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High voltage direct current circuit breakers (HVDC CBs) are necessary for reliable and safe operation of future multi-terminal meshed HVDC grids. So far no commercially mature products of such equipment exist. A few industrial concepts as a result of advances in power electronics have been proposed and prototypes have been built. However, performances of these concepts have never been demonstrated under realistic operation conditions. Since these tests require construction of high power DC sources incurring significant investment costs, alternative test circuits providing equivalent stresses must be considered. In this paper various test methods and circuits used for testing HVDC CBs are investigated and their performance is evaluated against the stresses in a conceptual future HVDC grid. A novel method of testing an HVDC CB using existing installations in a high power ac test laboratory is proposed and its prospective fault current and voltage is experimentally demonstrated. It is concluded that adequate test circuits need to maintain the supply voltage not only up to the current zero in the main interrupter unit of the HVDC CB, but also during the entire energy dissipation phase of the interruption process. [ABSTRACT FROM AUTHOR]

The transients in power system cause serious disturbances in the reliability, safety and economy of the system. The transient signals possess the nonstationary characteristics in which the frequency as well as varying time information is compulsory for the analysis. Hence, it is vital, first to detect and classify the type of transient fault and then to mitigate them. This article proposes time-frequency and FFNN (Feedforward Neural Network) approach for the classification of power system transients problems. In this work it is suggested that all the major categories of transients are simulated, de-noised, and decomposed with DWT (Discrete Wavelet) and MRA (Multiresolution Analysis) algorithm and then distinctive features are extracted to get optimal vector as input for training of PNN (Probabilistic Neural Network) classifier. The simulation results of proposed approach prove their simplicity, accurateness and effectiveness for the automatic detection and classification of PST (Power System Transient) types

This letter presents a closed-form expression for ground return admittance for a system of underground cables. It is based on the approximation of the infinite integral found using a quasi-TEM (transverse electromagnetic) formulation of the electromagnetic field. The results indicate that the frequency behavior of the closed-form expression provides useful responses up to a few megahertz, thus being a suitable alternative to the numerically challenging infinite integrals. The agreement of the closed-form results and those obtained using the infinite integrals is very good regardless of the ground conductivity considered. [ABSTRACT FROM AUTHOR]

An auto‐buck–boost single‐inductor multiple‐output (SIMO) dc–dc converter with duty‐cycle‐constrained comparator control is presented in this Letter. Combined both comparator‐based and duty‐cycle‐constrained controllers enable the dc–dc converter attaining fast transient response and low cross‐regulation (CR). The proposed algorithm is independent of the precision of current sensor and suppresses CR robustly with the proposed tri‐feedback loop control of comparator‐based voltage control, duty‐cycle‐constrained distribution and average current control. The proposed scheme is suitable for auto‐buck–boost SIMO dc–dc converter design for dynamic voltage scaling applications. [ABSTRACT FROM AUTHOR]

Transient rotor angle stability assessment and oscillatory rotor angle stability assessment subsequent to a contingency are integral components of dynamic security assessment (DSA) in power systems. This study proposes a hybrid algorithm to determine whether the post-fault power system is secure due to both transient rotor angle stability and oscillatory rotor angle stability subsequent to a set of known contingencies. The hybrid algorithm first uses a new security measure developed based on the concept of Lyapunov exponents (LEs) to determine the transient security of the post-fault power system. Later, the transient secure power swing curves are analysed using an improved Prony algorithm which extracts the dominant oscillatory modes and estimates their damping ratios. The damping ratio is a security measure about the oscillatory security of the post-fault power system subsequent to the contingency. The suitability of the proposed hybrid algorithm for DSA in power systems is illustrated using different contingencies of a 16-generator 68-bus test system and a 50-generator 470-bus test system. The accuracy of the stability conclusions and the acceptable computational burden indicate that the proposed hybrid algorithm is suitable for real-time security assessment with respect to both transient rotor angle stability and oscillatory rotor angle stability under multiple contingencies of the power system.

This paper proposes a new approach for power system transient stability simulation, which is based on a semi-analytical solution (SAS) of power system differential-algebraic equations. In this paper, an SAS is derived using the Adomian decomposition method as a closed-form explicit function of symbolic variables such as time, the initial state, and other variables on system conditions and; hence, it can directly give a power system's dynamic trajectory being accurate for a certain time window. Unlike a traditional numerical integration based simulation approach, the proposed new approach offline derives an SAS and online evaluates the SAS by plugging in values of symbolic variables for a series of time windows making up the desired simulation period. This paper further studies the maximum length of the time window for an SAS being accurate and proposes a divergence indicator for simulation using adaptive time windows. Implementation of this new approach on parallel computers is also studied. The new approach is validated through contingency simulation of the IEEE 10-generator 39-bus system with detailed generator models. [ABSTRACT FROM AUTHOR]

The dynamic processes of a power system during grid fault are being changed by the large‐scale applications of wind generation. The transient characteristics of a single doubly fed induction generator (DFIG) have been widely researched. However, the overall characteristics of a wind farm have not been obtained because the existing models of a wind farm cannot cover the differences caused by normal instruction values, controller responses, and protections of the DFIGs. The equivalent model of a doubly fed wind farm used for the electromagnetic transient analysis is studied. The feature information of the stator short‐circuit current (SCC) of a DFIG was excavated based on transient behaviour analysis. The structure similarity indices are established to evaluate the envelope curves of the SCCs. A clustering method based on transient physical process is then proposed to distinguish coherent DFIGs. The equivalent model represented by a small number of DFIGs is obtained by aggregating coherent groups. The simulations indicate that the method effectively recognises transient state differences of the DFIGs. Thus, the model meets the requirements of the transient analysis. [ABSTRACT FROM AUTHOR]

Power systems require a reliable supply and good power quality. The impact of power supply interruptions is well acknowledged and well quantified. However, a system may perform reliably without any interruptions but may have poor power quality. Although poor power quality has cost implications for all actors in the electrical power systems, only some users are aware of its impact. Power system operators are much attuned to the impact of low power quality on their equipment and have the appropriate monitoring systems in place. However, over recent years certain industries have come increasingly vulnerable to negative cost implications of poor power quality arising from changes in their load characteristics and load sensitivities, and therefore increasingly implement power quality monitoring and mitigation solutions. This paper reviews several historical studies which investigate the cost implications of poor power quality on industry. These surveys are largely focused on outages, whilst the impact of poor power quality such as harmonics, short interruptions, voltage dips and swells, and transients is less well studied and understood. This paper examines the difficulties in quantifying the costs of poor power quality, and uses the chi-squared method to determine the consequences for industry of power quality phenomenon using a case study of over 40 manufacturing and data centres in Ireland. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to modeling magnetic cores for high-frequency transient analyses in power system applications. A method is presented to obtain a frequency-dependent, nonlinear equivalent circuit model of magnetic cores, suitable for simulations of transients in high-frequency and high-current conditions. The model can be used in any Electromagnetic Transients Program (EMTP)-like simulation software for power system transient analyses and hardware design of transient mitigation solutions. The model has been developed based on the frequency characteristics of the complex impedance of a magnetic core, measured for different operating points on the magnetization curve. Based on the measured characteristics and on some basic material properties, a nonlinear equivalent model composed of a set of lumped elements was established. The presented method is generic; however, the results are presented for a magnetic core of nanocrystalline type and the model implementation is shown in EMTP simulation software. The exemplary model is dedicated for the frequency range $f=$ 1 kHz $\div $100 MHz, and for the current range $I=0\div 10$ kA. The model accuracy was validated with selected measurement results, and the accuracy of the method is thoroughly discussed. [ABSTRACT FROM PUBLISHER]

This study analyses the voltage dip behaviour of the doubly‐fed induction generator (DFIG) connected to a common dc link on both the stator and rotor sides, via a diode bridge and a voltage source inverter (VSI), respectively. After a voltage dip in the dc grid, the rotor VSI can transiently lose control so that rotor currents circulate through the VSI free‐wheeling diodes. However, during the uncontrolled period, both stator and rotor voltages are clamped to the same dc‐link voltage and no rotor overvoltage occurs. In order to analyse the behaviour of the system during the first periods of the uncontrolled current transients, this study presents a simplified average model which is validated through simulations. Voltage dips are classified into three types depending on their severity. A simple analytical expression is derived for the maximum amplitude of the current during the voltage dip, and an overcurrent chart in the plane 'rotor speed – dip amplitude' is deduced. These results provide deep insight into the DFIG‐DC system behaviour and are useful for design purpose. [ABSTRACT FROM AUTHOR]

In extra/high-voltage power systems, electromagnetic transient phenomena (e.g. from switching events) are analysed by time-domain simulation based on Electromagnetic Transient Program-type simulation tools. For the particular combined power cable-overhead line studied in this paper, it can be time-consuming especially if the effect of design parameters are studied systematically. A tailored solution based on solving the system's impedance and admittance matrix in frequency domain can serve as alternative approach. It also allows for including design details, which can be hard to implement in Electromagnetic Transient Program-type simulation tools designed for general application. The method is applied to analyse transient behaviour (upon no-load energising and no-load switching surge response) of a mixed double circuit connection including a section with essentially four parallel cables per phase, regularly cross-bonded over a length of 10.8 km. It is validated by comparison with pscad/emtdc simulation. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study presents an efficient current tracking method of power frequency signals using Rogowski coil. To compensate the output voltage of the Rogowski coil, a direct and simplified digital compensation technique is proposed to reconstruct the input current. Different high‐frequency reconstructing techniques are used to emphasise estimating and reforming the fundamental input current from Rogowski coil output. Then, a new method is presented for extracting the fundamental current phasors from the Rogowski coil by processing its terminal voltage using the discrete Fourier transform. For experimental evaluation, a digital signal processing board‐based test setup is utilised. For the simulation study, accurate Rogowski coil modelling in alternative transients programme–electromagnetic transients programme is developed to evaluate the proposed method under special testing conditions concerning step change and DC decay. The results validate the efficacy of the proposed method in power frequency tracking for metering and protective relaying purposes. [ABSTRACT FROM AUTHOR]

This paper discusses methods for estimation of area's frequency response characteristic (AFRC) during large frequency changes. The operating point changes significantly during such transient events; consequently the estimation method should adapt to the time-varying nature of the AFRC. Moreover, available measurements have a poor time resolution and are considerably contaminated by errors. Therefore, new estimation methods are proposed that are based on local correlation between the frequency deviation and interchange power variation measured on all area's tie-lines. The presented estimation methods were compared with a classical approach that is based on the ratio of mean changes as well as with conventional least squares parameter estimators. Extensive numerical simulations and field measurements were applied for performance evaluation, where the obtained results show robust and satisfactorily accurate responses of the proposed estimation methods. [ABSTRACT FROM PUBLISHER]

Power Quality Assessment (PQA) is a critical issue both in transmission and distribution networks. Therefore, it is necessary to precisely classify the disturbances in shortest possible time to prevent the malfunction or increase of losses in the electrical equipment through appropriate remedial techniques. This paper proposes a highly accurate method of PQA through data acquisition using smart sensors, the Rogowski coils (RCs). RCs with wide band width and linear characteristics allow faithful reproduction of high-frequency (HF) signals. In the proposed method, simulated disturbance signals are applied to RC. The output signals are subjected to multilevel wavelet decomposition and then computation of the energy difference in the detailed components between the disturbance signal and the pure sinusoidal waveform is performed to design a fuzzy logic Power Quality Classifier. The classifier is tested by varying the magnitude, frequency and duration of the disturbance and found to be accurate to 98.38%. The classification accuracy depends mainly on the performance of sensors at HFs. Thus, with RCs as sensors instead of conventional instrument transformers, it is found that the precision of power quality classification is greatly improved. [ABSTRACT FROM AUTHOR]

This paper proposes a novel approach for testing dynamics and control aspects of a large scale photovoltaic (PV) system in real time along with resolving design hindrances of controller parameters using Real Time Digital Simulator (RTDS). In general, the harmonic profile of a fast controller has wide distribution due to the large bandwidth of the controller. The major contribution of this paper is that the proposed control strategy gives an improved voltage harmonic profile and distribute it more around the switching frequency along with fast transient response; filter design, thus, becomes easier. The implementation of a control strategy with high bandwidth in small time steps of Real Time Digital Simulator (RTDS) is not straight forward. This paper shows a good methodology for the practitioners to implement such control scheme in RTDS. As a part of the industrial process, the controller parameters are optimized using particle swarm optimization (PSO) technique to improve the low voltage ride through (LVRT) performance under network disturbance. The response surface methodology (RSM) is well adapted to build analytical models for recovery time ( R t ), maximum percentage overshoot (MPOS), settling time ( T s ), and steady state error ( E ss ) of the voltage profile immediate after inverter under disturbance. A systematic approach of controller parameter optimization is detailed. The transient performance of the PSO based optimization method applied to the proposed sliding mode controlled PV inverter is compared with the results from genetic algorithm (GA) based optimization technique. The reported real time implementation challenges and controller optimization procedure are applicable to other control applications in the field of renewable and distributed generation systems. [ABSTRACT FROM AUTHOR]

Multi-terminal HVDC is an important new technology for bulk power transfer from large sources of remote renewables to large load centers. Recently MTDC grids have become more technically feasible due to improvements in VSC based converters, which can reverse currents and generally have greater control than LCC. Furthermore, emerging DC breakers technology unlocks the possibility of de-energizing only the faulted section of an MTDC without losing the whole grid. The protection relaying in such grids is not trivial: it must be very reliable, robust to the converter control system׳s effect on the post fault transients and act quickly, before the fault current develops beyond the presently modest interrupt capability of DC breakers. Within this challenging environment, this paper discusses in detail the important considerations for designing MTDC protection, including accurate modeling of the converter topology, associated control scheme and the DC link itself, supported by the results of novel transient simulation studies. This context is then used to appraise the suitability of the existing protection of HVDC and MTDC grids and suggests future work in the area. [ABSTRACT FROM AUTHOR]

This study presents the modelling of transformers for voltage disturbances. The focus in this study is on the security of the power supply for sensitive loads, for instance, the auxiliary systems for a nuclear power station feeding, for instance, pumps for emergency systems. Both steady‐state operation as well as transient conditions have been analysed. A five‐limb as well as a three‐limb 4 kVA transformer was designed in order to verify theoretical assumptions with experimental results. The results show that the theoretical models provided results in conformity to the actual experiments with an average discrepancy of 3%. Moreover, it is shown that a five‐limb transformer gives lower inrush currents, especially in the highly saturated region. In addition, it was demonstrated that an inductive load gives much higher inrush currents compared with a resistive load. A final observation was that the current drawn by the two transformers in their saturated state differ severely depending on the topology of the core. [ABSTRACT FROM AUTHOR]

In a multiterminal HVDC network, dc circuit breakers (CBs) are required at each end of a line to selectively isolate a fault. Several CB concepts have been implemented in PSCAD, which differ significantly in their structure and performance. This paper describes the interaction of the different HVDC CB topologies with a meshed four-terminal network and assesses their performance in terms of maximum currents and voltages. The tradeoff between network parameters and CB requirements is analyzed. [ABSTRACT FROM PUBLISHER]

This paper presents the analysis of possible transient overvoltages that can be generated during vacuum circuit-breaker (VCB) operation at the connection point of a photovoltaic powerplant. A typical switching event that is related to the VCB concerns energization and de-energization of the unloaded transformer. However, at the typical photovoltaic powerplant, the transformer is fed by an inverter equipped with LC (or LCL) filters that are necessary for limitation of harmonics and ripple in voltage and current. From the point of view of switching operations, the inductance and capacitance of the low-voltage (LV)-side connected filter affect the natural frequency of the transformer, which is reflected by different transient system response during VCB operation. In this paper, laboratory measurement of overvoltages generated during distribution transformer switching by means of VCBs is analyzed. The impact of the LC filter connected at the LV side on the overvoltages suppression was studied. Electromagnetic Transients Program–Alternative Transients Program simulations were conducted in order to verify the possibility of transients elimination by means of the additional series-connected RL choke at the transformer medium-voltage side. [ABSTRACT FROM PUBLISHER]

HVDC short-circuit calculation standards will be required to simplify the dimensioning and selection of circuit breakers (CBs) in future HVDC networks. This paper proposes new analytical formulas for the calculation of the ac-side contribution through the blocked half-bridge-based converters during pole-to-ground faults in multiterminal HVDC cable networks. Analytic approximations are derived for the steady-state short-circuit currents and the peak of the transient response for point-to-point HVDC links and extended to multiterminal HVDC cable networks with arbitrary grid topology. The results of the proposed expressions are compared with simulations in PSCAD and provide accurate calculations for the transient peak and steady-state values of the ac-side fault current contribution to the prospective CB current. [ABSTRACT FROM PUBLISHER]

Overvoltage transients due to lightning strikes is a common occurrence in power transmission lines which can ultimately lead to line outages. Simulation of transmission line networks under the influence of lighting plays a vital and essential role in predicting their transient behaviour. The transient behaviour of uniform transmission lines due to lightning has been studied extensively. However, in modern transmission line networks, nonuniformities and discontinuities such as nonparallel wire, line crossings or bends are becoming increasingly common. Therefore, in such cases, inaccuracies might be present in analysis performed using conventional uniform transmission line approaches. A recent publication by the authors analysed the transient behaviour of nonparallel and crossing transmission lines above perfect electric conductor (PEC) ground. However, the PEC assumption can only be used in a limited scope. In this paper a nonuniform transmission line model with external field coupling is presented to analyse the transient behaviour of a nonuniform wire structure due to the field coupling from a nearby lightning strike in the presence of lossy ground. Simulation results generated by the proposed model is compared with full-wave simulations and results published by other researchers. A case study to compare the results from the proposed model with a conventional uniform transmission line model under various ground-conductivity values and terminating conditions is also performed. The study indicates that the presence of nearby nonparallel lines can cause the transient behaviour of the structure to deviate from the behaviour predicted using uniform approaches. • The transient behaviour of a nonuniform wire structure a nearby lightning strike in the presence of lossy ground is studied. • Simulation results generated by the proposed model is compared with full-wave simulations and results published by other researchers. • Results from the proposed model have been compared with a conventional uniform transmission line model. • The study indicates that the presence of nearby nonparallel lines intensify the transient behaviour. [ABSTRACT FROM AUTHOR]

• Penstock water start time. • Water conduit transients. • Modelling of hydraulic conduits. • Solving travelling wave equations. • Power system dynamics for hydro generators. Almost all electrical power systems literature assumes that the shaft mechanical torque of a water turbine is linearly proportional to the wicket gate position and ignores the dynamics in the shaft torque due to the propagation of the water from the reservoir to the turbine. This propagation is usually modelled very simply using the water start-time equation and ignoring the travelling wave dynamics along possibly long conduits. This simplified modelling may introduce significant errors in the frequencies of oscillation which are in the range of 0.5–2 Hz and often fall within the range of slow oscillations in power system dynamics. This paper introduces the EMTP-H model for water dynamics based on the analogy between the hydraulic equations and the EMTP transmission line equations. The proposed model is validated with a field test and is applied to a simple power system frequency dynamics case. [ABSTRACT FROM AUTHOR]

Historically, failures of distribution transformers due to transient overvoltage phenomena have led to the development of resistor–capacitor snubber circuits for the protection of the transformer and winding insulation. These transients are most often observed when dry-type transformers are close coupled to vacuum switching devices. Typically, snubber circuit design has been specific for the particular application, and complex engineering studies were required. However, the design of a snubber circuit itself may be performed without these detailed studies. If snubber studies are required, the procedures for system modeling and simulation are explained in a step-by-step manner. [ABSTRACT FROM AUTHOR]

In modern power grids more and more switching and reconfiguration operations are performed, leading to harmful overvoltages. In addition, external factors causing overvoltages may also be dangerous to insulation systems, especially those which occur during lightning strikes. Overvoltages propagate in power transformers along the windings and between them, influencing the insulation systems of the windings as well as those of other electrical devices. An interesting phenomena which takes place in the networks relates to the transferred overvoltages propagating through distribution transformers. The internal and transferred overvoltages for transformers with a conventional steel core and for those with an amorphous core are analysed in this study. The frequency response of overvoltages which occur when the transformer is exposed to a voltage impulse of rectangular shape form the basis of the analysis. Surges of rectangular shapes simulate transient voltages occurring at surge arresters. The frequency response of overvoltages reveals the transformer response to oscillating transient components of overvoltages generated in the power systems. The coincidence of frequency responses of overvoltages and admittances for transformers is also presented. [ABSTRACT FROM AUTHOR]

A procedure for computing customized wavelets suitable for identifying the location of a fault along the length of a transmission line is proposed. Measuring the time difference of arrival (TDOA) between two consecutive transient reflections or the TDOA between the two initial peaks of two synchronized voltage/current bus measurements provides an accurate fault-location estimate. Reliable TDOA estimates can be obtained only when the transformed fault signals consist of short/peaked pulses that arrive on a bus with a small group delay. Our customization method improves the “peakedness” and shortens the group delay of the transient signal by maximizing a suitable peakedness objective function. It is shown that this approach is superior in terms of accuracy compared to the “classic” (Daubechies) wavelet-based technique found in the literature. The proposed method is independent of the fault type and can be used to reduce the required data sampling rate while maintaining reliable TDOA estimates. [ABSTRACT FROM PUBLISHER]

Wind turbine gearbox bearings (WTGBs) are the most reliability critical component in wind turbine gearboxes because of their high failure rate and long downtime‐per‐failure. Current design methods predict bearing failure‐by‐fatigue life models. However, premature WTGB failures have been observed by many other modes. This study presents the development of a multibody dynamic gearbox model, used to determine maximum bearing contact stresses from laboratory measured shaft torque data during normal operation and shutdown conditions. The model was validated by comparing its results to other models of the 750 kW National Renewable Energy Laboratory test drive train by the Gearbox Reliability Collaborative. During normal operation, the maximum contact stress experienced by the planetary stage bearings exceeded recommended levels by 1% and during shutdown by 15%. High‐speed shaft bearings also exceeded recommended levels during shutdown by 18%. [ABSTRACT FROM AUTHOR]

The generalization of the probabilistic lightning limiting parameter (LLP) method for high-voltage substation lightning performance estimation due to the discharges into connected overhead lines (OHLs) is described. The method improvement is made only for the case of lightning strokes to the shield wire of OHL, causing back-flashover in front of the substation. The improved LLP method is illustrated at the insulation coordination study of the 400-kV line with long connecting cable with direct entry into the gas-insulated substation of the hydroelectric plant. The number of surge arrester sets and sensitivity analyses of the number of connected step-up transformers influence to the mean time between failures of the 400-kV transformer and equipment insulation are investigated. [ABSTRACT FROM AUTHOR]

The prescribed perspective of high accession of distributed generation photovoltaic (DG‐PV) units on low‐voltage distribution networks has brought up many issues regarding their performance in case of network transient phenomena. In this study, the design principles that DG‐PV units must incorporate in order to meet the requirements of low‐voltage ride through capability (LVRTC) are investigated through detailed theoretical analysis and calculations. The analysis shows that a realistic over‐sizing of interfaced inverters of DG‐PV as well as an appropriate selection of the equivalent interconnecting reactance XDG, in conjunction with high penetration levels, can lead to satisfaction of LVRTC demands without violating the protection limits of the network. Moreover, the scenario of uniform dispersion along the distribution lines is proved rather favourable concerning the demand of LVRTC for voltage selectivity. Finally, considering the derived outcomes, a methodology of optimum design about LVRTC is proposed within the framework of reasonable constraints, which can be applied to any low‐voltage distribution network. [ABSTRACT FROM AUTHOR]

Power system operation practices are changing with the addition of renewable energy resources such as photovoltaic (PV) sources. The diverse and intermittent nature of these resources demands new operation strategies to ensure system reliability. As more PV units are added to power systems, the power generated by conventional generation resources should be reduced to accommodate these new resources. The reduction in fossil-fired generation allows realization of benefits in the sustainability of the generation mix. While some of the conventional generating units are retired, some should be retained for system reliability. This paper investigates the impact of generation redispatch or generation displacement in systems with high PV penetration. Comparing various study scenarios, a method based on regression techniques and Chebyshevs inequality is introduced in this paper. This method is used to calculate the dispatch or displacement ratio of the conventional generators for optimal steady state and transient response of the system. Recommendations are formulated based on an actual large-scale power system in the western United States. [ABSTRACT FROM PUBLISHER]

Phasor measurement units (PMUs) are taking an increasingly important role in power system dynamic security monitoring and control. However, traditional discrete Fourier transforms (DFTs) used by PMUs cannot obtain accurate phasor measurements during frequency excursion and transient events, being limited by its static phasor model. In this paper, a synchrophasor estimation algorithm for M-class PMUs based on the dynamic phasor model is proposed. In this algorithm, the dynamic phasor within an observation data window is approximated by the second-order Taylor expansion. The linear relationship between the second-order coefficients of the Taylor expansion and the errors caused by the DFT averaging effect is explored. Then, the linear relationship is used to compensate the raw measurement errors under a dynamic condition. Two digital filters are applied not only to eliminate the spectrum leakage caused by the dynamic inputs, but also to make the PMU immune to the out-of-band signals. The algorithm is investigated through simulation, laboratory experiments, and real data from the power system according to IEEE C37.118.1. The test results demonstrate that the proposed algorithm can meet the requirements of the standards. [ABSTRACT FROM AUTHOR]

A 500-kV dc hybrid transmission line consisting of a gas-insulated line (GIL) with lengths up to 10 km connected at both ends to long overhead lines is applied for lightning overvoltage studies. For this system, the conventional application of external surge arresters results in high electrical stress on the insulation of GIL. Therefore and because of the modular structure of GIL, the application of internal surge arresters and two combinations of external and integrated surge arresters are investigated. The influence on the voltage buildup in GIL of variation in the position of integrated surge arresters is explained and the best positions are calculated by a sensitivity study. All variants of the application of integrated surge arresters result in a reduction of voltage stress within the GIL compared to the conventional application of external surge arresters. [ABSTRACT FROM AUTHOR]

This study presents a new, generalised method for the calculation of resonance frequencies (RFs) in transmission line (TL) responses. The proposed method calculates the RF of any propagation mode and is applicable to all types of TL configurations, taking also into account the effect of the source and load impedances as well as of possible transpositions or cross‐bondings. The results are validated with the corresponding results obtained from frequency‐domain transient simulations and laboratory measurements, whereas simple theoretical formulas for both overhead lines and underground cables are also investigated, revealing their limited accuracy. Practical cases of engineering interest are demonstrated, where the required single or multiple RFs are accurately calculated by the proposed method. Finally, the performance of the presented methodology is thoroughly examined incorporating two diagonalisation approaches for the calculation of the modal propagation velocities. [ABSTRACT FROM AUTHOR]

This paper presents a novel wavelet based approach for fault location using voltage transient waveforms in power distribution systems. The proposed method includes two main stages. Firstly, the approximate location of the fault or fault section is determined using a new algorithm with discrete wavelet transform. The difference between arriving times of transient components in different measurement units is used for this purpose. The accurate location of the fault is determined in the second stage. Depending on the determined fault section, the difference between arriving times of transient components in different measurement units or the frequency content of the voltage transients are used. The time difference and frequency content are calculated using discrete and continuous wavelet transform (DWT and CWT) respectively. The proposed technique is implemented on an unbalanced 34 bus distribution system with two distributed generation units which is simulated in ATP–EMTP. The comparison of the results of the proposed method with previous works verifies its better accuracy and more robustness to fault conditions including fault inception angle and fault resistance. [ABSTRACT FROM AUTHOR]

Transients from lightning strikes can enter underground cables at overhead line to power cable transitions. Possible overvoltages on these surges at cross‐bonding connections of the cable screens are of major concern. A model is developed for modelling overvoltages from transient signal propagation through a combined cross‐bonding cable and box. This model is applied to the first Dutch 400 kV cable connection. Such model incorporates model parameters whose values depend on design details of the cross‐bonding box. The values for these model parameters are extracted from the measured transmission and reflection signal on steep pulses injected into the actual cross‐bonding box configuration. The model combines transmission line description for the cross‐bonding cables with mainly inductive behaviour of the cross‐bonding box. The obtained results are verified by measurements. The model is applied to investigate overvoltages induced at the cross‐bonding cable and box on 1.2/50 µs impulse voltage injection representing a lightning impulse voltage applied to the core conductor of the cross‐bonding cable. Furthermore, the effectiveness of surge arresters to reduce overvoltages at the cross‐bonding cable screen is demonstrated by simulations with this model in PSCAD. [ABSTRACT FROM AUTHOR]

With the increasing penetration of distributed generation, distribution networks are evolving from passive to active. New transient simulation methods are required to study the detailed dynamic characteristics of large‐scale active distribution networks. A model order reduction method based on Krylov subspace theory is introduced in this study to reduce the overall model scale of active distribution networks for transient simulations. A modified state‐space model of linear distribution networks is developed to replace the conventional models for improvement in model reduction efficiency, while guaranteeing the passivity and stability of the reduced models. The proposed model order reduction method is validated with the IEEE 123‐node test network. The results prove that the proposed method is effective for different applications to improve the simulation efficiency of large‐scale active distribution networks. [ABSTRACT FROM AUTHOR]

Power frequency phasors are widely used in the measurement, analysis, control and protection of power systems. When disturbances occur in such systems, power frequency phasors must be estimated quickly to ensure an accurate restoration to normal operation. Hence, a fast and accurate estimation algorithm would be a significantly useful tool. In consideration of the composition of transient signals in power systems, a novel algorithm for power frequency phasor estimation is proposed. Based on the double matrix pencil method, a unitary reference matrix of complex‐valued exponential signals is formed. The power frequency phasor estimation is then transformed to a brief multiplication of matrices. Thus, the QR decomposition, generalised eigenvalue calculation, and secondary estimation can be avoided and no complex multiplication is introduced. Therefore, the computational efficiency of the proposed method is improved compared with previous estimation techniques. Analytical and experimental investigations show that the proposed algorithm can extract power frequency phasors accurately, stably and quickly under power system transients. [ABSTRACT FROM AUTHOR]

Finite difference time domain (FDTD) is widely used to compute the transient behavior of transmission lines. However, the time step of classic FDTD is limited by the Courant–Friedrich–Lewy (CFL) condition, which makes it not sufficiently efficient for relative low frequency (compared with computation cell size and wave length) signals. The FDTD with alternating direction implicit (ADI) technique is not restricted by the CFL condition, but suffers from numerical dispersions. This paper employs the spectral deferred correction method as the time marching scheme to solve the semidiscretized form of the telegraph equation. The method is unconditionally stable, which allows a larger time step, and can be essentially arbitrary high order accurate. [ABSTRACT FROM PUBLISHER]

The present paper proposes a dual-tree complex wavelet transform (DTCWT) based approach for recognition of power system transients. Several researchers, all over the world, have so far attempted to solve the problems of recognition of power system transients, hybridizing transform-based techniques with popular computational intelligence based tools, for example, using wavelet transform and S-transform for feature extraction, followed by artificial neural networks (ANN) or fuzzy logic-based classifiers. The proposed method of hybridizing DTCWT-based feature extraction with ANN-based classification could efficiently detect several commonly occurring power quality (PQ) disturbance events. The PQ disturbance events considered include four different transient conditions, namely transients due to capacitor switching, transformer inrush currents, transients due to motor switching and transients due to short circuit faults. A detailed performance comparison with several contemporary, competing methods existing in the literatures for similar problems aptly demonstrates the suitability of the proposed method. [ABSTRACT FROM AUTHOR]

This paper studies the average value modelling (AVM) of medium frequency (200 Hz–2000 Hz) dc–dc converters, which are becoming increasingly important in high-power dc grids and distributing microgrids. The most convenient modelling is based on transfer function and power components which are available in common simulation platforms, such as PSCAD/EMTDC. However, these models are found to require very small simulation steps and the achieved time-domain accuracy is not satisfactory for medium frequency converters. The core issue of accuracy loss is identified and corresponding improvement is proposed. User written state-space models in the abc frame and the dq frame are analyzed in depth. Different solvers, including the Dommel's method, the Heun's method, and the Runge-Kutta method were adopted and compared in solving the state-space models. A high-power 2-kHz LCL dc-dc converter is taken as the test system. It is found that the AVM in the dq rotating frame based on the Runge-Kutta solver is able to generate very accurate time-domain responses compared to the detailed switching model with almost 100 times improvement in simulation speed. It is demonstrated that a dc-dc converter with 2-kHz inner ac circuit frequency can be accurately simulated at a 50-\mus time step. [ABSTRACT FROM PUBLISHER]