Verification tests of a novel ferroresonance detection technique

Abstract. Ferroresonance is a complex electromagnetic phenomenon that affects voltage transformers. The appearance of the ferroresonant phenomenon provokes important oscillations that are responsible for serious thermal and dielectric overstresses, which may lead to catastrophic failures in the electrical power system. This paper analyzes the behaviour of a novel ferroresonance detection technique, based on artificial neural networks, through the results obtained in several verification tests conducted in a real voltage transformer

Simulated tempering with irreversible Gibbs sampling techniques

We present here two novel algorithms for simulated tempering simulations, which break the detailed balance condition (DBC) but satisfy the skewed detailed balance to ensure invariance of the target distribution. The irreversible methods we present here are based on Gibbs sampling and concern breaking DBC at the update scheme of the temperature swaps. We utilize three systems as a test bed for our methods: a Markov chain Monte Carlo simulation on a simple system described by a one-dimensional double well potential, the Ising model, and molecular dynamics simulations on alanine pentapeptide (ALA5). The relaxation times of inverse temperature, magnetic susceptibility, and energy density for the Ising model indicate clear gains in sampling efficiency over conventional Gibbs sampling techniques with DBC and also over the conventionally used simulated tempering with the Metropolis–Hastings (MH) scheme. Simulations on ALA5 with a large number of temperatures indicate distinct gains in mixing times for inverse temperature and consequently the energy of the system compared to conventional MH. With no additional computational overhead, our methods were found to be more efficient alternatives to the conventionally used simulated tempering methods with DBC. Our algorithms should be particularly advantageous in simulations of large systems with many temperature ladders, as our algorithms showed a more favorable constant scaling in Ising spin systems as compared with both reversible and irreversible MH algorithms. In future applications, our irreversible methods can also be easily tailored to utilize a given dynamical variable other than temperature to flatten rugged free energy landscapes

Microgrid Protection: Technical challenges and existing techniques”, Renewable Energy and Power Quality

Abstract. The design of protection systems associated with medium and low voltage networks has traditionally been based on the assumption of unidirectional power flows, making the use of time coordinated overcurrent relays an efficient and reliable way of protecting against network faults. The changes that these systems have undergone over the recent decades regarding distributed generation, along with the fact that many of these sources can be connected to form independent microgrids, have challenged this perspective. A number of alternative solutions have recently appeared in technical literature. Therefore, this paper aims to provide a comprehensive overview of the existing proposals for protection design in microgrids. Apart from describing the most relevant options presented to date and classifying them in specific groups, a comparative analysis is performed in which the most important benefits and drawbacks of each approach are presented. Finally, some conclusions and practical recommendations are derived from the analyzed references

Protection systems for multi-terminal HVDC grids

Publisher Copyright: © 2018, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved.Nowadays the protection of Voltage Sourced Converters (VSC-HVDC) is still a challenge as the high fault currents can damage seriously the converters. Nevertheless, the protection of HVDC grids is more complicated than point-to-point links, because of the specific requirements of HVDC grids. The protection system must detect and clear the faults within a demanding time. Moreover, HVDC circuit breakers are still not available, complicating the selective protection of the grid. Accordingly, since the protection of HVDC grids is so demanding, this issue is one of the biggest obstacles to develop HVDC grids. In this paper the protection system for HVDC grids is presented, including the measurement technology, fault detection and location algorithms and HVDC circuit breaker technology.Peer reviewe

Quaternary atoll development : new insights from the two-dimensional stratigraphic forward modelling of Mururoa island (central Pacific ocean).

International audienceKnowledge about the Quaternary evolution of mid-ocean atolls comes mainly from drilling and field observations carried out on a number of Pacific carbonate islands. However, little is known about the early to mid Pleistocene atoll development history, especially at margin and foreslope settings. Using previous field and subsurface data from Mururoa Atoll and a process-based modelling software (DIONISOS), a two-dimensional forward stratigraphic model of atoll development is proposed for the past 1·8 million years (Myr). Observational data from vertical to inclined coring, seismic and bathymetric surveys indicate that, from approximately 0·45 to 0·40 million years before present (Ma), carbonate deposition at Mururoa Atoll resulted in a series of mostly prograding reef units. The model is first constrained at the base by the shape and topography of the pre-Quaternary basement. A number of sensitivity tests were performed to define the respective influence of variant parameters. The best-fit development scenario that accounts for the overall geometry and stratigraphic architecture of the Quaternary sediment packages is obtained by using the sea-level curve by Miller et al. (2005), uniform subsidence rate of 105 m Myr−1, and carbonate production rates gradually increasing from 0·50 to 8 mm yr−1 between 1·80 Ma and the present. Additional controlling parameters include subaerial erosion (at a constant rate of 0·25 m/kyr), wave-energy and sediment-transport processes. The stratigraphic forward model predicts a succession of three distinct types of carbonate systems that have developed since the earliest Pleistocene: toe of slope systems from 1·80 Ma to about 0·80 Ma, open-platform systems from 0·80 Ma to 0·50 Ma, and framework-reef systems from about 0·50 Ma to the present. The development of these different systems is most likely to be controlled by climate and changes in sea-level cycles. During the low-amplitude 41 kyr cycle periods of the earliest Pleistocene, ambient conditions were not conducive to framework-reef growth; shallow-water carbonate sedimentation was dominantly gravity-driven, operating along the platform foreslopes only. During the Mid-Pleistocene Climate Transition, narrow, open-platform units have developed at the upper parts of the pre-Quaternary basement flanks. With the onset of the high-amplitude 100 kyr sea-level modes and climate restoration, reef frameworks started to be generated. These models from Mururoa agree with a number of previous studies suggesting that most of the true framework reefs were not initiated prior to 0·50 Ma. Mururoa Atoll is demonstrated to be a robust analogue for providing more realistic interpretations of the development history of Pacific atolls. Further modelling with three-dimensional DIONISOS could generate better predictions by taking into account hydrodynamic and transport parameters more accurately