Impulse Voltage Research Articles

Electric Field Analysis on the Corona Discharge Phenomenon According to the Variable Air Space between the Ionizer and Ground Current Collector

In this paper, we present the optimized air space of the lightning protection rod (SK-AOR380) with the function of a charge transfer system (CTS). For evaluation of CTS in the laboratory setting, some studies have focused on the modification of the structure and shape of the CTS; the air space is designed (>2 mm) as an empirical design without quantitative data. However, in this paper, we have focused on the air space between the ionizer conductor and current collector to control the inception and occurrence position of corona discharge in air insulation. This is because the performance, such as the initial corona discharge inception of CTS, is determined by the air space. The simulation analysis was performed in a narrow, micro-sized air space as a first step, where the air space was reduced to the extent possible for simulation. To evaluate the performance of SK-AOR380 according to the narrow air space, we considered the numerical analysis method. The fundamental equations consist of Poisson’s equation and the charge continuity equation. Poisson’s equation for electric fields is a fully coupled numerical model based on the charge continuity equations for a positively charged ion, negatively charged ion, and free electron. Fowler–Nordheim electron emission was employed for the boundary condition at the surface of the ionizer conductor. To simulate the corona discharge behavior under standard lightning impulse voltage, we used a source of lightning voltage with 1.2/50 μs based on a double exponential equation; the corona discharge behaviors (electric field distribution, free electron density, positive and negative ion density) were investigated dependent on each time step (0.5, 1 and 1.2 μs) until 3.5 μs. The results revealed that the characteristics graph of free electron density, positive and negative ion density showed similar trends, with lightning impulse voltage increasing with increasing time steps until 1.2 μs and each density resulted in a decreasing trend from 1.2 μs to 3.5 μs. The SK-AOR380 is improved with a decreasing air space in terms of electric field distribution, electron, and ion density. In other words, the 0.0005 mm air space created a non-uniform electric field distribution with a large field enhancement, causing ionization to initiate corona discharge. In addition, in the case of a 0.0005 mm air space, the electric field and electron density are increased by 1.3 and 1.9 times, respectively, than that of 0.001 mm. However, there was no longer a significant difference under 0.0005 mm in the simulation results. To improve the CTS, we suggest the air space between the ionizer conductor and current collector should be less than 2 mm than that of conventional CTS from our research work.

Empirical Characterization of Cable Effects on a Reference Lightning Impulse Voltage Divider

The effect of measurement cables on impulse voltage measurement system signal transmission has been widely ignored by the high-voltage community. During the last years, the cable length effects have been reported, but the results have not been fully consistent. This article characterizes cable effects on a resistive impulse voltage divider system using three different empirical test methods. The used methods are step response analysis using convolution, low-voltage analysis with an impulse calibrator, and high-voltage impulse analysis with an impulse generator. Results show that with reasonable cable lengths up to 25 m, the time parameter errors increase almost linearly with the cable length. The tested divider system was not sensitive to the tolerance of the 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> termination at the cable end. The cable effect seems to be related to the current flowing through the cable, and the related errors can be reduced using a high-impedance termination at the digitizer end of the cable. Either short cable or high-impedance termination at the digitizer end is recommended for this type of divider. In addition, the results show that the three applied methods produce comparable results.

Experimental investigation on breakdown performance of coconut oil for high voltage application

• Dielectric breakdown performance of RBD and virgin coconut oil was studied as against standard natural ester. • After thermal aging, viscosity of coconut oil remained steady like the other natural ester. • No significant drop in AC or impulse breakdown voltage of RBD coconut oil due to thermal aging. • Most importantly, resistivity of RBD coconut oil did not decline rapidly with aging, unlike the standard natural ester. • Differences in the molecular structure in natural esters may be attributed to the differences in their dielectric strength. This paper investigates the electrical breakdown performance of coconut oil, viz. refined, bleached, and deodorized (RBD) and virgin grade. The primary objective is to determine whether they can perform equivalent to natural ester, e.g., MIDEL eN1215, commonly developed for transformers, so electric utilities can use coconut oil in tropical countries. Experimental results show that after aging in a sealed environment, the viscosity of coconut oil remained steady like the other natural ester. Most importantly, its resistivity (especially for RBD coconut oil) did not decline rapidly with aging, unlike the standard natural ester. Furthermore, it was demonstrated that thermal aging at 130°C, which is capable of lowering the AC breakdown strength in virgin coconut oil or MIDEL eN1215, did not result in a significant drop in the case of RBD coconut oil. Further, no measurable effect of oil moisture was detected upon the AC breakdown strength of RBD coconut oil. Overall, it is shown that RBD coconut oil is the most encouraging, whether subjected to AC or impulse voltage, as it shows the highest breakdown performance.

Frequency analysis of the typical impulse voltage and current waveshapes of test generators

Frequency analysis of the impulse waveshapes of generators which are commonly used for testing of the equipment in high-voltage engineering is presented in this paper. Some of the typical impulse waveshapes, such as 1.2/50 ?s/?s, 10/350 ?s/?s, 10/700 ?s/?s, 10/1000 ?s/?s, and 250/2500 ?s/?s, are approximated by the Double-exponential function (DEXP) and by the terms of Multi-peaked analytically extended function (MP-AEF). Experimental set ups for impulse signal generation are based on the desired outputs as given in the IEC 60060-1 Standard. Dumped oscillations are characteristic of the standardized 8/20 ?s/?s waveshape. The positive part of the normalized Sinc function with dumped oscillations is also approximated by MP-AEF terms. The corresponding frequency spectra of these aperiodic signals are obtained analytically by using Piecewise Fourier transform (PWFT). This paper presents the procedure to obtain Fourier transforms of the functions with multiple and sharp peaks typical for the impulse current and voltage test generators? waveshapes.

Study of PD Signatures in Transformer Using Impulse Voltage by Holo-Hilbert Spectral Analysis

Study of PD Signatures in Transformer Using Impulse Voltage by Holo-Hilbert Spectral Analysis

An Improved Parametric Method for Selecting Different Types of Tesla Transformer Primary Coil to Construct an Artificial Lightning Simulator

Due to the intermittent and hazardous nature of lightning impulse, researchers rely on artificial impulse generators to study it. The Tesla coil is a commonly used device to generate artificial lightning. This paper presents a parametric analysis of the primary side coil of the Tesla transformer. The analysis employs seven key electrical properties: skin depth, current density, voltage distribution, Ohmic loss, electric field strength, charge density, and energy content. These parameters are used to evaluate the response of various coil types to high voltage impulses. The Ansys high-frequency electromagnetic solver is used to perform a comparative analysis of essential parameters. The results can aid lightning researchers and Tesla coil designers in determining the optimal designs for Tesla primary coils in the future. The analyzed data is validated using Tesla coil hardware, which is used as an artificial lightning producer to test the feasibility of a lightning energy harvester.

Distribution Voltage of Quadruple Circuit Dual Voltage Tower Model During Lightning Strike

Lightning strikes on transmission lines often triggers electrical blackout. A direct lightning strike to the ground wire or the structure of tower makes voltage rise along the tower and the voltage stress appear along the installed string insulators at the tower. A back flashover occurs as the voltage along the string insulator exceeds the maximum insulator withstand. Most of previous works carried out the impact of lightning strike for conventional tower with single voltage and maximum two circuits. In this report, the assignment was carried out by modelling the quadruple circuit dual voltage tower model. The tower carries two circuits with 500kV and other two circuits with 150kV working voltage. In this work, an approach to estimate passive element of tower impedance surge was implemented and then it is followed by several experiments through a simulations program to investigate to determine voltage stress of each stage of tower and the string insulations. Keywords: Tower Transmission, Lightning Strike, Impulse Voltage Stress

Study of the waves propagation of lightning overvoltage impulse in the catenary system of electrified railways

Introduction. The article is devoted to the study of the waves propagation of lightning overvoltage impulse in the catenary system of electrified railways. The purpose of the work is to determine the zone of waves propagation of lightning overvoltage impulse along the catenary system, the degree of attenuation and the influence of the soil condition on the mode of their propagation.Materials and methods. The authors carried out tests on the waves propagation of lightning overvoltage impulse along the catenary system of the 1st (ring) track and the 15th (dead end) track of the Experimental Loop of the Railway Research Institute at the Shcherbinka station using a high-voltage impulse voltage generator.Results. During the tests, the influence of the soil condition on the mode of waves propagation of lightning overvoltage impulse was determined. The degree of attenuation of the lightning overvoltage impulse wave in the catenary system in the looped and dead end sections is determined, considering the influence of the reverse (reflected) overvoltage wave, as well as changes in the voltage level during the wave process occurring in the catenary system. The data obtained during the tests enable to determine the propagation speed of the lightning impulse wave.Discussion and conclusion. The obtained test results will be useful for improving the reliability of lightning protection devices of the catenary system against external overvoltages and can be used to improve insulating elements.

Study of Discharge Inception and Propagation in Liquid–Solid Insulation System under DC–LI Superimposed Constraints

High-voltage direct current (HVDC) links are starting to become widely implemented thanks to their interesting advantages such as reduced operation losses, the absence of reactive power, which allows energy transport via underground cables over long distances, and improved power control. The latter advantage is very essential for renewable energy resource integration into power grids. However, a thorough understanding of the behavior of insulation systems for HVDC components is critical so as to ensure a more reliable service. Indeed, the existence of the direct current (DC) voltage in HVDC components may induce surface and space charge accumulation that can stress insulation further or even promote discharge inception and propagation. As such, this work focuses on showcasing the effect of surface charge on streamers that develop on the interface of liquid–solid insulation due to the advent of lightning impulse (LI) voltage in the HVDC link. This study was performed using finite-element-based numerical simulations that include a quasi-electrostatic model for surface charge accumulation and an electrohydrodynamic fluid model for streamer initiation and propagation. The geometry used was point–plane configuration where the high voltage is applied to the needle electrode located above the liquid–solid interface. The obtained results suggest that streamer initiation is affected by both the accumulated surface charge density and polarity. For a positive streamer, an accumulation of positive surface charge increases the discharge inception voltage as a result of a weakening in the electric field, while an accumulation of negative surface charge decreases the discharge inception voltage due to an intensification in the electric field. Moreover, streamer travel distance and velocity are also both shown to be affected by surface charge accumulation.

Discharge characteristics of leader inception and development under 10 m long air gap—experimental observation and simulation results

AbstractThe physical mechanism of leader formation and development is not well understood. In this study, we present experimental and simulation results obtained with a 10 m long air gap discharge. A 10 m outdoor discharge experiment is carried out to obtain the current, voltage, and optical image during the leader discharge process. Four different impulse voltages were applied to the rod‐plane gap. The measured current is used as an input for a plasma model, then the temperature and electric field could be calculated. The simulation results show that the temperature of the streamer stem during the dark period may exceed 2000 K. In addition, the critical charge required for leader initiation can be as low as 0.27 μC for a 10 m air gap. The channel temperature is relatively stable in the process of leader development, which is maintained at about 4500 K. The electron density is about 0.5–3 × 1020 m−3, and the discharge channel conductivity fluctuates in the range of 1–10 S/m for the leader current between 1 and 2 A. A long dark period is tended to be associated with a higher injected charge by the first streamer. It is inferred that the voltage increments during the dark period play an important role in promoting streamer‐to‐leader transition, except for temperature and the injected charge.

Partial Discharge Measurement and Analysis of Transformer Under Oscillating Lightning Impulse Voltage

Oscillating lightning impulse (OLI) voltage is recommended for on-site testing due to its high generation efficiency. In this article, partial discharge (PD) characteristics under field impulse voltage waveforms are investigated. The experiment is carried out on a scaled transformer model with a protrusion defect inside as the PD source. Both oscillating and standard lightning impulse (SLI) voltages are acquired as test waveforms. Main discharges and reverse discharges are detected simultaneously under both OLI and SLI voltage. The increasing applied voltage amplitude advances the main discharge and enlarges its amplitude, and it also prolongs the duration of the reverse discharge and increases the number. The amplitude of main discharge is related to the PD voltage, while that of reverse discharge depends on the dynamic variation of the impulse voltage. Since OLI voltage contains multiple rising edges during the oscillation period, more PDs are excited. A disruptive effect (DE) model is extended for the PD analysis to show the oscillation effect on the PD distribution. The OLI test with PD measurement performed on a 220-kV transformer proves that PD detection during impulse voltage withstand test reflects more detailed information that can be used for early diagnosis of power transformers.

Design of an Effective Antenna for Partial Discharge Detection in Insulation Systems of Inverter-fed Motors

Partial discharge (PD) measurements under repetitive impulse voltages are critical for the qualification of inverter-fed motor insulation systems. Severe electromagnetic interference due to high frequency switching from power electronic devices can cause the traditional PD detection techniques of sinusoidal voltage unfeasible. This article presents the design of an Archimedes spiral antenna that can work effectively for PD detection under fast rise time repetitive impulse voltages. The antenna structure is optimized by a media superstrate with a high dielectric constant over the radiant surface. Through the optimized design, both the gains of the antenna in the 0.5–1.5 GHz frequency range and the signal-to-noise ratio for PD detection are increased substantially. Modeling and experimental results prove that the gain of the antenna can reach 2.5 dB in the frequency range of 500–900 MHz and become higher than 7.0 dB in the frequency range of 900–2.0 GHz, with a voltage standing–wave ratio smaller than 1.4. This seems to be a significant achievement for PD detection under fast rise time impulse voltages.

Key Parameters of Electromagnetic Compatibility of On-line Monitoring Sensor Device for Power Converter Valve

Converter valve is the key equipment of power grid, the safety and reliability deeply affect the reliability of power grid. In the industry, infrared and discharge sensors have been widely used to realize on-line condition monitoring. However, devices’ failure and accuracy reduced often happen, and the complex electromagnetic environment caused by converter valve are difficult to resisted. It is necessary to study the electromagnetic interference produced by the converter valve in order to guide the electromagnetic compatibility design of the sensor or monitoring device. Based on the typical electromagnetic interference mode, the interference models of converter valve elements are established, and the calculation methods of EMC of converter valve are proposed. According to FDTD method, the electric field distributions under the operation and impulse voltage are calculated, based on which, the EMC requirements of monitoring device for converter valve are proposed.

Electric field equivalent method for AC/DC hybrid electric equipment adapted to digital twin with low latency

• The equivalence of electric field is mainly related to the excitation source. • The 2D axisymmetric model under various excitations is constructed and verified. • This method can ensure the real-time and high fidelity in electric field digital twin technology. • A novel isolated power supply transformer in flexible DC transmission is introduced and the method is applied. Real-time synchronization and high fidelity are the most important features of the digital twin technology. When constructing the digital twin of power equipment in flexible DC transmission technology, the simulation analysis based on transient electric field is accurate, but the real-time is difficult to guarantee due to complex structure and various working conditions. In order to reduce the delay caused by the solution as much as possible, starting from the type of excitation source, an electric field equivalent method for AC/DC hybrid electric equipment adapted to digital twin with low latency is proposed: electrostatic field equivalent is used under power frequency AC or impulse voltage excitation, and constant electric field equivalent is used under typical DC voltage at the converter station. The method has been theoretically deduced in detail and verified by using a RC voltage divider model. The results show that the method proposed in this paper can shorten the solution time to 6.4% of the original, and ensure that the error after equivalence is within 5‱ . Finally the method is actually applied to the digital twin electric field analysis of a power supply transformer for 535 kV DC circuit breaker. The time required for solving is 40 min and 14 s. It can fully meet the demand of the dispatching department to update and calibrate the electric field once every hour and ensure safe and stable operation of equipment without corona.

Response of a Surge Arrester With a Series Gap for 6.6-kV Distribution Lines to Steep-Front Transients

Surge arresters with a series gap are commonly installed in distribution lines to effectively protect insulators, transformers, and other equipment from lightning threats in Japan. On the other hand, it has been well known that the high-altitude electromagnetic pulse (HEMP) at an early stage, called E1 HEMP, may extensively cause overvoltage on distribution lines, and the rise time of the E1 HEMP is as short as a few nanoseconds, which is much shorter than that of lightning electromagnetic pulses. To evaluate the effectiveness of surge arresters with a series gap against overvoltage induced by the E1 HEMP, it is necessary to evaluate the effect of a discharge delay due to the series gap on the protection level of surge arresters for steep-front transients. In this work, using a pulse current injection system, we apply a high voltage to a surge arrester with a series gap widely used for 6.6-kV distribution lines in Japan and measure the response of the surge arrester to steep-front transients. From the measured results, we obtain the voltage–time characteristics of the surge arrester with a series gap and residual voltages, which are compared with the results for lightning impulse voltage.

Voltage Distribution Characteristic of the D-Shaped Coil of HTS-SMES Under High-Frequency Impulse

The application of D-shaped coils to large-scale toroidal high-temperature superconducting magnetic energy storage (HTS-SMES) magnets can effectively suppress the large bending moment caused by uneven tension and reduce the section stress. The HTS-SMES system may be subjected to high-frequency transient overvoltage due to lightning impulse or switching operations. Transient overvoltages can potentially result in insulation failure or breakdown, which seriously endangers the safety of equipment and the stability of the power system. To investigate the transient voltage distribution characteristic of the D-shaped coil under transient impulse, a calculation method of the D-shaped double-pancake (DP) coil is proposed in this article, which is based on the equivalent circuit and lumped parameter model. In this method, each turn of the coil is represented as a lumped parameter unit. In addition, a small-size D-shaped DP coil was wound for verification. The voltage distribution under the lightning impulse voltage was measured at room temperature and liquid nitrogen at 77 K, respectively. The results indicate that the proposed method can calculate the transient voltage distribution of the D-shaped DP coil quickly and accurately. Then, we investigated the effects of the turn-to-turn insulation thickness and the height between the upper and lower pancake of the HTS-SMES D-shaped DP coil on the transient voltage distribution.

Rancang Bangun Pembangkitan Generator Marx 10 Tingkat pada Uji Kapasitor 220 pF dan Lightning Protector

The Marx generator circuit is an impulse voltage multiplier that is used to represent lightning overvoltage and switching overvoltage. In this research, a 10-level Marx Generator impulse generator design was carried out by varying the distance between the spark gaps of 2.5mm, 5.0mm, 7.5mm, and 10.0mm and the test load was a 220pF capacitor and a lightning protector. The results of the design and simulation of the 10-level Marx Generator produce an impulse voltage according to the IEC 60060-1 lightning impulses standard, which is 20.20kV with a wavefront and tail time of 2.29 µs and 52.3 µs. The test results for the 220pF capacitor load at a distance of 2.5 mm, the resulting voltage is 23.5 kV with a wavefront and tail time of 1.7 µs and 25 µs, while the lightning protector test load produces a voltage of 24 kV, with a wavefront and tail time of 2.1 µs and 43 µs

Impact of steady state and impulse excitations on CuSO4 based memristor

The memristor technology will replace nonlinear resistor applications in suppression of power system overvoltages. A characterization study on Memristance is useful to predict current–voltage characteristics of memristors under different source voltages. A Liquid Memristor (LM) has been chosen in order to study its suitability as a nonlinear resistance for mitigation of an Instrument Transformer overvoltages. The motivation is to investigate the nonlinear property of LM under DC and AC supply voltages in terms of pinching nature and memristance. The simulation response of LM has been validated experimentally for steady state and impulse excitations. The LM is subjected to sinusoidal and triangular supply voltages at 50 Hz and verified for its pinched hysteresis. The response of LM satisfies the standard specifications for (1.2/50) μs lightning and (250/2500) μs switching impulse voltages. The nonlinear resistance of LM shows a varying response for DC voltage instead of single operating point. The memristance of LM is observed to be 1.5 mS under steady state voltage and varied up to 2.89 mS under impulse excitations. The study investigates the dynamic response of LM as a nonlinear system.

Double-integral sliding mode control of the switched-inductor quasi-Z source boost converter

Compared with the traditional converter, the switching inductance quasi-Z source DC-DC boost converter has the characteristics of wide output voltage, small capacitor size and more reliable circuit. However, in the process of DC voltage boost, the system is prone to high startup impulse voltage, output voltage fluctuation, and other problems. Therefore, a double integral sliding mode control (DISMC) method is proposed. The control method takes the capacitance voltage error, the inductance current error and their sum of single integral and double integral as state variables, and derives the equivalent control law from the sliding mode surface. A Lyapunov function is constructed to analyze the existence conditions of DISMC method. And the effects of abrupt changes of input voltage, negative reference voltage and load power on transient oscillation, steady state error and overshoot of the system are analyzed. This control method solves the non-minimum phase problem of capacitor voltage, so as to improve the start-up performance of the controller and speed up the response of the system. Finally, the superiority and effectiveness of the control method are verified by simulation.

Lightning attachment characteristic of wind turbine generator: Experimental investigation and prediction method based on simulations

AbstractAs the height of wind turbine increases, the lightning strike accident has become a non‐negligible issue. In this paper, the lightning attachment characteristic of a 2‐MW wind turbine generator (WTG) is investigated using a model with a reduced scale of 100. The WTG model is equipped with receptors on the blades and a lightning rod on the nacelle, both serving as its external lightning protection system (LPS). The high‐voltage electrode, which delivers a lightning impulse voltage from a Marx generator, is used to simulate the final stage of downward negative lightning strikes from 29 coming‐leader positions. The experimental results indicate that lightning leaders from either front directions or side directions could be intercepted effectively by LPS, whereas the back‐direction lightning could not. Moreover, with the increase of striking distance, the capture ratio for the insulation part of blade decreases. Electric field intensity distribution simulations for the full‐scale WTG model, using conditions similar to their experimental counterparts, are conducted and compared with the lightning attachment distribution. Based on classical electro‐geometrical model, a simulative method is proposed to predict the lightning attachment distribution of WTG. Our results indicate that it is feasible with this method to produce a satisfactory approximation to the experimentally obtained lightning attachment distribution.