Non-standard Lightning Impulse Waveforms Research Articles

Lightning Impulse Voltage Stresses In Underground Cables

Underground power cables are crucial for transmission and distribution. Lightning can stress their insulation, but not directly. So, impulse cable testing is studied. This research examines the cable’s transient response to standard and non-standard lightning impulse voltage waveforms. MATLAB Simulink was used to model a 132 kV wire with standard and non-standard impulse voltages. The IEC60060-1(2010) lightning impulse test uses a conventional waveform impulse voltage with a front time and a tail time of 1.2/50μs half value, while the non-standard test uses a front time and a tail time of 0.8/12s half value. Non-standard impulse waveforms are more accurate than standard waveforms. The impulse test voltage is four to five times the underground cable’s operational voltage and must withstand five applications without damage. Standard and non-standard impulse waveforms are injected with 132 kV and 550 kV to evaluate insulation failure or damage. Standard lightning and non-standard impulse voltage waveforms do not cause insulation failure or damage. When 132 kV and 550 kV are introduced into the normal and non-standard lightning impulse waveforms, the overshoot voltage increases. The peak voltage of a non-standard 550 kV impulse voltage waveform exceeds the IEC impulse withstand voltage. The finding shows that non-standard impulse voltage waves create increased cable voltage stress.

Breakdown characteristics of oil-paper insulation under lightning impulse waveforms with oscillations

The non-standard lightning impulse waveforms (N-SLIWs) including oscillating lightning impulses, very fast transient voltages (VFTOs) and steep waveforms in the power system gravely endanger the inner insulation of power transformer. To prevent insulation failure and provide guidance for robust transformer design, in this paper, two typical insulation models of oil-immersed transformer were established and their breakdown characteristics under N-SLIWs were investigated. The research mainly focused on the influence of front time and oscillation frequency of N-SLIWs on the breakdown characteristics. The experimental results showed that the breakdown voltage increased with the decrease of front time. For low frequency-oscillating lightning impulse waveforms (LF-OLIWs), breakdown voltage increased with the increase of oscillation frequency and was up to 30% higher than that under standard lightning impulse waveform (SLIW). For VFTOs, with the increase of frequency, breakdown voltages presented a law of inverted U type. Insulation model could withstand the highest value of VFTO when the oscillation frequency was around 2.4 MHz. But when the frequency was as high as 9 MHz, breakdown voltage was close to that under SLIW. A very high frequency oscillation was the main reason for the reduction of breakdown voltage as its steepness dV/dt assisted the effective transmission of the sphere’s potential to the head of the streamer channel.

Simulation of overvoltage stresses on surge arrester insulation

Impulse voltage testing is generally carried out for assessing the insulation strength of power equipment using standard impulse voltage waveforms in high-voltage laboratory. However, in actual field, the power equipment experiences standard and non-standard lightning impulse voltages. The main objective of this work is to analyse the voltage stress on surge arresters under standard and non-standard lightning impulse waveforms. Surge arrester models are developed in matlab (The MathWorks, Inc., Natick, Massachusetts, United States), and residual voltage test results are compared with manufacturer data for validation. Impulse voltage test is performed on the Institute of Electrical and Electronics Engineers surge arrester model using standard and non-standard lightning impulse voltage waveforms. The obtained test results showed that non-standard impulses have the potential to develop higher voltage stress and hence pose a high risk to surge arresters. However, results of this study provide the basis for further laboratory-based investigation considering a wide variety of impulse voltage waveforms representing the real lightning overvoltages. The test results will contribute to identify the need for modifying existing test standards or introducing new standards for impulse testing of surge arrester. Copyright © 2015 John Wiley & Sons, Ltd.

Evaluation of breakdown characteristics of N2 gas for non-standard lightning impulse waveforms - breakdown characteristics in the presence of bias voltages under non-uniform electric field

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 N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas, which has relatively good insulation characteristics among gases with a low environmental impact. To use this N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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.

Evaluation of breakdown characteristics of N2 gas for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

SF <SUB xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</SUB> gas, an insulation medium used for gas insulated switchgear (GIS), is known for its high global warming potential, hence the search for an effective alternative from an environmental perspective. As a potential alternative, the authors are focusing on N <SUB xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</SUB> gas. To use this N <SUB xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</SUB> gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (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 N <SUB xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</SUB> gas for nonstandard lightning impulse waveforms. Consequently, similarly to the previous study using SF <SUB xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</SUB> gas, the insulation characteristics could be expressed by one characteristic line using the duration as a parameter. In addition, based on the characteristic line, a method of evaluating insulation specifications for generated waveforms was established and applied as an example to actual surge waveforms in a substation. Furthermore, it emerged that the insulation specifications could potentially be reduced by about 10% for actual surge waveforms used in the present study.

Evaluation of breakdown characteristics of CO2 gas for non-standard lightning impulse waveforms - breakdown characteristics in the presence of bias voltages under non-uniform electric field

To lower the lightning impulse withstand voltage of gas insulated switchgear (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 that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the previous work, the dielectric breakdown voltage - time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gap and partly the cone-shaped insulating spacers that represent an insulation element of GIS for six kinds of non-standard lightning impulse waveforms associated with lightning surges and disconnector switching surges. This paper, describes detailed examination in non-uniform electric field, and the pattern in which a disconnector switching surges are superposed on residual DC elements generated through the operation of disconnectors (bias voltages). This is intended to simulate more severe conditions in an actual system. Consequently, it was found that the presence of a bias voltage in the nonuniform electric field resulted in lower breakdown voltage values for single-frequency oscillation waveforms both in the positive and negative polarities. However, the breakdown voltage values under positive-polarity waveforms posing more severe insulation conditions were higher than the ones under the standard lightning impulse waveforms. Despite the presence of a bias voltage, it was possible to evaluate these breakdown voltage values in the positive polarity using the concept of a duration examined in the past.

Evaluation of breakdown characteristics of n2 gas for non-standard lightning impulse waveforms - breakdown characteristics under double-frequency oscillation waveforms and pressure-distance characteristics

SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, an insulation medium used for gas insulated switchgear (GIS), is known for its high global warming potential, hence the search for an effective alternative from an environmental perspective. As a potential alternative, the authors are focusing on N2 gas. To use this N2 gas for actual GIS, the insulation characteristics for actual overvoltage waveforms generated in the field (non-standard lightning impulse waveforms) must be obtained. To do so, the earlier study experimentally obtained and evaluated the insulation characteristics for single-frequency oscillation waveforms as a representative among nonstandard lightning impulse waveforms under the quasi-uniform electric field, which was considered to be a basis for the insulation design of GIS. The present study obtained the insulation characteristics for double-frequency oscillation waveforms to investigate surge waveforms generated in substations in more detail. Consequently, it emerged that negative polarity waveforms were more severe in terms of insulation, as was the case for single-frequency oscillation waveforms. The insulation performance was consistently higher than that for the standard lightning impulse waveforms, which were 1.08 to 1.09 times. In other words, it was confirmed that the insulation specification could be rationalized by about 10%, even for complex oscillation waveforms, such as those of double-frequency oscillation. Furthermore, a study was conducted on the influence of the gas pressure and gap length for single-frequency oscillation waveforms. Consequently, it emerged that the results under the basic experimental conditions were likely to be applicable to actual GIS under wider-ranging conditions.

Evaluation of breakdown characteristics of CO2 gas for non-standard lightning impulse waveforms - breakdown characteristics under double-frequency oscillation waveforms and single-frequency oscillation waveforms in the presence of bias voltage

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. Accordingly, in previous studies, the insulation characteristics for single-frequency oscillation waveforms were experimentally obtained in the quasi-uniform electric field, which is the basis when performing the insulation design of GIS, and its evaluation method was examined. In this paper, to further elaborate the evaluation method established thus, the insulation characteristics in relation to complex oscillatory waveforms generated in actual substations, e.g. double-frequency oscillation waveforms and single-frequency oscillation waveforms on which a dc component (bias voltage) that remains due to the superimposed operation of a switching device, were obtained. Consequently, the results obtained indicated that negative polarity waveforms were more severe in terms of electrical insulation under the double frequency oscillation waveforms as well as under the single-frequency oscillation waveforms. Therefore, when considering a dielectric strength, it is reasonable to conduct experiments using negative-polarity waveforms for the complex oscillatory waveforms, such as the double frequency oscillation waveforms. Furthermore, a study was performed on a method of evaluating insulation characteristics for non-standard lightning impulse waveforms of the CO2 gas gap via a comprehensive approach using the results including the previous ones. As a result, as in the case of studies conducted previously on SF6 gas, the insulation characteristics, including complex oscillatory waveforms generated in actual power systems, could be expressed by a single characteristic line by using the parameter of duration.

Evaluation of breakdown characteristics of N2 gas for non-standard lightning impulse waveforms under non-uniform electric field - breakdown characteristics for single-frequency oscillation waveforms -

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.

Evaluation of breakdown characteristics of CO2 gas for non-standard lightning impulse waveforms - Method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> 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 CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas, which has a lower global warming potential, as one of its potential alternatives. To use this CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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%.

Evaluation of breakdown characteristics of N2 gas for non-standard lightning impulse waveforms - breakdown characteristics under single-frequency oscillation waveforms and with bias voltages

SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> 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 N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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.

Breakdown characteristics of gas‐insulated switchgear for nonstandard lightning impulse waveforms under nonuniform electric field

AbstractTo improve the insulation specification of gas‐insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF6 gas during actual surges (called nonstandard lightning impulse waveforms) occurring at field substations. The authors observed the insulation characteristics of SF6 gas gap under various types of nonstandard lightning impulse waveforms and compared them quantitatively with those obtained with standard lightning impulse waveforms. The experimental results were used to derive an evaluation method for real surges, which was applied to typical surges for various UHV and 500‐kV systems. In the preceding study, therefore, only the case of a quasi‐uniform electric field (with a typical range of field utilization factors in the bus of a GIS) was investigated. In the present investigation, the insulation characteristics of an SF6 gas gap for a nonuniform electric field were observed experimentally and an evaluation method for converting nonstandard lightning impulse waveforms equivalently to the standard lightning impulse waveform was investigated. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(1): 11–18, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21144

Evaluation of breakdown characteristics of CO2 gas for non-standard lightning impulse waveforms under non-uniform electric field - breakdown characteristics for single-frequency oscillation waveforms -

SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> 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 CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas, which has relatively good insulation characteristics among gases with a low environmental impact (natural gases). To use this CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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.

Evaluation of breakdown characteristics of CO2 gas for non-standard lightning impulse waveforms - breakdown characteristics under single-frequency oscillation waveforms of 5.3 MHz to 20.0 MHz

SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> 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 CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas, which has a lower global warming potential (GWP), as one of its potential alternatives. In order to use this CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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.

Evaluation of Κ-Factor Based on Insulation Characteristics under Non-Standard Lightning Impulse Waveforms

The IEC, which defines the lightning impulse test methods for electric power equipment, is about to introduce the K-factor method for evaluating overshoot of lightning impulse waveforms. There is an urgent need to examine the K-factor method using such parameters as the types and sizes of insulating media and structures. This paper evaluates the K-factor method in the high-voltage test techniques using the insulation characteristics of overshoot waveforms in non-standard lightning impulse waveforms. The insulation elements of oil-immersed transformers and gas-insulated switchgear (GIS) used in this study are oil gaps, turn-to-turn insulations, and gas gaps (field utilization factor ? = 0.45 and 0.60), all of which showed results close to the proposed K-factor curve.

Evaluation of Breakdown Characteristics of Gas Insulated Switchgears for Non-standard Lightning Impulse Waveforms - Breakdown Characteristics for Double-frequency Oscillations under Non-uniform Electric Field

An effective means of rationalization of insulation design for gas insulated switchgear (GIS) is the evaluation of insulation characteristics under actual surge waveforms in the field called non-standard lightning impulse waveforms (non-standard-LIWs). The preceding researches examined quasi-uniform electric field SF6 gas gaps and partly the cone-shaped insulating spacers that represent an insulation element of GIS in order to obtain the insulation characteristics under various non-standard-LIWs. As a result, the breakdown voltages under non-standard-LIWs are higher than those under standard-LIWs, allowing the authors to identify a road map for rationalizing GIS insulation designs. In applying this rationalization technique, experimental study was conducted on single-frequency oscillations to identify the influence of the non-uniform electric field. As a result, the breakdown characteristics were found to be different from those in a quasi-uniform electric field. This paper describes the insulation characteristics under double-frequency oscillations as typical examples of nonstandard-LIWs while varying the applied voltage polarities, frequencies, and damping factors in order to study the influences of non-uniform electric field in further detail. The experimental results show that positive-polarity waveforms pose more demanding insulation requirements and that it is appropriate to conduct experiments using positive-polarity in order to consider dielectric strengths. Moreover, it was confirmed that changing the waveform parameters under positive-polarity did not cause major changes in the breakdown voltages, which remained constantly higher than those under standard-LIWs, and gave little influence to the application of the rationalization techniques.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - breakdown characteristics in the presence of bias voltages under non-uniform electric field

To lower the lightning impulse withstand voltage of gas insulated switchgear (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 that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the previous work, the dielectric breakdown voltage - time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gap and partly the cone-shaped insulating spacers that represent an insulation element of GIS for six kinds of non-standard lightning impulse waveforms associated with lightning surges and disconnector switching surges. This paper, describes detailed examination in non-uniform electric field, and the pattern in which a disconnector switching surges are superposed on residual DC elements generated through the operation of disconnectors (bias voltages). This is intended to simulate more severe conditions in an actual system. Consequently, it was found that the presence of a bias voltage in the nonuniform electric field resulted in lower breakdown voltage values for single-frequency oscillation waveforms both in the positive and negative polarities. However, the breakdown voltage values under positive-polarity waveforms posing more severe insulation conditions were higher than the ones under the standard lightning impulse waveforms. Despite the presence of a bias voltage, it was possible to evaluate these breakdown voltage values in the positive polarity using the concept of a duration examined in the past.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

To lower the lightning impulse withstand voltage of gas insulated switchgear (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 that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six kinds of non-standard lightning impulse waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Then, the dielectric breakdown voltage iquest time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gaps and partly the coneshaped insulating spacers that represent insulation elements of GIS for six kinds of nonstandard lightning impulse waveforms. In this paper, the resultant breakdown voltages were evaluated in terms of the overvoltage duration, which led to their formulation in a unified way. On the basis of these insulation characteristics and their unified formulation, the paper investigated a method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. When the constructed algorithm was applied to five examples of representative two type waveforms in the lightning surge time region, they were converted into standard lightning impulse waveforms with crest values reduced by 20% to 34%, suggesting potentiality for reduction of lightning impulse insulation specifications of GIS.

Insulation characteristics and its evaluation method of N2 gas for nonstandard lightning impulse waveforms

AbstractUntil recently, SF6 gas has widely been used as the best insulating medium in substation equipment. However, SF6 gas was specified to be a greenhouse gas at COP3 in 1997 because of its high global warming potential (GWP), and alternative insulation gases to SF6 have been sought for a long time. Alternatives using the natural gases are considered to be suitable, but none of them show better properties for insulation as well as good environmental compatibility. Therefore, it is necessary to rationalize the equipment insulation level and reduce the test voltage of electric power apparatus to as low a level as possible. The actual lightning surge waveform (so‐called nonstandard lightning impulse waveform) occurring in the actual field is different from the standard lightning impulse waveform (1.2/50 μs). There are many cases in which the actual lightning surge waveform has a steep rise and large decay of overvoltage, and the insulation requirements are not as severe as those for the standard lightning impulse waveform. In this paper, we focused our research on N2 gas as an SF6 substitute and investigated the insulation characteristics of N2 gas for a single‐frequency oscillatory waveform with various frequencies from 2.7 to 20.0 MHz and damping ratios. Based on the experimental results, it might be possible to reduce the test voltage of N2 gas insulation by evaluating the crest value of the actual lightning surge waveform that has been converted into an equivalent standard lightning impulse waveform. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 10–20, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20754

ガス絶縁開閉装置の非標準雷インパルス波形に対する不平等電界下での絶縁破壊特性

To improve insulation specification of a gas insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF6 gas under actual surge (called non-standard lightning impulse waveform) occurring in the field substation. The authors had observed the insulation characteristics of SF6 gas gap under various types of non-standard lightning impulse waveforms and compared them with under standard lightning impulse waveform quantitatively. From the investigation of the experimental results, the evaluation method for real surges is shown and the method is applied to typical surges for various UHV and 500kV systems. In the proceeding study, therefore, only for the quasi-uniform electric field (with a typical range of the field utilization factors in the bus of a GIS) was investigated. In this paper, the insulation characteristics of SF6 gas gap for non-uniform electric field were observed experimentally and investigated about the evaluation method of converting non-standard lightning impulse waveforms equivalently to the standard lightning impulse waveform.