Gapless Metal Oxide Surge Arresters Research Articles

On the Computation of the Voltage Distribution along the Non-Linear Resistor of Gapless Metal Oxide Surge Arresters

The voltage distribution along the non-linear resistance of metal oxide surges is of great importance for their proper operation, since the non-uniform potential distribution results in higher thermal stresses of the varistor discs near the high voltage electrode, leading to a faster ageing of the discs at the top and, consequently, a downgrade in arrester effectiveness and reliability or even failures. The current work deals with the examination of the voltage distribution along the non-linear resistance of medium voltage metal oxide gapless surge arresters, using an appropriate computer tool, discussing configuration that improve the voltage distribution. Moreover, the impact of various factors on the voltage distribution is examined. The extracted results can contribute to the more efficient design of modern metal oxide gapless surge arresters, in an effort to ensure their reliable operation to protect the electrical equipment against lightning surges.

Effects of operation temperature in artificially aging of zinc oxide varistors by high current short impulses

Nowadays surge arresters combine a complex metal oxide varistor (MOV) technology inside a polymeric housing. MOV is a sintered polycrystalline ceramic based on zinc oxide (ZnO) and small amounts of other metallic oxides (additives) usually applied to the manufacturing of surge protective devices for overvoltage protection at all power system voltage classes. The effect of operation temperature on the chemistry and microstructure of commercial zinc oxide varistor (ZOV) submitted to accelerated electrical aging by high-current short impulses were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), optical microscopy (OM), Vickers micro hardness and X-ray diffraction (XRD). The SEM analysis indicates the formation of micro voids in grain and some larger voids in grain boundary with increase of operation temperature. The EDS and XRD measurements suggests that the operation temperature in the interval of 333 K–353K during the high-current short impulses promotes the volatilization of the Bi2O3 phase and formation of the pyrochlore in the ZOV body. The results of this paper suggest the necessity of getting a better knowledge of the aging process of ZnO-based varistors submitted to high operational temperatures applied to the manufacturing of gapless metal oxide surge arresters (MOSA).

An artificial neural network software tool for the assessment of the electric field around metal oxide surge arresters

The paper presents an artificial neural network (ANN) software tool that has been developed in order to assess the electric field around medium-voltage surge arresters. The knowledge of the electric field around gapless metal oxide surge arresters is very useful for diagnostic tests and design procedures. For the training, validating, and testing of the ANNs, real data have been used collected from hundreds of measurements. The developed ANN software can be used by electric utilities in order to diagnose the condition of the surge arresters without stopping their operation and by laboratories and manufacturing/retail companies dealing with medium-voltage surge arresters and either face a lack of suitable measuring equipment or want to compare/verify their own measurements.

Zinc Oxide Surge Arresters and HVDC 125kV-upgrade 500kV Converter Stations -Power Technology of Japan through the Experience of Developments and Applications of Gapless Metal Oxide Surge Arresters-

Gapless Metal (Zinc) Oxide Surge Arresters for a.c. systems contribute to the insulation co-ordination based on the suppression of lightning surges and switching surges. These gapless metal oxide surge arresters using ZnO elements are effective to HVDC systems. This paper describes basic characteristics of ZnO (zinc oxide) elements for d.c. systems and applications of gapless surge arresters to HVDC 125kV frequency converters, HVDC 250kV, upgrade HVDC 500kV converter stations, and HVDC 500kV cables of Japan through the experience of developments and applications of gapless metal oxide surge arresters.

Parameter Determination for Modeling Systems Transients—Part V: Surge Arresters IEEE PES Task Force on Data for Modeling System Transients of IEEE PES Working Group on Modeling and Analysis of System Transients Using Digital Simulation (General Systems Subcommittee)

The performance of surge arresters during electromagnetic transients on power systems can be simulated with Electromagnetic Transient Program (EMTP) type computer programs. This paper discusses the steps to be performed for deriving the parameters needed to represent gapless metal-oxide surge arresters in transient simulations. The paper includes a summary of the mathematical representation, guidelines for choosing appropriate parameters, and the conversion procedures used to obtain parameters.

Evaluation of the Operational Condition and Reliability of Surge Arresters Used on Medium Voltage Networks

Laboratory studies were conducted on gapped silicon-carbide arresters and gapless metal-oxide surge arresters (MOAs) gathered from 24 kV networks in Finland. A total of 410 arresters of 21 different types from eight different manufacturers were investigated. A total of 246 silicon-carbide arresters (age from 14 to 38 years) and 164 MOAs (age from 4 to 15 years) were studied at the High Voltage Laboratory of Tampere University of Technology. The results of the measurements on MOAs were compared to the measurements conducted earlier on 16 new, unused MOAs of the same types as those taken from the field. A portion of 16.7% (41 specimens) of the silicon-carbide arresters failed in the ac voltage withstand test and 34.5% (85 specimens) did not pass the lightning impulse sparkover test. The current impulse test of the silicon-carbide arresters resulted in a lot of damage. Due to the damage and failures in the electrical tests the authors recommend the electricity companies in Finland to exchange 7 types of silicon-carbide arresters to new MOA types in order to reduce the risk of arrester failures and to improve the protection levels in MV networks. All the ten MOA types studied were generally in good condition after being used 4-15 years in networks. Only three specimens (out of 164) could be evaluated to be faulty. Comparisons between the MOAs gathered from the networks and the unused MOAs showed that the protection levels of the MOA types studied had remained stable and the ac durability of these MOA types had not remarkably weakened during the use in networks.

Investigation of diagnostic techniques for metal oxide surge arresters

Gapless metal oxide surge arresters (MOSA) have been available in the market for many years since they were first introduced in the 1970's. The aim of this study is to investigate some reliable diagnostic techniques to assess the condition of a metal oxide surge arrester when subjected to severe lightning strikes in the field. A number of nondestructive and destructive diagnostic techniques for metal oxide surge arrester (MOSA) are discussed in this paper. The nondestructive techniques include the standard 1 mA reference voltage, lightning impulse discharge residual voltage and a number of modern diagnostics based on polarization methods: Return voltage and polarization/depolarization current measurements. In order to observe, analyze and correctly explain the degradation phenomena, a number of destructive techniques based on microstructure observation are also conducted. The techniques include optical microscopy, scanning electron microscopy, X-Ray diffraction and energy dispersive spectrometry. The single and multipulse currents of 8/20 mus wave shape were used to artificially degrade the MOSA. The before and after diagnostic results of the nondestructive and destructive techniques are presented and interpreted to understand the aging mechanism in MOSA. The importance of modern nondestructive electrical diagnostics based on polarization methods is validated by test results and is highlighted in detail in this paper. Finally the correlation of the results of different diagnostic techniques with each other and with the results of standard techniques is discussed

Methods for analyzing the performance of gapless metal oxide surge arresters

The development and use of practical methods for analyzing the performance of gapless metal oxide surge arresters under various surge and power frequency overvoltage conditions is described. Using these methods, the thermal requirements of ANSI and IEC standards are examined in detail. The results, showing large differences between the two standards, indicate the need for further harmonization of standards. Recommendations are made to bring ANSI and IEC standards to a closer agreement. >

A Procedure for Estimating the Lifetime of Gapless Metal Oxide Surge Arresters for AC Application

The development of the gapless metal oxide (ZnO) surge arrester has presented the arrester engineer with new materials and an opportunity for new designs. This situation arises because the gapless surge arrester is electrically active throughout its lifetime whereas its predecessor, the silicon carbide arrester, was electrically passive since it was electrically isolated with gap structures. The prime consideration is one of reliably estimating the lifetime of a gapless ZnO surge arrester under continuous ac stress while maintaining the capability not only to limit surge voltages but also to absorb energy inputs resulting from lightning or switching surges and temporary overvoltages. In this paper we establish a procedure for estimating the lifetime of gapless ZnO surge arresters for ac application by incorporating the device characteristics into design requirements. This method is illustrated for ZnO-surge-arrester elements that exhibit a predictable linear resistive current versus time?? behavior as a function of applied voltage and temperature.

A Procedure for Estimating the Lifetime of Gapless Metal Oxide Surge Arresters for AC Application

The development of the gapless metal oxide (ZnO) surge arrester has presented the arrester engineer with new materials and an opportunity for new designs. This situation arises because the gapless surge arrester is electrically active throughout its lifetime whereas its predecessor, the silicon carbide arrester, was electrically passive being electrically isolated with gap structures. The prime consideration is one of reliably estimating the lifetime of a gapless ZnO surge arrester under continuous ac stress while maintaining the capability not only to limit surge voltages but also to absorb energy inputs resulting from lightning or switching surges and temporary overvoltages. In this paper we establish a procedure for reliably estimating the lifetime of gapless metal oxide surge arresters for ac application by incorporating the device characteristics into design requirements. This method is illustrated for metal oxide surge arrester elements that exhibit a predictable linear resistive current versus time1/2 behavior as a function of applied voltage and temperature.

Development of Gapless Metal Oxide Surge Arresters for 362 KV Gas Insulated Substations

A 362 kV gapless metal oxide surge arrester for gas-insulated substations is described. The active stack consists of 3 parallel 250 cm-long columns, each column made up of ten modules of soldered MOV blocks. Satisfactory thermal performance is achieved by a thermal electric design model, confirmed by thermal mock-up tests and temperature recordings during final prototype tests. Ceramic capacitors are employed for uniform voltage grading. Dielectric design is used to keep electric stress below 4 kV (rms)/mm at maximum expected operating voltage. Laboratory testing of the prototype was performed up to 285 kV (rms) Insulation coordination studies show the advantages of using gapless gas-insulated arresters for improved performance.

Development of Gapless Metal Oxide Surge Arresters for 362 kV Gas Insulated Substations

Development of Gapless Metal Oxide Surge Arresters for 362 kV Gas Insulated Substations