Switching Impulse Research Articles

Stepping Development of 6-m Long-Gap Discharge Produced by Standard Switching Impulse

A switching overvoltage discharge experiment was conducted on a simulated tower head. The gap spacings among the six-multiple conductor, the cross arm, and the tower were 6.07 m, respectively. The discharge development driven by a 250/2500-μs standard switching impulse was captured by a high-speed camera. The images show that the discharge path presents a stepping mode, and only one streamer guides the leader development. The discharge forms a snake-like route. Each segment of the stepping development is with a length of 1-3.5 m, and the observed curve angle ranges from 40° to 60°.

Long front time switching impulse tests of long air gap in UHV projects at altitude of 2100 m

The past and recent investigations show that front time of switching overvoltage waveforms in Ultra High Voltage (UHV) system of long distance transmission are mostly in long wave front time exceeding 1000μs. The long front time of switching impulse voltage has been deviated from the critical front time. This paper is involved with breakdown characteristics and external insulation design under long front switching impulse voltage in UHV system. All the Tests were performed on an outdoor UHV test site at altitude of 2100 m, China Southern Power Grid Co. Ltd. (CSG). Breakdown characteristics of rod-plane and actual size tower-conductor in /spl l.chemo/800 kV UHV DC transmission line are obtained under wide front time switching impulse voltages from 100 to 2350 μs. From the comprehensive studies of such tests, it is proposed that U50 of front time exceeding 1000 μs increases 20% compared with the results of standard switching impulse (250/2500 μs) tests and standard deviations of U50 is 6% in UHV transmission system. Finally, an air gap insulation design procedure in conductor-tower of UHV transmission line at altitude of 0-2000 m is presented. Long front time switching impulse strength of conductor-tower gap is proposed into selection by reference in UHV transmission line insulation design.

Breakdown characteristics of long air gap with negative polarity switching impulse

Breakdown characteristics of air gaps under negative switching impulse are complicated. To better understand the nonlinear discharge characteristics of long air gaps, the 50% breakdown characteristics of rod-rod gaps, rod-plane gaps and rod-conductor gaps, with air gap distance ranged from 1 m to 10 m, are studied thoroughly, with two waveforms of negative switching surges. Saturating characteristics have been obtained for the above three typical gaps. For air gaps exceed 4 m, the 50% breakdown voltage appears to be lower for rod-plane gaps than that for rod-rod gaps, while the average breakdown electric field decreases with the length of air gaps. Gap factors under negative impulses tend to level off with gap spacing. Furthermore, new knowledge is obtained indicating that, the 50% breakdown voltage for rod-conductor gaps may be lower with conductor grounded than that with conductor ungrounded. Finally, it also indicates that the wave front of the applied voltage has great influence on the breakdown time of rod-rod air gaps.

Fault Detection for a Class of Impulsive Switched Systems

The problem of fault detection for a class of nonlinear impulsive switched systems is investigated in this paper. Fault detection filters are designed such that the augmented systems are stable, and the residual error signal generated by the filters guarantees the H ?; performance for disturbances and faults. Sufficient conditions for the design of fault detection (FD) filters are presented by linear matrix inequalities. Moreover, the filter gains are characterized according to a solution of a convex optimization. Finally, an example derived from a pulse-width-modulation-driven boost converter is given to illustrate the effectiveness of the FD design approach.

Effect of Accelerated Laboratory Aging on Selected Electrical Properties of Medium-voltage Heat Shrink Cable Joints

Cross linked polyethylene (XLPE) cables are being used extensively in high-voltage power transmission and distribution networks around the world. However, such joints suffer high failure rates in extreme weather conditions. To investigate this issue, selected properties of 15-kV heat shrinkable XLPE cable joints produced by four manufacturers that are widely being used by electric power utilities in Saudi Arabia were evaluated before and after accelerated multi-factor aging. Aging stresses included high voltage, temperature cycling, and periodic applications of switching impulses while keeping joints in air as well as in water. Partial discharge characteristics, dissipation factor at 60 and 0.01 Hz, and breakdown voltages were measured for un-aged and aged joint samples. The results show that partial discharge characteristics supplemented with a 0.01-Hz dissipation factor provide useful diagnostic information about the condition of such joints. Moreover, these properties also provide useful information about the comparative performance of joints produced by different manufacturers.

Partial discharges in SF<sub>6</sub> gas filled void under standard aperiodic and oscillating switching impulses

Partial discharges (PDs) in the void filled with SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas were investigated under IEC60060-3 standard aperiodic switching impulse (SI) and oscillating switching impulse (OSI). Some single discharges and discharge sequences with different characteristics were detected. A theoretic voltage-time lag (V-t) curve of the first discharges was proposed and proved to be effective in analyzing the occurrences of the first discharge by comparing the calculated V-t curve and experimental V-t point distribution under test situations. The PD activity in terms of the discharge magnitude and number had significantly associations with the gas pressure in the void and the void shape (dimension ratios). Furthermore, a hypothetical physical model with charge memory effect was proposed to interpret the mechanisms underlying the different PDs in sequence under the two impulses, by which the simulation was carried out, showing a roughly consistency with the measured distribution.

Partial discharges in SF&lt;sub&gt;6&lt;/sub&gt; gas filled void under standard oscillating lightning and switching impulses in uniform and non-uniform background fields

Behaviors and characteristics of partial discharges in SF6 gas filled void are investigated under oscillating lightning impulse voltage (OLI) and switching impulse voltage (OSI). The negative and positive PD sequences under impulses are described and analyzed under the applications of uniform and non-uniform background fields. Four types of discharge pulses in sequences are distinguished by their magnitudes, waveforms and time interval and well interpreted by a charge memory physic model. The distribution of PD points under OLI and OSI in normalized phase range (φN, Im) are proposed to describe the occurrence of PD under periodic oscillation impulses statistically. It is indicated that the discharges with low magnitudes are distributed in the relative large ranges of phase and the discharges with high magnitudes are mainly distributed in the relative narrow ranges of phase. By experimental results, the influences of the gas pressure and the void dimension ratio are studied and it is concluded that both the increases of these two factors could bring the obvious restrictions on PD activity under oscillating impulses.

Partial discharges in SF6 gas filled void under standard oscillating lightning and switching impulses in uniform and non-uniform background fields

Behaviors and characteristics of partial discharges in SF6 gas filled void are investigated under oscillating lightning impulse voltage (OLI) and switching impulse voltage (OSI). The negative and positive PD sequences under impulses are described and analyzed under the applications of uniform and non-uniform background fields. Four types of discharge pulses in sequences are distinguished by their magnitudes, waveforms and time interval and well interpreted by a charge memory physic model. The distribution of PD points under OLI and OSI in normalized phase range (φN, Im) are proposed to describe the occurrence of PD under periodic oscillation impulses statistically. It is indicated that the discharges with low magnitudes are distributed in the relative large ranges of phase and the discharges with high magnitudes are mainly distributed in the relative narrow ranges of phase. By experimental results, the influences of the gas pressure and the void dimension ratio are studied and it is concluded that both the increases of these two factors could bring the obvious restrictions on PD activity under oscillating impulses.

Exponential Synchronization of Stochastic Complex Dynamical Networks with Impulsive Perturbations and Markovian Switching

This paper investigates the exponential synchronization problem of stochastic complex dynamical networks with impulsive perturbation and Markovian switching. The complex dynamical networks consist ofκmodes, and the networks switch from one mode to another according to a Markovian chain with known transition probability. Based on the Lyapunov function method and stochastic analysis, by employingM-matrix approach, some sufficient conditions are presented to ensure the exponential synchronization of stochastic complex dynamical networks with impulsive perturbation and Markovian switching, and the upper bound of impulsive gain is evaluated. At the end of this paper, two numerical examples are included to show the effectiveness of our results.

Dielectric response of oil-impregnated paper by utilizing lightning and switching transients

On-line monitoring of insulation systems in power components such as power transformer bushings has significant value for their reliability. Dielectric spectroscopy is known as a powerful tool in condition assessment of power components’ solid insulation. However, it is difficult to apply it on-line. Therefore, a new approach of intended use for on-line diagnosis of oil-impregnated paper, as a major insulation component of power transformers and bushings, is presented. In this technique, natural transients such as lightning and switching impulses are used as stimuli for on-line dielectric response measurements. The wide frequency range of these transients is their advantage as stimuli for dielectric spectroscopy. The influence of moisture content and temperature on the dielectric response of oil-impregnated paper has been investigated for performance evaluation of the proposed technique. It is shown that this technique can track the changes caused by moisture content and temperature in the dielectric response of oil-impregnated paper. The results of both low and high voltage study cases have been verified by comparison with Frequency Domain Spectroscopy (FDS). According to the well-matched results with FDS, the proposed technique can offer a valuable approach for frequent monitoring of dielectric properties of oil-impregnated paper insulated systems such as those commonly encountered in power transformer bushings. However, the validity range of the results depends on the bandwidth of the applied transients and other discussed measurement considerations.

Basic analysis of a hyperchaotic spiking circuit with impulsive switching

Basic analysis of a hyperchaotic spiking circuit with impulsive switching

The Simulation Study of Transformer Inductive Oscillating Switching Impulse Voltage Generation

According to IEC60060-1, IEC60060-2 requirements, the large transformer should take impulse voltage test in site. However, this test is not performed in the field for the impulse voltage generator huge and difficult to operate. To solve this problem, IEC60060-3 propose using oscillating impulse voltage for equipment on-site impulse withstand voltage test. Oscillating impulse voltage has higher generation efficiency and close to the actual voltage waveform that electrical equipment bear. For the transformer, the oscillating impulse voltage can generated through inductive method. In order to study the generation of oscillating impulse voltage through inductive method for transformer, the simulation circuit is established using ATP soft and the oscillating switching impulse voltage characteristics is studied in this paper. The result show that the oscillating switching impulse voltage waveform that accordance with IEC requirements can be generated through inductive method for transformer.

Test Research on Phase-to-Ground Air-Gap Discharge Characteristics of UHV Substation

In order to optimize the design of UHV substation and reduce its construction investment, it is necessary to take further research of UHV substation air-gap discharge characteristics. In this paper, by using sub-conductor and tower to simulate UHV substation air-gap, lightning and switching impulse discharge characteristics tests of UHV substation are taken in the UHV AC test base of SGCC. The results show that, when the distance of conductor between tower is in range of 4m to 7m, the 50% lightning impulse and switching impulse discharge voltage rise along with the rise of air gap distance. As the air-gap increases, the switching impulse discharge voltage presents the trend of saturation. According to the analysis of test results, we can draw a conclusion that the gap factor of switching impulse discharge can be 1.22 when the minimum distance between conductors and tower is 5~8m.

Research on Complex Gap Discharge Model of Live Working on EHV and UHV High-Voltage Transmission Lines

This paper obtained the switching impulse flashover characteristic of live working complex gap on extra high voltage (EHV) and ultra high voltage (UHV) high-voltage transmission lines by a large number of experiments. Based on the experimental data and the leader inception discharge model, the complex gap discharge development during the process of entering equipotential and its influencing factors have been analyzed with the electric filed calculation method. Moreover, considering the practical conditions in live working sites, a complex gap discharge model appropriate for side live working on EHV and UHV high-voltage transmission lines has been proposed by introducing a revision coefficient km. It has been found that km is related to the working position and the structure of high-voltage electrode. Through further research on the establishment of the functional relationship, it can provide a comparable accurate theoretical calculation method for the research on the complex gap of live working and can give a guideline for optimizing the test plans.

Exponential Stabilization of Impulsive Switched Systems with Time Delays Using Guaranteed Cost Control

This paper investigates the stabilization problem for impulsive switched systems with time delays. First, exponential stability criteria of the delayed impulsive switched systems are established by use of the Lyapunov-Krasovskii functional method. Based on these results, sufficient conditions for the existence of a guaranteed cost control are also given. Subject to these sufficient conditions, the closed-loop impulsive switched system under the guaranteed cost control law will be exponentially stable with a guaranteed cost value.

Effects of SiO2 and TiO2 Nano Fillers in Enhancing the Insulation Breakdown Strength of Epoxy Nano Composite Dielectric under Divergent Electric Fields

The proper mixing of nanoscale fillers in conventional dielectric materials leads to an enhancement in the breakdown strength and voltage endurance. In this study experimental investigations are carried out to compare the breakdown characteristics of epoxy nano-composites with that of a base epoxy resin under the influence of divergent electric fields so as to obtain inferences on its breakdown performances. This would in turn enable providing solutions to acquire more effective electrical insulation systems and explore the prospect of tapping the merits of utilizing the rapid strides made in field of fabrication of nano-dielectrics. The main objective is such studies are to enhance the electrical properties of the epoxy dielectric by employing nano-fillers such as SiO2, TiO2 etc. This research envisages the use of epoxy resin mixed with nano-fillers for ascertaining the ability of the nano-composite to be utilized as a dielectric/ insulator in power apparatus. The epoxy resin is mixed with appropriate proportion of SiO2 and TiO2 and experimentation is carried out under the influence of divergent electric fields. Classical breakdown voltage withstand tests such as AC power frequency, DC voltage, lightning impulse and switching impulse test is carried out on epoxy dielectrics (with and without nano-fillers) and the results are compared. In addition, a non-classical breakdown voltage test (high frequency high voltage) is also devised to analyze and ascertain the breakdown characteristics due to varying frequencies so as to investigate the possibility of utilizing such nano-composites in applications related to high speed switching devices.

Study on arc temperature calculation model for air gap discharge

Summary A model to calculate arc temperature of air gaps discharge is presented in this article. Based on the energy balance equation, we obtained the mathematical method to evaluate the arc temperature. According to the model, arc temperature was calculated for two air gaps with different distance, respectively. The results showed that the peak arc temperature of 16.7 m air gap is 36 368°K, and the peak arc temperature of 10 m air gap is 34 277°K, which are in good agreement with the experiment results. The model built in this article can be used for lightning and switching impulse discharges in air gaps. Copyright © 2013 John Wiley & Sons, Ltd.

An experimental and numerical study of leader development in rod-rod gaps under positive switching impulse voltage

The main form of electrical discharge in long air gaps is broken down by leader mechanism. The leader development in rod-rod gaps under positive switching impulse was investigated by using two high-speed CCD cameras. The clearer and more particular colorized physical morphology of the leader propagation process than the traditional image converter cameras was recorded and the leader development parameters were also obtained. As a comparative study, an improved simplified model for rod-rod configuration was performed to simulate the leader development. The numerical simulations of leader development characteristics were in a close agreement with that of experimental measurements.

Study On Pollution Performance on a Wind Turbine Blade Using OES Technique for Lightning and Switching Impulse Voltage Profiles

Lightning damage to offshore wind turbine power plants require an immediate attention, due to its severe damage to wind blade causing outage for a long time. The risk of lightning striking the blade is expected to be higher when they are located in a highly polluted and humid zone. Sodium chloride (NaCl) is considered to be among the severe pollutant near sea transported through air and gets deposited on the blade surface thereby increasing the surface conductivity of the material. Lightning can strike any part of the blade other than the receptors and the polluted surface with higher conductivity can allow discharge current to propagate over the surface thus causing severe burning of material and damaging the blade. Hence it is necessary to study the influence of salt deposit on a wind turbine blade injected with standard lightning impulse and switching impulse voltages. Wave profile and polarity has an effect during discharge because of its unique discharge formation process. Preliminary experiments are carried out in laboratory to study the influence of salt deposit on a blade sample by adopting IEC 60507 standards. Experimental results clearly show the extent of surface damage increases with increase in salt concentration. Optical emission based non-intrusive technique is used for an elemental analysis during the discharge process. Optical Emission Spectroscopy (OES) studies clearly show switching impulse voltage of both polarities induce a significant damage to the glass fiber reinforced plastic (GFRP) material.

Modelling of Power Converters Using Z-Transform

The paper introduces a novel method of analysis and modelling of power electronic converters. Z-transform, numerical series (sequences) are used for both steady and transient states investigation of converters. The new impulse switching functions are created which are used as exciting functions of one- and multidimensional state-space models. Theoretical waveforms are compared with simulation results.