Overvoltage Protection Devices Research Articles

Surge arrester modeling using Micro-Cap

In this paper the results of circuit simulation of metal-oxide surge arrester using the Micro-Cap evaluation version are presented. Nowadays a surge arrester is the most common type of overvoltage protection device and appropriate modeling of such power system’s component is a significant task. Moreover, metal-oxide arresters have dynamic characteristics that are significant for studies involving lightning and other steep-front surges. Two methods of metal-oxide surge arrester modeling are described. The main innovation introduced by the paper lays in the usage of analog behavioral voltage-controlled current source and current-controlled voltage source for non-linear varistor modeling. The residual voltage test results obtained by the manufacturers were compared with the results of simulations performed with the Micro-Cap evaluation version. Both proposed models fits with a high accuracy the arrester performances reported in the data sheet. Two different lightning current waveforms were used. One of them has its first derivative equal to zero at the initial moment of time and other one does not. For both waveforms maximal residual voltages obtained in the simulation are almost equal. Effectiveness and simplicity of use make the proposed way of modeling a useful tool for insulation coordination and lightning protection studies.

Effect of Different Types of Overvoltage Protective Devices Against Vacuum Circuit-Breaker-Induced Transients in Cable Systems

Transient overvoltages due to circuit-breaker switching may occur if certain conditions regarding system layout and type of switching operations are fulfilled. In such applications, overvoltage protection should be used. Different types of protective devices exist, such as surge arresters and RC snubbers, and they can be installed in different configurations. The purpose of the presently published results is to show the effect of the different protective devices. Laboratory testing has been performed, focusing on the disconnection of an inductively loaded transformer at a phase angle causing multiple reignitions. It was found that surge arresters limit the voltages to well-defined amplitudes, but a number of reignitions occur up to this level. RC snubbers, on the other hand, reduce the risk of having reignitions and the number of reignitions in case they do occur, but the voltages are not limited at well-defined amplitudes. All of the tested configurations of protective devices limited the voltages below the basic insulation level of the transformer.

Study on Electrical Characteristics of Metal-Oxide Surge Arresters in Medium Voltage Power System

The index system for electrical characteristics of metal-oxide surge arresters is proposed and established, which is based on rated voltage (Ur), continuous operating voltage (Uc), nominal discharge current (In), overvoltage protection and insulation coordination including lightning overvoltage protection level, operating overvoltage protection level and coordination coefficient (Ks). The study considers both selection and application of overvoltage protection devices for the electrical equipments in 3-35kV medium voltage power system, and comparatively calculates and analyzes the main parameters between two types metal-oxide surge arresters (without gaps and containing series gapped structures), and illustrates their technical features and puts forward suggestions on how to improve the effective utilization. The results of 10kV power distribution system are simulated to show that the conclusions are feasible and available in the practical engineering application.

Resonant overvoltage assessment in offshore wind farms via a parametric black-box wind turbine transformer model

The protection of offshore wind farms (OWFs) against overvoltages, especially resonant overvoltage, is of paramount importance because of poor accessibility and high repair costs. In this paper, we study how switching overvoltages at the wind turbine transformer (WTT) medium voltage (MV) side can lead to high overvoltages on the low voltage (LV) side. The effect of overvoltage protective devices is analyzed. A detailed model of an OWF row is developed in electromagnetic transients program–alternative transients program (EMTP-ATP), including interconnecting cables, WTT, surge arresters and resistive–capacitive filters. A parameterized black-box WTT model is obtained from measurements and is used for investigating the transfer of resonant overvoltages from the MV to the LV side. The model is capable of shifting systematically the frequencies and adjusting the transformer input impedance. Simulation results show that wind turbine energization in an OWF can lead to overvoltages on the LV terminals. The rate of rise of overvoltages (du/dt) is in the range of 300–500 pu/µs. It is found that resistive–capacitive filters should be installed on both MV and LV terminals of WTTs to decrease both resonant overvoltages and du/dt, which is unachievable by surge arrester alone. Copyright © 2014 John Wiley & Sons, Ltd.

Analysis on Self-breakdown Statistics Properties for a Spark Switch

AbstractAccording to the working characteristics of over-voltage protective device for series compensation, the principle and structure of spark switch were introduced in this paper briefly. Special test loop and HV fast switch-off device were designed to evaluate the performance of spark swich in trials. Test data and mathematic statistic results revealed that the self-breakdown probability of spark switch obeyed the normal distribution and the cumulative distribution of spark switch self-breakdown had been less affected by different enviroment temperature. The number of trials was restricted to the characteristics of insulated gas and the electrode surface state in the practical application. Reasonable choice of test number can keep estimation error at a relatively low level, particularly for parameter estimation by using small sample of self-breakdown voltage. The conclusion is instructive to the development and engineering application of spark switch for over-voltage protective equipment of series com...

Effects of Vehicle Running Mode on Rail Potential and Stray Current in DC Mass Transit Systems

The ungrounded scheme with overvoltage protection device (OVPD) has been adopted in the construction of Nanjing Metro Line 1. During the operation of Line 1, a high rail potential was observed, which caused the OVPDs installed at some traction supply substations (TSSs) to keep turning on at any moment, and the stray-current leakage increased obviously. Since the magnitude of rail potential and stray current depends on the modes of a running vehicle, including accelerating, coasting, constant speed, or braking, Line 1 suspected that the vehicle running modes were the cause of a potential rise in the rail. This paper presents the results of field tests and numerical simulations to study whether different vehicle running modes have an impact on rail potential and stray current in Line 1. The results show that the rail potential in the acceleration and brake modes is significantly higher than that in the other modes, which are in the opposite direction. Moreover, within the stray-current interference, the maximum shifts of buried-conductor potential may exceed the limit in these two modes. In addition, the high rail potential and buried-conductor potential occur when the running mode changes from acceleration to coasting or the maximum brake power is reached. As a vehicle is running between two different TSSs, the rail potential is highest in its position.

Study on a New Method of Metal Oxide Surge Arrester Monitoring

Metal oxide surge arresters (MOA) is a power system overvoltage protection device, and the online monitoring of the MOA is an important means to ensure the safe operation of the power system. This paper presents a new MOA insulation defects monitoring method. This method is based on the relative change in capacitance to MOA insulation defects as characteristic parameter, the aging classified as a kind of local defects, the system disturbance contains higher harmonic of transient voltage and current as the signal source, dynamically generated MOA partial insulation discriminant function of the defects in the diagnosis. The maximum value of the discriminant function corresponds to the local insulation defects. The proposed method contributes to the MOA monitoring methods and the development of technology.

A Novel SPD Design for Lightning Protection of Intelligent Buildings

The surge protective device (SPD), as buildings over-voltage protective device, has been widely used in building’s power distribution system. A novel SPD based on hollow cathode effects is designed. In both air and nitrogen gas, the relationship of discharging voltage and gas pressure are measured, and the critical pressure ranges are determined in the condition of UpUp is pulse voltage protection level). The results indicate that, in the condition of the gap distance D=3 mm and the small hole diameter φ=3 mm, the operating gas pressure ranges are from 50 to 5×104 Pa. With the gap distance D increasing, the pulse voltage protection level Up is decreasing slightly. While D=3 mm, φ=3 mm, and gas pressure (nitrogen) is 600 Pa, the DC voltage protection level and pulse protection level are 784 V and 2.4 kV, respectively. In the action of 10/350 µs pulse current waveform, the quantity of transferred charge Q is 48.26 C, and the ratio energy W/R is up to 2 MJ/Ω. The results testify that the design of SPD in this paper can be used as buildings class B over-voltage protection.

Analysis and Suppression of the Coupling Capacitor Voltage Transformer Ferroresonance Phenomenon

This paper provides a detailed core model for the step-down transformer (SDT) of the coupling capacitor voltage transformer (CCVT) to investigate the CCVT transients and ferroresonance behavior. The core model represents hysteresis symmetric and asymmetric minor loops, remnant flux, and the eddy current effects. Based on the developed model, the impacts of passive and active ferroresonance suppression circuits (PFSC and AFSC) and overvoltage protection devices (OPDs) for fast suppression of the CCVT ferroresonance phenomenon are also studied. This paper also presents a generalized methodology to select the AFSC parameters. The simulation results, in the PSCAD/EMTDC environment, indicate that the hysteresis and eddy current effects of the SDT core significantly influence the CCVT ferroresonance behavior. The study results also show that: 1) in both the presence and the absence of arresters and spark gaps, the AFSC can mitigate the phenomenon faster than the PFSC, i.e., in about two cycles and 2) the output fidelity of the AFSC-based CCVT is less dependent on the burden as compared with that of the PFSC.

Characterization of Ionization Phenomena in Soils Under Fast Impulses

Protective devices such as spark gaps and surge arresters are used to divert surges to earth. It is, therefore, necessary that earthing systems are designed with a low-magnitude earth impedance value so that the overvoltage protection devices can divert high fault currents effectively to earth for all types of fault. Power frequency characterization of earthing systems is extensively researched and fairly well understood. However, the behavior of such systems under transient conditions is still not fully clarified. This paper addresses some of these shortfalls. Laboratory experiments were set up to study the characteristics of the ionization phenomenon in various soil conditions. The soil ionization characteristics were investigated using a proposed new concept of pre- and post-ionization resistances. A measurement technique was developed to establish more accurate estimates of ionization electric field threshold, and an equivalent circuit representation is proposed.

Electron Holography of Potential Barriers in Zno Varistors

ZnO varistor materials are polycrystalline materials that exhibit strong non-linear current-voltage characteristics. Their non-ohmic behaviour makes them suitable for overvoltage protection devices. It is the interfaces between ZnO grains that are the key to the non-linear behaviour of the varistor materials. Previous work has shown that the local microstructure determines the breakdown voltage of the individual ZnO/ZnO interface [1]. The pre-breakdown conductivity and the non-linearity in the breakdown region, which are both crucial to the performance of the varistor, are also affected by the height and the width of the potential barriers. In the present work, electron holography has been used to investigate the potential barriers in ZnO varistor materials.Electron holograms were recorded at 200kV using a Hitachi HF-2000 field emission gun transmission electron microscope [2]. The electrostatic bi-prism was located near the second image plane. The bi-prism voltage was about 9 V and the fringe spacing in the holograms was about 1 nm.

Method to improve digital distance relay impedance measurement when used in series compensated lines protected by a metal oxide varistor

A novel method is described that enhances the accuracy of digital distance relays applied on series-compensated lines where the series capacitors are protected against overvoltages by a metal oxide varistor (MOV). The technique is applicable to systems where the relaying voltage is taken from the busbar side of the series capacitor. The basis of the technique is a method known as voltage compensation. The voltage across the series capacitor and overvoltage protective device is calculated in the relay and hence the relaying signal is modified by the relay. The new compensation technique makes the impedance measurement immune to the MOV operation, thus enhancing the relay integrity and the accuracy of impedance measurement. The technique is simulated in a typical differential equation distance relay algorithm and is examined for ground and phase faults using the EMTP (ATP) simulation package.

A new multipurpose CO2 laser therapy instrument.

A new multipurpose CO2 laser therapy instrument has been developed. It is a highly efficient medical instrument. By use of high laser power density to coagulate, evaporate, and cut body tissue on the nidus, the operation can be controlled and has obvious curative effects. Unlike other kinds of CO2 laser therapy instruments, this device has an advanced switching power supply (SPS) and red guiding light system. With an overcurrent protective device, an overvoltage protective device, and a high-voltage shield device, it provides efficiency, stability, reliability, and low loss. The plastic casing does not leak electricity and the film switches are designed for clinical practice convenience. Additionally, the laser power is numerically displayed and can be set prior to the procedure. The distinct visible guiding light of the laser output makes the operation more convenient and accurate. Because of this unique design and properties, it is a leading model in China. The instrument can be widely used for surgery, gynecology, dermatology, and otolaryngology. The radiation therapy of low laser power density has the effect of being antiinflamatory, analgesic, and antipruritic, and promotes cure of the epithelium. Moreover, it is effective to treat all sorts of sprains, scapulohumeral periarthritis, arthritis, sciatica, and surface ulcers.

Guidelines for the Application of Vacuum Contactors

The overvoltage phenomena associated with switching currents in vacuum and their effects on motor insulation are described in some detail, and a practical guideline for the application of overvoltage protective devices is presented.

Improved varistor nonlinearity via donor impurity doping

Zinc oxide (ZnO) varistors exhibit a voltage upturn at higher current densities which reduces their effectiveness as over-voltage protection devices. This effect has been attributed to a limiting series impedance offered by the ZnO grains. Based on literature data, the varistors were made for this investigation wherein the grain impedance has been reduced by doping with Al2O3 or Ga2O3. The high current surge and high frequency impedance data combined with microstructural investigation indicated an improved varistor nonlinearity via donor doping. A simple defect model developed for a pure ZnO crystal has been used to explain the doping behavior of the varistor grain.

Pilot Wire Relay Applications in Industrial Plants Utilizing a New Static Pilot Wire Relay

Pilot wire relaying is an extremely effective way to provide fast, selective protection for industrial plant cable tie circuits. The operating principles of popular pilot wire relay schemes will be reviewed, and special attention will be given to a new static pilot wire relay which offers an improvement in ground fault sensitivity, an especially significant consideration on resistance grounded industrial systems. A discussion of pilot wire overvoltages and overvoltage protective devices is also presented.

Service Experience with Lightning Arresters Under Contaminated Conditions

The Working Group on Lightning Arrester Contamination Performance and Durability of the Overvoltage Protective Devices Subcommittee of the IEEE Surge Protective Devices Committee has prepared a final report summarizing the replies to a questionnaire on arrester serviceability under contaminated conditions. The questionnaire was distributed in 1966 by members of the working group to electric utility companies throughout the United States. An evaluation of the responses is presented in this paper, and several significant observations are made and conclusions reached. A variety of contaminants which might affect arresters is described in addition to the extent to which preventative practices and procedures are utilized to minimize the effects of contamination on arresters. A distinction is made between station or intermediate class arresters and distribution class arresters concerning the possible processes contributing to failure from contamination.

A simple over-voltage protection device for a low-frequency power amplifier

A 120 w amplifier is used as a source of electrical power at or near mains frequency. A simple device is described, incorporating a Mullard lamp-photocell unit type ORP39, which gives limited but acceptable protection to the amplifier load from over-voltages, but has no effect on amplifier gain at output voltages equal to or less than the nominal maximum. After an initial overshoot lasting some 0.1-0.7 sec, the amplifier output voltage is restricted to a low value and then allowed to rise asymptotically to the nominal value. In this way the load is given an opportunity to recover from thermal effects.

Triggered vacuum gaps

Characteristics of a sealed vacuum gap are described and the difficulties encountered in applying this gap as an overvoltage protection device are discussed. It is shown how these difficulties can be ameliorated by the use of gas-free electrode materials and by triggering the gap when breakdown is required. Several methods of triggering are discussed and some practical triggering devices are described that inject minute quantities of ionized hydrogen into the gap. The hydrogen is eventually recovered by the use of a titanium hydride getter. It is shown that breakdown of the gap can be accomplished in less than one-tenth microsecond by first producing a glow discharge that is rapidly transformed into a metal-vapor arc. Properties of the metal-vapor arc are described which have an effect on the characteristics of the vacuum gap. A number of practical sealed-off triggered vacuum gaps are illustrated. These are used to carry microsecond capacitor discharge currents and 60-cycle power line currents for ½ cycle. The operating voltage range is from a few hundred volts to 100 kV. The advantages of vacuum gaps over gas-filled gaps are given and a number of overvoltage protection and switching applications are listed.

Characteristics and Applications of the Centralab Spark Gap Capacitor

The spark gap Capacitor is a low cost overvoltage protective device which finds broad application in Color T.V. receivers and other electronic equipment. The discussion which follows covers the theoretical basis of an atmospheric spark gap, the performance characteristics of a practical unit, and some typical applications.