Withstand Voltage Level Research Articles

Control strategy of transfer branch for reducing peak value of DCCB breaking current

A high-voltage DC circuit breaker is one of the key equipment that constructs the DC power grid. Therefore, reducing the peak value of the breaking current and shortening the fault removal time are the main research directions for its performance optimization. This paper first analyzes the basic topology and the traditional breaking strategy of a hybrid high-voltage DC circuit breaker with forced current commutation. Then, the theoretical analysis of the fault current, voltage, and the relationship between the withstand voltage level of the fast mechanical switch and the exit time of the transfer branch, is conducted. A new breaking strategy is proposed, which can effectively reduce the peak value of the breaking current by turning off the transfer branch step by step. When a fast mechanical switch reaches the corresponding withstand voltage level, it sends the OFF signals to each sub-module of the transfer branch; thus, the energy consumption of the DC circuit breaker is reduced and the fault removal time is shortened. Finally, the PSCAD/EMTDC simulation platform is used to build the test system, which verified the effectiveness of current limiting and other functions of the proposed breaking control strategy.

Multi-spark modeling of very fast transient overvoltages for the purposes of developing HV and UHV gas-insulated switchgear and of conducting insulation co-ordination studies

AbstractVery fast transient overvoltages (VFTO) originate from steep voltage breakdowns in SF6gas that are inherent to operation of any switching device of the gas-insulated switchgear (GIS) type. For power stations with voltage ratings exceeding 500 kV, the ratio between equipment rated- and withstand-voltage levels becomes relatively low, which causes the VFTO peak values to reach the component’s insulation withstand-voltage levels, thus becoming a design factor for high- and ultra-high voltage GIS. While well-established approach to VFTO analyses involves only single VFTO events (the so-called single-spark approach), there is often the need to analyze the entire VFTO generation process, for which the multi-spark approach to VFTO modeling is to be employed. The multi-spark approach allows one to evaluate the VFTO impact on the GIS disconnector design along with the impact of the VFTO on selection and dimensioning of the VFTO damping solutions. As the multi-spark approach to VFTO modeling is now being increasingly used in UHV GIS developments as well as for the insulation co-ordination studies of power stations, the present paper is motivated by the need to report on the VFTO multi-spark modeling approach and to lay a common ground for development works that are supported extensively with VFTO simulations. The paper presents physical assumptions and modeling concepts that are in use in such modeling works. Development of the multi-spark GIS disconnector model for VFTO simulations is presented, followed by an overview of examples of the model application for the GIS development works and for insulation co-ordination studies.

Research on energy coordination between multi-level surge protective devices with the transmission line theory

Surge protective device is widely used in the lightning protection of electric appliances. In order to meet the withstand voltage level of those protected devices, multi-level surge protective devices are applied in the practical situation. Therefore, the optimal choice of decoupling elements is vital to realize the energy coordination between multi-level surge protective devices. This paper intends to expatiate on the process of coordination between these low-voltage multi-level surge protective devices, which is based on the transmission line theory. Through a series of experiments, we found the transmission line theory could be applied to describe the transmission process of lightning wave in the low-voltage system; When a 5-meter-long wire whose inductance is 5.6 micro-henry was used as the decoupling element, the average shunt ratio between multi-level surge protective device in the first level and multi-level surge protective devices in second was about 0.9: 0.1; upon the experimental results, it was proposed that two voltage limiting type multi-level surge protective devices had a better performance to clamp the overvoltage, which has a certain reference value in the practical application.

Developed of High Voltage Bushing with New Shielding Technology for High Voltage Switch Cabinet

TGZ10A-40.5 wall bushing of high voltage switch cabinet from one company was taken as applied research object. Reference the development process of high voltage cable shielding technology, three samples were designed and produced depending on different sets of the shield system. The result show that: surfaces processed by the way that the inner (aluminum cylinder) and the outer (metal mesh ring) shielding components were coated with a semi-conductive material, made little sense to improve the withstand voltage level and reduce the partial discharge; surface processed by the way that inner shield component (aluminum cylinder) was coated with semi-conductive material, the outer shield component (metal mesh ring) was not coated with semi-conductive material, was obviously influenced the improvement of the withstand voltage level and reduction of the partial discharge, compared with traditional technology, the average start voltage of corona increased 23.8%, the average value of partial discharge dropped 27.7%.

Network Instrument of Harness Based on Embedded System

This paper designs a universal intelligent wiring harness tester with the Cortex-A8 processor and embedded ARM-Linux operating system as the core, which is able to detect and diagnose the fault of harness including dislocation, short circuit, open circuit quickly and accurately. It also can achieve the test function of on-state resistance, insulation resistance and withstand voltage level and other additional features of the test data analysis, storage and network communication, which can be widely used in various occasions where harness are tested automatically.

Study of Overvoltage Protection and Insulation Coordination for MMC Based HVDC

This paper focus on overvoltage protection and insulation coordination in Modular Multilevel Converter based HVDC system planning. An overvoltage protection scheme, which bases on the topology used inTransbay project by Siemens, is proposed in this paper. Thescheme draws fromthe characteristics of MMC-HVDC systems and the research results in classic HVDC systems, byplacing arresters at some key locations in the MMC-HVDC converter station.With this scheme, the overvoltage at those key pointscan be limitedto an acceptable range and hence protect the key equipment concerned. Since all the DC lines of the project are undersea cables, no lighting overvoltage is considered and 14 faults which could happen are carefully selected to serve as the verification conditions for the insulation design. Based on the PSCAD/EMTDC simulations and the deterministic method, the specified withstand voltage levels of the critical equipment in the converter station is calculated.

Study on the Application of Regional Risk Assessment of Lightning in Electrical Equipment Insulation

With the rapid development of urbanization and the power system, the damages for the power system and electrical equipments which due to lighting strike are increasing. As the distributions of lighting activity are regional and random, the requirements for electrical and electronic equipment, voltage and insulation level are varied from lighting activity in different regions. This paper adopts the Lightning Location Data on the Pearl River Delta in the last 10 years, and uses the method of probability statistics to analyze the regional ground flash density, the probability of lightning strike accident, the damages of the lightning strikes accidents and other risk factors. It takes the topography, regional features, population density and other factors into account, and uses the weighted scores to establish the risk assessment model for the lightning strikes, programs to achieve the automatic calculation in allusion to the risk of lightning strikes in different types of buildings and insulation levels of the electrical and electronic equipment, and assess the risk of lightning strikes on the electrical and electronic equipment. And based on the risk assessment result, it incorporates the installation location, characteristics, importance and other factors to study the electronic equipment withstand voltage and insulation level.

Statistical analysis of the AC breakdown voltages of ester based transformer oils

Recent decades have seen the rapid and successful deployment of ester oils as transformer dielectrics. When evaluating the compatibility of ester oils with existing transformer insulation designs, it is essential to not only compare the mean breakdown voltages of the oils, but also to consider the role of dispersion and thus the withstand voltage levels (with the acceptable breakdown likelihood). Insulation designers sometimes estimate the withstand voltage of mineral oil from the dispersion of the data, assuming that the breakdown voltages of the oil follow a parametric distribution. However, there is a lack of discussion as to whether this method would be suitable for estimating the withstand voltages of ester oils. This paper uses samples of breakdown voltages of a synthetic ester, a natural ester and a mineral oil to analyze their distributions, and discusses the applicability of using Weibull and Gaussian distributions to estimate the withstand voltages of the esters. It is found that the distributions of ester breakdown voltages, in particular the lowest breakdown voltage, are similar to those of mineral oil. Consequently there is evidence that from the ac withstand voltage point of view the tested esters are compatible for the use in power transformers.

Insulation characteristics of CO2 gas for nonstandard lightning impulse oscillations: Evaluation method of nonstandard lightning impulse waveform for CO2 gas insulation

AbstractSF6 gas is widely used in electric power apparatus such as gas‐insulated switchgears (GIS), because of its superior dielectric properties; however, it has been identified as a greenhouse gas at COP3 in 1997, and alternative insulation gases to SF6 have recently been investigated. One of the candidates is CO2 gas, which has lower global warming potential (GWP). However, CO2 gas has a lower withstand voltage level than SF6 gas; therefore, it is necessary to rationalize the equipment insulation level and reexamine the insulating test voltage for electric power apparatus as low as possible. From our previous investigation, in SF6 gas insulation system, we obtained that the insulation requirements of the real surges (called nonstandard lightning impulse waveform) are not as severe as those of the standard lightning impulse waveform. This paper describes the evaluation method for real surges, based on insulation characteristics of CO2 gas gaps. Furthermore, the method was applied to typical field overvoltage waveform in the lightning surge time region for 500‐kV systems and it is obtained that the equivalent peak value of the standard lightning impulse waveform is possibly reduced by 10 to 15%. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(3): 1– 9, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20560

Conditioning of Series Vacuum Interrupters (VIs) for Medium Voltage by Applying High-Frequency (HF) Current to Increase the Dielectric Strength of VIs

According to well-known standards, e.g., IEC 62271-100, vacuum circuit breakers and particularly vacuum interrupters (VIs) have to fulfill miscellaneous forms of dielectric strength requirements depending on the rated voltage. Besides conventional conditioning methods, e.g., with alternating current, further techniques have to be investigated in the case of higher voltage levels. This paper describes the high-frequency (HF) current conditioning method with the objective to increase the dielectric strength of modern and very compact VIs for medium voltage applications. A test setup for conditioning of VIs in kilohertz range is presented. The conditioning current has peak values up to 10 kA, with durations of microseconds and voltages up to 135 kV (peak). The dielectric properties of the investigated VIs are described with emphasis on the obtainable lightning impulse withstand voltage level after one or more HF sequences. In addition, the surface microtopography and roughness of contact surfaces are analyzed by means of scanning electron and atomic force microscopy before and after applying HF conditioning.

CO<sub>2</sub>ガスの非標準雷インパルス振動波形に対する絶縁特性（その1）

Since SF6 gas was identified as a greenhouse gas at COP3 in 1997, alternative insulation gases to SF6 have been investigated. The CO2 gas insulation is one of the candidates, which is a natural gas and has lower global warming potential (GWP). However, CO2 gas has a lower withstand voltage level than SF6; therefore, it is important to rationalize the equipment insulation level and reduce the test voltage of electric power equipment as low as possible. The actual lightning surge waveform (called non-standard lightning impulse waveform) in actual substations is different from the standard lightning impulse waveform (1.2/50μs). The actual lightning surge waveform generally rises steeply, however, the decay of the overvoltage is large, and the insulation requirements are not as severe as those of the standard lightning impulse waveform.This paper describes the insulation characteristics of CO2 gas for single-frequency oscillatory waveforms with various frequencies from 1.3 to 4.0MHz and damping ratios. From experimental investigation, similarly to SF6, it might be possible to reduce the test voltage of CO2 gas insulation system by evaluating actual lightning surge waveform in terms of the equivalent standard lightning impulse waveform.

Substation outage rate prediction method based on lightning characteristics

AbstractA unique method of predicting lightning outage rates for substations, taking into account statistics‐based lightning characteristics, has been developed. The proposed method features the application of a combination of two processes: a high‐accuracy lightning surge analysis applying the electromagnetic transient program (EMTP) and a statistical data analysis using a general‐purpose spreadsheet software. By employing an original tool applying the proposed prediction method, which is installed in a personal computer, an optimal lightning protection for substations can be designed. In this paper, several analysis models are proposed for lightning characteristics including lightning surge. The validity of the proposed method was confirmed by comparing the transmission line outage rates derived by the models with the outage data gained during actual observations. It was found that the predicted lightning outage rates for 500‐kV substations were relatively low, and this finding revealed that it is possible to decrease the impulse withstand voltage level (LIWV). © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 64–75, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10300

Substation Outage Rate Prediction Method Based on Lightning Characteristics.

A unique method of predicting lightning outage rates for substations, taking into account statistics-based lightning characteristics, has been developed. The proposed method features the application of a combination of two processes: a high-accuracy lightning surge analysis applying the electromagnetic transient program (EMTP) and a statistical data analysis using a general-purpose spreadsheet software. By employing an original tool applying the proposed prediction method, which is installed in a personal computer, an optimal lightning protection for substations can be designed. In this paper, several analysis models are proposed for lightning characteristics including lightning surge. The validity of the proposed method was confirmed by comparing the transmission line outage rates derived by the models with the outage data gained during actual observations. It was found that the predicted lightning outage rates for 500-kV substations were relatively low, and this finding revealed that it is possible to decrease the impulse withstand voltage level (LIWV). © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 64–75, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10300

Influence of Radius of Curvature, Contact Angle and Material of Solid Insulator on the Electric Field in Vacuum (and Gaseous) Gaps

The insulation strength of a vacuum gap bridged by a solid insulator is lower than that in the absence of the solid insulator. The triple junction formed by the solid insulator, electrode, and vacuum in vacuum devices (or a gas in high-pressure apparatus) has a critical influence on the withstand voltage level of the insulating gap. The electric field is calculated using the charge simulation technique at the triple junction as a function of the junction geometry. The dependence of the field is studied for a varying contact angle a between the solid insulator and the electrode in the range 0 to 90°, for a varying ratio r/D of the radius of curvature r of the rounded edge of the solid insulator at the junction to the length of the insulator D, at a fixed r/D and varying r and D and for different practical insulator materials having relative dielectric permittivities ε£ in the range 2.1 to 12000. It has been found that the electrical field at the electrode-solid insulatorvacuum junction has a strong dependence on both the contact angle and the solid insulator material. The tangential and normal components of the electric fields are determined at the solid insulator-vacuum boundary and away from the boundary both inside the solid insulator and in the vacuum. Large enhancements in the electric field at the triple junction are found. The effects of the parameters α, r, and εr on the with-stand voltage of the insulating gap are discussed.

Safety Aspects of Live-Line Work Methods

Extensive switching surge tests on various live-line tool configurations for 230-and 500-kV lines have been carried out by Ontario Hydro using undamaged and punctured insulator strings. Also, protective gaps have been developed for 230-and 500-kV live-line work methods. Test procedures are described and withstand voltage levels for the various tool configurations are given.

A Proposed Test Specification for HVDC Thyristor Valves

This paper presents a proposal for a test specification for HVDC thyristor valves. The test specifiation includes a discussion of the criteria for successful type testing, a proposal for selection of test withstand voltage levels and a description of proposed dielectric and operational tests. The dielectric tests are intended to verify the withstand and other voltage-related characteristics of the valve and the operational tests are intended to demonstrate the correct operation and capabilities of the valve under various operating conditions including critical faults. The test series consist of type tests and production sample tests performed at the manufacturer's test facilities prior to shipment. Manufacturer's equipment development tests, routine factory tests, commissioning tests and other site tests are not within the scope of the test specification, and hence are not included.

Particularities of air insulation behavior

In actual practice the withstand voltage level of air insulation is estimated by an extrapolation based on the 50% breakdown voltage, U 50% , and the standard deviation, σ both obtained by laboratory tests. For this extrapolation to be possible it is assumed that the breakdown probability follows a gaussian distribution. It is observed however that in many cases this distribution deviates appreciably from a normal. Unexpected inconsistencies of the breakdown probability are also observed. This particular behavior of air insulation is studied in the present report and a physical explanation is attempted.