue, was superimposed. The correct base curve of the actual waveform was derived through detailed analysis of the equivalent circuit of the test circuit and the overshoot rate was calculated based on this correct value. This correct overshoot rate was compared with that calculated using each of the fitting methods to evaluate which was an optimum fitting method. Consequently, it was found that an overshoot rate close to the correct value could be derived using the new base curve extraction method for the actual waveform. Meanwhile, it should be noted that the kfactor filtering scheme was implemented after the application of various fitting methods, and then the shape parameters of the test voltage waveforms, such as the crest value, wavefront duration, and wavetail duration, were almost identical, which confirmed that fitting methods had only a minor influence on the test voltage waveform. [ABSTRACT FROM AUTHOR]

SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence an effective alternative means is expected from the environmental perspective. As one of its potential alternatives, the authors are focusing on CO2 gas, which has relatively good insulation characteristics among gases with a low environmental impact (natural gases). To use this CO2 gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (known as nonstandard lightning impulse waveforms) must be obtained. The present study, with singlefrequency oscillation waveforms as a representative basis, experimentally obtained the insulation characteristics by changing the polarity, frequency, and damping rate of the applied voltage in the non-uniform electric field represented by the presence of metallic particle in the equipment. As a result, the breakdown voltage was lower for the positive polarity under the non-uniform electric field. In this polarity, the breakdown voltage was 1.05 to 1.68 higher than that by standard lightning impulse waveforms even if the frequency and damping rate were changed. These results support the rationalization of insulation for actual surge waveforms under the quasi-uniform electric field. [ABSTRACT FROM AUTHOR]

SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence the search for an effective alternative means from the environmental perspective. The authors are focusing on CO2 gas, which has a lower global warming potential (GWP), as one of its potential alternatives. In order to use this CO2 gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (called non-standard lightning impulse waveforms) must be obtained. For this purpose, the preceding study experimentally obtained and evaluated the insulation characteristics for relatively low frequency oscillation waveforms in disconnector switching surges generated in the actual field. In this paper, the insulation characteristics of the CO2 gas gap for higher frequency oscillation waveforms were experimentally obtained while changing the frequency and damping rate. Consequently, in the high frequency area, if the frequency was raised or the damping rate increased, the dielectric breakdown voltage tended to increase, consistently remaining higher than that for standard lightning impulse waveforms at a level of 1.08 to 1.36 times. Accordingly, it was found that the insulation specification could be rationalized by approximately 10% by converting non-standard lightning impulse waveforms to equivalent standard lightning impulse waveforms. In addition, the influence of gas pressure and gap length was examined and it emerged that the results obtained under basic experimental conditions were likely to be applicable to the conditions close to actual GIS conditions. [ABSTRACT FROM AUTHOR]

SF6 gas, an insulation medium used for gas insulated switchgear (GIS), has a high global warming potential, hence the search for an effective alternative means from the environmental perspective. One of the alternative candidates is CO2 gas, which has a lower global warming potential. In order to use this CO2 gas for actual GIS, the insulation specification must be rationalized by lowering the lightning impulse withstand voltage because the dielectric strength of CO2 gas is lower than that of SF6 gas. To lower the lightning impulse withstand voltage of GIS while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms (non-standard-LIWs) that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform (standard-LIW) quantitatively. In this paper, with single-frequency oscillations as typical examples of non-standard-LIWs, the insulation characteristics for the CO2 gas gap were experimentally obtained while changing the frequency and damping rate. Consequently, even if the frequency and damping rate were changed, the dielectric breakdown voltage varied little, consistently remaining higher than that with standard-LIW at a level of 1.08 to 1.17 times. Accordingly, it was found that, for GIS using CO2 gas, the insulation specification could be rationalized by approximately 10% by converting non-standard-LIWs to equivalent standard-LIWs. In addition, the influence of gas pressure and gap length was examined and it emerged that the results obtained under basic experimental conditions were likely to be applicable to the conditions close to actual GIS conditions. [ABSTRACT FROM AUTHOR]

The authors have studied fitting methods to extract a more reasonable base curve from the lightning impulse voltage test waveforms. In this paper, by assuming a test circuit of actual large-sized UHV class equipment, simulated recorded waveforms were created, to which various fitting methods were applied in order to study their merits and demerits. Consequently, it was found that a new base curve extraction method could calculate an overshoot rate close to the correct value for waveforms actually generated. In particular, while the existing method resulted in significant dissociation for waveforms superimposed by oscillation waves of several hundred kHz, which was actually at issue, the new method significantly improved the evaluation results of the overshoot rate. Meanwhile, it should be noted that the k-factor filtering scheme was implemented after the application of various fitting methods, and then the shape parameters of the test voltage waveforms, such as the crest value, wavefront duration, and wavetail duration, were almost identical, which confirmed that fitting methods had only a minor influence on the test voltage waveform. [ABSTRACT FROM AUTHOR]