Showing papers on "Electrical network published in 1997"

Coarse-grained distributed optimal power flow

Abstract: We present an approach to parallelizing optimal power flow (OPF) that is suitable for coarse-grained distributed implementation and is applicable to very large interconnected power systems. We demonstrate the approach on several medium size systems, including IEEE Test Systems and parts of the ERCOT system. Our simulations demonstrate the feasibility of distributed implementation of OPF. Rough estimates are made of parallel efficiencies and speed-ups.

Distribution circuit state estimation using a probabilistic approach

Abstract: Past work on distribution circuit state estimation has focused on the adoption of a transmission state estimator approach, without necessarily accounting for the specific requirement of a distribution circuit-based analysis. On distribution circuits, typically, there are very few available real-time measurements, and thus, researchers have treated customer load demand estimates as pseudo-measurements in a weighted-least-squares formulation. This can lead to convergence problems and also, the approach effectively assumes that all bus load demands are normally distributed (Gaussian) which may not be valid on distribution circuits. This paper presents an alternative approach to distribution circuit state estimation using a probabilistic extension of the radial load flow algorithm while accounting for real-time measurements as solution constraint. The algorithm which takes advantage of the radial nature of distribution circuits also accounts for other issues specific to distribution circuits. Namely, the algorithm accounts for nonnormally distributed loads, incorporates the concept of load diversity (load correlation) and can interact with a load allocation routine. The effectiveness of the algorithm is illustrated through comparisons made with Monte Carlo simulations.

An active power filter and unbalanced current compensator

Abstract: This paper presents the synthesis and performance of a shunt active power filter based on the three-phase pulsewidth modulation (PWM) voltage converter connected to the AC mains. Current harmonics and asymmetries caused by nonlinear loads can be compensated. A decoupled system in Park's variables is achieved and so simple controllers with excellent performance can be used. The controllers are implemented directly in the Park's referential. Expressions for the controller's synthesis are derived. Experimental results from a 2 kVA IGBT prototype showing excellent dynamic and steady-state system's performances are presented. The control circuit is implemented with analog and digital electronic circuits. A considerable amount of electronic circuits are needed. The method presented in this paper can also be implemented with a digital signal processor.

Parallel simulated annealing applied to long term transmission network expansion planning

Abstract: The simulated annealing optimization technique has been successfully applied to a number of electrical engineering problems, including transmission system expansion planning. The method is general in the sense that it does not assume any particular property of the problem being solved, such as linearity or convexity. Moreover, it has the ability to provide solutions arbitrarily close to an optimum (i.e. it is asymptotically convergent) as the cooling process slows down. The drawback of the approach is the computational burden: finding optimal solutions may be extremely expensive in some cases. This paper presents a parallel simulated annealing (PSA) algorithm for solving the long-term transmission network expansion planning problem. A strategy that does not affect the basic convergence properties of the sequential simulated annealing algorithm have been implemented and tested. The paper investigates the conditions under which the parallel algorithm is most efficient. The parallel implementations have been tested on three example networks: a small 6-bus network; and two complex real-life networks. Excellent results are reported in the test section of the paper: in addition to reductions in computing times, the PSA algorithm proposed in the paper has shown significant improvements in solution quality for the largest of the test networks.

Optimal coordination of directional overcurrent relays considering dynamic changes in the network topology

Abstract: This paper presents a method to consider the dynamic changes in the network's topology for the coordination of directional overcurrent relays using linear programming The proper coordination constraints are included by using linear approximations for the relay dynamics The application of the methodology as well as the importance of considering the transient configuration changes are illustrated with a practical example and a test case consisting of a real industrial power system

A simple approach to voltage stability assessment in radial networks

Abstract: Analytical approach to voltage collapse proximity determination is proposed for radial networks. Under corresponding assumptions, a radial network with arbitrary bus loads is transformed into a two bus equivalent. The voltage phasors at the generator bus and at the last load bus of the radial network are transformed to form the voltage phasors of the two bus equivalent. The latter are further used for assessment of voltage collapse proximity. Exact stability limit relations for a two bus system derived from Jacobian matrix can be exploited. Moreover, an analytical expression is derived for calculation of active and reactive power reserve margins for a radial network equivalent. The proposed procedure has been tested for practical examples of radial networks with inductive and capacitive loads.

Harmonic modelling of non-linear load by means of crossed frequency admittance matrix

Abstract: An alternative harmonic model for representing power system nonlinear loads by a "crossed-frequency" admittance matrix is presented in the paper. This harmonic model is applicable to passive and stationary electrical loads assuming a constant fundamental frequency voltage. Results of the proposed harmonic model are reported and compared with experimental tests.

Fast estimation of voltage and current phasors in power networks using an adaptive neural network

Abstract: A new algorithm for the estimation of parameters of voltage or current waveform of power networks contaminated by noise is proposed. The problem of estimation is formulated by using an adaptive neural network consisting of linear adaptive neurons called adaline. The learning parameters of the adaline are adjusted to force the error between the actual and desired outputs to satisfy a stable difference error equation, rather than to minimize an error function. Illustrative computer simulation results confirm the validity and accurate performance of the proposed method. Laboratory test results are also presented in this paper to support the effectiveness of the proposed approach in tracking the waveforms in real-time.

Digital algorithms for measurement of voltage flicker

Abstract: The fluctuation of utility voltage often becomes so serious that the flicker of electrical lighting equipment is visible and sometimes irritable. In order to solve the problems related to voltage fluctuation, many definitions and meters had been proposed and developed. In this paper, these meter principles are categorised, and the digital algorithms used to calculate voltage flicker are discussed. Special attention is focused on the pitfalls of the fast Fourier transform, which is the spectrum of voltage fluctuation signals. Since the trivial system frequency deviation may cause serious leakage under proper frequency resolution, the directly digital demodulation method is not suggested. In order to reduce aliasing, a low-pass filter (LPF) is necessary, and the sampling frequency of the analog to digital converter (ADC) must be not less than two multiples of the cut-off frequency of the LPF. The frequency resolution must be raised as much as possible to lower the inherent picket-fence effect, owing to the approximately continuous spectrum distribution of the voltage fluctuation. Based on the above considerations, a developed microcomputer-based instrument system prototype was used to validate the operation of the proposed algorithm, by the voltage-flicker measurement of a voltage-flicker generator and an arc-furnace feeder.

Improved voltage and reactive power distribution factors for outage studies

Abstract: This paper presents the development of a simple and fast method to calculate a new set of distribution factors using the sensitivity property of Newton-Raphson load flow Jacobian at a base operating point. These factors have been used to calculate the post-outage voltages and reactive power output of the sources following outage of a transmission branch or a generator. The accuracy of post-outage results using these distribution factors has been established with respect to full AC load flow results on IEEE 14-bus, IEEE 57-bus and a practical 75-bus Indian power systems.

Dynamic modelling of a unified power flow controller

Abstract: A method to regulate the unified power flow controller (UPFC) to improve the dynamic performance of power systems is proposed in the paper. The series voltage responds to the power variations of the transmission line, while the shunt compensation is controlled to maintain the power system bus voltage and to stabilise the DC link of the UPFC. Decoupled control algorithms for active and reactive power are developed. A nonlinear dynamic model of the power network is established for transient studies. The small-signal model is derived using linearisation and network reduction. An integrated formulation can be achieved which represents the dynamics of the generators, loads and the UPFC. The effectiveness of the UPFC and the accuracy of the analytical models are examined using numerical examples.

Optical interconnection system

Abstract: An opto-electric jack (40) is provided which can be used as a drop-in replacement for a standard electrical jack such as an RJ-type or D-subminiature type jack. The opto-electric jack (40) includes housing (12) having a receptacle (120) for receiving an optical plug (500) which is coupled to a fiber optic cable, and a plurality of electrical terminals (70) for connection to an electrical circuit. Preferably, the terminals (70) are arranged in a predetermined array which corresponds to the terminal array (70) of a standard electrical jack. An opto-electric conversion circuit is disposed within the housing (12), and is operable to convert optical signals received from the optical plug into electrical signals for transmission to the electrical circuit via the terminals (70), and to convert electrical signals received from the electrical circuit via the terminals (70) into optical signals which are transmitted to the optical plug (500).

Voltage control by tap-changing transformers for a radial distribution network

Abstract: Voltage control is of interest to many researchers, and is currently being considered by many utilities for implementation in their energy control centres. Transformers with tap-changing facilities constitute an important means of controlling voltage throughout the system at all voltage levels. A new method for determining the minimal changes in transformer taps to control voltage levels is presented. The problem to be solved is cast into a nonlinear constraint optimisation. The constraints are tackled in the minimisation algorithm by forming the Lagrangian. Necessary conditions for optimality are derived and solved using the Newton-Raphson method.

Electrical apparatus for overcurrent protection of electrical circuits

Abstract: An electrical apparatus comprising first and second PTC elements composed of a polymer composition with conductive particles dispersed therein, an insulating body, and first and second conductive terminals. Flexible conductive members having a first end that can be electrically connected to a source of electrical power and a second end that is adapted to receive and make electrical contact with the apparatus are provided. The PTC element and the insulating body are positioned between the first and second conductive terminals so that when the apparatus is inserted between the flexible conductive members, the members exert a pressure on the insulating body.

Linear indicator for voltage collapse in power systems

Abstract: A new linear indicator is presented together with a comparative study with other published works. The salient advantage of the linear characteristic is emphasised. The new index is tested utilising the IEEE 30 bus test power system.

Modelling and numerical solution of multibranched DC rail traction power systems

Abstract: Based on the method of nodal voltage circuit analysis, a complex DC-fed traction power network with multibranched lines has been modelled. The model also incorporates detailed return circuits so that rail potentials can be calculated, a requirement which arises because of safety and stray current considerations. The introduction of branch joints and divided rail cells greatly increases the quantity of circuit nodes and gives rise to a large sparse conductance matrix. After establishing a set of simultaneous linear equations describing the behaviour of the network, consideration is given to the most suitable method of solution to prevent excessive computation times and storage requirements. Sample calculation results for train, substation busbar and branch joint voltages and currents are given, together with rail potential profiles.

A computational comparison of steady state load shedding approaches in electric power systems

Abstract: This paper presents a formulation of the optimal steady state load shedding problem that uses the sum of the squares of the difference between the connected active and the reactive load and the supplied active and reactive power. The latter are treated as dependent variables modelled as functions of bus voltages only. An investigation of the performance of the proposed algorithm over a range of generation deficits as well as overload conditions is presented. Testing is done using IEEE 14, 30, 57, and 118 bus power systems, representing small and medium power systems. The optimal results are compared with results obtained using two earlier approaches. The results obtained using the proposed approach appear to give a better optimal state of the power system.

The effects of voltage collapse problems in the reliability evaluation of composite systems

Abstract: This paper describes an approach to calculate voltage collapse related bulk reliability indices as well as their impact on the adequacy reliability indices of power systems. In this approach, the adequacy analysis of each selected system state is carried out in two steps. In the first, the minimum load shedding to restore system solvability is computed, neglecting operational constraints such as bus voltage levels and circuit power flows. In the second, the additional minimum load curtailment to alleviate any operating limit violations is calculated. In each step, optimal power flow is solved by a direct interior point algorithm, and related reliability indices are evaluated. The proposed methodology can be used in both enumeration and Monte Carlo methods. Case studies with a practical 11-bus network (the Brazilian Reduced Mato Grosso system) and with a 1600-bus network derived from the Brazilian South/Southeast/Central West system are presented and discussed.

Vector space decomposition of reactive power for periodic nonsinusoidal signals

Abstract: A vector space is used to represent periodic voltage and current signals in a single port electrical network. This representation is convenient for expressing time average power quantities, such as average power, apparent power, and certain definitions of reactive power. The vector representation for reactive power provides insight into the difficulty of finding a consistent definition for a scalar measure of reactive power when harmonics are present. Instead, a reactive power vector is defined and shown to obey conservation according to Tellegen's theorem. Projections of the reactive power vector are shown to obey conservation and can be used as signed, scalar measures of reactive power.

AC power line network simulator

Abstract: In an illustrative embodiment, the AC power line network simulator includes an enclosure for containing elements of the system. An AC coupling network coupled to the network simulator implements the functions relating to a particular simulation. A distribution panel connected to a power feed distributes power and includes outgoing circuits and circuit breakers for protecting the outgoing circuits. A plurality of outlets are connected to the breakers of the panel. Through the use of the simulator, with the AC coupling network, simulation of an AC power line network, such as measuring electrical signals, recording electrical signals, simulating electrical signals and inserting electrical signals, can be easily performed. The measured, recorded, simulated and inserted signals correspond to electrical characteristics of elements found in an AC power line network, and can be stored for later analysis. In addition, once simulation information has been stored, it can be reproduced as desired.

Electrotherapy method and apparatus for external defibrillation

Abstract: An electrotherapy method and apparatus for delivering a multiphasic waveform from an energy source to a patient. The preferred embodiment of the method comprises the steps of charging the energy source to an initial level; discharging the energy source across the electrodes to deliver electrical energy to the patient in a multiphasic waveform; monitoring a patient-dependent electrical parameter during the discharging step; shaping the waveform of the delivered electrical energy based on a value of the monitored electrical parameter, wherein the relative duration of the phases of the multiphasic waveform is dependent on the value of the monitored electrical parameter. The preferred apparatus comprises an energy source; two electrodes adapted to make electrical contact with a patient; a connecting mechanism forming an electrical circuit with the energy source and the electrodes when the electrodes are attached to a patient; and a controller operating the connecting mechanism to deliver electrical energy from the energy source to the electrodes in a multiphasic waveform the relative phase durations of which are based on an electrical parameter monitored during delivery of the electrical energy. The preferred defibrillator apparatus weighs less than 4 pounds and has a volume less than 150 cubic inches, and most preferably, weighs approximately three pounds or less and has a volume of approximately 141 cu.in.

An Abductive Inference Technique for Fault Diagnosis in Electrical Power Transmission Networks

Abstract: This paper introduces a system modeling concept and a new algorithm based on abductive inference for handling diagnostic problems in electrical power transmission networks. The overall technique relies on the inherent functional and logical relationships between system elements such as lines, buses, relays and breakers to generate a diagnostic model rather than on experientially derived heuristics. This approach allows for a systematic implementation scheme that is more readily adapted to any power system. Logical models for relays, breakers, lines and buses are presented along with examples on how these models can be interconnected to represent a power system. The resulting system model can simulate the "forward" behavior of a power system. Inputs to the forward model consist of disorders or disturbances, and the outputs are manifestations or alarms. Using abductive logic, a "reverse" system model can be generated. This system model takes the alarms as inputs and produces a diagnosis by generating sets of disorders or disturbances that explain the observed alarms.

Damping of electro-mechanical oscillations in a multimachine system by direct load control

Abstract: Electric utility-controlled customer loads as actuators present new possibilities for power system control. The use of active loads controlled by local bus frequency is proposed for the damping of power system electromechanical oscillations. The viability of the idea is studied for one load in a three-machine power system with a meshed network. Active power mode controllability and phase angle mode observability are determined from the eigenvectors of a differential algebraic description of the uncontrolled system. The geographical variations in the entire network of controllability and observability are shown to be identical. It is presented graphically on a 3-D view of the network topology and is used as a generalization of the term mass scaled electrical distance. System zeros limit the maximum damping. An electromechanical mode pendulum analog is introduced that explains this. Time simulations verify the final controller design.

A deterministic/stochastic framework for power system harmonics modeling

Abstract: A mixed deterministic/stochastic vector process able to describe the behavior of power system harmonics is discussed in this paper. The process consists of a framework where the recorded signal is decomposed in deterministic functions and a normalized gaussian vector. Validation resorts to measurements performed on medium voltage networks, showing that the model appears to be an effective tool for calculation of the statistical properties of the quantities which are usually involved in compensation-system design for electrical networks.

Combining functional and structural reasoning for safety analysis of electrical designs

Abstract: Increasing complexity of design in automotive electrical systems has been paralleled by increased demands for analysis of the safety and reliability aspects of those designs. Such demands can place a great burden on the engineers charged with carrying out the analysis. This paper describes how the intended functions of a circuit design can be combined with a qualitative model of the electrical circuit that fulfils the functions, and used to analyse the safety of the design. FLAME, an automated failure mode and effects analysis system based on these techniques, is described in detail. FLAME has been developed over several years, and is capable of composing an FMEA report for many different electrical subsystems. The paper also addresses the issue of how the use of functional and structural reasoning can be extended to sneak circuit analysis and fault tree analysis.

Method for improving fault coverage of an electric circuit

Abstract: The present invention is a method and system which determine signal probability and transfer probability for each node in a netlist describing an electrical circuit; determine, using the signal probability and transfer probability, a fault detection probability for each node; and, using the fault detection probabilities, determine overall fault coverage of the electrical circuit described in the netlist. The method and system of the present invention then, using the fault coverage data, heuristically determine a set of testpoints to be inserted into the netlist which increase the overall fault coverage of the electrical circuit above a predetermined value.

Development of an energy function reflecting the transfer conductances for direct stability analysis in power systems

Abstract: Direct stability analysis using an energy function has recently been widely used for angular and voltage stability analysis in electric power systems. Considerable efforts have concentrated on seeking energy functions for lossy power systems, accomplished only for the simple two-bus system. A new approach is presented to derive an energy function by using the complex integral of bus current equations with respect to bus voltages. Under an assumption that all transmission lines have a uniform R/X ratio, it is shown that the energy function can be developed for multimachine power systems with losses. The proposed energy function is tested on sample systems by comparing the time simulation method, which shows the validity of the proposed method.

An on-line self-learning power system stabilizer using a neural network method

Abstract: Based on the extensive theoretical analysis of a self-learning algorithm, a novel on-line neural network self-learning algorithm is proposed. This algorithm aims to learn the inverse dynamics of a controlled system. Samples can be easily obtained by the measurements. A reference model or a given orbit is used to generate ideal system responses. A scheme for on-line real-time implementation of such a controller is given. The proposed algorithm has been used to design a self-learning power system stabilizer. Simulation results show that the proposed self-learning neural network based PSS is very effective in damping out the lower frequency oscillations.

Voltage stability analysis considering dynamic load model

Abstract: The modeling of loads has a significant effect on the accuracy of voltage stability analysis. This paper investigates the dynamic nature of voltage instability considering the dynamic load model. It develops the system small-signal voltage stability models adopting exponential recovery load models and adaptive load models. Moreover it investigates the influence of the parameters related to the load models and of the consequent change of the operating points on the voltage stability. The differences and similarities of the two specific models are also pointed out.