Analysis Of Overvoltages Research Articles

Analysis of Cable Overvoltages in Symmetrical Monopolar and Rigid Bipolar HVDC Configuration

The symmetrical monopolar configuration is the prevailing scheme configuration for high voltage direct current (HVDC) interconnectors utilizing the modular multilevel converter (MMC) topology. However, the rigid bipolar configuration is gaining significance, as first projects are currently in planning stage. The purpose of this paper is to analyse both HVDC scheme configurations with regard to cable voltage stresses originating from short-circuit faults. The study focuses on HVDC cables with extruded insulation connected to MMCs equipped with half-bridge (HB) submodules. Basic design aspects in rigid bipolar configuration such as the station grounding concept are discussed. Moreover, various station internal as well as dc faults are examined by means of electromagnetic transient (EMT) simulations. Occurring cable voltage stresses are analyzed with respect to voltage polarity, peak value and wave front-parameters and compared in symmetrical monopolar and rigid bipolar configuration. It is demonstrated that cable overvoltages with same polarity as the dc operating voltage are significantly reduced in schemes operating in rigid bipolar configuration. Voltage reversals caused by the discharge process during a cable fault are nearly independent of the selected scheme configuration. Obtained results are relevant with regard to upcoming projects in rigid bipolar configuration and provide insights to further refine insulation co-ordination aspects related to dc cable systems.

Statistical analysis of switching overvoltages in UHV transmission lines with a controlled switching

The objective of this work is to present a more precisely controlled switching strategy to reduce overvoltages due to ultra-high voltage (UHV) transmission line closing. Essentially the switching strategy is to find a suitable circuit breaker (CB) optimal instant of closing. The electric field variation in the arc-extinguish chamber has great effect on rate of decrease of dielectric strength (RDDS), when calculating optimal instant of closing with pre-breakdown between the contacts. The relative value k of a CB is defined as the ratio of RDDS to the rate of voltage approaching the zero cross. In this calculation, the electric field E should be as a variation due to the uneven medium of SF6. Consequently equations were derived from calculating the pre-breakdown instants. The ATP model of controlled closing UHV transmission line was built for switching overvoltage simulations considering RDDS and mechanical dispersion. The simulation results show that switching overvoltages are more accurate and closer to reality when regarding the electric field E as a variation. Contrarily, assuming E as a constant will increase the risk of failure via controlled switching. Furthermore, the simulation results demonstrate that k value can change the effect of the mechanical dispersion on switching overvoltages.

낙뢰 시 태양광발전소의 개별접지 및 통합접지에 따른 낙뢰 유도 과전압 비교 분석

낙뢰 시 태양광발전소의 개별접지 및 통합접지에 따른 낙뢰 유도 과전압 비교 분석

Sensitivity analysis of reignition overvoltage for vacuum circuit breaker in offshore wind farm using experiment-based modeling

This paper investigates the characteristics of reignition overvoltage of vacuum circuit breaker, and analyzes the influences of reignition overvoltage on a power collection grid in offshore wind farms. An offshore wind farm model, including an opening model of VCB, is developed based on a parameter fitting method in PSCAD/EMTDC, which is experimentally validated covering main offshore wind farm components. The established laboratory experiment setup comprises vacuum circuit breakers, cables, transformers and equivalent equipment of a wind turbine. The experiment reignition overvoltages and currents are recorded to analyze its transient behavior, contributing to understanding the occurrence mechanisms of reignition overvoltages in offshore wind farms. Moreover, a sensitivity analysis is performed to identify factors affecting reignition overvoltages based on the developed simulation model. The statistical result analysis indicates that four out of seven investigated factors (including the capacitance (stray capacitance and cable length), the rate of rise of dielectric strength and the opening phase angle of vacuum circuit breaker) have remarkable influences on reignition overvoltages of offshore wind farms.

Switching overvoltage analyses under distorted supply voltage conditions

Switching overvoltage analyses under distorted supply voltage conditions

Book Reviews [7 Books reviewed

The following 7 books were reviewed: Interval Finite Element Method with MATLAB;S . Nayak and S. Chakraverty; Measurements and Analysis of Overvoltages in Power Systems; J. Li; Power Microelectronics - Device and Process Technologies, 2nd Edition; Y. C. Liang, G. S. Samudra, and C. Huang; Advanced DC/DC Converters, 2nd Edition; F. L. Luo and H. Ye; Analog Electronics for Measuring Systems; D. Bucci; Astrochemistry - Big Bang to the Present Day; C. Vallance; Concepts in Physical Metallurgy; A. Lavakumar.

State of charge dependency of the overvoltage generated in commercial Li-ion cells

The overvoltage that is produced in the cells under operation limits the capacity and power they can deliver. A detailed study about the mechanisms that contribute to that overvoltage—and thus to their lifetime—is required for optimizing the use of batteries as well as their manufacturing process.We investigate galvanostatic discharge at low and moderate rates in an LCO-NMC/graphite cell in order to quantify the ohmic voltage drop and activation and concentration polarizations. For doing so, we compare half-cells to full cell overvoltages. We find that the ohmic drop and concentration polarization dominate at high rates and low rates, respectively. Moreover, we track the evolution of concentration polarization with State-of-Charge (SoC) and we observe that there exists a relationship between diffusion and phase transformations. Specifically, we validate experimentally that initial stages of a phase formation are not dominated by diffusion. Phase transitions are commonly evaluated by incremental capacity analysis. However, we determine that it is more appropriate to obtain that information from the full cells by the overvoltage analysis. Furthermore, we suggest that the working SoC range can be optimized from the overvoltage analysis by avoiding the particular SoCs at which the most detrimental phase transitions take place.

Researches on grounding modes of the AC/DC hybrid system with various distributed renewable energy

With the considerable demand for distributed renewable energy and the significant increase of generalised DC loads, such as IT equipment, DC air-conditioner, electric vehicle, the traditional AC distribution network is no longer efficient. Driven by the rapid development of power electronics technology, the AC/ DC hybrid system is an effective way for large capacity AC/DC sources and loads efficient integrated. To ensure the stable operation of AC/DC hybrid system, the grounding mode analysis is necessary, which is the precondition for overvoltage analysis, lightning arrester configuration, and protection design. To select grounding mode of AC/DC hybrid system, the detailed system structure scheme is first determined considering the factors such as integrated object, reliability requirement, capacity of sources and loads, and converter type. Then the main connection scheme is selected considering the principle of line insulation, economy, and reliability. Based on the system structure and main connection scheme, a suitable grounding mode is selected for the AC/DC hybrid system with various distributed renewable energy, by weighing various factors such as power supply reliability, protection sensitivity, insulation level, and personal safety.

Analysis of impact of atmospheric overvoltages in Kosovo Power System

In this paper are given aspects of modelling and analysis of atmospheric overvoltages for Kosovo power system. Atmospheric overvoltages are one of the leading causes of outages in Kosovo power system. Analysis of the impact of these overvoltages increases the effectiveness of the functioning process of transmission of electric energy in general and also involves the use of effective protective equipment in power systems like surge arresters, mainly for improving the performance of high-voltage transmission lines. Different location models for the establishment for surge arresters are also discussed. Transmission lines with poorest performance are discussed, regarding the atmospheric overvoltages. For the analysis of these overvoltages is used ATP/EMTP software, to solve efficiently and economically reasonable protection. In the simulation is used the metal-oxide surge arrester nonlinear model, dependent on the frequency. This model is proposed by the IEEE 3.4.11 working group and it has nonlinear V-I characteristic.

Research on overvoltage and fault of a UHV AC/DC hybrid system

In view of the overvoltage problem of an ultra-high-voltage DC (UHVDC) AC/DC hybrid system, this study analyses the overvoltage condition under various fault types and gives the identification criterion of the overvoltage form. Firstly, the model of the ± 800 kV UHVDC and 1000 kV UHV AC hybrid system was established in Simulink. The relevant parameters of current and voltage in the hybrid system were simulated and analysed to verify the accuracy and effectiveness of the model. Secondly, the fault simulation of the two system models of AC and DC, respectively, is carried out, and the theoretical analysis of the internal overvoltage caused by the fault is made. Finally, the simulation of the overvoltage condition of the hybrid system under two conditions is carried out, and the waveforms of the important parameters of the AC system and the DC system are obtained. The waveform of each parameter is analysed and the conclusion is obtained. The type of the overvoltage fault of the UHV AC/DC hybrid system is analysed, which provides the basis for fault type judgement.

Simulation Analysis of Overvoltage of Single Phase Grounding Fault in Paralleled 12-Pulse Rectifier System

In order to solve the problem of overvoltage of single phase grounding fault of paralleled 12-pulse rectifier system, firstly the common mode wave problem of monopole in DC side at fault is analyzed. Secondly, the transient overvoltage of the system at the AC side single phase fault is analyzed by simplifying the charging and discharging circuit of capacitances on DC side. Finally, the theory of frequency extinguishing arc is used to simulate the intermittent arc grounding overvoltage. It is proved that the capacitance on DC side also affects the AC overvoltage in the system that provides a basis for the better suppression of overvoltage in the project. The correctness of the conclusion is verified by PSCAD/EMTDC simulation software in the analysis process.

Influence of energy characteristics of surge arresters on their selection

For analysis of thermal processes occurring in SA under conditions of presence of overvoltage of different nature in the electric network, it is necessary to conduct research using volt-ampere characteristics. Thus, energy, released in SA, has to be determined. This approach is essential for correct selection of parameters of SA not only in terms of protection of electrical networks, where it is installed, but also to provide proper operation of a protective device itself. This approach will allow choosing parameters of SA at a design stage, which greatly reduce emergency rate throughout the entire period of operation. Presented results of calculations show that at standard pulse of atmospheric overvoltage, SA maintains thermal balance at values of current of lightning of up to 75 kA. Design lightning currents for electrical networks are about 30 kA. However, it should be noted that this approach cannot be applied to the selection of SA in the assigned network, because it may be different in values of amplitudes of lightning currents, rates of increase and the number of lightning strikes in one channel (as we know, there may be 10 of them). All presented parameters will influence thermal balance of SA, and, at some values, they can lead to its disturbance, which will cause the failure of SA and the damage to equipment of electric network. This conclusion emphasizes the need for detailed analysis of overvoltage that may occur within the network when selecting parameters and the place of SA installation. Taking into account the magnitudes and composition of overvoltage will make it possible to provide serviceability of SA throughout the entire period of operation.

Parameter Extraction and Wideband Modeling of $\pm $ 1100 kV Converter Valve

As the key equipment of ultra-high-voltage direct-current (UHVDC) transmission systems, the converter valve would bear different forms of overvoltage. Consequently, a wideband model for the $\pm $ 1100 kV UHVDC converter valve is essential for the converter system to make overvoltage analysis, insulation design, and electromagnetic disturbance prediction. This paper proposed a wideband modeling method for the $\pm $ 1100 kV converter valve. First, the physics-based wideband model for the key component in the converter valve module is built, of which the parameters could be obtained through genetic algorithm. Second, the parasitic capacitances are obtained through a simplified boundary-element method according to the given structure of the $\pm $ 1100 kV converter valve. By combining wideband models for key components in the converter valve module and the parasitic capacitances of the valve tower, the integrated wideband model for the converter valve could be obtained. The systematic modelling method proposed in this paper could also be of reference value to the modelling of other large-scale complex high-voltage power-electronic equipment. Finally, the experiments for converter valve module and converter tower are carried out, and the corresponding results justified the effectiveness and correctness of the proposed wideband model for the converter valve tower.

Stationary and Damped Oscillations in a Direct Formic Acid Fuel Cell (DFAFC) using Pt/C

Herein, we report damped and stationary oscillations during Formic Acid oxidation (FAO) under galvanostatic control in a Direct Formic Acid fuel cell (DFAFC). Using Pt/C catalyst in a practical DFAFC, the anodic electrode are allowed to rise its potential up to 600mV, at the most, which, in turn leads to solely presence of damped oscillations during FAO. When employing dynamic hydrogen electrode (DHE) for measuring anodic voltage values, in a half-DFAFC, larger potential accessed with anodic gas diffusion electrode (GDE) undergoing FAO. With it, stationary oscillatory patterns are observed with an average potential equal to 1V and with maximum potential equal to 1.25V. Such high maximum-potential oscillations are reproduced in experiments with rotating disc electrode (RDE), indicating, thus, that such behaviour derives from chemical mechanism rather than possible spatial coupling in a DFAFC. And, to explained it, we suggest to add to current oscillatory mechanism for FAO the steps originally proposed by Tian and Conway (2005) that involves direct chemical reaction of surface oxide with the bulk formic acid (or formate). Finally, we found that maximum potential of stationary oscillations is controlled by bulk formic acid diffusion, thus, a DFAFC with improving FA diffusion on the GDE would allow the presence of stationary oscillation in practical conditions, which is wanted given the improved efficiency as elucidated with the help of overvoltage analysis.

The Analysis of Overvoltage on 220kV Transmission Line in Single-phase Reclosing

Because of line-to-line inductance and capacitance, overvoltage may occur in single-phase reclosing process when breaker is reclosed on unloaded 220kV long distance transmission line. The paper establishes a model system of single generator to infinite bus power system with PSCAD simulation software, analyzes overvoltage in reclosing operation of 220kV long distance transmission line, studies the influence factors as reclosing phase angle, system equivalent impedance, transmission line parameters etc. It shows that reclosing phase angle and zero sequence line parameters have large effects to overvoltage, as the system equivalent impedance has lower effects.

Investigation and Analysis of Temporary Overvoltages Caused by Filter Banks at Onshore Wind Farm Substation

Parallel resonance generated by capacitive elements on the wind farm amplifies the current distortion caused by harmonic emission from the wind turbines and results in high voltage and current distortion through the transmission equipment connected to the grid. Similarly, series resonance amplifies the harmonic voltage distortion from the HV bus to MV bus, causing the same effect. Harmonic filters are used to screen out the unwanted harmonic effects on the wind farm. The switching activities of the harmonic filter bank may cause overvoltages on the onshore wind farm substation, thus, they are investigated in this paper with the aid of ATP/EMTP software. Temporary overvoltages caused by energising and de-energising of the filter were investigated to understand whether they exceed the withstand limits of the system. It was found that the overvoltages for both energization and denergization were beyond the power frequency withstand level. By then using statistical studies on the mitigation methods, it was found that the use of pre-insertion resistors and surge arresters greatly mitigated the overvoltage caused by energization.

Optimal design of RC snubber circuit for mitigating transient overvoltage on VCB via hybrid FFT/Wavelet Genetic approach

This paper presents a new approach to the analysis of the transient overvoltage (TOV) generated during switching of vacuum circuit breaker (VCB). The new technique overlaps the merits of both Fast Fourier Transform (FFT) and Wavelet Transform (WT). The new approach was applied on a real case study of a pumping station of a wastewater treatment plant located at Abu Rawash, Egypt. The pumping station is driven by induction motors. Alternative transients program (ATP) is used to simulate the selected case study. The Referential Integrity between FFT and WT analyses (RI-FFT/WT) is employed to choose the RC snubber circuit parameters (R and C). The optimal snubber circuit parameters design was determined from the hybridization between genetic algorithm (GA) and RI-FFT/WT. It is evident from the simulation results that the new hybrid GA-FFT/WT approach succeeded in the selection of the most optimal RC-snubber circuits required for the mitigation of the TOV.

Propagation of overvoltages transferred through distribution transformers in electric networks

The increasing requirements for improved reliability of electrical power devices and optimisation of dielectric insulation design means that the analysis of impact due to overvoltages is of high importance. This analysis should also consider propagation of overvoltages transferred through power transformer windings to other parts of the electrical network. Hazard levels of overvoltages affected the insulation systems of electrical devices are determined by wave propagation conditions of overvoltages as well as the protection level of applied overvoltages protection. The analysis of overvoltages transferred to low voltage networks is very important due to the increasing number of electrical devices and electronic apparatus with low resistance to overvoltages. This study presents a detailed analysis of the propagation of overvoltages transferred through distribution transformer windings, in typical medium and low-voltage electrical networks. The analysis is based on simulation results carried out by the use of electromagnetic transients program–alternative transients program (EMTP–ATP). A high-frequency model for transformers done on the basis of frequency characteristics of admittance measurements was used in simulations. Detailed analysis of influence of length of medium- and low-voltage lines connected to the distribution transformers and metal oxide surge arresters on switching overvoltages transferred to low-voltage networks are presented in the study.

Enhanced analysis of oscillatory undamped overvoltages in transformer energization

This paper proposes an enhancement on the methodology commonly used for overvoltage analysis motivated by the excitation of electric network resonance points due to injection of harmonic currents by equipment with nonlinear characteristics. The improvement proposed comprehends inclusion of effects caused by nonlinear equipment into the frequency scan study, harmonic content survey, transformation of currents and/or voltages from phase to sequence domain, and application of the Windowed Fast Fourier Transform (FFT). This enhanced methodology was applied in the investigation and identification of unexpected resonant behavior causes observed in pre-operational electromagnetic transient studies for an autotransformer energization.

Digital model of a vacuum circuit breaker for the analysis of switching waveforms in electrical circuits

The article presents a method of modelling a vaccum circuit breaker in the ATP/EMTP package, the results of the verification of the correctness of the developed digital circuit breaker model operation and its practical usefulness for analysis of overvoltages and overcurrents occurring in commutated capacitive electrical circuits and also examples of digital simulations of overvoltages and overcurrents in selected electrical circuits.