Switching Impulse Research Articles

Study on switching impulse test waveform for UHV-class electric power equipment

Ultra high voltage (UHV) systems are increasingly being planned and constructed, hence studies are promoted on the standard for high-voltage test techniques for UHV-class equipment, the scope of which includes the switching impulse voltage test waveform. Influences that must be considered to study this test waveform are those of actual switching overvoltage waveforms generated in the UHV system and applied to equipment and the change in the breakdown characteristics associated with a longer insulation length such as an air gap clearance. In the present paper, to determine the switching impulse test waveform, switching overvoltage waveforms applied to the UHV equipment were initially investigated. As a result, it emerged that the time to peak Tp was long, ranging from 700 μs to 1000 μs, for closing overvoltage which is relatively high switching overvoltage. When other types of overvoltage in the switching surge range were considered, the Tp varied widely from 100 μs to 1000 μs. Subsequently, the insulation characteristics of UHV-class long air gaps for switching impulse waveforms were investigated. It emerged that, for the fundamental model, namely rod-plane electrodes, the Tp of switching impulse waveforms with the lowest breakdown voltage (critical time to peak, Tcr) ranged from 350 μs to 550 μs whereas it shifted to a shorter time of 200 μs to 350 μs when environmental conditions, such as humidity and precipitation, were taken into consideration. For basic structure models assuming actual facilities and real scale structure models, the Tcr ranged from 100 μs to 300 μs. Furthermore, the internal insulation characteristics for switching impulse waveforms, such as SF6 gas and oil-paper insulation, were also investigated. Consequently, in the case of the internal insulation of equipment such as gas insulated switchgears (GIS) and transformers, the Tp of switching impulse waveforms had a minor influence on the insulation characteristics, even if it varied from 100 μs to 1000 μs. Following comprehensive evaluation of these characteristics, it was concluded that, in the switching impulse test for UHV-class equipment, it is reasonable to apply a waveform of 250/2500 μs, which is the same as that for equipment of 800 kV or less.

Robust exponential stability of nonlinear impulsive switched systems with time-varying delays

This paper deals with a class of uncertain nonlinear impulsive switched systems with time-varying delays. A novel type of piecewise Lyapunov functionals is constructed to derive the exponential stability. This type of functionals can efficiently overcome the impulsive and switching jump of adjacent Lyapunov functionals at impulsive switching times. Based on this, a delay-independent sufficient condition of exponential stability is presented by minimum dwell time. Finally, an illustrative numerical example is given to show the effectiveness of the obtained theoretical results.

Finite-Time Stability Analysis of Impulsive Switched Discrete-Time Linear Systems: The Average Dwell Time Approach

This paper investigates the finite-time stability problem for a class of discrete-time switched linear systems with impulse effects. Based on the average dwell time approach, a sufficient condition is established which ensures that the state trajectory of the system remains in a bounded region of the state space over a pre-specified finite time interval. Different from the traditional condition for asymptotic stability of switched systems, it is shown that the total activation time of unstable subsystems can be greater than that of stable subsystems. Moreover, the finite-time stability degree can also be greater than one. Two examples are given to illustrate the merit of the proposed method.

Optimization of Air Insulation Clearances for EHV/UHV Transmission Lines

This paper presents the results of the study conducted on 400 kV, 800 kV and 1200 kV transmission line insulator strings and conductor–tower window geometries with an aim to optimize air insulation clearances. Laboratory investigations were carried out to evolve the switching impulse performance of phase–to–earth and conductor–window confi gurations in addition to the reference rod plane air gap lengths in EHV/UHV range. Tests were conducted on 400 kV, 800 kV and 1200 kV line confi gurations of I, Vee, double Vee, etc., by simulating the tower windows. The paper also presents results of the study on optimization of conductor-tower air insulation clearances for adoption in 1200 kV AC transmission lines using 8 bersimis conductor bundle carried out for establishment of 1200 kV Test Station at BINA, Madhya Pradesh, by Power Grid Corporation of India. Results of the tests and the data presented in the paper will be useful for design of phase-to-ground air insulation for adoption in EHV/UHV Transmission lines.

Robust Finite‐Time H∞ Control for Impulsive Switched Nonlinear Systems with State Delay

This paper investigates robust finite‐time H∞ control for a class of impulsive switched nonlinear systems with time‐delay. Firstly, using piecewise Lyapunov function, sufficient conditions ensuring finite‐time boundedness of the impulsive switched system are derived. Then, finite‐time H∞ performance analysis for impulsive switched systems is developed, and a robust finite‐time H∞ state feedback controller is proposed to guarantee that the resulting closed‐loop system is finite‐time bounded with H∞ disturbance attenuation. All the results are given in terms of linear matrix inequalities (LMIs). Finally, two numerical examples are provided to show the effectiveness of the proposed method.

Modelling and Regularity of Nonlinear Impulsive Switching Dynamical System in Fed‐Batch Culture

A hybrid system with state‐based switchings is proposed to describe the fed‐batch production of 1,3‐propandiol from glycerol in our previous work. However, the on‐off switching of alkali is too frequent, which greatly increases the computational cost of the numerical solution to the system so as to locate the state‐based switchings in strict time order and implement the correct mode changes. To deal with this problem, we consider the switching of alkali pump as an impulsive event and present a nonlinear impulsive switching system to describe the fed‐batch culture. It is proved that the impulsive switching system is non‐Zeno. Some basic properties of solutions to the impulsive switching system are also explored. In order to overcome the discontinuities of the system, the Skorohod topology is induced and a specific form of λ is constructed to prove the main theorem. Additionally, a numerical simulation is carried out to show that the proposed system can describe the fed‐batch culture properly and the essential difference with the previous work.

Comparison of Positive Leader Propagation in Rod–Plane and Inverted Rod–Plane Gaps

In order to investigate the different features of the positive leader propagation in the rod-plane and inverted rod-plane gaps, the discharge experiments in a 3-m rod-plane gap and a 3-m inverted rod-plane gap were carried out under switching impulse voltage. The positive leader propagation process was recorded by using a high-speed CCD camera. Some aspects to describe the positive leader propagation characteristics of the rod-plane and inverted rod-plane gaps are obtained and compared in this paper, including the critical corona radius, the average continuous leader inception voltage, the axial leader velocity, and the final jump length. The possible reason resulting in those differences is also discussed here.

Stability criteria of a class of nonlinear impulsive switching systems with time-varying delays

This paper investigates stability problems of a class of nonlinear impulsive switching systems with time-varying delays. Based on the common Lyapunov function method and Razumikhin technique, several stability criteria are established for nonlinear impulsive switching systems with time-varying delays. Our results show that switching systems can be stabilized by impulsive switching signals even if the system matrices are all unstable. In the absence of impulses, some of our results reduce to similar stability criteria for nonimpulsive switching systems in some recent research articles. Several examples with simulations are given to illustrate the efficiency of our results.

Connecting Leaders in a Nonuniform Spark Gap

Still photographs of discharge events reveal a multitude of phenomena, most of them well known, but sometimes, an unexpected phenomenon appears. Here, a photograph where leaders meet midgap in a positive 1-m rod-to-plane electrode configuration subjected to a switching impulse voltage is presented. The appearance of a connecting negative leader originating from the plane electrode was not expected. The positive leader propagating from the rod is inhibited by a large series resistor in the discharge circuit, thereby giving a negative connecting leader time to develop from the plane electrode.

Effects of corona ring design upon impulse voltage withstand level of 380 kV V-strings

This study presents the influence of corona rings on impulse withstand performance of 380 kV V-insulator strings. Those strings comprising cap-and-pin type glass insulator units are one of the most common configurations in Turkish National Power Transmission System. Laboratory test setup was constructed for the centre phase of a full scaled tower. Laboratory tests are performed to investigate the lightning and switching impulse performance of the strings equipped with the existing racket type corona rings and the circular type corona rings. Withstand voltages, lower flashover probability levels, flashover routes and times to flashovers are determined under dry and wet test conditions. In addition, some 3D field simulations regarding potential and electric field distributions are also performed for the interpretation of insulator surface flashovers.

Robust exponential stability of impulsive switched systems with switching delays: A Razumikhin approach

In this paper, we focus on the robust exponential stability of a class of uncertain nonlinear impulsive switched systems with switching delays. We introduce a novel type of piecewise Lyapunov–Razumikhin functions. Such functions can efficiently eliminate the impulsive and switching jump of adjacent Lyapunov functions at impulsive switching instants. By Razumikhin technique, the delay-independent criteria of exponential stability are established on the minimum dwell time. Finally, an illustrative numerical example is presented to show the effectiveness of the obtained theoretical results.

Preliminary study on the modelling of negative leader discharges

Nowadays, there is considerable interest in understanding the physics underlying positive and negative discharges because of the importance of improving lightning protection systems and of coordinating the insulation for high voltages. Numerical simulations of positive switching impulses made in long spark gaps in a laboratory are achievable because the physics of the process is reasonably well understood and because of the availability of powerful computational methods. However, the existing work on the simulation of negative switching discharges has been held up by a lack of experimental data and the absence of a full understanding of the physics involved. In the scientific community, it is well known that most of the lightning discharges that occur in nature are of negative polarity, and because of their complexity, the only way to understand them is to generate the discharges in laboratories under controlled conditions.The voltage impulse waveshape used in laboratories is a negative switching impulse. With the aim of applying the available information to a self-consistent physical method, an electrostatic approximation of the negative leader discharge process is presented here. The simulation procedure takes into consideration the physics of positive and negative discharges, considering that the negative leader propagates towards a grounded electrode and the positive leader towards a rod electrode. The simulation considers the leader channel to be thermodynamic, and assumes that the conditions required to generate a thermal channel are the same for positive and negative leaders. However, the magnitude of the electrical charge necessary to reproduce their propagation and thermalization is different, and both values are based on experimental data. The positive and negative streamer development is based on the constant electric field characteristics of these discharges, as found during experimental measurements made by different authors. As a computational tool, a finite element method based software is employed. The simulations are compared with experimental data available in the literature.

Research and development of UHV AC transformer and shunt reactor

SUMMARYThe Jingdongnan‐Nanyang‐Jingmen UHV AC Pilot Project has already been put into service in China. In this paper, insulation level of power transformer and shunt reactor for 1000 kV power transmission project in China are introduced. UHV AC transformer and shunt reactor structures are given. Key technologies, including cooling type, regulating method for UHV AC transformer, pattern of outgoing line, and noise controlling, are discussed. Besides, due to the high voltage class, high capacity, and super size of UHV power transformer, the size of its test circuit is correspondingly enlarged, the impacts of stray inductance and capacitance will be more intense consequentially, thus in factory test including lighting impulse test, switching impulse voltage test, short‐duration induced AC voltage test at 500 kV side, and long‐duration induced AC voltage test with partial discharge measurement are presented. Copyright © 2011 John Wiley & Sons, Ltd.

Positive impulse flashover along smooth cylindrical insulating surfaces under variable humidity

Positive impulse flashover along smooth cylindrical insulating surfaces bridging a short rod-plane gap under standard lightning and switching impulse voltages is investigated under variable absolute humidity and by regarding the case of air alone as reference. Flashover is closely related to predischarge phenomena, specifically secondary corona under lightning impulses and corona streamers arrival at the earthed plane under switching impulse voltages. Under lightning impulses the dielectric strength of the gap is highest for air alone and decreases with material permittivity; the opposite is true, although less marked, under switching impulse voltages. Flashover voltage increases with absolute humidity, this being more pronounced for switching than lightning impulse voltages. The inhibitory effect of humidity on flashover, mainly determined by the trajectory of the spark channel with respect to the insulating surface, is similar to that observed in air alone where flashover occurs away from the insulating surface but reduced where the discharge develops close to the insulating surface. For insulating arrangements where at flashover the spark channel adheres to the insulating surface the IEC 60060-1:1989 atmospheric conditions correction procedure should be optimized by considering a reduced humidity correction factor.

임펄스전압에 대한 N2가스의 절연파괴특성

This paper aims to examine the possibility of using an environmentally friendly N₂ as an alternative gas to SF?. For this purpose, we have investigated breakdown characteristics of N₂ under impulse voltages in a quasi-uniform electric field gap. The 1.2/50[㎲] lightning impulse voltage, switching impulse voltages and oscillatory impulse voltages were applied at the test gap. The electric field utilization factor ranges from 0.5 to 0.8. The experimental data of SF6 and N₂ acquired in the same experimental condition are presented in parallel for comparison. As a result, the breakdown voltages in SF? and N₂ are linearly increased with the gas pressure, also the breakdown voltages in N₂ are increased with increasing the gap distance and electric field utilization factor. The positive breakdown voltages are higher than the negative breakdown voltages. The nagative basic lightning impulse withstand level of 150[㎸] in N₂ of about 0.5[㎫] is nearly equal to that in SF? of 0.15[㎫]. It is seen from the results obtained in this work that N₂ can be used as an eco-friendly alternative gas to SF? in distribution power equipment.

Finite element analysis of electric field around an ice-covered semi-conducting glazed insulator using a form of Kelvin transformation

This paper describes electric field distributions around a semi-conducting glazed standard post insulator for power frequency, lightning impulse(1.2/50 μs) and switching impulse(250/2500 μs) voltages under icing conditions, which were computed numerically using finite element method. Thin glaze coating on the insulator requires a very large number of elements for finite element analysis because of an open boundary around an ice-covered insulator. To reduce number of elements and hence computation time, the region between domain of interest and infinity was modeled by a form of Kelvin transformation. Simulation results are compared with laboratory experiments and are found to be in agreement.

Negative impulse flashover along cylindrical insulating surfaces bridging a short rod-plane gap under variable humidity

Negative impulse flashover along insulating surfaces bridging a short rod-plane gap is investigated under variable humidity. The specimens, cylindrical in shape and with a smooth surface, were made of PTFE, silicone-rubber, nylon and glazed porcelain and were bridging the gap, which was stressed by standard lightning and switching impulse voltages. Breakdown probability distributions were obtained and the breakdown voltage and time to breakdown were measured. The gap was overstressed by applying voltages higher than that causing 100% breakdown so as to study the effects of the applied peak voltage on breakdown characteristics. When breakdown occurs over an insulating surface the breakdown voltage is significantly lower compared to that obtained for air alone, especially at lower breakdown probabilities and under switching impulse voltages. It is also lower for lightning than switching impulse voltages, this being less marked with increasing material permittivity. Breakdown is closely related to negative corona growth. The effect of absolute humidity on breakdown voltage is minimal. The IEC atmospheric conditions correction procedure yields satisfactory results when breakdown occurs both in air alone and along an insulating surface.

Exponential Stability With $L_{2}$-Gain Condition of Nonlinear Impulsive Switched Systems

In this technical note, we consider exponential stability and stabilization problems of a general class of nonlinear impulsive switched systems with time-varying disturbances. By using the switched Lyapunov function method, sufficient conditions expressed as algebraic inequality constraints and linear matrix inequalities are obtained. They ensure that the nonlinear impulsive switched systems are not only exponentially stable but also satisfy the L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -gain condition. Based on the stability results obtained, an effective computational method is devised for the construction of switched linear stabilizing feedback controllers. A numerical example is presented to illustrate the effectiveness of the results obtained.

준평등전계에서 임펄스전압에 대한 N2가스의 절연파괴특성

This paper presents dielectric characteristics of gas under impulse voltages in a quasi-uniform electric field gap. The experiments were carried out at the test gap applied by the 1.2/50[] lightning impulse voltage, 180/2500[] switching impulse voltage, 500[ns]/1[MHz] very fast transient overvoltage(VFTO). The gap separation of sphere-to-plane electrodes was 14[mm] and the electric field utilization factor was about 71.2[%]. The gas pressure ranges from 0.2 to 0.6[MPa]. As a result, the electrical breakdowns are occurred by streamer discharge. Breakdown voltages are linearly increased with the gas pressure and the highest breakdown voltage is appeared under the VFTOs having fast rising time. Breakdown voltages under the positive impulse voltages were higher than those under the negative ones, and also the time to breakdown in the positive polarity is longer than that in the negative polarity.

On optimal control problems of a class of impulsive switching systems with terminal states constraints

The global optimal control problem is proposed for a special class of hybrid dynamical systems, i.e. impulsive switching systems. Then the necessary condition of the above problem, the minimum principle, is given. Ekeland’s variational principle and the matrix cost functional structure expression are utilized in the process of the proof. Based on the main result, a special linear hybrid impulsive and switching system (HISS) is illustrated and the optimal control algorithm is presented. Moreover, the cases of pure impulsive systems and pure switched systems are included in this paper.