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A stochastic lightning attachment model for evaluating the lightning performance of overhead transmission lines is introduced. The proposed model considers the stochastic nature of lightning attachment by taking into account the lightning discharge branched and tortuous behavior. It integrates physical criteria on leader inception by adopting the Petrov and Waters model, as well as leader discharge progression considering also the competing interaction of multiple upward leaders. A generalized methodology combining stochastic modeling of lightning incidence with an electromagnetic transients (EMT) simulation model is proposed so as to estimate the backflashover and shielding failure flashover rates of HVDC overhead lines; an application to a monopolar −400 kV line sheds light on the basic parameters that affect the lightning performance of HVDC lines. The probability of shielding failure is higher than that obtained by the deterministic lightning attachment models. The stochastic nature of lightning attachment and the effect of lightning peak current distribution should be considered for the design and evaluation of the lightning performance of the emerging HVDC systems. [ABSTRACT FROM AUTHOR]

Modeling of battery energy storage systems used for applications, such as electric vehicles and smart grids, emerged as a necessity over the last decade and depends heavily on the accurate estimation of battery states and parameters. Depending on the battery-cell type and operation, a combination of algorithms is used to identify battery parameters and define battery states. This paper deals with robust Li-ion batteries modeling with a specific focus on a hybrid approach for a more accurate state-of-charge (SOC) estimation. The analysis presents a detailed description of the state-of-the-art stand-alone SOC estimation methods and focuses on a hybrid SOC estimation technique to improve accuracy under varying conditions. Emphasis is given on performance improvements of the proposed hybrid approach compared to the conventional methods, whereas a thorough experimental validation is presented to evaluate the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, two discretization techniques are combined to present a coupled electro-thermal model for the transient analysis of gas-insulated transmission lines (GILs). The analysis of the thermal problem is based on the volume-element-method, representing heat transfer equations on a 2-D axisymmetric GIL model and determining temperature distribution over space and time. For the electrical formulation, the finite-difference time-domain method is adopted considering constant parameters calculated at the frequency of interest. The coupled electro-thermal problem in the case of transient conditions is solved by means of a bidirectional procedure. A set of test cases is imposed on the electric part, and transient analysis is conducted while considering the line coupled electro-thermal performance. [ABSTRACT FROM AUTHOR]

Accurate load modeling is essential for power system stability analysis and control. This topic has regained interest, due to the high penetration of new types of loads and the increased availability of measurements in extended power grids. In this paper, an aggregated load model based on measurement data is formulated for dynamic simulations of large power systems. The proposed model employs variable-order transfer functions, enabling the accurate simulation of complex load dynamics. A complete methodology for the automatic derivation of the minimum-required model order is proposed with the model parameters calculated via a robust multisignal identification procedure. For this purpose, the vector fitting method is introduced as a technique for measurement-based load modeling. Several simulations are performed using the NEPLAN software to investigate the accuracy and the generalization capabilities of the proposed model. The model performance is thoroughly compared with other conventional load models, also using measurements recorded on a laboratory-scale microgrid. [ABSTRACT FROM PUBLISHER]

In this paper, detailed mathematical formulation of a coupled electro-thermal model for transient studies of high-temperature superconducting (HTS) transmission systems is presented. Regarding the thermal modeling, the volume-element method is used in order heat transfer equations on a two-dimensional axisymmetric cable model to be solved and temperature distribution over space and time to be determined. For the modeling of the electric part, a constant-parameter finite-difference time-domain method is utilized to calculate voltages and currents over space and time as well. The analysis is conducted on a bipolar cable suggested by the Electric Power Research Institute for long-distance HTS dc transmission to highlight the electric and thermal domain interaction under transient conditions. Different test cases are conducted to evaluate the electric and thermal transient performance of the examined HTS cable. [ABSTRACT FROM AUTHOR]

The ever increasing need for cost-efficient, high-density power transmission brought to the fore applied superconductivity as an alternative worth investigating. Especially, high-temperature superconducting (HTS) dc cables emerge as a promising solution for bulk power transmission and their use in the near future is expected to be increased. HTS cables have the special characteristic of varying performance under different critical conditions, especially under different operating temperatures. Therefore, detailed thermal analysis of HTS cables representing thermodynamics and heat transfer for varying length and time is of significant importance. The analytical mathematical formulation presented in this paper solves heat transfer equations for a two-dimensional axisymmetric cable model and identifies temperature distribution over length and time. The analysis is conducted on a bipolar cable suggested by the Electric Power Research Institute for long-distance HTS dc transmission, while both steady-state and transient scenarios are examined. [ABSTRACT FROM PUBLISHER]

This letter delivers a method to extend the use of the exponential recovery model (ERM) for the dynamic simulation of active distribution networks (ADNs). The conventional ERM uses exponential functions to describe the steady-state and transient characteristics of the grid, failing to replicate reverse power flow phenomena which may occur in modern ADNs during or after voltage disturbances. To solve this issue a new formulation employing polynomial functions instead of the original exponential is proposed. [ABSTRACT FROM AUTHOR]

This paper presents a new method for the calculation of smooth frequency-dependent transmission-line (TL) transformation matrices. The proposed method, based on the Levenberg–Marquardt algorithm, solves an equivalent real-valued approach of the generalized complex eigenproblem. The implemented formulation incorporates a robust convergence criterion and is applicable to all TL configurations, due to the included numerically well-defined computational scheme. Smooth modal transformation matrices are calculated for overhead and underground TL configurations under different representations of the imperfect earth. Results are compared and validated with the corresponding results obtained from the Newton–Raphson and the sequential quadratic programming methods, revealing the accuracy, efficiency, and robustness of the proposed formulation, even in cases where the other methods fail. [ABSTRACT FROM AUTHOR]