Overvoltages In Power Systems Research Articles

Application of artificial intelligence methods for determination of transients in the power system

Numerous factors, including sudden load reductions, switching transient loads, lightning strikes, and malfunctions of control devices, can result in overvoltage. Overvoltage can harm associated power supply components and result in insulation failure, electronic component damage, flashovers, etc. A machine learning technique called a "neural network" estimates computation results that depend on a lot of inputs. For a variety of reasons, neural networks have recently been used to manage and optimize the power system. This paper presents an artificial neural network (ANN)-based approach to determining overvoltages in power systems. To simulate overvoltages, many simulations were performed in Electromagnetic Transient Program (EMTP). Variations of parameters of interest that have an influence on overvoltages were made using JavaScript that was connected to EMTP models. The extraction of characteristic parameters from overvoltage waveshape is a demanding task, and it was conducted in MATLAB, as was a overvoltage classification methodology based on neural networks. Results were presented and discussed.

Impact of steady state and impulse excitations on CuSO4 based memristor

The memristor technology will replace nonlinear resistor applications in suppression of power system overvoltages. A characterization study on Memristance is useful to predict current–voltage characteristics of memristors under different source voltages. A Liquid Memristor (LM) has been chosen in order to study its suitability as a nonlinear resistance for mitigation of an Instrument Transformer overvoltages. The motivation is to investigate the nonlinear property of LM under DC and AC supply voltages in terms of pinching nature and memristance. The simulation response of LM has been validated experimentally for steady state and impulse excitations. The LM is subjected to sinusoidal and triangular supply voltages at 50 Hz and verified for its pinched hysteresis. The response of LM satisfies the standard specifications for (1.2/50) μs lightning and (250/2500) μs switching impulse voltages. The nonlinear resistance of LM shows a varying response for DC voltage instead of single operating point. The memristance of LM is observed to be 1.5 mS under steady state voltage and varied up to 2.89 mS under impulse excitations. The study investigates the dynamic response of LM as a nonlinear system.

Statistical Failure Characteristics of Air Gap Subjected to Damped Alternating Overvoltages and Its Risk Assessment

This paper examines characteristics of the statistical failure of rod-plane air gap (RPAG) under damped alternating overvoltage (DAOV) as their parameters, including the frequency and the damping factor, are varied. The failure probability is calculated by considering the probability density distribution of overvoltage in power systems, and the results show that the failure probability of insulation under the DAOV is higher than that under double exponential impulse waveforms (DEIW), where this shows the risk of the prevalent insulation design. We then propose a 3D model to predict the characteristics of failure that shows that the probability of failure increases with the frequency and the damping factor. We use a 3D analytical formula to propose a method characterized by a failure graph to search for typical parameters of the area of the waveform that poses a high risk to the insulation. The results of a verification experiment show that the risk of failure of the DAOV in the search area of the waveform is significantly higher than those of other DAOV. Both the proposed 3D prediction model and the search area can help improve the design of the insulation, and can be used to apply statistical methods for insulation coordination in power systems.

Discrete-Time Fourier Series to simulate transient over voltages in power systems

This paper presents a methodology based on the Discrete-Time Fourier Series (DTFS) to calculate transient over-voltages in power systems. The proposed algorithm determines the time window with sufficient width to allow the time constants of the transients to decay to a small value. This method is simpler than the traditional numerical Laplace transform (NLT) and does not require parameters adjustment to obtain accurate results. The test case is based on a study to calculate Transient Over-Voltages (TOV) for 138 kV transmission lines in British Columbia, Canada. To assess the accuracy of the results, the DTFS solution is compared with the traditional NLT solution with optimized parameters and with the frequency-dependent time-domain models: fdLINE (JMARTI Model) and Universal Line Model (ULM).

Improving the protective effect of surge arresters by optimizing the electrical property of ZnO varistors

In the present research, we studied ZnO varistors having multiple dopants and optimized their microstructure and electrical properties by tailoring the sintering process. At certain concentrations of the rare-earth elements yttrium and indium, the voltage gradient decreased from 683.7 to 293.0V/mm as the sintering temperature was increased from 1160 to 1320°C. In addition, the nonlinear coefficient first increased and then decreased as sintering temperature was increased. When sintered at 1240°C, the multiple doped ZnO varistors samples showed excellent performance, exhibiting a voltage gradient of 520V/mm, a residual voltage ratio of 1.55, and a density of 63.7A/cm2 under a current waveform of 8/20μs, and a nonlinear coefficient of 74.5. These optimized properties will be of great utility in the manufacture of metal oxide arresters. When the high-performance varistors were used in surge arresters of ultra-high voltage grids, the overvoltage level along the transmission line and in the substation were reduced by 31.14% and 33.53%, respectively. This combination of characteristics will dramatically improve the protective effect of surge arresters for deeply suppressing over-voltages in power systems, significantly reduce the insulation requirement and cost of power apparatus as well as greatly increase the safety of power systems.

Electromagnetic resilience of critical national infrastructure

With the increase in the system scale and informatization level of the critical national infrastructures, the electromagnetic security in extreme electromagnetic environments such as the high-altitude electromagnetic pulse, the intentional electromagnetic interference and the geomagnetic storm has attracted more attention. Unlike conventional electromagnetic events such as the lightning and the overvoltage in power systems, extreme electromagnetic environments are small-probability but high-risk events whose impact mechanisms and evaluation methods are quite different. And the conventional reliability analysis, which adopts the expected value indexes, is difficult to effectively evaluate and manage the risks related to extreme electromagnetic environments. In this context, this paper presents a triangular pyramid model for the study of electromagnetic security of critical infrastructures. Then taking the power grid as an example, it discusses the implication and significance of electromagnetic resilience to critical infrastructures, and finally makes a proposal for the future study of electromagnetic resilience.

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.

Electro-Thermal Modeling of Metal-Oxide Arrester under Power Frequency Applied Voltages

Metal-oxide arresters (MOAs) are used to absorb the electrical energy resulting from overvoltages in power systems. However, temperature rises caused by the absorbed energy can lead to the electrothermal failure of MOAs. Therefore, it is necessary to analyze the electric and thermal characteristics of MOAs. In this paper, in order to study the electric and thermal characteristics of MOAs under power frequency voltage, an improved electrothermal model of an MOA is presented. The proposed electrothermal model can be divided into an electric model and a thermal model. In the electric model, based on the conventional MOA electric circuit, the effect of temperature on the voltage–current (V–I) characteristics of an MOA has been obtained. Using temperature and applied voltage as input data, the current flows through the MOA can be calculated using the artificial neural network (ANN) method. In the thermal model, the thermal circuit of a MOA has been built. The varistor power loss obtained from the electric model is used as input data, and the temperature of the zinc oxide varistors can be calculated. Therefore, compared with the existing MOA models, the interaction of leakage current and temperature can be considered in the proposed model. Finally, experimental validations have been done, and the electrothermal characteristics of an MOA have been studied by simulation and experimental methods. The electrothermal model proposed in this paper can assist with the prediction of the electric and thermal characteristics of MOAs.

Application of Genetic Algorithm to Estimation of Function Parameters in Lightning Currents Approximations

Genetic algorithm (GA) is applied for the estimation of two-peaked analytically extended function (2P-AEF) parameters in this paper. 2P-AEF is used for approximation of measured and typical lightning discharge currents. Lightning discharge channel is often modeled as thin-wire vertical antenna at perfectly conducting ground. Engineering lightning stroke models assume that the current along that channel is related to the channel-base current which may be measured at the instrumented tall towers and in triggered lightning experiments. Mathematical modeling of lightning currents is important in verification of lightning strokes models based on simultaneously measured electromagnetic fields at various distances, so as in lightning protection studies, computation of lightning induced effects and simulation of overvoltages in power systems. Typical lightning discharge currents of the first positive, first negative, and subsequent negative strokes are defined by IEC 62305 Standard based on comprehensive measurements. Parameters of 2P-AEF’s approximation of the typical negative first stroke current are determined by GA and compared to approximations obtained by other functions. Measured currents at Monte San Salvatore in Switzerland, at Morro de Cachimbo Station in Brazil, and in rocket-triggered lightning experiments at Camp Blanding in Florida are approximated by 2P-AEFs, and good agreement with experimentally measured waveshapes is obtained.

Internal Protection of Transformer Windings Against Transeint Surges Using ZnO Varistors

Power system overvoltages due to switching, lightning and other disturbances are the main problem for designers of the power transformers. Once some frequencies of the incoming surges match with some of the natural frequencies of transformer winding, the resonance phenomenon is expected in transformer winding. The resonant overvoltages may destroy the insulation between turns and cause to insulation failure or transmformer damage. In this paper, the transformer winding is modeled based on the lattice diagram concept with variable parameters and the IEEE model of surge arresters has been utilized in order to perform the simulations. For internal protection of transformer windings, it is assumed that ZnO varistors are installed in parallel to the winding turns. Also the effect of ZnO varistors in reducing the voltage stress across the transformer winding has been investigated for the case of grounded and insolated nutral winding.

Non-contact measurement of lightning and switching transient overvoltage based on capacitive coupling and pockels effects

Measurement of lightning and switching transient overvoltage in power system is significant to the research that guides the protection of power system. A new type of sensor for non-contact measurement of lightning and switching transient overvoltage in power system is designed in this study. This sensor is composed of two parts, namely, voltage induction and optoelectronic conversion units. Given the existing stray coupling capacitor C1 between the transmission line or bus bar and a metal plate placed under it, a voltage induction unit is designed by utilizing the C1 and a capacitor with fixed value C2 connected in series, then the high-voltage non-contact induction on a transmission line or bus bar is achieved. The optoelectronic conversion unit is designed based on the Pockels effect of the LiNbO3 crystal. The voltage signal induced by the voltage induction unit can be converted to an optical signal by the optoelectronic conversion unit for long-distance transmission through optical fibers without power supply at the monitoring site. Laboratory and field tests revealed that the new developed sensor possesses good linear region, high precision, and wide frequency band of the response to lightning and switching transient overvoltage in power system. The sensor can also be applied to the non-contact measurement of lightning and switching transient overvoltage in power system with different voltage levels by conveniently adjusting the distance between the sensor and the line.

An engineering approach to calculation of channel-base lightning current parameters

An alternative approach to calculation of the channel-base lightning parameters using a well-known Heidler function without discontinuity of its first derivative at t=0 of the lightning current is presented in the article. Based on a graph-analytical method, the lightning parameters of the Heidler current can be derived from statistical characteristics of the registered lightning activity such as the current peak, the current rise-time and decay-time to half of the peak value. The effect of the lightning current wave-shape on the estimated over-voltages has been studied during lightning strikes to a 500 kV overhead power line in a vicinity of a transformer-generator block of a power station using the Heidler and double exponential functions. It appears that the calculated over-voltages in power systems depend on the adopted channel-base lightning current. This becomes very critical for fast transient processes of less than 2μs current rise-time with reactive electrical plants in the circuit.

Model Reduction of Potential Transformer Based on Revised Minimum Information Loss Method

The circuit model of potential transformer (PT) is indispensable in accurately simulating the electromagnetic characteristic under the lightning overvoltage and very fast transient overvoltage in power systems. This paper utilizes a reduction algorithm for potential transformer based on revised minimum information loss method (RMIL). First, we measured a 10 kV single phase potential transformer using the Agilent 4395A network/spectrum/impedance analyzer. Second, we obtained the rational approximation of two-port circuit parameters by vector fitting (VF). At last, revised minimum information loss method is applied to reduction the state equation of circuit parameters. Comparisons between the reduced and original are given to illustrate the approximating performance of RMIL.

765 kV power transformer losses upon energizations: A comparison between field test measurements and EMTP-RV simulations

Transformer energization tests were performed in Hydro-Québec Chateauguay substation on a 300 MVA single-phase 765/125/12.5kV Yg-Yg-Δ power transformer in order to improve power transformer modeling for harmonic over-voltage evaluations upon energizations and fault removals close to HVDC converters with associated filters and capacitor banks. From these results, an enhanced transformer model has been developed in EMTP-RV Software. Subsequent simulations show that accurate modeling of the power transformer losses does only have minor influences on harmonic over-voltages damping. It is shown however that the usage of the proposed model is essential to predict adequately the risks of ferroresonance and generated over-voltages in power systems.

Simulation of transient processes on overvoltage in electric transmission lines using ATP-EMTP

In this paper, the mathematical modeling and simulation of electromagnetic transient processes is considered, which is of vital importance for examining the overvoltage phenomenon of power transmission systems. In the mathematical models of the AC power transmission systems that contain a power source, the power transformer, transmission line, and power autotransformer block are presented. The mathematical model of each system component is obtained based on the branch voltages, flux linkages, and branch voltages of the magnetic circuits individually. As for the simulation, an alternative transient program (ATP) environment is used to model the electric power system's elements. One of the power system's overvoltages occurs because of the fault and switching events. The usage of reactors at the sending and receiving ends of the line limits the overvoltages. The ATP has a powerful tool to simulate the transient events: specifically, the fault transients in the time domain. In order to test the simulation model's performance, the overvoltage measurements from a field test of a 500 kV electric transmission system is used. The simulation shows that the obtained results give satisfactory solutions to investigate the power system's overvoltage events. Selected results of the evaluation are presented.

Side effects of Current-Limiting Reactors on power system

Air-cored Current-Limiting Reactor (CLR) has already been widely applied to limit the magnitude of fault current in power systems in many countries, Brazil for example, and meanwhile the CLR has made a significant contribution to the severity of transient overvoltages in power systems, such as transient recovery voltage (TRV), switching overvoltage (SOV), and temporary overvoltage (TOV). The present paper here did a lot of simulations on the application of CLR for a real-life transmission line, suggesting that with equipment parameters of originally draft, TRV would have exceeded the circuit breakers’ TRV ratings and necessary measures should be taken to decrease TRV. Digital simulations were made with PSCAD/EMTDC software and the results implied that the magnitude of the SOV and the TOV increased up to or even exceeded the safe limits with the CLR installed. Relevant studies are strongly recommended before the CLR is applied to ensure the safety of equipment and transmission system.

Analysis of the Ferroresonance of 110 kV Power Systems

Ferroresonance is a usual internal overvoltage in power system; it mostly occurs in distribution network that neutral hasn’t grounded directly, but it also happens in the high voltage grid that neutral-grounded system frequently. This paper introduced the fundamental theory of ferroresonance. An 110kV substation has been used as the model, to emulate the waveform of its ferroresonance, and also discussed the measure to remove the ferroresonance.

Mixed Over-Voltage Decomposition Using Atomic Decompositions Based on a Damped Sinusoids Atom Dictionary

The main purpose of this paper is to establish a signal decomposition system aiming at mixed over-voltages in power systems. In an electric power system, over-voltage presents a great threat for the system safety. Analysis and identification of over-voltages is helpful to improve the stability and safety of power systems. Through statistical analysis of a collection of field over-voltage records, it was found that a kind of complicated signals created by mixing of multiple different over-voltages is difficult to identify correctly with current classification algorithms. In order to improve the classification and identification accuracy of over-voltages, a mixed over-voltage decomposition system based on the atomic decomposition and a damped sinusoid atom dictionary has been established. This decomposition system is optimized by using particle swarm optimization and the fast Fourier transform. Aiming at possible fault decomposition results during decomposition of the over-voltage signal, a double-atom decomposition algorithm is proposed in this paper. By taking three typical mixed over-voltages as examples, the validity of the algorithm is demonstrated.

Investigation of Transmission Line Overvoltages and their Deduction Approach

The two significant overvoltages in power system, switching overvoltage and lightning overvoltage, are investigated in this paper. Firstly, the effect of various power system parameters on Line Energization overvoltages is evaluated by simulation in ATP. The dominant parameters include line parameters; short-circuit impedance and circuit breaker parameters. Solutions to reduce switching overvoltages are reviewed and controlled closing using switchsync controllers is proposed as proper method. This paper also investigates lightning overvoltages in the overhead-cable transition. Simulations are performed in PSCAD/EMTDC. Surge arresters are applied in both ends of cable to fulfill the insulation coordination. The maximum amplitude of overvoltages inside the cable is surveyed which should be of great concerns in insulation coordination studies.

The mechanism of eliminating harmonic resonance with controllers by over-voltage in the power systems

The phenomenon of anti-symmetrical bifurcation of periodic solutions occurring near an integral manifold is the intrinsic cause resulting in harmonic resonance over-voltage in power systems. On the basis of this conclusion, the principle of eliminating harmonic resonance by using an anti-bifurcation approach is presented, which means that the theoretical basis of every measure to eliminate resonance is unified firstly from a point of view of basic theory. Our discussion models depend on a class of non-linear control model produced by over-voltage in the power systems. Using the direct Lyapunov technique, a complete theoretical proof is given in accordance with the measure of eliminating resonance by connecting non-linear resistors in series to the neutral point of PT and applying the feedback control law. It comprises the action of the parameters of the resistors to eliminate resonance and the actual process of eliminating resonance, that is, to go against the bifurcation process which forces the big harmonic solutions to retreat to the integral manifold gradually and disappear eventually, by using the non-linear controllers. This ensures that the intrinsic cause of resonance is eliminated thoroughly.