Ferroresonance in Voltage Transformer ConsideringLinear and Nonlinear Core Losses Effect

Accurate model of permanent magnet synchronous machine (PMSM) is significant for high-performance control. The machine model can be affected by various factors such as magnetic saturation and core loss effect, especially in the deep saturation and high-speed regions. This article proposes a data-driven-based machine modeling and compensation approach to improve the model accuracy by considering saturation and core loss effect. In the proposed approach, magnetic saturation is initially modeled using nonlinear polynomials and core loss effect is modeled with various speed data. The model mismatch due to these effects is then derived to generate the training data for the neural network (NN), which can accurately predict the model mismatch under various operating conditions. In comparison to the conventional model, the proposed approach adds compensation terms directly to the machine models, which can achieve better accuracy with efficiency and simple implementation, which can be utilized in motor control and parameter estimation. The proposed approach is validated on a laboratory interior PMSM and compared with existing methods under various operating conditions.

Ferroresonance an electrical phenomenon may cause overvoltages in the electrical power system. In this paper, an overview of available papers is provided, at rst ferroresonance is introduced and then various type of ferroresonance in a voltage transformer (VT) is simulated. Then eect of new model of circuit breaker (CB) on damping ferroresonance oscillation is examined. Finally eect of earth resistance on the stabilizing these oscillations in the case of nonlinear core loss has been studied. Core loss is modelled by third order power series in terms of voltage and includes nonlinearities in core loss. For conrmation, the simulation is done on a one phase voltage transformer rated 100VA, 275kV. The simulation results reveal that novel modeling of circuit breaker exhibits great controlling eect on ferrores- onance overvoltages.

Electromagnetic voltage transformers (VT) included in the scheme of ice melting (SIM) with direct current on overhead transmission lines (OTL) must be switched off during SIM assembling and switched on during disassembling, that increases the OTL taken out of service time and reduces the reliability of the electric power system. Three variants, in which the disconnection of the VT is not required, for installing capacitors to protect the VT from direct voltage are considered. A conclusion is drawn on the conditions of applicability of each option based on an analysis of the main SIM. Necessary for practical use the equivalent circuits and the values of DC voltages on the VT in the main schemes of ice melting by direct current at OTL are presented. A methodology and an example of capacitors' block and additional resistor's parameters calculating are given. Calculated values provide the required accuracy class of VT when it is constantly switched on both in the normal scheme and in the SIM.

Ferroresonance is a nonlinear oscillatory phenomenon, which occurs in capacitor-coupled saturable core transformers under certain conditions in a power system. The major part of the ferroresonance analysis is to find out the appropriate model of the B-H loop of the transformer. The magnetizing branch of the transformer at no load is modeled by nonlinear equation. R. Rudenburge in his graphical approach, proposed in the year 1950, took the magnetizing curve as a single line. Then, the occurrence of ferroresonance was examined by varying different circuit parameters. In this paper to incorporate the variable core loss, two separate equations are used to represent the B-H loop. Then, the new model is used to verify the occurrence of ferroresonance with the variation of different circuit parameters.KeywordsFerroresonanceB-H loopTransformer’s nonlinear characteristicsVariable core loss

Ferroresonance suppression in power transformers using chaos theory

With the advent of smart grid, smart transmission lines as an important part of smart grid gradually entered the construction. In view of this, installing various testing equipment on the transmission line tower is the basic work of building intelligent transmission line. However, limited by geographical conditions or insulation conditions, there are few low-voltage power supply near the transmission line towers. It is a big problem to supply power to the low-voltage detection equipment on the towers. In this paper, a new method of capacitive buck charging for transmission line towers is proposed. A special high voltage line capacitor and voltage transformer are used in series to extract energy directly from the high voltage line. The insulator string is used as the insulation support of the overvoltage of the transmission line, and the line capacitor and voltage transformer are connected in parallel. Stable energy output is obtained to achieve reliable power supply for transmission line tower monitoring equipment. However, the power supply will inevitably suffer from lightning strikes if it is exposed to nature for a long time. Therefore, it is of great practical significance to study the transient characteristics of Lightning Overvoltage in capacitor power supply system and to study its protection technology to ensure its safe and reliable operation.

A comprehensive analysis of the development prospects of optical current and voltage trans-formers in electric power systems has been carried out. These transformers represent a new class of products that use the latest advances in optics, electronics, digital signal processing and transmission systems

This paper addresses the problem of Bayesian wavelet estimating the mean vector of multivariate normal distribution under a multivariate normal prior distribution based on linear and nonlinear exponential balanced loss functions. The covariance matrix of multivariate normal distribution is considered known. Bayes estimators of mean vector parameter of multivariate normal distribution are achieved. Then two soft shrinkage wavelet threshold estimators based on Stein’s unbiased risk estimate (SURE) and Bayes estimators are provided. Finally, the performance of the soft shrinkage wavelet estimators was checked through simulation study and Electrical Grid Stability Simulated data set. Simulation and real data results showed the better performance of SURE thresholds based on linear and nonlinear exponential balanced loss functions compared to other classical wavelet methods. Also, they showed better performance for SURE threshold based on nonlinear exponential balanced loss function in multivariate normal distribution with small dimensions.

Recently there has been much interest in designing optical tapers for nonlinear pulse manipulation in both standard[1] and semiconductor filled fibres[2]. Such tapers can be used to overcome the large linear losses in semiconductor filled fibres while allowing parabolic pulse generation or soliton propagation for example. However once the taper profile has been chosen to overcome the linear loss problem in semiconductor filled fibres the problem of two photon absorption (TPA) and associated free carrier effects remain. In this work we show that it is possible to use a genetic algorithm to design tapers that alleviate both linear and nonlinear losses and hence should allow high quality pulse propagation over several centimetres of semiconductor filled fibres.

Due to the increasing penetration of gas-fired units and power to gas facilities, the electrical power system and natural gas system are more and more bi-directionally coupled. To tackle the challenges on the optimal scheduling operation of an integrated gas and power systems (IGPS), this article focuses on developing a novel approach to build a continuous spatial-temporal optimal operation schedule model. In the light of different time constants of the electrical power and natural gas systems, the continuous spatial-temporal optimal operation schedule model of IGPS is formulated in function space. Additionally, Bernstein polynomials are used to reformulate the continuous spatial-temporal optimization problem of IGPS to mixed-integer linear programming. In the study cases, the simulation results of a simple integrated system and a combined IEEE 39-bus power system and Belgian natural gas network demonstrate the accuracy and effectiveness of the proposed model.

We report experiments on high-amplitude sound wave propagation in an acoustic metamaterial composed of an air-filled waveguide periodically side-loaded by holes. In addition to the linear viscothermal and radiation losses, high amplitude sound waves at the locations of the side holes introduce nonlinear losses. The latter result in an amplitude-dependent reflection, transmission, and absorption, which we experimentally characterize. First, we evidence that nonlinear losses change the nature of the device from a reflective to an absorbing one, showing the possibility to use the system as a nonlinear absorber. Second, we study the second-harmonic generation and its beating phenomenon both experimentally and analytically. We find that when considering the propagation of both the fundamental and the second harmonic, nonlinear losses cannot be neglected. Our results reveal the role of nonlinear losses in the proposed device and also provide a quite accurate analytical model to capture the effect of such losses.

The characteristics and effects of nonlinear loads in the commercial office environment are discussed. The interaction of distorted currents drawn by these loads with the power system are described. An approximate approach for evaluating potential problems within a given facility is discussed, which, while not rigorous, can be used as a screening tool by building designers and engineers to make assessments of the potential for harmonic problems. Effects of high relative levels of harmonic current generation in commercial buildings include harmonic voltage distortion, transformer and motor overheating, and neutral conductor overloading. Reasonable estimates of the impacts of nonlinear loads can be made from generalized harmonic current source characteristics of three basic nonlinear types. Interactions with the electric power system can be predicted with simplified representations of the building electrical system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

When designing an electric power system (EPS) architecture for a more electric aircraft (MEA), the total weight of the system is treated as one of the most important criteria. For the weight saving purpose, this paper proposes an optimal power flow (OPF) based architecture design method to minimise the redundancy of the EPS of MEA, which includes reducing the generator overloading requirements for lighter generator design, and cutting down the excessive harness and number of contactors to lighten the wiring system. Based on the formulized mixed-integer linear programming (MILP) model, the addressed optimal architecture design (OAD) problem can be solved by optimising the power routing with minimum transmission losses in different flight stages simultaneously to minimise generator sizing and number of connections. The model contains both decision variables indicating the system architecture (e.g. cables existences and generator capacity) and the ones indicating the power flows with regards to the flight stages. In addition, the total transmission losses in the system are considered by formulizing the non-linear transmission losses of the DC/DC converters and cables losses in model constraints. By minimising the transmission losses, the generator overload capacity, as well as the cable needed for the connections, an optimised architecture with less redundancy and having optimal power routing in different flight stages can be realized, leading to lighter generator and wiring system for EPS.

Ferroresonance is a complex phenomenon in power systems for its very complicated behavior. This paper proposes a new method for ferroresonance behavior analysis using it steady state peak voltage value distribution on a three-dimensional space, by which the peak voltage behavior can be clearly detected with the change of the system parameters. Then, a new pulse suppression strategy for ferroresonance is also proposed. Pulse width modulation and proportional-integral (PI) control methods are used in the strategy. Simulation study shows that the fundamental, sub-harmonic and chaotic ferroresonance can all be suppressed by the pulse suppression strategy easily.

The objective of this thesis is to design distributed software agents for reliable operation of integrated electric power systems of modern electric warships. The automatic reconfiguration of electric shipboard power systems is an important step toward improved fight-through and self-healing capabilities of naval warships. The improvements are conceptualized by redesigning the electric power system and its controls. This research focuses on a new scheme for an energy management system in the form of distributed control/software agents. Multiagent systems provide an ideal level of abstraction for modeling complex applications where distributed and heterogeneous entities need to cooperate to achieve a common goal. The agents' task is to ensure supply of the various load demands while taking into consideration system constraints and load and supply path priorities. A self-stabilizing maximum flow algorithm is investigated to allow implementation of the agents' strategies and find a global solution by only considering local information and a minimum amount of communication. (Abstract shortened by UMI.).