Overvoltage Protection Research Articles

Terrestrial Microwave Power Beaming

This paper establishes the practicality of terrestrial microwave power beaming at distances >1 km. To beam microwave power along the surface of the earth, it is necessary to consider and, where possible, exploit the effects of microwave propagation across terrain. Key design considerations include the effect of scattering from surface topography, approaches for characterizing the beam in the presence of multipath, safety, and efficiency. A rapid demonstration at the US Army Research Field in Blossom Point, MD, delivers 1.6 kW of electrical power at a 1046 m standoff from a 5.4-m-diameter X band transmitter. The transmitter is a reflector antenna with a linearly actuated feed horn that can focus the power density at specific standoff distances. Experimental results over cluttered, irregular terrain achieve a 2.3 dB (70%) enhancement in power density at the target site by deliberate exploitation of a ground bounce. A 4 m² rectenna receiver produces the 1.6 kW of output power at a 73% RF-to-DC conversion efficiency, which exceeds the current state of the art at X band. In addition, a test to destruction of 4 large rectenna arrays demonstrates how overvoltage protection circuits can improve the RF power handling of rectenna arrays by >1 dB. A final experiment demonstrates >1 kW delivered at >1 km distance to a light display. Since these results should readily scale to higher levels of power and performance, recommendations are provided to mature the technology for operational use.

Naprezanja izolacije elektroenergetske opreme pri nestandardnim talasnim oblicima prenapona

During its operation, electrical equipment is constantly exposed to overvoltages of various waveforms, such as lightning discharges, switching operations, faults, etc. Therefore, adequate selection of overvoltage protection and equipment insulation withstand voltages are key factors in increasing system reliability. In general, insulation coordination is carried out by analyzing the insulation behavior for standard impulse and switching overvoltage waveforms. However, overvoltages that occur in operating conditions can significantly deviate from the standard waveforms of insulation withstand voltages, in terms of the front time, the duration of the wave, the existence of highfrequency components as result of reflections in the facility and other factors. This paper presents possible methods of assessing the behavior of equipment insulation for real voltage waves to which the insulation is exposed during exploitation and which deviate from standard waveforms, by analysis in the frequency domain. As there are different components in the overvoltage signal at different frequencies, which a different energy, the main goal of this paper is to analyze the insulation characteristics of a specific transformer from the point of view of the energy spectral density of the voltage wave that occurs at its terminals when an atmospheric discharge occurs. The analysis is based on the determination of the safety margin on the entire frequency spectrum of the overvoltage wave, that is, on the calculation of the so-called FDSF (Frequency Domain Severity Factor). The calculation results show that although the overvoltage amplitude is lower than the withstand voltage of the transformer insulation with an appropriate safety margin (the condition of the classic approach to insulation coordination is satisfied), the spectrum analysis of the voltage wave in the frequency domain shows that the insulation may still be compromised.

Influence of radiation on the stability of electrical filters characteristics as components for overvoltage protection

The paper represents the results of testing the effect of neutron and gamma radiation of radioactive 60Co on electrical filters. Neutron and gamma radiation was chosen because of its conductivity. The analysis of the standard structure of the electric filter found that neutron and gamma radiation can affect the value of the capacitance as the most important component of the filter. The presented results are a contribution to the wider research of the radiation resistance of elements for the coordination of insulation at the low-voltage level. The experiments were performed on commercial capacitors that are installed in electric filters. Measurements were made with professional equipment under well-controlled laboratory conditions. The combined measurement uncertainty of the experimental procedure was less than 5%.

Influence of Ca-doping on the nonlinear properties of novel ZnO-Cr2O3-based varistor ceramics

The influence of Ca-doping on the microstructure development and electrical characteristics was studied in the novel, ZnO-Cr2O3-based, varistor ceramics with the nominal composition (99.47-x) mol% ZnO + 0.1 mol% Cr2O3 + 0.33 mol% Co3O4 + 0.1 mol% La2O3 + x mol% CaCO3, with x ranging from 0 to 6, sintered at 1200 °C. The results showed that, within the limits of the solid solubility of CaO in ZnO, the addition of CaO greatly enhanced the diffusion processes and hence the grain growth, thus broaden the range of breakdown voltages. Moreover, the Ca-doping simultaneously increases the height of the electrostatic Schottky barrier, resulting in a higher nonlinear coefficient of 40 and a lower leakage current of 2.8 μA/cm2. The results are important for the potential application of these novel ZnO-Cr2O3-based varistors, having different nominal voltages and yet suitable dimensions, in overvoltage protection across a broad range of voltages.

A Multi-Output Multi-String High-Efficiency WLED Driver Using 40 nm CMOS Technology

In this work, a multi-independent-output, multi-string, high-efficiency, boost-converter-based white LED (WLED) driver architecture is proposed. It utilizes a single inductor main switch with a common maximum duty cycle controller (MDCC) in the feedback loop. A simple pulse skipping controller (PSC) is utilized in each high-side switch of the multiple independent outputs. Despite the presence of multiple independent outputs, a single over-voltage protection (OVP) circuit is used at the output to protect the circuit from any voltage above 27 V. An open circuit in any of the strings is addressed, in addition to the LED’s short-circuit conditions. Excellent current matching between strings is achieved, despite the low ON-resistance (Rdson) of transistors used in the 40 nm process. Most circuits are designed in digital CMOS logic to overcome the extreme process variations in the 40 nm node. Compared to a single output parallel strings topology, a 50% improvement in efficiency is achieved relative to extremely unbalanced strings. Three strings are used in this proposal, but more strings can be supported with the same topology. Each string is driven by a 25 mA current sink. An input voltage of 3.2–4.2 V and an output voltage up to 27 V are supported.

Development of a Smart Supercapacitor Energy Storage System for Aircraft Electric Power Systems

This paper presents the development of a supercapacitor energy storage system (ESS) aimed to minimize weight, which is very important for aerospace applications, whilst integrating smart functionalities like voltage monitoring, equalization, and overvoltage protection for the cells. The methodology for selecting the supercapacitor cells type/size is detailed to achieve the safest and most energy-dense ESS. Additionally, the development of the interface electronics for cells’ voltage monitoring and overvoltage protection is presented. The proposed design implements a modular distributed architecture coordinated using communication buses to minimize the wirings and associated complexity and to enable system reconfiguration and expansions, as well as fault diagnoses. Validating the proposed ESS functionalities has been done via experimental testing and the results are presented and discussed.

Two-Feedback Loop Shunt Regulator Based on PWM RF Power Detector Aiming RFID Applications

The paper presents a novel shunt voltage regulation architecture that uses an RF power detector, based on Pulse Width Modulation (PWM) technique, aiming at magnetic coupled Radio-Frequency Identification (RFID) transponders. The proposed regulator architecture implements two feedback loops: a voltage clamping circuit that composes a fast correction loop and a slow but accurate power detector loop. The first clamping loop guarantees fast over-voltage protection, mainly in high RF power condition (short reading distance), but degrades power efficiency when in low power condition (large reading distance). The second loop corrects the imprecision of the first loop according to the detected RF input power. Therefore, it increases power efficiency and reading distance when in low RF power condition. The RF power detector architecture, based on a PWM technique, and the shunt regulator design are presented and discussed in detail. RFID power regulation issues are also discussed, followed by a brief review of RF power detector circuits. The complete regulator architecture was implemented in a 180nm CMOS low cost process and prototyped as part of a commercial low-frequency (134 kHz) RFID transponder. The complete transponder area is 870 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 870 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}^{2}$ </tex-math></inline-formula> , being 130 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 230 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}^{2}$ </tex-math></inline-formula> related to the regulator circuit only. Both resonant and supply capacitors are implemented on chip. The analog and digital functional blocks of the RFID system consume 4.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> . Performance of the transponder is measured with the shunt regulator enabled and compared with the power limiting approach using only clamping diodes. Measured results show an improvement of 16.7% in the maximum communication distance between the transponder and the reader because of the proposed regulation strategy.

Transient DC Over-Voltage Protection for ITER PF AC/DC Converter

The International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) AC/DC converters are composed by thyristor-based phase controlled converter modules. As the core component of ITER PF AC/DC converter, the thyristor is very sensitive to over-voltage and damaged in microseconds, therefore, the transient over-voltage protection strategy is desperately essential to ensure the converter safety operation. In this paper, a nanosecond respond and high reliability protection strategy which combined by Metal Oxide Varistor (MOV) and external bypass is proposed to protect the ITER PF AC/DC converter from transient DC over-voltage. The MOV is designed to certify the fast respond in nanosecond. Moreover, a bidirectional BreakOver Diode (BOD) circuit board is designed to activate external bypass to ensure the reliability of the transient DC over-voltage protection strategy. The performance-testing platform is built to study its performance. The experiments on ITER PF AC/DC converter test facility are carried out. According to the experiment results, the external bypass is triggered by BOD board effectively and the load current is transferred to the external bypass in 2 us when BOD suffers from an over-voltage. The effectiveness of the proposed transient DC over-voltage protection strategy is verified.

Silicate conductive composites with graphite-based fillers

Electroconductive composites are modern materials that are commonly used in many industries such as construction industry and machine-building industry. For example, these materials can be useful as sensors for monitoring changes in constructions, shielding stray currents from electrification networks, shielding electromagnetic radiation in operating rooms, cathodic protection against moisture or overvoltage protection of buildings. The topic of this post is the research of electrically conductive silicate composites with graphite-based fillers. In this research will be tested composites with different ratio and types of graphite and monitor their electroconductive properties like impedance, and physical-mechanical properties like compressive and tensile strength. The post describes basic properties and interactions of silicate electrically conductive composites with graphite fillers. It was found that by adding 10 % wt. graphite into silicate composites, impedance is reduced by 50% and compressive strength by 40%. The flexural tensile strength depends mainly on the roughness of the particles, where the coarser flaky particles transfer the load better and increase the strength while very fine graphites reduce the flexural tensile strength. Furthermore, it has been found that very finely ground synthetic graphites are most suitable for achieving low impedance of composites.

The Fast Overvoltage Protection Consideration and Design for SiC-Based Matrix Converters

AbstractMatrix converters feature low switching loss, small electromagnetic interference filter, and potential for achieving high power density. With the employment of wide-bandgap devices, such as silicon carbide devices, the converter performance can be further improved. For a safe operation of matrix converters, an overvoltage protection circuit is necessary to limit the voltage stress of the devices during fault conditions. Due to the high switching speed of silicon carbide devices, the topology and layout design of the overvoltage protection circuit is critical to ensure fast and robust protection for the devices. In this paper, a detachable overvoltage protection circuit was designed for each phase-leg of the matrix converter. The topology and hardware layout design are elaborated. A 15 kW full silicon-carbide implemented matrix converter was built and the designed overvoltage protection circuits were employed and tested.

Evaluation of the Influence of Lightning Overvoltage Propagation on Wind Turbine and “Mix” Overhead-Cable Lines

Due to the growing demand for new and renewable energies and a favorable geographical position, Vietnam is constructing many wind farms. Besides the advantages of being environmentally friendly and the primary endless source of materials, wind farms have disadvantages, for example, high-structured wind towers are usually built in high, empty places and the resistivity of large soil is vulnerable to lightning damage. In this research, we investigate the effects of overvoltage due to lightning strikes on the wings of wind turbines and propagation causing overvoltage on the insulation of cable in the control cable and mixed-lines. The paper also considers the overvoltage protection measures propagated into the insulation equipment and cable insulation using EMTP-RV simulation software

A Novel Voltage Clamping-Based Overvoltage Protection Strategy to Avoid Spurious Trip of Inverter-Based Resources and Eliminate the Risk of Wildfire Following the REFCL Operation in Compensated Networks

This article investigates the operational performance of the rapid earth fault current limiter (REFCL) that has been employed in Australia to reduce the risk of wildfires and shows that after the REFCL activation, an overvoltage is imposed on the grid which can lead to wildfire by creating a cross-country fault. Moreover, by increasing the penetration level of the inverter-based resources (IBRs), the potential inverter trip on transient overvoltage can become a vital issue. Since the protection functions of the IBRs are very sensitive to any transient overvoltage, their overvoltage or dc reverse current protection functions will trip the IBRs immediately following any overvoltage condition such as those caused during the REFCL operation. To tackle the mentioned problems, a novel voltage clamping-based overvoltage protection strategy is proposed and developed through a smart power electronic topology. The article presents the analytical analysis and the mode of operation of the proposed overvoltage protection strategy. The effectiveness of the proposed overvoltage protection strategy is tested through a comprehensive set of simulation studies in Power System Computer-Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC). The simulation results show that the proposed strategy can immediately limit the magnitude of the overvoltage, thereby it can not only reduce the risk of cross-country faults and wildfires but it can also mitigate the spurious trips of the IBRs.

Novel Ultrahigh-Performance ZnO-Based Varistor Ceramics.

The nonlinear response of a material to an external stimulus is vital in fundamental science and technical applications. The power-law current–voltage relationship of a varistor is one such example. An excellent example of such behavior is the power-law current–voltage relationship exhibited by Bi2O3-doped ZnO varistor ceramics, which are the cornerstone of commercial varistor materials for overvoltage protection. Here, we report on a sustainable, ZnO-based varistor ceramic, without the volatile Bi2O3, that is based on Cr2O3 as the varistor former and oxides of Ca, Co, and Sb as the performance enhancers. The material has an ultrahigh α of up to 219, a low IL of less than 0.2 μA/cm2, and a high Eb of up to 925 V/mm, making it superior to state-of-the-art varistor ceramics. The results provide insights into the design of materials with specific characteristics by tailoring states at the grain boundaries. The discovery of this ZnO-Cr2O3-type varistor ceramic represents a major breakthrough in the field of varistors for overvoltage protection and could drastically affect the world market for overvoltage protection.

Research on measures suppressing high frequency transient overvoltage in offshore wind farms

A large number of different types of cables, wind turbines, transformers and vacuum circuit breakers (VCBs) are used in power collecting system of offshore wind farms (OWFs). Due to the phenomenon of traveling wave refraction and reflection in cable collector system, transient overvoltage with high amplitude and high steepness will be generated when reignition phenomenon occurs in frequent operation of vacuum circuit breakers on wind turbines, which will cause serious damage to transformers, the problem of overcurrent is also becoming more and more serious. Therefore, through the electromagnetic transient simulation software of ATP-EMTP, a single-phase model of VCB switching-off transformer in offshore wind farm is built to study the influence of the separation speed of contacts of vacuum circuit breaker, high-frequency arc quenching capability and arching time on overvoltage. Then, the medium voltage cable collector system of OWF is built. Installing ferrite ring near the VCB or on the high-voltage side of transformer can suppress high frequency transient overvoltage. The results show that the high frequency transient overvoltage generated by offshore wind farm can be well suppressed after the installation of overvoltage protection device.

Design of SMPS Buck Converter with Protection Circuits for Automotive Charger

The automotive manufacturers are working towards enhancing sophisticated designs and technologies that enable better vehicle-user connectivity by integrating all the control units to one infotainment system. This key feature with high-level intelligence and competency plays an important role with an increase in demand in the production process of the automotive industry. This paper proposes a unique design of USB smart charger module that is designed in a way to fit into limited space in a front panel of the vehicle. The specific design methodology of the DC-DC SMPS buck converter with the protection circuits which serves as the important section of the smart charger is explained. The module is designed with both single and double port that are identical to each other. Each of these models provides effective connectivity of devices in the vehicle network with secured over-current, over-voltage and short circuit protection circuitry. The configuration of controllers and connectors used is implemented in Altium. The functionality of the system designed is examined and verified in TINA-TI tool.

OVERVOLTAGE PROTECTION OF PV MICROINSTALLATIONS – REGULATORY REQUIREMENTS AND SIMULATION MODEL

In low-voltage power networks with a large share of distributed energy sources, the phenomenon of overvoltage is increasingly observed. Although it may be desirable to raise the voltage value downstream of the network, in some cases the upper allowable voltage limit is exceeded. The method of eliminating voltage rises commonly used in the Polish power system is the installation of overvoltage protections, disconnecting the source from the grid. Such action reduces the profitability of prosumer installations, discouraging future potential investors. It turns out, however, that this is not the only disadvantage of such a solution. Sudden and uncoordinated disconnections and reconnections of more energy sources cause abrupt voltage changes that negatively affect the voltage conditions in the network. The aim of the paper is to present the operating algorithms of a standard overvoltage relay used in inverters of photovoltaic microinstallations. These algorithms – described in standards and national regulations – were tested in a typical inverter used in public low-voltage networks and implemented in the created simulation model of the relay. The described tests will be used for further work to demonstrate the need to coordinate the operation of overvoltage protections or replace them with other measures to improve voltage conditions in the grid with high share of photovoltaic sources.

Review of Technical Design and Safety Requirements for Vehicle Chargers and Their Infrastructure According to National Swedish and Harmonized European Standards

Battery electric vehicles demand a wide variety of charging networks, such as charging stations and wallboxes, to be set up in the future. The high charging power (typically in the range of a couple of kW up to a couple of hundred kW) and the possibly long duration of the charging process (up to more than 24 h) put some special requirements on the electrical infrastructure of charging stations, sockets, and plugs. This paper gives an overview of the technical design requirements and considerations for vehicle charging stations, sockets, and plugs, including their infrastructure, according to the Swedish Standard 4364000, “Low-voltage electrical installations—Rules for design and erection of electrical installations”, and the corresponding harmonized European standards. In detail, the four internationally categorized charging modes are explained and the preferable charging plugs, including their two-bus communication, according to European Directives are shown. The dimensioning of the supply lines and the proper selection of the overcurrent protection device, the insulation monitor, and the residual current device are described. Furthermore, a comprehensive overview of the required safety measures, such as the application of an isolation transformer or the implementation of an overvoltage protection mechanism, and the limits for conducted electromagnetic emissions, such as low-frequency harmonics or high-frequency (150 kHz to 108 MHz) emissions, are given.

STATCOM integration into a DFIG-based wind park for reactive power compensation and its impact on wind park high voltage ride-through capability

This paper presents static synchronous compensator (STATCOM) integration into a doubly-fed induction generator (DFIG) based wind park (WP), analyses the impact of STATCOM on the WP high voltage ride-through (HVRT) capability, and proposes a transient function for the STATCOM to improve the WP HVRT capability. An actual WP is adopted as a test system. The STATCOM size is selected considering the grid code requirement for power factor control, and various wind turbine (WT) and medium voltage (MV) feeder outage scenarios. The WP HVRT capability is assessed with electromagnetic transient (EMT) simulations by analyzing the responses to a parametric voltage waveform. The external system is represented by a Thevenin equivalent. The pre-described voltage waveforms are applied to the Thevenin source in order to assess the conformity of the HVRT capability to Hydro-Quebec specifications. The WP simulation model includes all details regarding collector grid and overvoltage protection. The simulation results demonstrate that, STATCOM usage provides a noticeable improvement in HVRT capability of the WP, especially with the proposed transient function.

Lightning Impulse Overvoltage Propagation in HVDC Meshed Grid

This paper reports on the propagation of lightning overvoltage in a high-voltage direct current (HVDC) meshed grid. Since several topologies of meshed grids have been elaborated in the last decade, we used a common comprehensive reference test platform. The lightning impulse propagation was investigated with regard to the impact of surge arresters and the polarity of the lightning stroke concerning the DC line polarity (±500 kV). Various scenarios were considered, including a direct lightning strike to the DC+ conductor, to the tower, and to the shielding wire in the middle of the span, including backflash on the insulators. The influence of tower footing impedance on overvoltage levels at various nodes was assessed, depicting the critical value. A description of the models used in the simulations was provided. The main focus of the paper was on the wide-area propagation of the overvoltages in the meshed grid, at distant terminals and inside the feeders. An interesting observation was the effects of lightning at the far end of the analyzed grid, propagating through multiterminal and long-distance connections. The presented analysis, based on an exemplary meshed HVDC grid, underlines the importance of the insulation coordination studies and system security studies with respect to the localization of overvoltage protection systems.

Study of the Lightning Overvoltage Protection Effectiveness of High Voltage Mixed Overhead Cable Power Lines

In this paper, the effectiveness of lightning overvoltage protection of cables in high voltage overhead cable lines has been analyzed. Because of the high overvoltage level, the cables are protected by surge arresters and by metallic sheath earthing. However, in practice, quite a lot of cases of electricity-evoked damage to the cable outer sheaths are observed, proving that the effectiveness of the protection used is insufficient. As a result, the cables are exposed to environmental factors, especially moisture penetration, which contributes to cable degradation. To explain the causes of this situation, simulation studies were carried out to determine the relevant factors affecting the level of expected overvoltages. The circuit-field model of the overhead cable line in EMTP-ATP, COMSOL and MATLAB software was used for determining overvoltages on the main cable insulation and the outer protective sheath. The studies reveal that the efficiency of the cable insulation overvoltage protection is ensured regardless of the lightning strike location and the crest value of its current. However, the obtained results confirm that no matter the applied protection, the cable outer sheaths may be exposed to overvoltages with higher values than those of the main insulation. Although the analysis was performed for 110 kV lines, the conclusions are general and are also applicable to power lines with higher rated voltages.