Overvoltage Waveforms Research Articles

Research on Ultra-Fast Transient Overvoltage Characteristics of Electric Locomotive

Operating overvoltage occurs when the pantograph or main breaker of an electric locomotive is operated, which is prone to causing insulation failure of high-voltage equipment. The HXD1 electric locomotive is taken as the research object in this paper to explore the characteristics and influencing factors of operating overvoltage. Under pantograph lifting, main breaker closing, main breaker opening, and pantograph dropping, operating overvoltage waveform in the high-voltage system is recorded by a high-speed oscilloscope and resistance–capacitance voltage divider to analyze the overvoltage characteristics and distribution law. Tested data show that the amplitude of operating overvoltage is in the range of 80 to 330 kV with ultra-high steepness, which is similar to the Very Fast Transient Overvoltage (VFTO) in power systems. The maximum overvoltage during the entire test occurred during the main breaker closing and its amplitude is 328.60 kV with a steepness of 4.21 × 104 kV/μs. The max overvoltage of the other operations (pantograph lifting, main breaker opening, and pantograph dropping) are 280.60 kV, 194.73 kV, and 305.56 kV with ultra-high steepness. High-amplitude overvoltage is predominantly located at the pantograph, while the low-amplitude sort is mainly observed around other high-voltage equipment. The result indicates that operating overvoltage belongs to ultra-fast transient overvoltage and its amplitude and steepness are higher than existing research.

Feature statistics and analysis of transient overvoltage waveform measured from 220 kV substation

The electromagnetic transient overvoltage in the substation is an important factor that affects the life of insulation equipment. For evaluate the economy and reliability of the insulation design of substation equipment, it is necessary to study and analyze the actual measured overvoltage waveforms in the substation. In this paper, firstly, the 3018 pieces of overvoltage data monitored in the 220 kV substation from 2018 to 2019 are preprocessed to obtain the required overvoltage waveform. Next, by analyzing and classifying the overvoltage data, four typical overvoltage waveforms suffered by the insulation equipment in the substation are extracted. Combined with the IEC60060 standard, the time parameters of the overvoltage waveform are selected and defined: wave-front time (Tf), half-value time (Thalf), main oscillation frequency (f), and attenuation constant (α). Further, statistical analysis is performed on the parameters of each waveform. The distribution law, distribution characteristics and distribution range of the parameters are obtained. Finally, the parameters of four typical overvoltage waveforms are summarized and compared, the cumulative distribution functions are obtained. This results can guide and optimize the insulation design of the insulation equipment in the substation, reduce design errors. It provide data support for the economy and reliability of insulation design.

Study on long front time wave switching impulse of rod-plane air gap

In long-distance transmission lines, the switching overvoltage waveform differs from that of ordinary lines. The wave front time is primarily distributed above 1000 μs. And the switching overvoltage waveform has an important influence on the design of external insulation. This paper aims to deeply study the effect of various factors on the discharge of air gaps under the long front switching impulse voltage. This paper selects three kinds of rod-plane air gaps, and the switching impulse discharge experiments with different front lengths and absolute humidity under positive polarity are carried out. The effects of front time Tf, absolute humidity h, and gap distance d on the discharge characteristics of the air gap are analyzed. The results show that the U50% of an air gap is positively correlated with absolute humidity, front time, and gap distance. When considering the additional influence of humidity, the humidity additional influence factor c and the atmospheric parameter influence index n at different front times are almost unchanged. With the increase in gap distance, the influence of front time on U50% is more obvious. With the growth of the operating wave front time, the rising rate of U50% tends to slow down. The discharge time of the air gap under different conditions is mainly determined by the front time. The research results can provide a theoretical and experimental reference for the influence of front time Tf and atmospheric parameters on the discharge characteristics of air gaps under long front switching impulse.

Overvoltage Response at the Terminal for Impulse Current Injection to 10 kV Distribution Line

This paper presents the three-phase impulse overvoltage measured at the terminal of a 10 kV distribution line when the impulse current was injected into the phase conductor of the distribution line. The overvoltage observation station was installed at the terminal of the line to record the three-phase overvoltage waveforms. It is shown that the struck phase overvoltage consists of three components including the negative pulse, the stage of residual voltage maintenance and the overshoot oscillation part. The observed negative peak values of the struck phase overvoltage range from −85.4 kV to −96.0 kV in three different injected impulse levels at 90,120,150 kV charging voltage. The duration of residual voltage depends on the duration time of injected current. Furthermore, there is a strong positive relationship between the oscillation amplitude of the struck phase overvoltage and the injected current amplitude. The peak amplitudes of three-phase overvoltage always have the following magnitude relationship: struck phase C > induced phase B > induced phase A. The voltage coupling coefficients of induced phases will not exceed 0.4. The test method proposed in this paper will be helpful to the research on the lightning overvoltage response characteristics of the distribution line and the protection analysis of arresters.

Identification of Lightning Overvoltage in Unmanned Aerial Vehicles

This paper presents research on the model developed in the Matlab environment for simulating effects of overvoltage in an unmanned aerial vehicle (UAV) upon lightning discharge. They are based on transmittance obtained from voltage surge impulse measured in drone circuits. Overvoltage waveforms were measured at the input and output of different parts of the machine. It was then possible to calculate the transmittance of those (chosen) circuits. The motors, supply system, communication lines, and sensors were primarily tested. Both positive and negative polarization of the surge pulse were used and compared. The shape of pulse, is standardized by international norms for avionics tests (RTCA DO-160). The special surge generators were used to prepare the same repetition of each pulse (for all measurements). The simplified model of surge pulses propagation in drone circuits was prepared in Matlab. The differential between direct and step-by-step paths of pulse propagation in some connected circuits were also compared.

Three‐phase overvoltage at lightning strike point due to direct triggered lightning to the phase wire of 10 kV power distribution line

This paper reports the observation results of three-phase overvoltage at the lightning strike point of a 1.5 km, 10 kV power distribution line that was struck directly by rocket triggered lightning to its phase wire C. The arrester of the direct struck phase at the lightning strike point operated in all return strokes corresponding to return stroke current from −3.3 kA to −32.9 kA. The waveform of direct struck phase includes an initial spike before negative peak, operation area of metal oxide varistor, and the final attenuation with oscillation. The overvoltage waveforms of the indirect struck phase at the lightning strike point show a small initial negative peak, rapid transition to a large positive peak, and the final negative attenuation with oscillation. The negative peak value of the indirect struck phase at lightning strike point ranged from −4.1 kV to −25.2 kV and that of the direct struck phase was between −78.1 kV and −167.8 kV. The positive peak value of indirect struck phase was between 0.2 kV and 49.8 kV. The negative peak value, zero-crossing time and the peak-to-peak value of voltage all have a good linear relation with the peak value of lightning return stroke current.

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.

Transient Overvoltage on HVDC Overhead Transmission Lines With Background DC Space Charges and Impulse Corona

The space charges around a HVDC transmission line may not only lead to electromagnetic environmental problems but also affect the occurrence of impulse corona and then the transient overvoltage propagation. This paper derives the equations governing the transient overvoltage propagation along a HVDC transmission line when there is either space charges surrounding the line or impulse corona. In contrast to conventional transmission line equations, the proposed equations adopted the dynamic capacitance C ′ and conductance G to characterize the corona discharge in all cases, which can be obtained by a time-domain finite element method. A finite-difference time-domain method is introduced to solve the nonlinear transmission line equations. The validity of the proposed approach is verified by comparison with the lightning overvoltage waveforms measured in a literature. The transient overvoltage propagation along a long UHVDC transmission line surrounded by space charges is analyzed.

Transmission Line Energisation Transients a Case with Steep Fronts and Spikes.(Dept.E)

The magnitudes and waveforms of overvoltages produced by the energisation operation of a transmission line depend, among other factors, on the source-side circuit configuration, line trapped charge, and pre-insertion resisters. This paper investigates the effects of these three factors in case of steep fronts and severe spikes appear in the overvoltage waveform obtained at the remote end of the energized line. Computer study is reported and the results show that the steep fronts and spikes are largest when trapped charge is present.

Statistical analysis of non-standard overvoltage waveforms measured at 220 kV terminals of a power transformer,,

Power transformers are designed to withstand switching and lightning overvoltages which can occur in the power system. The knowledge about waveshapes of these events grows rapidly with the introduction of online transient monitoring systems. Consequently, it is important to compare standard test voltage impulses with the ones existing in the power system. In this paper, 123 measured overvoltages in 220 kV air-insulated substation are analyzed. The observed overvoltages are fitted using double exponential mathematical function. Function parameters are calculated using genetic algorithm. To compare measured signals with the standard ones, statistical analysis of their parameters is performed. This approach can help in better dimensioning of the transformer insulation in order to withstand the real overvoltages that can occur in the power network and in avoiding potentially dangerous situation due to the resonances. Additionally, frequency domain severity factor is calculated for the observed signals.

Research and simulation of line overvoltage in HVDC transmission system

The distribution of heavy load area and resource area is seriously unbalanced in China. HVDC transmission system project with long-distance and large capacity transmission characteristics has practical significance in today’s social development. Firstly, this paper discusses the basic knowledge of over-voltage in DC transmission system and analyzes the formation mechanism of internal overvoltage, and enumerates and analyzes the common overvoltage faults at AC side and DC side. Secondly, the electromagnetic simulation software PSCAD/EMTDC is selected to build the model, and CIGRE HVDC standard control model strategy is adopted in each module. Finally, the simulation analysis is carried out, mainly aiming at the AC bus grounding fault of converter station, and the overvoltage waveform under fault condition is recorded. The over-voltage characteristics of rectifier side and inverter side under AC bus fault of converter station are compared and analyzed, which provides reliable suggestions for overvoltage and insulation coordination in future design projects.

Research on Resonance Overvoltage of EHV Transmission Lines Caused by Lightning Strike

This paper studies the mechanism and influencing factors of resonance overvoltage of EHV transmission lines caused by lightning. By analyzing the time domain steady state of the simplified resonance circuit, the physical mechanism of resonance is revealed. The characteristics of resonance transient process and overvoltage waveform are analyzed by using electromagnetic transient simulation. The main influencing factors of overvoltage amplitude are also studied. The results show that: 1) During uneven open-phase conditions, resonant circuit involving shunt inductors and line equivalent capacitor obtains energy from lightning strikes, which may lead to resonance. 2) the transient process of resonance can be divided into three stages, including lightning stage, lightning-resonance conversion stage and steady-state resonance stage, among which the voltage of the first two stages are higher; 3) the lightning strike time, lightning current parameters and subsequent lightning strike affect on the overvoltage amplitude, which leads to the random amplitude in overvoltage.

Coupled Inductance Model of Full-Bridge Modules in Hybrid High Voltage Direct Current Circuit Breakers

Extraction of the current commutation loop (CCL) inductance is necessary for the overvoltage analysis of power devices. In general, each transient process of a converter corresponds to a specific CCL. However, there is no such single CCL in the full-bridge module in hybrid dc circuit breakers during the turn- off transient. First, this article proposes a coupled inductance model of full-bridge modules. The model has less number of inductance compared to the traditional partial inductance model. Second, this article proposes the extraction method of inductances that can be easily obtained by both simulation and measurement. Moreover, the measured overvoltage waveforms of insulated gate bipolar translators (IGBTs) in the full-bridge module agree with the simulation results. Third, we propose an equivalent circuit of the series full-bridge modules in a 500 kV hybrid circuit breaker based on the proposed coupled inductance model. The mutual inductances among different modules are considered due to the compact structure of the series modules. The measured results show that the overvoltage of the IGBT in the series module could be well-predicted by the proposed equivalent circuit.

Effects of waveform parameters on the breakdown characteristics of OIP subjected to impulse voltages and evaluation method for waveform equivalence

The impulse voltage wave invading a transformer is not the double exponential impulse wave (DEIW) specified by the IEC but a non-standard waveform with oscillation attenuation characteristics, and this fact leads to doubts about the scientificity and optimality of insulation coordination. A key solution for this issue is the establishment of an equivalent relationship between the measured non-standard impulse voltage wave and the DEIW. In this study, a test platform of multiparameter impulse voltage was set up. Then, the authors obtained the 50% breakdown voltage (U50%) of the oil-impregnated paper (OIP) for transformer under the bipolar oscillatory attenuated impulse wave (BOAIW) and the DEIW with different waveform parameters. The effects of waveform parameters on the breakdown characteristics of the OIP were finally revealed. On the basis of experimental data and several mathematical methods, the authors established the U50% prediction mathematical models for the OIP under the BOAIW and DEIW. Based on the prediction models and the microfluctuation characteristics of measured overvoltage's waveform parameters, the authors proposed a method for evaluating the waveform equivalence. The characteristics of voltage amplitude and change rate were regarded as the two key factors for the waveform equivalence of this method.

Internal Overvoltage Identification of Distribution Network via Time-Frequency Atomic Decomposition

Internal overvoltage accidents in the distribution network are likely to cause an equipment insulation breakdown and result in system power outages and economic losses. Therefore, an internal overvoltage identification method based on the time-frequency atomic decomposition is investigated in this study. Firstly, the overvoltage waveforms are divided into four time periods. Then, the waveforms during these four time periods are decomposed by the atomic decomposition algorithm to obtain the effective atoms from the waveforms. Moreover, the root-mean-square (RMS) value of the zero-sequence voltage, the dominant atom frequency, the total relative matching degree, and the effective atom frequency are extracted as major features. In addition, the layered identification of the overvoltage types can be realized by combining the corresponding identification criteria. The salient advantage is the features with low dimension and a high degree of discrimination. Various overvoltage types can be identified just by the corresponding thresholds, and it is easier to deploy in the field than conventional methods based on classifier training. The effectiveness of the proposed method is verified by experimental results, and it concludes that the proposed algorithm has high accuracy and strong adaptability.

Transient overvoltage response performance of transformer windings with short‐circuit fault

The fault diagnosis of transformer windings is a basis for condition maintenance. Conventional online or offline diagnosis methods require additional pulse or impulse signal. If the overvoltage signal can be regarded as the broadband excitation source for the fault diagnosis of transformer windings, the interference caused by signal injection is likely eliminated without additional pulse or impulse signals. In this study, the transient overvoltage response performance of transformer windings with short-circuit fault is presented, which could provide a new method for the diagnosis on transformer fault diagnosis. A 10 kVA, 2400 V/220 V, 50 Hz, 1-phase tapped transformer was designed, and a test platform for the fault diagnosis of transformer windings is established. The excitation signals for the fault diagnosis of the transformer windings included different lightning waves and damped oscillation waves, as indicated by the differences among actual overvoltage waveforms. The voltage and current of windings under normal and fault conditions are determined, and the frequency responses of admittance and voltage transfer function are calculated. The criterion for the fault diagnosis of transformer windings is obtained by comparing and analysing statistical indicators that reflected the differences in the frequency response of transfer function under normal and fault.

A Framework for Automatically Extracting Overvoltage Features Based on Sparse Autoencoder

With the development of smart grid, it is of increasing significance to identify and cope with various types of overvoltages, faults and power quality disturbances effectively and automatically. In this paper, a framework for overvoltage identification and classification based on sparse autoencoder is proposed. By using single-layer and stacked sparse autoencoders, dimensionality reduction and automatic feature extraction of ferroresonance overvoltage waveforms in power distribution systems are achieved as an example, which does not require feature engineering to produce a series of features. Classification of different ferroresonance modes is then implemented with a softmax classifier, and favorable classification results are obtained after parameters of feature extraction and classifier models are determined. Application of the proposed framework in smart grids is discussed. The proposed framework provides a brand new idea for establishing a smart identification and classification system for overvoltages, which can be generalized to classification of faults and power quality disturbances.

Full-Maxwell Simulations of Very Fast Transients in GIS: Case Study to Compare 3-D and 2-D-Axisymmetric Models of 1100 kV Test Setup

Development and type testing of gas-insulated switchgear (GIS) disconnectors are supported with the simulation-based analyses of very fast transients (VFTs) that are associated with the disconnector switching operations. In order to analyze local field values in the entire GIS geometry, the full-Maxwell approach needs to be involved for simulating the VFT generation process. According to power substation layout studies, 90 ${}^{\circ }$ -angled GIS disconnectors are often used in GIS projects, since they offer most layout options and, at the same time, require the lowest number of GIS components. This implies that the test setups are asymmetric, thus the direct use of the full-Maxwell approach requires 3-D models, the application of which is considered to be highly demanding from a numerical point of view. The paper shows a comparison of the results obtained from full-Maxwell numerical simulations for a development test setup of 1100 kV GIS. The analyses are conducted for full 3-D geometry and for the corresponding 2-D-axisymmetric geometry. Example simulations of the VFT overvoltage (VFTO) waveforms are presented for both geometries, together with a comparison of the numerical effort needed for solving the associated field equations. The presented approach based on the 2-D-axisymmetric GIS model allows one to significantly reduce the numerical effort involved to support design work and development tests.

Effect of Neutral Grounding Protection Methods for Compensated Wind/PV Grid-Connected Hybrid Power Systems

The effects of the wind/PV grid-connected system (GCS) can be categorized as technical, environmental, and economic impacts. It has a vital impact for improving the voltage in the power systems; however, it has some negative effects such as interfacing and fault clearing. This paper discusses different grounding methods for fault protection of High-voltage (HV) power systems. Influences of these grounding methods for various fault characteristics on wind/PV GCSs are discussed. Simulation models are implemented in the Alternative Transient Program (ATP) version of the Electromagnetic Transient Program (EMTP). The models allow for different fault factors and grounding methods. Results are obtained to evaluate the impact of each grounding method on the 3-phase short-circuit fault (SCF), double-line-to-ground (DLG) fault, and single-line-to-ground (SLG) fault features. Solid, resistance, and Petersen coil grounding are compared for different faults on wind/PV GCSs. Transient overcurrent and overvoltage waveforms are used to describe the fault case. This paper is intended as a guide to engineers in selecting adequate grounding and ground fault protection schemes for HV, for evaluating existing wind/PV GCSs to minimize the damage of the system components from faults. This research presents the contribution of wind/PV generators and their comparison with the conventional system alone.

Lightning performance of transmission lines based upon real return-stroke current waveforms and statistical variation of characteristic parameters

This paper presents investigative studies concerning the lightning performance of 500kV transmission lines considering the characteristic parameters of first stroke current observed in measurement data along with its statistical variation. Therefore, advanced electromagnetic models were applied during the development of computational models, thus allowing a realistic representation of the first stroke current waveform. Lightning performance studies were conducted applying two of the most commonly used return-stroke current models, besides the first stroke current model recommended by CIGRÉ. The aim therefore is to identify which of these present the most accurate results, when compared to the use of real return-stroke current waveforms. The volt–time characteristics produced by each of the return-stroke current waveforms were evaluated using both the leader progression model (LPM) and volt–time curve. The breakdown process modelled through LPM is able to represent accurately the physical process established along the perimeter of the insulator strings, during a backflashover event. Analysis of leader length and velocity can reveal the influence of particular characteristics of lightning overvoltage waveform across the insulators produced by different return-stroke current waveforms in the assessment of the lightning performance of a transmission line. The computational modelling developed herein, allows identifying the critical current, the amplitude of the overvoltage that produces the backflashover, and the instant of time that breakdown occurs. The proposed modelling also makes it possible to determine in which insulator string and tower the backflash happens.