Effect Of Overvoltage Research Articles

The Effects of Transient Overvoltages on the Reliability of HVDC Extruded Cables. Part 1: Long Temporary Overvoltages

Extensive simulations have been carried out so far of transient voltages superimposed onto the DC voltage of HVDC cable transmission systems. With the advent of VSC HVDC cable systems, attention has turned to long Temporary Over-voltages in such systems. Preliminary experiments on the possible adverse effects of these long TOVs on the insulation of VSC HVDC cables have started, but no simulation models for estimating their effect on cable life and reliability have been developed yet. This investigation fills this gap by carrying out the simulative evaluation of the life lost by HVDC extruded cables subjected to long TOVs (Part 1) and switching impulses applied during Type Tests (Part 2), so as to compare the severity of these two transient voltages superimposed onto the DC voltage of HVDC extruded cables. This Part 1-paper is focused on estimating the severity of TOVs on extruded cable insulation by: calculating the electric field during the TOV; comparing it with the field during Type Test load cycles; using Miner's law of cumulated damage to calculate the life lost during the TOV, thereby also locating the most severely stressed point of insulation. In Part 2-paper, a similar evaluation for switching impulses and an overall comparison are performed.

Effect of Electrode Overpotential in Secondary Solution on Lithium Recovery Rate for Electrodialysis with Two Power Supplies and Three Electrodes

Demand for lithium-ion batteries (LIB) is rapidly increasing with the electrification of automobiles and the spread of new energy management systems. It is desired to recover lithium resources, whose supply and demand are tight, from spent LIB and seawater. Lithium for LIB must have a high purity of 99.9% or higher. The electrodialysis method using a lithium ion electrolyte has a high potential for recovering such high-purity lithium. Kunugi et al. [1] reported that only lithium ions could be recovered from LiCl-NaCl-KCl mixed aqueous solution by electrodialysis using La0.55Li0.35TiO3 as an electrolyte. Hoshino [2] demonstrated the possibility of using lithium ion conductive glass ceramics (LICGCTM). However, in either method, the lithium recovery rate is too low for practical use. We have devised an electrodialysis system with two power sources and three electrodes, which is different from a general electrodialysis cell consisting of two electrodes and one power source, and experimentally confirmed a large lithium recovery rate. In this study, we investigate the effect of electrode overvoltage in the secondary solution on the lithium recovery rate by this new electrodialysis method. An anode (primary solution side) and a cathode (secondary solution side) were formed on both sides of the La0.57Li0.29TiO3 (LLTO) by firing a Pt paste. As a third electrode, a Ni mesh electrode was placed in the secondary solution at a position apart from the cathode. A constant DC voltage was applied between the anode and the cathode. A constant DC voltage of another magnitude was also applied between the cathode and the Ni mesh electrode. The electric resistance of the solution between the cathode and the third electrode was changed by changing the lithium concentration in the secondary side solution or the distance between the cathode and the third electrode. The change in the lithium recovery rate due to this change in electrical resistance was investigated. The recovery rate was calculated using the lithium concentration in the secondary side solution measured by inductively coupled plasma optical emission spectroscopy. The electrical resistance of the solution between the cathode and the third electrode decreased due to the increase of the lithium-ion concentration in the secondary side solution, and the overpotential for the electrochemical reaction on the cathode and the third electrode increased. As a result, the lithium recovery rate was increased.[1] S. Kunugi, Y. Inaguma and M. Itoh, Solid State Ionics, 122, 35-39 (1999).[2] T. Hoshino, Desalination, 359, 59-63 (2015).

Research on switching overvoltage suppression of 35 kV shunt reactor

In recent years, a number of equipment abnormal events caused by operating overvoltage have occurred during the interruption of 35 kV shunt reactors, which jeopardizes the safe and stable operation of the grid. In order to explore the mechanism of operating overvoltage when 35 kV shunt reactor is cut off and the effect of various suppression measures, this paper carries out simulation analysis and research, mainly considers several factors to the effect of overvoltage, such as bus outlet, circuit breaker switching position and overvoltage protector.

Corona lightning overvoltage analysis for a 500 kV hybrid line

In this paper, the overvoltage distributions due to the lightning stroke are analyzed for a 500 kV hybrid OHTL-Cable-GIL circuit beside substation, in which the section length is variable. Corona effect is incorporating in order to estimate the attenuation and deformation of overvoltage's travelling waves on transmission lines near substations. The influence of connecting substations surge arrester, direct, and indirect lightning strokes are investigated. ATP/Electro Magnetic Transients Program(EMTP) simulation program is applied to analyze the lightning overvoltage of a 500 kV hybrid OHTL-Cable-GIL system. It was discovered that OHTL-Cable, OHTL-GIL, and hybrid systems produces lightning overvoltages higher than those of a fully cable system and very likely lower than those of a fully OHTL system with the same transmission lengths. This means that the risk of experiencing high lightning overvoltages and stressing system components is higher in a fully-Overhead Line (OHL)circuit than in a partial or full cable or GIL line. Furthermore, using the Cable with MOSA (Metal Oxide Surge Arrester), the results have more regular voltage waveform at substation entrance; also Hybrid line has the same effect of fully GIL. Finally, the corona has a less attenuation effect of overvoltage reached to substation by about 2.7% in case short length OHTL.

Analysis and Control of Low-Voltage Ride-Through Capability Improvement for PMSG Based on an NPC Converter Using an Interval Type-2 Fuzzy Logic System

Wind farms must be linked to the grid during the voltage sag. Therefore, the improvement of low-voltage ride-through (LVRT) capability of wind turbine (WT) is a vitally issue. Protection system based on an interval type-2 fuzzy logic system (IT-2 FLC) is presented to improvement of LVRT capability of permanent magnet synchronous generator (PMSG) based on WT during the voltage dip. The presented control system prevents the power converters from the damaging effects of over-voltage during LVRT time. In addition to, the proposed protection system based on IT-2 FLC provides constant DC link voltage, reduces the amplitude of stator fault voltages, and enhances all response of PMSG. The proposed method is applied wind turbine using a 1.5MVA PMSG during different voltage sag types in the MATLAB/Simulation. The effectiveness of presented technique is verified by simulation results.

An Overview on Overvoltage Phenomena in Power Systems

Overvoltage happens in a condition where the voltage is increased and exceed its design limit. This situation may lead to harmful damage to machines or related equipment that connected to the system. Overvoltage can exist in a form of transient, voltage spike or permanent, depending on its duration. Types of overvoltage consist of lightning overvoltage and switching overvoltage. Overvoltage that caused by lightning is considerate as natural phenomena, while switching overvoltage exists from the system itself, either by the interruption of faults or inappropriate connection of circuit breaker contacts. This paper is discussed about overvoltage phenomenon including causes and effects of overvoltage and overvoltage protection towards power system.

Highly Efficient Multilevel Frequency Converters of Metallurgical Production Facilities

A comparative analysis of traditional and multilevel low-voltage frequency converters was performed. Calculation methods were proposed that make it possible to evaluate the technical and economic indices of multilevel semiconductor devices. The attractive qualities of low-voltage multilevel frequency converters as compared with high-voltage (with rated voltage exceeding 1 kV) multilevel semiconductor devices were distinguished. In low-voltage multilevel converters, the loss in semiconductor rectifiers was reduced by about 1.5 times, the effect of overvoltage in the load was decreased, and the operating speed of the active rectifier was increased. A method of estimation of the loss in semiconductor converters with two-level standalone inverters based on mathematical models and experimental studies is proposed, which made it possible to clarify the parameters of analytical equations. It is stated that using the three-level bridge inverters (rectifiers) in active rectifiers makes it possible to shorten the durability of transient process of the system in the regeneration mode because of a reduced level of switching overvoltages. A method of choosing the optimal number of phases of semiconductor multilevel low-voltage frequency converters for metallurgical production facilities according to the criterion of maximum probability of failure-free operation was developed.

Time lag characteristics of spark discharge in humid air with increased voltage

This study investigates experimentally the time lag (τ) characteristics of lightning impulse spark discharges in air with relative humidity (RH) over the range 20 to 80%. The experiment was conducted using a wire-plate electrode system with a 30 mm gap and with overvoltage of 30 to 50% of the DC sparking voltage. The statistical and formative time lags (τs and τf) are discussed relative to the effects of RH and overvoltage on electron attachment and detachment mechanisims.

Overvoltage effect on electrical discharge type in medium-conductivity water in inhomogeneous pulsed electric field

The transition between thermal and streamer discharges has been observed experimentally in water solution with conductivity 100 μS/cm applying positive voltage pulses to pin-to-rod electrodes. The transition happens at five-fold pulse amplitude. Considering streamer propagation as an ionization wave helped to establish relation between the parameters governing transition from one to another discharge mechanism.

Simulation Analysis of Suppression of Resonant Overcurrent by Nonlinear Components

For the development of distributed power supply active distribution network system, the instability of the power supply side causes the system frequency to be disturbed, and harmonics, voltage fluctuations, or ferromagnetic saturation causes resonance and other series of power quality problems; what resulting in the over-voltage and over-current can easily damage components and threaten the system's safe and stable operation. In order to solve these problems, this paper compares some harmonic detection and filtering methods, devices and methods for suppressing resonance in recent years, and combines the principle of resonance to design a nonlinear inductive circuit that can suppress resonant overcurrent according to the characteristics of nonlinear inductors. Compared with the Resistance (R) series Induct Capacitance (LC) parallel circuit composed of common inductors, the circuit described in this paper is not affected by overcurrent, and the influence of overvoltage is relatively greatly reduced. The simulate-on proves that this circuit suppresses the effects of resonant overvoltage and overcurrent.

Study of the effect of atmospheric overvoltages on overhead lines of medium voltage classes

The article is devoted to the effect of atmospheric overvoltages on the operation of overhead lines of electrical distribution networks with protected and bare wires. The article deals with the methods of protection and their effectiveness in lightning storms used in Ukraine and in the world. The influence of lightning and line parameters on the probability of a direct lightning strike in the overhead line is considered. The technique for calculating direct lightning strikes in a line is analyzed. A new approach to the simulation of overhead lines affection by direct lightning strikes is applied by modeling the height of the orientation of the lightning. It is described the creation of a large-scale model for conducting experimental studies, with the possibility of changing the parameters of lightning (lightning current) and overhead line parameters (line voltage, type of wire). The data allowing to determine the zone of the zipper capture for the lines with the protected wires and the bare wires by the experimental method are obtained. Due to the obtained data, it is possible to more accurately determine the number of direct lightning strikes in overhead lines. The possibility of creating an overhead transmission line using a combination of bare wire and protected wires is considered. With this configuration, the striking effect of lightning on bare wires will be significantly reduced, and the bare wire in addition to the phase conductor will act as a lightning protection cable. An experimental model of a combined power transmission line has been created and its effectiveness has been experimentally confirmed. Conclusions are made about the possibility of using an overhead power line with combined wires for medium voltage classes

Electrochemical balancing of lithium-ion cells by nickel-based cells

This paper presents a topology to passively balance two types of lithium-ion cells without using additional active electrical components or employing any algorithm based balancing management systems. We connect nickel-metal hydride or nickel-zinc cells in parallel to lithium-ion cells. The hydrogen/oxygen recombination process of the nickel-based cells can be used to balance lithium-ion cells. Two serially connected lithium iron phosphate cells, combined each with two serially connected nickel-zinc cells, show a successful balancing of 8% of the lithium iron phosphate cell's initial capacity. A lithium titanate cell connected in parallel to two nickel-metal hydride cells can be fully charged without suffering from over-voltage effects by constant current charging.

A modelling of AC voltage stabilizer based on a hybrid transformer with matrix converter

AbstractThis article presents a study of an AC voltage stabilizer based on a three-phase hybrid transformer combined with a matrix converter. The proposed solution is used to control AC voltage amplitude and phase shift. By adjustment of these voltage parameters we can reduce the effects of overvoltage, voltage dips or lamp flicker. Such negative phenomena are very significant, particularly from the perspective of the final consumer and sensitive loads connected to the power network. Often the voltage in the power system can be adjusted using a mechanical or thyristor controlled regulator, which in a stepwise manner switches the taps of the electromagnetic transformer. The method for obtaining continuous control of the voltage magnitude and phase shift with the use of a conventional transformer with two output windings and a matrix converter is presented in this paper. The operating principles, mathematical model and properties of the proposed voltage stabilizers are discussed in this paper. The main part of the article will be devoted to the mathematical model which is based on an averaged equation. Computer simulation results are presented and compared with the results of a mathematical study.

Synergistic effect of the insulation characteristics of gas mixtures under the influence of pulse voltages

The character of the paper is purely experimental. The pulse breakdown voltage as well as impulse characteristics of the SF 6 +He and SF 6 +N 2 gas mixture were examined by reliable and highly reproducible procedure. The obtained results were compared to the matching results for the pure SF 6 gas (that was obtained under the same conditions). It was found that the positive synergy of the SF 6 +He gas mixture is higher than the positive synergy of the SF 6 +N 2 gas mixture. That result was explained by more appropriate moderation effect of the He atom (than the N 2 molecule) at the conditions of the fast pulse voltages. The results shown in this paper are significant for engineering practice in the fields where an efficient replacement of the pure SF 6 gas is required as an insulation gas in the conditions of rapid overvoltage effect.

Optimal fitting of high-frequency cable model parameters by applying evolutionary algorithms

Due to the widespread use of electronic power converters, low-voltage high-frequency cable models are being increasingly applied in industry, automobile or aeronautics applications among others. It is known that depending on switching frequency, cable configuration and length, transient overvoltage effects comprising a wide frequency range from dc up to several tens of MHz can appear. However, to accurately reproduce the wide-band frequency response, such models often require the use of ladder networks, thus being necessary to adjust the values of a relatively large number of R, L and C components, which is a complex task. This paper is focused to solve this problem, which is done by applying an iterative genetic algorithm (IGA) optimization approach. From a set of experimental short circuit and open circuit tests the high-frequency cable model of a given cable configuration is obtained, whose parameters are fitted by means of the proposed IGA-based method. Finally, the accuracy of the model obtained is validated experimentally by comparing the frequency-domain and time-domain responses through overvoltage predictions of different samples of the analyzed cable.

A Study on Overvoltage Distribution Across the High Voltage Winding of an Electric Power Transformer

The main objective of this paper is to represent effects of overvoltage on a transformer winding by analysis and modelling with special attention given to the voltage distribution across the winding. The authors have considered both approaches in modelling the winding: windings with distributed electrical parameters, and secondly disk coils with concentrated parameters. All known models are assembled in a general model based upon distributed parameters, while the excitation voltages display sinusoidal variation in time (commutation) or step. Both induced and commutation voltages, applied across the transformer winding, will generate free oscillations which are analyzed further on. According to the model, the transformer’s windings are divided in several disk coils with concentrated known parameters. This results in a complete electrical network used for simulations. All simulations have been performed using the software package SYSEG (SYmbolic State Equation Generation). Using SYSEG package, from the state equations assembled in terms of the disk coils voltages, one can obtain the overvoltage across the transformer winding as function of time. If the frequency of the commutation voltage and the frequency of the free oscillations are in close range, then the voltage across the disk coils shows a non-uniform distribution. An important aspect of this paper is accounting for asymmetry of the transformer by modelling the reinforced insulation of the first turns of the disk coils of the transformer’s high voltage winding. This affects the value of the inter-turn capacitance of these coils, and is an aspect which is treated in our simulations.

Overvoltage Minimization in Induction Motors employing Long Cable PWM Drives

The employment of PWM drives in induction motors control has been widely used in industry. However, in some applications in hazardous areas, such as drilling, the PWM drive cannot be physically close to the motor, being necessary the use of long cable drives. This fact leads to the generation of overvoltage peaks on the induction motor terminals, which can cause interference in the speed control, reduction of equipment lifetime, or even, permanent damages. In this context, this work presents alternatives to minimize the overvoltage effect based on the use of transformers and analyzes the performance of the speed control of each proposed technique.

Probabilistic Risk Assessment of MV Insulator Flashover Under Combined AC and Lightning-Induced Overvoltages

The effect of lightning-induced overvoltages is more profound in overhead distribution lines due to their limited height and low insulation level. Consequently, there is a high risk of line insulation flashover when exposed to lightning-induced overvoltages. This paper presents a probabilistic method to assess the risk of insulator flashover in medium-voltage overhead lines due to lightning-induced overvoltages. In order to accomplish this, a modified Gaussian cumulative distribution function has been used to predict the probability of single-phase, two-phase, and three-phase flashover of insulators under combined ac- and lightning-induced overvoltages. The validity of the modified probabilistic model is confirmed through experiments carried out in the high-voltage laboratory. Next, Monte Carlo simulations were performed on the simplified Rusck's model to generate the distribution of peak lightning-induced overvoltages. Finally, the risk of insulator flashover is calculated based on the distributions of lightning-induced overvoltages and insulator flashover voltages. The proposed procedure could be considered beneficial to select the optimum insulation level required against lightning-induced overvoltages by distinguishing between single-phase and multiphase flashover faults.

Anomalous Voltage Change in Charge and Discharge Curves for Electrode Materials Showing Plateau-like Behavior

An overvoltage phenomenon was investigated that occurs during partial charge-discharge experiments for LiFePO4 as electrode material showing a plateau-like behavior. The temperature was varied in order to determine the influence on the voltage change (overvoltage). This overvoltage effect was recently reported by another group and discussed in light of a many-particle model. However these measurements were carried out only at room temperature. Hence temperature influence was supposed to be worth of consideration. Indeed, an increased overvoltage was observed at lower temperature, while an opposite effect was obtained at higher temperature. Increasing the number of partial charge-discharge cycles leads to an interference of single voltage bumps, but the overvoltage seems to saturate at a given voltage level.

Spatial Uniformity of Atmospheric Pressure Discharges: A Simulation Study

AbstractSpatial uniformity is important in most applications of dielectric barrier discharges operating at atmospheric pressure. However, such uniformity is not easily achieved. Under many conditions, a filamentary structure usually develops. In this paper, we employ a two‐dimensional self‐consistent fluid model to explore the influence of several factors on the evolution of spatial structure of dielectric barrier discharges. In particular, we contrast the behavior of discharges in pure helium and He‐N2 gas mixture, which represent the reduction in breakdown voltage of gas during the evolvement of uniform glow discharge plasma. The transformation from filamentary to uniform mode of discharge plasma is analyzed by the phenomenon of coalescence of filaments and we investigate the effect of several external discharge parameters, such as driving frequency and effect of overvoltage, and the dielectric constant of the barrier material for the uniform and filamentary discharge plasmas. This simulation study is useful to describe the spatio‐temporal profiles of electron density in different phases of the filamentary, uniform Townsend and glow discharge regimes under various constraints. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)