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• EMTP-based results clarify that SPCB operation results in WF voltage swell. • The results show that the CSC and DSC controllers with the FRT, are not effective. • To improve the HVRT after the SPCB operation, a dc-link chopper is provided. For transient single phase-to-ground (SPG) faults in transmission lines, single-pole circuit breaker (SPCB) operation can improve system reliability. This issue is more critical in transmission lines emanating from wind farms (WFs). In the large-scale WFs, the grid codes necessitate that wind generation remains in operation during the transmission line faults. For this purpose, the grid codes focus on the development of fault-ride-through (FRT) requirements. In this paper, it is shown that after the SPCB operation, the terminal voltage of the permanent magnet synchronous generator (PMSG)-based wind turbine (WT) rapidly increases and may cross the high-voltage ride-through (HVRT) boundary. Therefore, the WT terminal overvoltage after the SPCB operation may result in undesirable tripping of the WT. The obtained results in this paper show that in most cases both the coupled and decoupled sequence controllers of the WT converter equipped with the FRT requirements are not able to improve the HVRT performance after the SPCB operation. To enhance the HVRT performance of PMSG-based wind turbines after the SPCB operation, a dc-link chopper controller is proposed. EMTP-RV simulation results on the IEEE 118-bus and 5-bus systems show the success and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper investigates impacts of various formations of hysteresis on the stability domain of ferroresonance modes of a voltage transformer (VT). Based on four different hysteretic and two single-valued polynomial models, ferroresonance behaviors of the VT are studied. The hysteretic models are developed based on the Preisach theory. The first hysteretic model accurately duplicates the measured hysteresis loops of the VT in a wide variation range of the core excitation level. The other three hysteretic models represent different hysteresis loop formations. The polynomial models are based on identical single-valued polynomial magnetization characteristics but represent different core loss resistances (i.e., constant and dynamically varying core loss resistances, respectively). All of the models represent the same core losses as the measured value to investigate impacts of hysteresis loop formations on ferroresonance modes, independent of the corresponding hysteresis losses. The studies are conducted in time domain in the PSCAD/EMTDC software environment. The studies indicate that the VT model, which duplicates the measured hysteresis loops and the measured core loss over a wide range of excitation levels, results in more ferroresonance modes, expanded stability domains, and higher overvoltages. This paper concludes that formation of hysteresis is an independent factor which significantly impacts the ferroresonance phenomenon. Not only is it a single-valued magnetization characteristic but also a generic hysteretic characteristic; if it is not accurately constructed based on the measured core hysteresis data, it can result in significant error in determining the ferroresonance overvoltages and stability domains of the ferroresonance modes. Index Terms--Bifurcation diagram, core loss, ferroresonance, hysteresis, Preisach theory, transformer.

The majority of transmission-line faults are temporary short circuits. The short circuit arc is usually self-extinguishing after opening the transmission-line circuit breakers. High-speed reclosure of transmission-line circuit breakers can improve system stability. As the voltage level increases, arc deionization time increases as well, endangering system stability. Application of automatic single-phase reclosing makes it possible to increase system stability even for extremely high voltage transmission lines. Automatic single-phase reclosing is used to clear single-phase-to-ground faults, which are about 80% of the transient faults. In order to have successful fast reclosing, different methods are used to extinguish the arc. One of the common methods is to use a single-phase reactor in the neutral of shunt reactor, when transmission line is compensated with shunt reactors. As of now, the effect and parameters of this neutral reactor are usually determined based on the steady-state analysis without exact system and arc modeling. In this research work, the investigation of a neutral reactor application is performed for transposed and untransposed transmission lines using transient simulation with appropriate models. Then, guidelines for selecting the appropriate amount for the neutral reactor are proposed. Index Terms--Arc modeling, neutral rector, secondary arc extinction, single-phase reclosing.

This paper introduces an accurate transformer core model, using the Preisach theory, to represent the core magnetization characteristic. This modeling approach provides the required precision to match major and minor hysteresis loops of the model with those of the actual transformer core material. Using the proposed model, the ferroresonance phenomenon of a voltage transformer (VT) is simulated and compared to the corresponding experimental results. In addition, the simulated ferroresonance behavior of the VT based on: 1) the Electromagnetic Transients Program (EMTP)-RV hysteric reactor model, 2) the EMTP reactor type-96 model, and 3) a single-valued polynomial as magnetization characteristic, is also deduced and compared with the proposed model and the experimental results. The investigations conclude that the proposed model provides the most accurate results in terms of the VT core losses and the VT voltage waveforms and their peak values during 1) normal operating conditions, 2) ferroresonance transients and jumping from normal to ferroresonance operating conditions, and 3) ferroresonance steady-state conditions. Furthermore, higher accuracy of the proposed model in representing the hysteresis loop provides the highest and the most accurate bifurcation point and the transient loss when compared with other models. This paper also concludes that major and minor hysteresis loops must be represented in the core model to accurately simulate ferroresonance phenomenon of the VT. Index Terms--Bifurcation, ferroresonance, hysteresis, minor loops, power loss, Preisach theory, transformer.