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.

A Method for Representing Non-Standard Waveform in Factory Tests Using Impulse Waveforms

The standard 1.2/50 lightning impulse test has been important for factory testing equipment and evaluating their performance in electrical systems. In practice, however, such equipment is subject to non-standard waveform (NSW) of high frequencies, which may not be covered by standard tests. To overcome this difficulty, the present article outlines a method that simulates NSW in laboratory tests. Based on multiresolution wavelet analysis, the method considers the correlation between amplitude and entropy in the decomposition levels between waveforms. To that end, changes are proposed to the following parameters of standard impulse tests: amplitude, cut-off instant, and front time. The results show that, mostly, the combination of a lightning impulse waveform (LIW) with impulse waves cut at different times, sufficiently represent the NSW. Only when the NSW's density falls predominantly in a frequency range above 3.125 MHz, will there be need for a complementary LIW with a steep front time. The method's application allows manufacturers and concessionaires to subject the equipment to conditions that properly represent the NSW effects, through lightning impulse tests carried out at the factory.

ANALISA SAMBARAN PETIR TERHADAP SISTEM PROTEKSI TOWER TELEKOMUNIKASI MENGGUNAKAN SIMULASI SOFTWARE ATP DRAW

The increase in the telecommunications network was accompanied by the addition of the number of BTS (Base Transceiver Station) in various regions. The BTS (Base Transceiver Station) tower is built with a minimum height of 25-100 meters. BTS towers are equipped with external and internal grounding protection systems that are designed and installed in accordance with SNI. The protection system is a unified protection system for towers and telecommunications equipment from lightning strikes. Lightning strikes occur randomly which cannot be ascertained and their occurrence is controlled and lightning strikes also cause damage to the object that is struck. ATP Draw is a graphical program from the Electromagnetic Transient Program (EMTP) for Windows. Software Alternating Transient Program (ATP Draw) is used for digital simulation of impulse waves. In this software a lightning protection system is modeled in the form of an electrical circuit, and a lightning impulse waveform against a lightning protection system circuit. analyzed the lightning protection system on the BTS tower by performing simulations using ATP Draw software with a power line model with Standard IEC 1.2 x 50 s showing the simulation results of a lightning surge current of 30389 A. for a lightning surge input current of 80 kA, 36088 A for a lightning current input lightning surge of 95 kA, and 37987 A for lightning surge input current of 100 kA. For modeling the standard CIGRE 3.3x77.5μs power line, the simulation results for a lightning surge current of 40644 A for a lightning surge input current of 80 kA, 48264 A for a lightning surge input current of 95 kA, and 50805 A for a lightning surge input current of 100 kA.

Effects of lightning impulse front time on substation grounding system performance

<table width="593" border="1" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top" width="387"><p>The role of the grounding system in the safety of the power system and protection of personnel is obvious during an unexpected short circuit or lightning discharge at the substation. The aim of this work is to analyze the effects of several parameters: lightning impulse front time, soil resistivity and types of grid materials on the grounding system of the Substation. The ground potential rise (GPR), touch voltage and step voltage of a 50 m x 60 m grounding grid buried at a depth of 0.5 m were computed using CDEGS when injected by impulse with different front times. Results show that the shorter the front time of lightning impulse waveform, the higher the value of GPR, touch voltage and step voltage. Meanwhile, when the value of soil resistivity is increased, the value of GPR, touch voltage and step voltage is also increased. Lastly, different types of grid conductor materials give different values of GPR, touch voltage and step voltage. However, it can be said that the differences are too small to be of any significance.</p><p> </p></td></tr></tbody></table>

On Site Oscillating Lightning Impulse Test and Insulation Diagnose for Power Transformers

This letter proposed a new lightning impulse test method for power transformers based on oscillating lightning impulse(OLI) waveform. The OLI has high generation efficiency and is easy to generate for field test. Partial discharge detection and transfer function analysis are used to evaluate the transformer insulation condition during the impulse test. The OLI waveform for transformer test satisfied with the requirements of the standard is obtained by altering the value of resistance and inductance in the circuit. The experiment was carried out on a transformer scale model to prove the validity of the proposed method. The results show that the current pulse method and the UHF method detect the PDs simultaneously as the insulation defect is excited at high voltage. Meanwhile, the transfer function changes due to the discharge in winding. It provides a new test and insulation diagnose method with application prospects for transformer lightning impulse test on site.

Lightning impulse breakdown characteristics of SF6 and 20% C3F7CN / 80% CO2 mixture under weakly non-uniform electric fields

This paper provides a comparative study on the impulse breakdown performance of SF 6 and 20% C 3 F 7 CN / 80% CO 2 gas mixture under weak non-uniform electric fields. Two geometrically distinct electrode configurations, with similar field utilization factor, were subjected to standard lightning impulse waveform (1.2/50 μs) and the effects of pressure, gap distance and impulse polarity on breakdown characteristics were studied. The results show that SF 6 has a higher breakdown voltage than the C 3 F 7 CN/CO 2 mixture and the positive 1.2/50 μs breakdown voltages were found to be higher than the negative counterparts. These results show that the effect of polarity on breakdown voltage does not exclusively depend on electrode geometry but also on pressure and gas type. The results of this paper identify the weaker polarity for 20% C3F7CN / 80% CO2 tested with hemispherical rod-plane and coaxial electrode configurations and the results contribute to the design of SF 6 -free gas insulated equipment.

Computation and Analysis of Electric Field Distribution Under Lightning Impulse Voltage for 1000-kV Gas-Insulated-Switchgear Spacer

The electric field distribution is critical to the insulation structure design of 1000-kV gas-insulated-switchgear (GIS) equipment. At present, it is not difficult to obtain the electric field distribution under commercial frequency sinusoidal voltage; however, for lightning impulse voltage, the electric field distribution is commonly substituted by electrostatic analysis under the peak voltage. As a result, this treatment may not embody the characteristics of the dielectric constant changing with frequency. In this paper, a frequency-domain mathematical model for transient analysis is established. The measured broadband frequency dielectric spectrum for the medium of a GIS spacer is well fitted by a H–N function model with three relaxation peaks. The transient analysis for a 1000-kV GIS spacer is realized by superposing the responses to the sinusoidal and direct current components of the lightning impulse waveform. The potential and electric field regulation for a 1000-kV GIS spacer under lightning impulse voltage is presented and analyzed. Furthermore, the computed results from traditional electrostatic analysis are introduced for comparison. The results indicate that the electrostatic analysis increases the computed electric field strength at the surface of the GIS spacer, while it decreases that at the interface between the GIS spacer and center conductor. It could provide computational support for the insulation structure design of 1000-kV GIS spacers.

A Simple Fast and Accurate Simulation Method for Power Transformer Lightning Impulse Test

Determining the Marx generator configuration, including the values of series and parallel resistors as well as the number of series and parallel stages to obtain standard lightning impulse (LI) waveforms, is usually done in a trial and error process in the high voltage test fields of power transformer manufacturers. This practical process may take excessive time and is boring for test engineers. In this paper, a simple simulation method is proposed to model the LI test circuit of the transformer by computer, which is helpful in identifying the Marx generator set up. This method is based on modeling the LI test circuit as well as the transformer's high frequency impedance in discrete frequency domain. The measured frequency response of the transformer is used to model its high frequency characteristics. Digital signal processing methods are used to simulate the circuit and obtain waveforms. The accuracy of the proposed method is validated using experimental tests performed on three transformers with different ratings.

The Impact of TiO2 Nanoparticle Concentration Levels on Impulse Breakdown Performance of Mineral Oil-Based Nanofluids.

The insulation of mineral oil-based nanofluids was found to vary with different concentration level of nanoparticles. However, the mechanisms behind this research finding are not well studied. In this paper, mineral oil-based nanofluids were prepared by suspending TiO2 nanoparticles with weight percentages ranging from 0.0057% to 0.0681%. The breakdown voltage and chop time of nanofluids were observed under standard lightning impulse waveform. The experimental results show that the presence of TiO2 nanoparticles increases the breakdown voltage of mineral oil under positive polarity. The enhancement of breakdown strength tends to saturate when the concentration of nanoparticle exceeds 0.0227 wt%. Electronic traps formed at the interfacial region of nanoparticles, which could capture fast electrons in bulk oil and reduce the net density of space charge in front of prebreakdown streamers, are responsible for the breakdown strength enhancement. When the particle concentration level is higher, the overlap of Gouy–Chapman diffusion layers results in the saturation of trap density in nanofluids. Consequently, the breakdown strength of nanofluids is saturated. Under negative polarity, the electrons are likely to be scattered by the nanoparticles on the way towards the anode, resulting in enhanced electric fields near the streamer tip and the decrement of breakdown voltage.

Impulse withstand voltage of single-phase compact distribution line structures considering bare and XLPE-covered cables

This paper is dedicated to investigate the impulse withstand voltage of single-phase compact distribution line structures of 15kV class. The structures are tested in laboratory with the application of standard lightning impulse waveforms of positive polarity. Three situations are considered: (i) XLPE-covered cables with brand new insulation; (ii) XLPE-covered cables with punctured insulation; (iii) bare cables, aiming at assessing the critical case in which the insulating layer of the cable is completely deteriorated. The results indicate that the presence of an XLPE layer covering the cable leads to a significant increase in the impulse withstand voltage of the investigated structures compared to the use of bare cables. In the cases considering brand new XLPE-covered cables, insulation breakdown leads to the formation of a pinhole in the insulating layer at points up to about 200cm from the tested structure. The presence of pinholes in the tested cable specimens has no significant effect in the breakdown voltage of the tested structures, except when the pinhole is sufficiently close to the pole. Finally, to provide elements for investigating the performance of the structures when subjected to nonstandard impulse voltages, parameters for volt-time curves and for the disruptive effect (DE) method are provided for the critical case of structures with bare cables.

Breakdown characteristics of oil-impregnated paper and influential factors for damped alternating oscillation waveforms

As striking lightning impulse waveforms in power transformers are quite different from the standard lightning impulse waveform (SLIW) used in the withstand voltage tests, it is essential to identify the breakdown characteristics of oil-impregnated paper (OIP) under non-SLIW and to quantitatively compare them with those under SLIW. On that basis, the impulse insulation levels of power transformers can be rationally determined and then the insulation specifications can be evaluated to maintain high equipment reliability. In this paper, with damped alternating oscillation waveform as a representative basis, the breakdown characteristics of oil-impregnated paper were experimentally obtained by changing the frequency and damping rate of the applied voltage. All experiments were conducted using a column-column electrode model. In addition to the 50% breakdown voltages (U50), Minimum breakdown voltage Umin and V-t characteristics under different circumstances, the influence of various parameters on breakdown characteristics and the possible reasons were discussed. After comparing waveforms and corresponding results, the specific relationship between waveform parameters and U50 were expressed as a single equation. As a result, the breakdown voltage was 1.106 to 1.435 times higher than that under SLIW depending on frequency and damping rate. The steepness of the wave peak and the duration of high voltage around wave crests are considered to be two important factors affecting the breakdown voltage. An effective way was proposed to predict U50 of oil-impregnated paper as a reference for insulation specifications irrespective of wave shape. These results support the rationalization of insulation for actual lightning impulse waveforms in the power transformers.

Breakdown of CF3I gas and its mixtures under lightning impulse in coaxial-gil geometry

SF6 is widely used in modern transmission and distribution networks because of its outstanding dual qualities: arc quenching and dielectric insulation. As a gas medium, SF6 is chemically inert, non-toxic, and non-flammable, which makes possible the construction of compact SF6 switchgear. One major known disadvantage of the gas is that it has a global warming potential which is 23,900 times higher than CO2. This has led to research into alternative gases with a much lower environmental impact, and one of the emerging candidates is CF3I. The high boiling temperature of CF3I means that it has to be used as part of a mixture inside gas-insulated equipment. To carry out the investigation on CF3I, a scaled-down coaxial system that replicates the maximum electric field of a 400 kV GIL system was designed and fabricated. The insulation performances of CF3I/CO2 and CF3I/N2 gas mixtures were then examined by measuring the 50% breakdown voltage, U50, using a standard lightning impulse waveform (1.2/50) under absolute pressures of 1 to 4 bar. The experimental results show that CF3I gas mixtures have promising potential as an insulation medium for application in gasinsulated lines.

Effect of the overshoot level in an alternative method for processing of tail chopped lightning impulses

The construction of new Ultra High Voltage laboratories requires more studies about standards for equipment as well as for testing and measurement techniques. Currently, the analysis of tail chopped lightning impulse waveforms is possible only by prior application of a full reference lightning impulse, creating difficulties for testing and processing of waveforms. A new method for evaluating the relevant parameters of tail chopped waveforms has been previously developed and this paper studies the effect of the overshoot in this alternative method.

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.

Uncertainty in K-factor measurement for lightning impulse voltage test

The IEC-60060-1 "High-voltage test technique" was revised in 2010 and an evaluation method using the k-factor function (test voltage function) was introduced for the lightning impulse voltage test, which involved the overshoot waveform being converted into the test voltage waveform. Test standards for UHV-class equipment are also presently being studied. To date, authors have measured k-factor values with the largest possible model, assuming actual UHV-class power equipment and proposed a new k-factor function for large-scale equipment. The present paper reports on the evaluation results of expanded uncertainty when measuring a k-factor value on the basis of the ISO/IEC Guide 98-3. As a result, it was clarified that significant uncertainty in measuring a k-factor value is brought about by the definition of the kfactor itself because small differences in the 50% breakdown voltage between the smooth lightning impulse and overshoot waveforms with respective uncertainties at a certain level were calculated. The expanded uncertainty when measuring the k-factor value in the present study for an overshoot rate of 10%, which is particularly important for practical use, was a large value of ±0.23 to ±0.36, or 0.46 to 0.72 in topto- bottom width compared to k-factor values themselves ranging from 0.2 to 1.0. However, this is actually considered a minimum level of uncertainty, which is inevitable in principle, and the best achievable measurement result rather than something caused by any problem in measurement itself.

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

Since 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, an effective alternative is sought from an 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 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 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 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.

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.

K-Factor Value and Front-Time-Related Characteristics in Negative Polarity Lightning Impulse Test for UHV-Class Air Insulation

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 nμ s. 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.