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Transformers are essential elements, which facilitate the transmission of electric power at high voltages over long distances and transformer energization is a common occurrence. The energization can lead to excessive transient inrush current, especially when the transformer core has remnant flux that adds to the flux build-up after switching. Inrush current sags the system voltage, thereby affecting the power quality of the network in proximity of the transformer. The extent to which power quality is degraded depends on short circuit MVA at the source bus, and the magnitude and decay time constant of the transient current. Present day thyristor-controlled machinery used in mining, pulp and paper industries and semiconductor manufacturing require high quality power. Some of these industries even pay a premium price for high quality power. It is, therefore, necessary to first assess the impact of energizing a large transformer on power quality and then develop a technique to limit this impact. This paper presents results from field tests and simulations using Electromagnetic Transients Program a 138 kV 315 MVA transformer energization in the BC Hydro system. The transformer is situated close to a pulp and paper mill with voltage sensitive loads. Methods to assess and to limit the voltage sags during energization are discussed. [ABSTRACT FROM AUTHOR]

In this paper, a novel control strategy for subsynchronous resonance (SSR) mitigation using a static synchronous series compensator will be presented. SSR mitigation is obtained by increasing the network damping only at those frequencies that are critical for the turbine-generator shaft. This is achieved by controlling the subsynchronous component of the grid current to zero. Using the IEEE First Benchmark Model, the effectiveness of the proposed control algorithm when mitigating SSR due to torsional interaction and torque amplification effect will be shown. [ABSTRACT FROM AUTHOR]

This paper presents a study on losses in cables and transformers considering nonsinusoidal conditions in commercial facilities. A mathematical development based on classical definitions available in the literature supports the proposal of a factor that is suitable to indicate where losses are significant and must be compensated. A case study is also presented and meticulously analyzed in order to validate the theoretical assumptions. [ABSTRACT FROM AUTHOR]

This paper studies the behavior of a high-voltage direct current link based on voltage-source converters, which feeds a weak ac network with power produced from an offshore wind farm (WF) of induction generators. Its control system, which is based on adaptive fuzzy controllers, manages to offer very satisfactory performance, without the need for a detailed mathematical model, but just prior knowledge of the behavior of the electrical system. Using the simulation program PSCADIEMTDC, the study was performed under both steady-state and transient conditions. The results show that the link supplies the variable power of the WF to a weak grid, keeping the ac voltage fluctuations in the point of common coupling at an acceptable level. Moreover, due to the ability of the control system to adjust the stator frequency of the induction generators in relation to the wind velocity, maximum wind power acquisition is achieved. [ABSTRACT FROM AUTHOR]

This paper has highlighted a major problem with the traditional excitation characteristic (TEC) of nonlinear inductors, in that the TEC contains harmonic voltages and/or currents, and has been used the way as if it were made up of pure fundamental voltage and current. In comparison to the TEC, a new concept, namely the power frequency excitation characteristic (PEC), which contains no harmonics, has been put forward. Two methods have been presented in obtaining the PEC. The first method is based on Electromagentic Transients Program simulation, resulting in discrete voltage and current pairs. This method essentially acts as a reference to validate the second one. The second method em- ploys Fourier and Maclaurin series approximation techniques, and brings forth a simple yet effective analytical expression. The expression is proven to have satisfactory precision in the saturated region of the PEC, especially in the extremely saturated region. [ABSTRACT FROM AUTHOR]

In this paper, a novel transformer structure is proposed in order to manufacture a high-power active filtering device. The novel transformer structure contains one primary and multiple secondary windings. The system configuration and compensation principle are addressed in detail. The fundamental magnetic flux compensation in the case of the transformer with multiple secondary windings is fulfilled. In addition, a three-phase active power filter topology consisting of three independent transformers with multiple secondary windings is presented so that the filter can run under unbalanced loads. The parameters of hysteresis current control are also analyzed in detail. A simple and practical fundamental detecting approach is discussed. Transient response and fault protection schemes are explained. A set of automatic three-phase active power filtering devices has been constructed and operated in the field. The field test results verify the validity of the novel transformer structure and the active power filtering system. [ABSTRACT FROM AUTHOR]

Potential applications of probabilistic modeling of current and voltage harmonics concern many aspects of power system engineering as accurate prediction of power system harmonic behavior provides important information to utility companies and equipment designers. In this paper, a method of reducing the expected value of the total voltage harmonic distortion for a specified range of source impedance values at different buses by using LC compensators, where it is desired to maintain a given power factor at a specified value, is presented. The criterion is based on mean value estimation of source and load characteristics, which are enabled by sampling measurements performed on the examined electrical plant as well as statistical analysis. [ABSTRACT FROM AUTHOR]

For ferroresonant circuits, the sufficient condition for preventing fundamental ferroresonance (FF) from occuring is that there is no intersection between the voltage-current characteristic of the linear part of the circuit, and the saturated power frequency excitation characteristic of the nonlinear part. Based on this understanding, part II of this paper has presented a criterion for the possibility of FF in the form of an analytical expression which is composed of the essential parameters of the circuit. By giving the critical resistance value for damping FF, the expression clearly indicates not only the possibility of FF but also the methods for eliminating the FE The possibility of FF is judged by comparing the critical resistance value with the real value. In the meantime, the expression suggests how to adjust the essential parameters to suppress FE The criterion has been proven by both simulation results and field tests. With this criterion, the possibility and elimination of FF can be studied for the first time by a simple yet effective analytical method. [ABSTRACT FROM AUTHOR]

This paper describes an algorithm for calculating the direction to a flicker source with respect to a monitoring point. The proposed algorithm is based on sampling of both the voltage and current. The low-frequency fluctuations in voltage and current are recovered from the input signals by demodulation, and passed through a bandpass filter as described in IEC 61000-4-15. A new quantity—flicker power—defined from the output signals of the two filters. The direction to a flicker source is obtained from the sign of this flicker power. The proposed algorithm has been validated by simulations and several field measurements. [ABSTRACT FROM AUTHOR]

A dynamic model which describes the impulse behavior of concentrated grounds at high currents is described in this paper. This model is an extension of previous models in that it can successfully account for the surge behavior of concentrated grounds over a much wider range of current densities. It is able to describe the well known effect of ionization of soil as well as the observed effect of discrete breakdowns and filamentary arc paths at much higher currents. Results of verification against experimental results are also presented. [ABSTRACT FROM AUTHOR]

Directional relays use voltage as the polarizing quantity. When three-phase faults occur close to the relay bus, the available voltage becomes nearly zero and this creates a problem in estimation of the fault direction. The capacitor coupling voltage transformer subsidence transients add to this problem. The memory voltage used as the polarizing quantity at these situations is a compromise. This paper highlights these issues and proposes a simple solution using the power-flow direction in addition to other information. The performance of the technique is evaluated through simulation in Power System Computer Aided Design. [ABSTRACT FROM AUTHOR]