1,720,984 research outputs found
On Hilbert transform methods for low frequency oscillations detection
No full textThis study tackles the issue of electromechanical modes identification through a measurement-based methodology employing a novel signal decomposition theorem based upon the Hilbert transform. The methodology aims to answer in a simpler and more pragmatic manner to the main weaknesses of the Hilbert-Huang transform with respect to the major refinements in the relevant literature. These weak points are discussed with sufficient detailed degree in the study. The main contribution of this study consists in combining a recent signal decomposition theorem for separating an assigned signal into elemental ones, each of them characterised by a single frequency component and a robust preliminary non-linear spectral analyser, named Lp periodogram. This procedure's results are very appropriate for analysing some critical cases of electromechanical oscillations, because of the Lp periodogram robustness against heavy-tailed noise and also its intrinsic ability in estimating closely spaced frequency components. The proposed approach is found to be inherently simple, reliable and consistent in performance as well as characterised by low computational burden. Some numerical applications validate the methodology and assess its own performance on synthetic signals, near real-life signals acquired by IEEE test networks and on a real measured signal from a wide-area monitoring system currently in operation
Improved non-linear least squares method for estimating the damping levels of electromechanical oscillations
No full textConceptualization and Experimental Deployment of an Adaptive Synchronized Sensing System for Power Line Thermal Monitoring
No full text
Availability analysis of photovoltaic inverters in presence of uncertain data via Bayesian approach
No full textThe paper presents an advanced Bayesian technique to carry out availability analyses of photovoltaic inverters in presence of uncertain reliability data. In order to proper take into account the above uncertainty, photovoltaic inverter hazard rate and repair rate are considered as random variables characterized by proper Log-normal and/or Gamma distributions. These assumptions are adequately motivated by well known and established physical and mathematical considerations. In this manner the photovoltaic availability uncertainty can be expressed as a function of the component uncertain data. Afterwards, thanks to the tailored Bayesian technique we demonstrate how, even in presence of scarce data, an efficient updating of the system performance can be accomplished during the photovoltaic inverter operating life. The methodology is really useful in view of an optimal allocation of the components’ reliabilities at the design stage and in order to establish the actual expected payback of the whole photovoltaic system. Extensive numerical simulations confirm the effectiveness and the validity of the developed Bayesian technique by also verifying its inherent robustness and efficiency through a rigorous analysis
Real time generator coherency evaluation via Hilbert transform and signals morphological similarity
No full textThe paper tackles the issue of evaluating in real time generator coherency through the employment of an adequate new measurement based algorithm. This algorithm combines Hilbert transform implemented via Boche method with a modified Bray-Curtis index. The first step ensures an inherent algorithm robustness against some Wide Area Monitoring Systems (WAMS) communication network effects. Numerical simulations performed on the IEEE 39 bus test system - New England - in the last part of the paper confirm the validity of the developed methodology, demonstrating furthermore the intrinsic regularizing action of the Hilbert transform against the data packet dropouts in WAMS
Availability - Based Wind Farm Design
No full textThe paper develops a methodology for the optimal sizing of a generic wind farms, focusing primarily on reliability aspects,
besides the traditional economic ones. A specific objective function is proposed in order to select the better wind farm configuration,
based upon the profits related to the economic trading in the deregulated electric market and the costs due to investment, operation &
management, and to system unavailability. This objective function is accurately investigated as a function of the turbines number in
order to derive the most convenient alternative, which implies also the optimal choice of the single wind generators size. The ranking
coming out from this assessment is then compared with that one established in terms of expected load not supplied. A compromise
choice, between the best alternatives provided by the two criteria has finally adopted. A simple numerical application is reported in the
last part of the paper for testing the validity of the proposed approach. Also uncertainty aspects in the basic input parameters are taken
into account and possible way of dealing with them is briefly illustrated
A Novel Approach to Design Cathodic Protection System for High-Voltage Transmission Cables
No full textCorrosion is an electrochemical process involving electrical currents. It consists of the destruction of a metal through its interaction with the environment. The phenomenon is observed in underground and buried structures, where aging can be strongly influenced by electrical currents flowing in the Earth. Methods of protection (i.e., “cathodic protection”) are related to the use of sacrificial anodes or more sophisticated systems, which impose a negative voltage to the metal structures to be protected. The corrosion phenomenon can be relevant also in electric power system applications. Underground or undersea electrical cables need to be protected as a consequence of stray currents flowing in the soil. This paper studies the problem of cathodic protection design for high-voltage transmission cables in undersea applications. The aim is to propose a design procedure which can be implemented by nonexpert electrical designers. A practical approach, which characterizes the distribution of the voltage on the outer layer of power cables, is formalized on the basis of common simplified assumptions. Numerical simulations give evidence to the formulation according to the features of environmental conditions
Lifetime characterization via lognormal distribution of transformers in smart grids: design optimization
No full textIn this paper, the problem of the optimal rating of transformers in smart grids is properly discussed with
respect to the specific load characteristics. The design is based on the accurate prediction of the lifetime
degradation of mineral-oil-immersed transformers subject to highly intermittent loads. In fact, by investigating
the nature of the loads in the smart grid scenario, it clearly appears that the intermittent nature
of the power demand increases drastically. In this context, specific tools for the characterization of the
lifetime duration are required, since severe reduction of the transformer’s life can be observed due to
overloads, even in the case of short-duration overloads. The classical approaches based on using the
equivalent thermal current to predict the transformer’s lifetime might result in incorrect estimates, thus
requiring advanced models that can deal with the time variability of the load. In this paper, the randomness
of the load powers is addressed in terms of stochastic processes. In particular, the Wiener process is
demonstrated to provide robust modeling of load variability. By starting from this assumption, it was
demonstrated analytically that the hot-spot temperature, which is a major contributor to the degradation
of the transformer’s lifetime, also is a stochastic process. Then, in spite of the nonlinearity of the thermal
model, the hot-spot temperature can be represented as a Wiener process, the robustness of which has
been verified adequately. By taking into account the nonlinear relationship between the hot-spot temperature
and the lifetime, the authors verified that the transformer’s lifetime is modeled as a lognormal,
stochastic process. Hence, a novel, closed-form relationship was derived between the transformer’s
lifetime and the distributional properties of the stochastic load. The usefulness of the closed-form expression
is discussed for sake of design, even if a few of the considerations also are performed with respect to
operating conditions. The aim of the numerical application was to demonstrate the feasibility and the
easy applicability of the analytical methodology
Transient stability margins evaluation based upon probabilistic approach
No full textThe paper proposes a new probabilistic approach for deriving the stability margins of an electrical power system, taking into account the stochastic nature of the main problem randomness: the fault clearing time, the reclosing time and the fault type and location. Differently from previous works, the probabilistic approach properly considers also the friction forces which make more difficult the mathematical formulation of the problem. In order to give a measure of the system exploitation with respect its own transient stability, a probabilistic stability index has been adopted in the work. In the last part of the paper, a numerical application is presented in order to show the feasibility and the effectiveness of the proposed methodology
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