Lightning Impulse Waveforms Research Articles

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - breakdown characteristics 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 preceding researches, the dielectric breakdown voltage-time characteristics were measured under several different conditions on the quasi-uniform SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> 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 obtaining through experiments the insulation characteristics for single-frequency oscillation waveforms as a representative waveform when there is a non-uniform electric field represented by metallic particles in the equipment while changing the applied voltage polarities, frequencies, and damping factors. As a result, it was found that the dielectric breakdown voltages are lower in the positive polarity and it was confirmed appropriate to conduct experiments mainly in positive-polarity in order to consider dielectric strengths. Furthermore, changing the frequencies and damping factors under positive-polarity waveforms did not cause major changes in the feature of the dielectric breakdown voltages, which remained constantly higher (by 1.41 to 2.58 times) than those under standard lightning impulse waveforms.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms under diverse conditions

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, 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. As a result, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than those for the standard lightning impulse waveform by 3% to 36%. In these experiments, parameters other than waveforms were fixed to standard conditions. In this paper insulation characteristics on quasi-uniform SF6 gas gaps were examined while changing conditions on gas pressures, gap lengths, electrode surface roughness, voltage polarities, and bias voltages. As a result, it was confirmed that the results under standard experimental conditions in the preceding experiments can be applied widely to the GIS actual equipment conditions.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - breakdown characteristics for non-standard lightning impulse waveforms associated with disconnector switching surges -

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary 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 paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage - time characteristics were measured under several different conditions for the quasi-uniform SF6 gas gap that represents an insulation element of a GIS toward two kinds of non-standard lightning impulse waveforms associated with disconnector switching surges. As a result, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 6% to 36%.

Evaluation of Breakdown Characteristics of Gas Insulated Switchgears for Non-Standard Lightning Impulse Waveforms - Breakdown Characteristics for Non-Standard Lightning Impulse Waveforms Associated with Lightning Surges

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary 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 paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage - time characteristics were measured under several different conditions mainly for the quasi-uniform SF6 gas gaps that represent an insulation element of a GIS toward four kinds of non-standard lightning impulse waveforms associated with lightning surges. As a result, in the tested range, the dielectric breakdown values for nonstandard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 3% to 32%.

Insulation characteristics of CO2 gas for nonstandard lightning impulse oscillations: Evaluation method of nonstandard lightning impulse waveform for CO2 gas insulation

AbstractSF6 gas is widely used in electric power apparatus such as gas‐insulated switchgears (GIS), because of its superior dielectric properties; however, it has been identified as a greenhouse gas at COP3 in 1997, and alternative insulation gases to SF6 have recently been investigated. One of the candidates is CO2 gas, which has lower global warming potential (GWP). However, CO2 gas has a lower withstand voltage level than SF6 gas; therefore, it is necessary to rationalize the equipment insulation level and reexamine the insulating test voltage for electric power apparatus as low as possible. From our previous investigation, in SF6 gas insulation system, we obtained that the insulation requirements of the real surges (called nonstandard lightning impulse waveform) are not as severe as those of the standard lightning impulse waveform. This paper describes the evaluation method for real surges, based on insulation characteristics of CO2 gas gaps. Furthermore, the method was applied to typical field overvoltage waveform in the lightning surge time region for 500‐kV systems and it is obtained that the equivalent peak value of the standard lightning impulse waveform is possibly reduced by 10 to 15%. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(3): 1– 9, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20560

Evaluation of breakdown characteristics of oil-immersed transformers under non-standard lightning impulse - insulation characteristics for non-standard lightning impulse waveforms with oscillations

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus reduce equipment cost while maintaining high insulation reliability, it is important to identify the insulation characteristics under non-standard lightning impulse waveforms that are associated with actual surge waveforms in the field besides the standard lightning impulse waveform and quantitatively compare them with the characteristics under the standard lightning impulse waveform. In a preceding paper, field overvoltages in the lightning surge time region were analyzed, and four typical non-standard lightning impulse waveforms were identified. Two of these including pulses were used to measure the breakdown voltages and the partial discharge inception voltages while changing the parameters, on three models of the winding insulation elements of oil-immersed transformers. This paper investigates the insulating properties of the other two types: "damped-oscillation waveform" and "rising-oscillation waveform", and evaluates the resultant average breakdown voltages in terms of the overvoltage duration, permitting their formulation in a unified way. In the examined range, the dielectric breakdown values under non-standard lightning impulse waveforms were up to 50% higher than those under standard lightning impulse waveforms in all cases. Further investigations will be expected for the reduction in insulation specifications.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - analysis and generation circuit of non-standard lightning impulse waveforms in actual field

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary 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 this paper, first, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Next, high-voltage circuits that generate these non-standard lightning surge waveforms were designed and constituted using EMTP (electro magnetic transients program) based on a circuit with a gap, inductors, and resistors connected in series and resistors and capacitors connected in parallel. Further, circuits were actually constructed, to obtain voltage waveforms approximately equal to those designed. Finally, the dielectric breakdown voltage-time characteristics were measured under several different conditions for the quasi-uniform SF6 gas gap that represents an insulation element of a GIS. As a result, it was found that, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 6% to 32%

Evaluation of breakdown characteristics of oil-immersed transformers under non-standard lightning impulse waveforms - definition of non-standard lightning impulse waveforms and insulation characteristics for waveforms including pulses

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus cut the equipment cost while maintaining the high reliability in its insulation performance, it is necessary to grasp in an organized way the insulation characteristics under non-standard lightning impulse voltage waveforms that represent actual surge waveforms encountered in the field and compare them with the characteristics under the standard lightning impulse waveform quantitatively. As described in this paper, the first step in a series of study for the purpose above was taken by analyzing lightning surge waveforms and restriking surge waveforms such as disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations and identifying four typical non-standard lightning impulse waveforms with basic frequencies of 0.24 to 1.0 MHz. Then, two of these non-standard lightning impulse waveforms, the single-pulse waveform which is the most basic type and the waveform with a pulse in the crest and a subsequent flat section, were used to measure the breakdown voltage and the partial discharge inception voltage while changing the parameters, on three models that represent the insulation elements of windings of oil-immersed transformers. Then, the resultant average breakdown voltages were evaluated in terms of the overvoltage durations, leading to a result of formulating them in a unified way. In the tested range, the dielectric breakdown values under non-standard lightning impulse waveforms were higher, marking 52% at the maximum, than those under standard lightning impulse waveforms in all the cases, suggesting a possibility of lowering the insulation specifications of an oil-immersed transformer

Influence of the Residual Inductance of the Impulse Generator for the Generation of the Lightning Impulse Voltage

This paper describes the theoretical analysis of lightning impulse voltage waveform with an overshoot or oscillation caused by the residual inductance of the impulse generator. The oscillating lightning impulse waveform is expressed by the following formula;vout (t) = A {e-α1t - e-α2t sin(ωt+θ)/sinθ}where A, α1, α2, ω, θ are constants, respectively. The front time, time to half value, peak value, oscillation frequency, overshoot voltage k-factor and virtual origin are derived from this expression. Some simulation results show the following merits;(1) The discussion on the definition of front time and tail time is possible by comparing with the base curve and overshoot.(2) The formula can analyze the effect of the residual inductance of the test circuit and express the overshot (i.e. k-factor and overshoot).(3) The formula can express the relationship between the oscillation frequency and the decay time.(4) The discussion on the meaning of base curve and waveform parameters is possible based on the theoretical analysis.

N&lt;sub&gt;2&lt;/sub&gt;ガスの非標準雷インパルス波形に対する絶縁特性と評価法

N&lt;sub&gt;2&lt;/sub&gt;ガスの非標準雷インパルス波形に対する絶縁特性と評価法

Prony Analysis Technique for Estimation of the Mean Curve of Lightning Impulses

This paper presents a novel technique for the determination of the parameters of the lightning impulse. Prony analysis is applied to analytical lightning impulse waveforms with oscillations and/or overshoots to decompose the waveform into its modal components. The mean curve of the lightning impulse is then reconstructed using a double exponential model after removing all high-frequency and damped components from the simulated impulse. Three cases of lightning impulse waveforms were investigated, including standard lightning impulse, lightning impulse with front and peak oscillations, and lightning impulse with overshoot. The simulation results show that the technique is applicable and easy to implement

Comparisons between impulse voltage calibrators and digitizers

AbstractComparisons between impulse calibrators and digitizers are useful in determining the uncertainties of the instruments, especially when multiple devices are being cross compared. In this paper, comparisons between calibrators and digitizers from NIT, Japan and NMI, Australia are reported. Comparisons of full lightning impulse and switching impulse waveforms were performed. The results of the comparisons are reported with an analysis of the sources of the uncertainties. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Comparisons between impulse voltage calibrators and digitizers

AbstractImpulse voltage calibrators are important instruments for the calibration of impulse voltage digitizers and other measurement devices. The impulse digitizers, on the other hand, are often sufficiently accurate for checking the performance of impulse voltage calibrators. Comparisons between impulse calibrators and digitizers are useful in determining the uncertainties of the instruments, especially when multiple devices are being cross compared.In this paper, comparisons among calibrators and digitizers from Nippon Institute of Technology (NIT), Japan, National Measurement Institute (NMI), Australia, and Korea Electrotechnology Research Institute (KERI), Korea, are reported. Comparisons of full lightning impulse and switching impulse waveforms were performed. The results of the comparisons are reported with an analysis of the sources of the uncertainties. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

CO&lt;sub&gt;2&lt;/sub&gt;ガスの非標準雷インパルス振動波形に対する絶縁特性（その1）

Since SF6 gas was identified as a greenhouse gas at COP3 in 1997, alternative insulation gases to SF6 have been investigated. The CO2 gas insulation is one of the candidates, which is a natural gas and has lower global warming potential (GWP). However, CO2 gas has a lower withstand voltage level than SF6; therefore, it is important to rationalize the equipment insulation level and reduce the test voltage of electric power equipment as low as possible. The actual lightning surge waveform (called non-standard lightning impulse waveform) in actual substations is different from the standard lightning impulse waveform (1.2/50μs). The actual lightning surge waveform generally rises steeply, however, the decay of the overvoltage is large, and the insulation requirements are not as severe as those of the standard lightning impulse waveform.This paper describes the insulation characteristics of CO2 gas for single-frequency oscillatory waveforms with various frequencies from 1.3 to 4.0MHz and damping ratios. From experimental investigation, similarly to SF6, it might be possible to reduce the test voltage of CO2 gas insulation system by evaluating actual lightning surge waveform in terms of the equivalent standard lightning impulse waveform.

GISにおける非標準雷インパルス波形の評価法

For rationalizing equipment insulation level which can subsequently lead to reductions in the cost of substation equipment such as GIS’s and transformers, it is necessary to reexamine insulating test voltages by investigating the method of evaluating lightning surge waveforms in terms of the equivalent standard lightning impulse waveforms. This paper describes the evaluation method for real surges (called non-standard lightning impulse waveform), based on insulation characteristics of gas gaps. The method is applied to typical surges in the lightning surge time region for various UHV and 500kV systems and it is obtained that the equivalent peak values of the standard lightning impulse waveform are possibly reduced by 20 to 30 percents.

Evaluation Method of Non-standard Lightning Impulse Waveform for Oil-filled Transformer

For rationalizing equipment insulation level which can subsequently lead to reductions in the cost of substation equipment such as GIS’s and transformers, it is necessary to reexamine insulating test voltages by investigating the method of evaluating lightning surge waveforms in terms of the equivalent standard lightning impulse waveforms. This paper discusses the evaluation method of non-standard lightning impulse waveforms, based on the insulating characteristics of the insulating models of oil-lled transformers under such non-standard waveforms. The method is applied to a few typical cases and it turns out to be that the peak values are lowered by 10 to 30 percents in conversion to the standard lightning impulse waveform.

実変電所に侵入する非標準雷インパルス波形の分析と発生回路

Evaluation of lightning surge waveforms that actually enter into substations is important when investigating the test voltage of electric power equipment. The standard lightning impulse waveform (1.2/50μs) is used for factory tests. However, the actual lightning surge waveforms in actual substations are complex waveforms in which various different oscillations are superimposed. Investigation of insulation characteristics of equipment against the complex waveforms and the standard one has significant importance. We analyzed these waveforms entering actual substations with respect to the insulation characteristics of gas insulated switchigear (GIS). From the results, we defined four types of non-standard lightning impulse waveforms. Then non-standard lightning impulse voltage is generated by an equipment circuit which is consisted of an impulse generator (IG), R, L and C is analyzed with EMTP. Voltage time characteristics were evaluated from the obtained impulse voltages.

Impulse Parameters Determination using Effective Curve Fitting Method

This paper proposes an efficient curve fitting technique used to determine the lightning impulse parameters. The fitting curve, a modified double exponential function, is introduced to describe not only an ideal lightning impulse wave form but also a deformed one theoretically described by a triple exponential function, which is caused by a residual inductance in a generating circuit. The proposed expression is applied to measured digital record set as well as theoretically generated data. By assigning suitable weights to an objective function, precise parameter values are deduced by Levenberg-Marquardt method after small iterative calculations. The conversion formula from the modified double exponential function to a triple exponential function is also introduced with a theoretical background.

Insulation Characteristics of GIS under Non-Standard Lightning Impulse Oscillations. Evaluation of Field Overvoltage Waveforms and its Applications.

To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatory overvoltage waveforms occurring in the field. This paper describes evaluation of field overvoltage waveforms and its applications using experimental data of insulation characteristics for single-frequency oscillatory waveforms and double-frequency oscillatory waveforms. As a result, it was obtained that the evaluation method based on duration for which applied voltage is more than 80% of peak voltage. This evaluation method can estimate the insulation levels for field overvoltage waveforms at these for standard lightning impulse waveform. Furthermore, this method was applied to evaluation of filed overvoltage waveforms. It was obtained that this method is applicative and has higher precision than conventional method for evaluation under experimental conditions.

The electrical breakdown characteristics of oil-paper insulation under steep front impulse voltages

Disconnecting switch operations in gas insulated equipment cause transient voltages with risetimes as steep as 5 to 20 nanoseconds and magnitudes as high as 2.5 pu. There is very little information on the effect of these transients on oil-paper insulated equipment. There have been reports, however of transformer and bushing failures caused by these transients. The electrical breakdown characteristics of oil-paper insulation under steep front impulse were studied in this project, which was co-sponsored by the Canadian Electrical Association and BC Hydro. V/sub 50/ (50% breakdown probability voltage) breakdown data was obtained with steep front (10 ns/2500 /spl mu/s), lightning and switching impulse waveforms. Insulation breakdown voltage vs breakdown time (V-t) data and multiple impulse breakdown data were obtained with the steep front impulse waveform. The V/sub 50/ results showed that the breakdown strengths were lower for steep front impulses than for lightning impulses. The multiple impulse breakdown results showed that oil-paper insulation breakdown strength can be lower than 100 kV/mm. These results are alarming, since they suggest that oil-paper insulated equipment subjected to steep front transients will fail at voltages below the lightning impulse design level (BIL). The volt-time data had a discontinuity. The breakdown process at risetimes below about 50 ns was different from the breakdown process at risetimes above 50 ns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>