Surge Withstand Capability Research Articles

Insulation Coordination Design for Grid-Connected Solid-State Transformers

The deployment of solid-state transformers (SSTs) in medium-voltage (MV) distribution systems is facing various challenges, especially the challenge of insulation coordination design against grid-originated lightning impulses. In this article, two challenges in existing insulation coordination designs for grid-connected SSTs are identified. One challenge is the mismatch between metal-oxide varistor (MOV) protective levels and SST insulation strength, the other challenge is the incompatibility of standard impulse test on SST protective structures. To address the MOV selection challenge, a novel lightning protection scheme is designed to protect a single-stage SST where the semiconductor modules are directly exposed to external lightning impulses. The in-lab lightning impulse tests are performed to verify the overvoltage attenuation performance of the prototyped lightning protection scheme. To address the impulse test challenge, the surge withstand capability of the protected SST is comprehensively evaluated with a complete set of insulation coordination design procedures beyond the basic insulation level (BIL) test. After these two challenges are addressed, a discussion is presented on substituting conventional transformers with the protected SSTs into insulation-coordinated distribution systems to facilitate the field deployment of SSTs.

Novel multifunctional capacitor-varistor ceramics based on SnO2

Up to now, multifunctional varistor-capacitor materials were based on TiO2, even though these materials failed to have practical applications. For the first time, in this research, multifunctional varistor-capacitor properties are observed in the CuO-doped SnO2-CoO-Sb2O3 system. The XRD analysis showed that this system has a single phase microstructure. SEM images indicated that the CuO addition resulted in a better densification and larger grain size. The very low electric breakdown field of the CuO-doped SnO2-CoO-Sb2O3 system (12 V/mm, similar to TiO2), is a consequence of coarse-grained microstructure. This varistor had a suitable surge withstand capability as well. The colossal dielectric constant of about 4.5 * 104 was observed in CuO doped-SnO2 system. This immense constant dielectric can be explained by the internal barrier layer capacitor model. These results attest that the novel multifunctional varistor-capacitor materials based on SnO2 can be used in practical applications.

The effect of TiO2 addition on microstructure and electrical properties of SnO2 varistors prepared from nanomaterials

The effects of various amounts of TiO2 in the composition of SnO2-based varistors made from nano-sized materials on microstructure and electrical properties have been investigated. Titanium oxide acts as both a densifier and grain growth enhancer resulting in relative densities in the range of 96–99%. The addition of TiO2 from 0 to 3mol% has changed the average grain size from 1.8 to 5μm. The introduction of TiO2 causes precipitation of Ta2O2.2 phase on the sample surfaces. The lowest breakdown field, 2kV/cm, has been observed for the sample containing 0.75mol% of TiO2, and the best surge-withstand parameters (residual voltage ratio, 2.4, withstanding surge current density, 5kA/cm2) have been observed for the sample with 0.25mol% TiO2. Larger amounts of TiO2 have had an adverse effect on the surge-withstand capability due to the loss of homogeneity in the samples caused by tantalum transpiration.

Effect of Micro Structure of Bi2O3 Based ZnO Varistor for Long Term Ageing Performance

The Bi2O3 based ZnO varistors (MOVs) are used in surge arresters or surge protective devices (SPDs) as key components. As their performance, MOVs shall have I-V non ohmic characteristics, higher surge withstand capability and reliability for ageing: When AC power line voltage is applied to MOV, its leakage current or watt loss shall be decreased continuously.In order to maintain reliability for ageing, it is known that additional heat treatment after sintering process in MOV manufacturing flow is effective. The mechanism of the heat treatment effect was considered to be realized by a crystal structure change of the bismuth oxide as a main material which forms a grain boundary. However, in this study, it is found that watt loss behavior does not necessarily correspond to crystal structure of the bismuth oxide. Besides, from the fact that ZnO which dissolve in Bi2O3 liquid phase is compounded with other additives by heat treatment, precipitation of ZnO in Bi2O3 liquid phase by heat treatment can be considered as important factor.In addition, uniformity not only in grain boundary structure from a microscopic of view, but also of size and its distribution of the multiple points from a macroscopic of view is integrant in order to realize MOVs having lower watt loss and its stability.

Degradation behavior against surge stress of Zn–Pr–Co–Cr–Y–Er varistor ceramics modified with Er2O3

The degradation behavior against a surge-current in the ZPCCYE (ZnO–Pr6O11–CoO–Cr2O3–Y2O3–Er2O3) varistors was investigated for different amounts of Er2O3. The addition of Er2O3 has a significant effect on nonlinear electrical properties and surge degradation behavior of the ZPCCYE varistors. Increasing amount of Er2O3 improved the clamp characteristics, in which the clamping voltage (K) decreases at a surge-current of 1–40A. The varistors added with 0.5mol% Er2O3 exhibited the strongest electrical stability, with the variation rate of the breakdown field of −3.2%, the variation rate of the nonlinear coefficient of −20.9%, and the variation rate of the leakage current of −40.0% after applying 1000 times for a surge-current of 100A/cm2. Furthermore, the varistors added with 0.5mol% Er2O3 exhibited the good surge withstand capability with the variation rate of the breakdown field of −7.9% after applying the surge-current of 400A. On the contrary, the varistors added with 0.25mol% were destroyed after applying the surge-current of 400A and the varistors added with 1.0mol% were destroyed after applying 55 times for a surge-current of 100A/cm2.

Electrical behavior against current impulse in ZnO–Pr 6O 11-based varistor ceramics with terbium addition

Tb 4O 7 addition effect on electrical behavior against current impulse in the Zn–Pr–Co–Cr-based varistors was investigated. The Tb 4O 7 did have a significant effect on electrical behavior against current impulse. Increasing Tb 4O 7 content improved the clamp ratio ( K), reaching nearly 2 at 1.0 mol%. The best stability against current impulse of 100 A/cm 2 was obtained at 0.25 mol% Tb 4O 7, where % Δ E 1 mA/c m 2 = − 0.8 % and %Δ α = +1.1%. In addition, the varistor doped with 0.5 mol% Tb 4O 7 were no less stable against current impulse than varistor doped with 0.25 mol% Tb 4O 7. Furthermore, the varistor doped with 0.5 mol% Tb exhibited the best surge withstand capability at a current impulse of 900 A. Conclusively, Tb 4O 7 content was optimized at 0.5 mol% in terms of the nonlinearity and surge withstand capability.

Effect of aluminum doping on electrical and dielectric aging behavior against current impulse of ZPCCY-based varistors

The electrical and dielectric aging behavior against current impulse (5–1,200 A) in the Zn-Pr-Co-Cr-Y-based varistors was investigated with aluminum doping level (0–0.01 mol%). The varistors doped with 0–0.001 mol% Al were destroyed at higher current impulse beyond 900 A and the varistors doped with 0.005–0.01 mol% Al exhibited high stability against current impulse. The clamp ratio (K) at given current impulse ranges decreased with increasing Al doping level. The varistor doped with 0.01 mol% Al exhibited the lowest K value, with 1.65 at a current impulse of 10 A and 2.38 at a current impulse of 1,200 A. The best electrical and dielectric stability against current impulse of 1,200 A was obtained at 0.01 mol% Al, where $$\%\Updelta E_{1\;\text{mA/cm}^2} = -3.4\%$$ , %Δα = 0%, %ΔJ L = −26.3%, %Δe′APP = +3.4%, and %Δtanδ = −7.7%. Conclusively, Al doping level was optimized at 0.01 mol% in terms of the surge withstand capability (SWC).

Lightning and Surge Protection in Photovoltaic Installations

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The aim of this paper is to give scientific background and essential assumptions to be introduced into the design of lightning and surge protection in photovoltaic installations (PVIs), with particular emphasis on the aspects of standardization to be covered. For this purpose, the relevant protective measures given in the standards for conventional low-voltage power distribution systems (CLVPDSs) are adapted in part. This revision is required because the peculiar characteristics of PVIs are different from those of CLVPDSs. The resulting protection approach that determines the advisable protective measures by a risk management has been applied to an actual grid-connected PVI (GCPVI), Univer Project. The extra cost of this protection in this PVI (approximately 3.6% of the system cost) is of secondary importance because of the increase of safety and availability. Furthermore, in order to fulfill with this protection, the surge withstand capability (SWC) of PV modules has been investigated as well. </para>

Surge protection for interface circuits of communication system

Microelectronic circuits are often damaged by surges. Surge protection for microelectronic circuits has some special requirements that are different than those for electrical equipment. The approach that the surge invades microelectronic circuits is studied in this paper. The surge withstand capability of some typical serial communication integrated chips, the behaviors of voltage-limiting components, and the influence of the connecting capacitance of a voltage-clamping device on digital signals are studied. Then, a design method of surge suppressor for communication systems is proposed.

Surge Protection for Interface Circuits of Communication System

Microelectronic circuits are often damaged by surges. Surge protection for microelectronic circuits has some special requirements different from those for electrical equipment. The approach that the surge invades into microelectronic circuits is studied. The surge withstand capability of some typical serial communication integrate chips, the behaviors of voltage limiting components, and the influence of the connecting capacitance of voltage clamping device on digital signals are studied. A design method of surge suppressor for communication systems is proposed.

Multi-Frequency Surge Withstand Capability Tests for Protective Relays

The reliability of solid state protective relays in the hostile electromagnetic environment of high-voltage switchyards and substations has been improved by the use of surge withstand capability (SWC) tests. Ontario Hydro relay specifications call for a SWC test with a surge test wave having frequency, amplitude, and source impedance as variable and interdependent parameters. The need for a multi-frequency SWC test with a frequency range of 0.1 to 2 MHz is confirmed by field surveys of surge characteristics, data from actual SWC tests, and laboratory investigations of SWC frequency dependence. A simple, moderately-priced SWC tester capable of generating accurately defined test waves within the defined range of test wave parameters is described

Multi-Frequency Surge Withstand Capability Tests for Protective Relays

Multi-Frequency Surge Withstand Capability Tests for Protective Relays

The Apple Grove 750-kV Project- 500-kV Switching Surge and Line Flashover Tests

Rational design of extra-high-voltage systems depends on analytic studies to predict switching surge overvoltage magnitude and probability, and on laboratory tests for tower system switching surge withstand capability. Laboratory tests have been confined to ideal waveforms applied to single window configurations. Correlation with flashover performance of a typical 3-phase installation exposed to actual switching surge waveforms is attempted. The influence of interphase coupling and multiple circuit breaker operations in promoting multiphase flashover, which may curtail system performance margins, is also studied.