Varistor Research Articles

A novel design of energy absorption branch for HVDC circuit breakers

Metal oxide varistors (MOV) used for energy absorption branch in DC circuit breakers are complex enough to meet the requirements for small volume, light weight, and reliability in future high-voltage direct current (HVDC) grids. Therefore, a new energy absorption branch circuit that combines MOV and a liquid metal alloy energy absorber (LMEA) is proposed. Based on the constructed equivalent mathematical model of LMEA, the working principle and energy absorption process of MOV and LMEA in DC breaking process are analysed in PSCAD/EMTDC simulation software. Results demonstrate that LMEA, in contrast to MOV alone, absorbs 2.12 MJ of energy, constituting 35.6% of the total energy. Moreover, LMEA enhances energy dissipation density while reducing volume. Experimental analysis reveals MOV’s energy absorption mechanism via achieving residual voltage with ZnO varistor’s non-linear properties, swiftly transitioning from high to low resistance states to absorb energy. Conversely, LMEA relies on pulse current amplitude to initiate internal arcing, sharply increasing internal resistance for effective energy absorption. Experimental findings validate LMEA’s contribution of one-third of total energy absorption when pulse current amplitude reaches critical arcing threshold, consistent with simulation results. The results provide theoretical support for the engineering application of the new liquid metal alloy energy absorption in DC circuit breakers.

A Cost-Effective Current-Limiting Hybrid DC Circuit Breaker Based on Hybrid Semiconductors

DC circuit breakers (DCCBs) are the key equipment to rapidly interrupt the fault current in high-voltage DC power grids and ensure the safe operation of the system. However, most DCCBs do not take current-limiting measures and rely solely on current-limiting reactors in the system to limit the rate of current rise during the interruption process. The extensive use of fully controlled power electronic devices in circuit breakers (CBs) results in high costs. To address the issues above, this paper proposes a DCCB topology with a current-limiting function based on thyristors and diodes, which can reduce the cost of CB while ensuring reliable interruption. The impact of various parameters on CB performance is analyzed using numerical calculations to optimize the parameters. Then, a simulation model of a 500 kV/16 kA DCCB is built in PSCAD/EMTDC, and the performance of the proposed CB topology is compared with the other CB topologies. By comparison, the proposed DCCB topology can reliably isolate fault currents and reduce the amplitude of fault currents and the cost of CBs. Significantly, the energy absorbed by the metal oxide varistor (MOV) during the interruption process decreases by 64.2%, reducing the cost and volume of the MOV. Finally, the feasibility of the CB is further verified in the ±500 kV 4-terminal high-voltage DC power grid simulation model. The results show that the proposed DCCB topology can limit the fault current rise rate, interrupt and isolate the fault reliably, and reduce the cost.

Power frequency shunting property of whole group 500kV UHV Series compensated MOVs containing 10 Served and 1 New MOVs

Metal OxideVaristors(MOV) are widely used as protective devices of series compensation capacitor banks for Extra-High Voltage and UHV (Ultra High Voltage) large capacity long-distance transmission lines. As MOVs work in the strong nonlinear part of the V-I curve, the aging and deterioration degree of different MOVs in parallel connection are different, leading to one or two MOVs in the entire heavy-duty group being the first to be damaged. The uniformity of current is an important criterion for how to control the power frequency shunting of multiple parallel MOVs for series compensation capacitor banks. In order to investigate whether replacing damaged MOVs with newly manufactured MOVs of the same specifications can meet the uniformity requirements, the power frequency reclosure tests are carried out with an average voltage peak of 166.3 kV on MOV group with 10 served and 1 new MOV for the first time with actual 500 kV MOVs. Research finds that when the DC (Direct Current) U2mA mean absolute error of MOVs is 0.2%, the current mean absolute error is about 6%. After testing, the temperature rise of each MOV ranges from 22.9 to 36.3 °C. The test results in this paper provide a direct data basis for confirming the criterion of DC reference voltage and shunt uniformity at large power frequency current on actual 500 kV series compensation MOVs apparatus.

مرحل حماية المسافة وتأثير MOV على مناطق المرحل بإستخدام الماتلاب

Transmission lines are an important part of the power system. Transmission lines are used to transmit power and are prone to many breakdowns. Therefore, protection relays are used to protect transmission lines. The purpose of the protection system is to isolate the faulty part from the healthy part, because large currents generated by faults may cause damage to electrical equipment. One of the protection relays is the distance relay and is mainly used in the transmission line. Sometimes these relays are used for backup protection. Distance relays to determine impedance need voltage and current. Transmission lines are usually protected by a distance protection relay. Distance relays are of the high-speed class and can provide transmission lines. Protection distance relays that use impedance measurements to determine the presence and location of faults, are "fooled" by a series capacitor mounted on the line, when the presence or absence of a capacitor in the fault circuit is not known in advance. This is because the capacitor cancels or compensates for some of the line inductance, so the relay may sense a fault in its first region when the fault is actually in the second or third region of the protection. Similarly, Zone one fault can be considered reverse faults. In fact, this can cause some costly operating errors. Series compensated lines are protected from overvoltage by metal-oxide-varistors (MOVs) connected in parallel with the capacitor bank. The nonlinear characteristics of MOV devices add complexity to fault analysis and distance protection operation. During faults, the impedance of the line is modified by an equivalent impedance of the parallel MOV/capacitor circuit. Worth noting is a method that determines the L and C string values of the font and the MOV effect at the time of the error. This is done by analyzing the synchronous and sub-synchronous content of the voltage and current signals separately which provides enough information to calculate the L and C series of the line. In this paper, the transmission line impedance Z, Z(f) as a function of frequency has been calculated and plotted by the sequence characteristics and the studied MOV effect on line protection and fault location. Proper operation of the distance protection relay is also shown, and its effect on relay regions. Keywords: Distance protection relay, transmission line, zones of relay, MOV.

Withstanding capability and aging mechanism of metal-oxide varistors under DC temporary overvoltage

With the development of low-voltage DC (LVDC) application scenarios, the application of Surge protective devices (SPDs) for the protection of LVDC systems from overvoltage requires urgent attention. Temporary overvoltage (TOV) withstanding capability is a critical parameter so that studying the withstanding capability and aging mechanism of metal-oxide varistor (MOV) which serves as the core component of SPD is significantly important. The numerical model of MOV is established in this paper to study the TOV performance in DC systems with different voltage levels. The 2D Voronoi network is employed to depict the microstructure of MOV. After validating the reliability of the microstructure model, the electrothermal characteristics and capability of the MOV to withstand TOV in LVDC systems at various voltage levels are investigated. The parameters for the DC TOV are obtained from the latest committee draft of IEC 61643-41. The aging mechanism based on double Schottky Barrier theory under DC TOV is discussed in detail, which can explain the initial rise followed by a subsequent decline in varistor voltage. The Voltage-Temperature-Time (V-T-t) curve of MOV is proposed for the first time which serves as a valuable theoretical reference for the development of overcurrent and overheat protection of DC SPD.

Snubber Branch Design and Development of Solid-State DC Circuit Breaker

This research proposes a solid-state DC circuit breaker for low voltage DC system based on reverse-blocking IGCT. The circuit breaker topology gets easier as a result of reverse-blocking IGCTs' ability to withstand reverse voltage. To further enhance the breaking process, we develop a snubber branch with metal oxide varistors (MOV) and capacitance. The advantages and disadvantages of three distinct snubber branches-the no-snubber, the resistance-capacitance (RC), and the MOV-C snubber branch-are then contrasted. In addition to suppressing high-frequency oscillation caught by the parasitic MOV parameters, the structure with MOV-C snubber branch also blocks low frequency harmonics brought on by RC snubber branch. Moreover, this structure can slow down the rate at which the voltage rises during the breaking process. Comparatively speaking to the RC snubber branch and no-snubber branch structures, it is more appropriate for solid-state DC circuit breakers. Finally, a solid-state DC circuit breaker prototype based on RB-IGCT and MOV-C branch has been created. The maximum overvoltage is 1.5kV, and the rated voltage is 750V. The maximum breaking current is 10kA, and the rated current can be 2kA.

Analysis of IGBT Pseudodesaturation Effect Caused by Stray Parameters in DC Circuit Breaker

As a highly integrated high-voltage power electronic equipment in the power grid, the DC circuit breaker (DCCB) has misjudged overcurrent protection caused by the IGBT pseudo desaturation effect (PDE) in DC short-circuit fault. To analyze the reasons for the effect, this paper established a wide-band equivalent circuit model of a hybrid high-voltage DCCB at the initial stage of DC fault. And revealed the mechanism of PDE: the stray inductance of series-connected solid-state switches, the junction capacitance of metal oxide varistors (MOVs), and the parasitic capacitance to the ground of DCCB form multiple resonant circuits. The external disturbance is converted into the interference of DCCB port through these stray parameters, and the interference would exceed the IGBT desaturation detection threshold. Furthermore, an equivalent experimental circuit that reproduces the electromagnetic interference of DCCB at the DC fault transient process was proposed, and the correctness of the mechanism analysis was verified by the scaled prototype of DCCB, the main resonance frequency error is less than 15%. Finally, the frequency domain and time domain characteristics of electromagnetic interference on the IGBT desaturation detection monitoring ports in 200kV DCCB at the initial stage of DC fault were analyzed. Based on these characteristics, a scheme of adding a delay time to the overcurrent protection criterion to avoid electromagnetic interference was proposed, which is adopted by an industrial project.

A Novel Methodology for Fault Sensing in Presence of Power Swing for Transmission Line with Thyristor Controlled Series Compensator

Digital distance relaying is implemented in extra high voltage (EHV) transmission network for speedy and reliable fault detection. But it should not activate in case of slow transients known as power swings. However, for occurrence of any type of fault during power swing, the relay should sense the faulty condition and send trip command to concerned circuit breaker. The detection of fault in a transmission line network with TCSC during the power swing condition has become further complex due to transients generated by series capacitor and the metal–oxide varistor (MOV) protecting it. This paper firstly presents effect of TCSC on distance relay operation for varied TCSC degree of compensation and firing angle values. Further, a discrete wavelet transform-based fast acting fault and swing classification algorithm is proposed which can sense all types of faults during slow as well as fast power swing in first decomposition level and within 0.001 sec. The proposed utilizes optimized threshold values both for swing and fault sensing by using Honey Bee Optimization Algorithm (HBOA). The proposed novel algorithm is coded in MATLAB software and the test system comprising of 400kV, 50Hz parallel transmission line network along with TCSC is built using MATLAB Simulink environment with sim power systems toolbox. It is tested for high/low resistance faults, symmetrical/asymmetrical faults and close-in/far end faults by changing TCSC compensation level and firing angle value. The simulation results prove the accuracy of proposed methodology for swing and fault classification.

DC Circuit Breaker Evolution, Design, and Analysis

While traditional AC mechanical circuit breakers can protect AC circuits, many other DC power distribution technologies, such as DC microgrids (MGs), yield superior disruption performance, e.g., faster and more reliable switching speeds. However, novel DC circuit breaker (DCCB) designs are challenging due to the need to quickly break high currents within milliseconds, caused by the high fault current rise in DC grids compared to AC grids. In DC grids, the circuit breaker must not provide any current crossing and must absorb surges, since the arc is not naturally extinguished by the system. Additionally, the DC breaker must mitigate the magnetic energy stored in the system inductance and withstand residual overvoltages after current interruption. These challenges require a fundamentally different topology for DCCBs, which are typically made using solid-state semiconductor technology, metal oxide varistors (MOVs), and ultra-fast switches. This study aims to provide a comprehensive review of the development, design, and performance of DCCBs and an analysis of internal topology, the energy absorption path, and subcircuits in solid-state (SS)-based DCCBs. The research explores various novel designs that introduce different structures for an energy dissipation solution. The classification of these designs is based on the fundamental principles of surge mitigation and a detailed analysis of the techniques employed in DCCBs. In addition, our framework offers an advantageous reference point for the future evolution of SS circuit breakers in numerous developing power delivery systems.

A multiport hybrid DC circuit breaker with high economic efficiency and adaptive reclosing capability

In a high voltage direct current (HVDC) grid, hybrid DC circuit breakers (HCBs) are one of the effective solutions to interrupt fault currents. The conventional two-port HCB features high economic costs since the expensive insulated gate bipolar transistors (IGBTs) are needed. Each line in the multiterminal HVDC grid must be equipped with the HCB, which is extremely costly to implement. In addition, the likelihood of temporary faults is considerably raised by the fact that the HVDC grid transfers power across overhead lines (OHLs). By reclosing operations after temporary faults, the HVDC grid can resume normal operation. However, it is vital to discern between temporary faults and permanent faults before reclosing operation to prevent secondary shocks to the HVDC grid caused by blindly reclosing on permanent faults. For the problems of high cost and blind reclosing of HCBs, this article proposes a multiport HCB (MHCB) with high economy and adaptive reclosing capability. All ports of the MHCB share a single main breaker (MB) for fault isolation. The MHCB utilizes the capacitor voltage to lower the operating voltage of the metal oxide varistor (MOV), which reduces the number of IGBTs connected together at both ends of the MOV. With the above design, the expense of the MHCB is significantly decreased. Additionally, the MHCB achieves adaptive reclosing by using the difference of current amplitudes in the capacitor branch under permanent and temporary faults.

A modified mutual impedance based backup protection for series-compensated transmission lines

This paper proposes a modified mutual impedance based backup protection for series-compensated transmission line. In case of failure of current-differential scheme, distance relaying scheme provides protection by calculating and comparing positive-sequence impedance up to fault point. However, non-linear operation of metal-oxide varistor (MOV) result in continuously varying equivalent impedance across series-capacitor during fault which affects the reach and directional discrimination feature. Inter-phase mutual impedance of line up to fault point is proportional to the distance of fault from relaying point and therefore can be exploited as a reliable relaying parameter for backup protection purpose. The reason is that the equivalent impedance across MOV protected series-capacitor does not alter inter-phase mutual impedance up to fault point. This mutual impedance can be computed utilizing sequence components of voltage and current phasors measured by phasor measurement unit (PMU) at line ends. Existing mutual impedance based scheme is highly influenced by fault resistance and synchronization error. The proposed modified algorithm is developed to overcome the effects of fault resistance and synchronization error as compared to previously developed scheme. The performance is assessed for different single line-to-ground (SLG) and double line-to-ground (LLG) fault cases with variations in fault resistance, fault distance (FD) and compensation level. Simulation results affirm the advantages of proposed scheme as an extra layer of protection over conventional schemes and prove superiority in performance over existing mutual impedance based scheme. Experimental results also demonstrate the feasibility of deployment for practical applications.

Application of Nonlinear Optimization for Fault Location in Transmission Lines with Series Compensation Protected by Varistors

This paper introduces a novel approach to fault localization in transmission lines with series compensation using nonlinear optimization. The objective function minimization provides information on the fault distance and the current at which the protective varistor starts conducting. Terminal source data, the maximum current capacity of the capacitor, and the operating curve of the metal oxide varistor protection element are not required. The proposed method successfully met the predefined objectives, with a maximum error of 1.13% in simulated scenarios. In validating the method using real cases from a Brazilian energy concessionaire, the errors were below 0.5%.

A Solid-State Circuit Breaker Without Current Limiting Inductor

This paper presents a high-density, high-efficiency megawatt (MW) medium-voltage (MV) solid-state circuit breaker (SSCB) for aviation hybrid electric propulsion applications. The proposed SSCB is based on the mature silicon (Si) insulated gate bipolar transistor (IGBT) devices. With reduced IGBT gate voltage, the proposed SSCB can limit the peak fault current without the fault current limiting inductor. Thus, the specific power density of the SSCB is substantially improved compared with the traditional design. This method has negligible impact on SSCB efficiency, reliability and energy absorbed by the metal-oxide varistor (MOV), while providing additional mechanical layout freedom for power density and insulation enhancement. The potential design challenges due to the extremely high ramp rate of the system fault current and the corresponding solutions are also discussed. The performance of the proposed SSCB is validated with experimental results.

Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review.

This article reviews the progress in developing ZnO-V2O5-based metal oxide varistors (MOVs) using powder metallurgy (PM) techniques. The aim is to create new, advanced ceramic materials for MOVs with comparable or superior functional properties to ZnO-Bi2O3 varistors using fewer dopants. The survey emphasizes the importance of a homogeneous microstructure and desirable varistor properties, such as high nonlinearity (α), low leakage current density (JL), high energy absorption capability, reduced power loss, and stability for reliable MOVs. This study investigates the effect of V2O5 and MO additives on the microstructure, electrical and dielectric properties, and aging behavior of ZnO-based varistors. The findings show that MOVs with 0.25-2 mol.% V2O5 and MO additives sintered in air over 800 °C contain a primary phase of ZnO with a hexagonal wurtzite structure and several secondary phases that impact the MOV performance. The MO additives, such as Bi2O3, In2O3, Sb2O3, transition element oxides, and rare earth oxides, act as ZnO grain growth inhibitors and enhance the density, microstructure homogeneity, and nonlinearity. Refinement of the microstructure of MOVs and consolidation under appropriate PM conditions improve their electrical properties (JL ≤ 0.2 mA/cm2, α of 22-153) and stability. The review recommends further developing and investigating large-sized MOVs from the ZnO-V2O5 systems using these techniques.

An intelligent protection scheme for series-compensated transmission lines connecting large-scale wind farms

Series-compensated transmission lines (SCTLs) are increasingly preferred for transmitting bulk amounts of electricity generated from the present-day large-scale wind farm to the utility grid due to several technical and economic benefits. However, when a fault occurs in such a wind farm-integrated SCTL, the impedance across the metal oxide varistor (MOV)-protected series capacitor varies non-linearly. Also, the fault current contributed from the wind farm side is quite different compared to the grid side. Consequently, the widely used fixed impedance-based distance relaying schemes showed limitations when used for protecting such crucial TLs. In this paper, the impacts of series compensation and wind farm integration on distance relay are investigated, and this paper proposes an intelligent relaying scheme using only the current measurements. In the proposed scheme, the fault detection task is performed using the signs of the half-cycle magnitude differences of the line end positive-sequence currents, and the fault classification task is performed using only the local current measurements processed through the Fourier–Bessel series expansion (FBSE) bagging ensemble (BE) classifier. The non-stationary components present in the current signal at the initiation of a fault are captured by calculating FBSE coefficients, and the singular value decomposition is applied for dimensionality reduction of the feature set. Finally, the extracted features are used by the BE classifier for fault classification. The method is evaluated in MATLAB/Simulink® on numerous fault and non-fault data simulated in two-bus systems and also validated through the OPAL-RT (OP4510) manufactured real-time digital simulation platform. The obtained results (response time for fault detection and classification <10 ms), including the comparative assessment results (fault detection accuracy =100% and fault classification accuracy =99.37%), justify the effectiveness of the proposed relaying scheme in protecting the wind farm-integrated SCTLs.

A failure detection method based on multivariate variational mode decomposition and skewness for modular DC circuit breakers

Modular DC circuit breakers (MDCCBs) are widely used to protect multi-terminal HVDC (MT-HVDC) girds. However, the metal-oxide varistor (MOV) failure detection of MDCCBs still poses a challenge for the reliability of MT-HVDC grids. To this end, this paper analyzes the faulty features of the MDCCB and proposes a failure detection method that uses a multivariate variational mode decomposition (MVMD) and a differential skewness. The proposed method is as follows. First, MVMD decomposes the differential current, which is obtained by the current of the MDCCB energy absorption branch, into its time–frequency components, and then the time–frequency component that has the highest frequency is selected as the feature component. Second, a differential skewness is constructed by the feature component, and the differential skewness is employed to detect the MOV failure of the MDCCB. Finally, the performance of the proposed method is evaluated by a four-terminal symmetric bipolar HVDC system with MDCCBs. The simulation experiment results show that the proposed method can correctly detect the MOV failures of the MDCCB in different faulty conditions, even in the weak failure condition with noise influence.

Wide Frequency Response of Varistors and Coordination With Transient Voltage Suppression Diodes

The voltage-current characteristic of metal-oxide varistors is experimentally investigated for a wide frequency range. Concave exponential and rectangular impulse currents that resemble lightning current field records are employed to investigate their energy coordination with transient voltage suppression diodes, commonly integrated into printed circuit boards to protect sensitive electronic components. Thus, the effective coordination is experimentally evaluated against high- and low-frequency surge events for components used in power, telecom, and automotive applications. Experimental results supported by ATP-EMTP simulations show that reliable coordination of conventional varistors with bidirectional diodes can be challenging; this finding reveals a risk for the uninterrupted operation and safety of equipment with built-in diodes. The satisfactory agreement of ATP-EMTP results with experimental data shows that electromagnetic transient simulations can be an effective tool for designing coordination circuits and evaluating the risk of failure in case of surge events and electromagnetic pulses.

A current-based algorithm for one-end fault location in series capacitor compensated double-circuit transmission lines

Fault location is essential in series capacitor compensated double-circuit transmission lines regarding their capacity in transferring large amounts of power. The main challenge in the fault location of these lines is the nonlinear behavior of the metal-oxide varistor (MOV) in protecting the series capacitor against overvoltage during faults. In this paper, considering the MOV model and zero-sequence mutual coupling impedance between the two circuits, a new algorithm is presented for the location of single-line-to-ground faults, using currents measured at one end of the line. In this algorithm, first, a fault location is obtained for each data window, and then the exact location is calculated using statistical techniques. The proposed algorithm is independent of the measured voltages, and as a result, no error in the voltage measurement affects its accuracy. In addition, needing no telecommunication channel to access the data of the remote substation leads to reliability increasing and cost reductions. Not requiring pre-fault data is another advantage of the algorithm. The results indicate that the algorithm is independent of fault location and resistance, fault occurrence time, load conditions, and compensation level. In addition, the fault location error in all scenarios is within the standard range.

Fast Y-Type Thyristor-Based DC SSCB Using Complementary Commutation in a Capacitor–Capacitor Pair Structure

This article proposes a new thyristor-based dc solid-state circuit breaker (SSCB) named Y-type. Main contributions focus on a new complementary commutation circuit including a capacitor–capacitor pair, which features three remarkable advantages. First, a fast commutation is achieved using a countercurrent pulse injection by the capacitor–capacitor pair structure. Second, metal-oxide varistors (MOVs) are disconnected from the power line when SSCB is <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> , which solves the reliability issue due to the MOV degradation and enhances the voltage utilization rate of the main switch. Third, benefiting from the capacitor–capacitor pair structure, reliable reclosing and rebreaking are obtained for practical applications. Experiments are conducted on a 400 V/120 A prototype to validate the proposed Y-SSCB. The peak voltage on the main and auxiliary thyristors reaches 773 and 400 V, respectively. Also, the peak voltage on the auxiliary capacitors pair reaches 740 and 400 V. The Y-SSCB achieves a fast reaction time of 80 μs in interrupting 120 A short-circuit fault current.

A High-Efficiency Protection Circuit Integrating Semi-Soft Switching and Voltage Limiting Functions for Solid-State Switch Applications

Despite the high performance of high-voltage direct current circuit breaker (CB) technology, its high cost restricts its further development. Thus, this article proposes a high-efficiency protection circuit for solid-state switches (SSs) that integrates semisoft switching and voltage limiting functions. The protection circuit also does not resonate with the system inductance which in turn does not affect the reclosing operation of the CB. The novel SS scheme reduces the cost and simplifies the layout of the SS. The special constraints for the parameter design of power electronics, gaps, and metal oxide varistors (MOVs) are proposed in this article for the first time, and a parameters design method that solves the transient power shock and voltage spike problems during the large current breaking process under multiple constraints is formed. Finally, an SS prototype is developed to verify the feasibility and the strong surge and turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ability of the novel SS and to test the robustness of the series-connected gapped-MOV circuits.