Showing papers on "Electrical network published in 1995"

Fast decoupled power flow for unbalanced radial distribution systems

Abstract: This paper presents a novel power flow formulation and an effective solution method for general unbalanced radial distribution systems. Comprehensive models are considered including lines, switches, transformers, shunt capacitors, cogenerators, and several types of loads. A new problem formulation of three-phase distribution power flow equations taking into account the radial structure of the distribution network is presented. A distinguishing feature of the new problem formulation is that it significantly reduces the number of power flow equations, as compared with the conventional formulation. The numerical properties as well as the structural properties of distribution systems are exploited resulting in a fast decoupled solution algorithm. The proposed solution algorithm is evaluated on three-phase unbalanced 292-bus and 394-bus test systems with very promising results.

Method and apparatus for inserting computer code into a high level language (HLL) software model of an electrical circuit to monitor test coverage of the software model when exposed to test inputs

Abstract: A method and apparatus, for determining test coverage estimation for an electrical circuit (10) formed in accordance with an original high level description (21), uses a central processing unit (CPU 18). The CPU (18) accesses the description (21) and parses the high level language description (21) to allow for the generation of new code. This new code is intermixed with code from the description (21) to form a new high level description (22) which not only can be used to simulate the electrical circuit but can collect test coverage information. A simulation of the description (22) is performed using test vector inputs to simulate operation of the circuit (10) and estimate it's test coverage for the test vectors. Various warning/error messages are derived to indicate where the test vectors are lacking in test coverage.

An efficient algorithm for real-time network reconfiguration in large scale unbalanced distribution systems

Abstract: Real-time applications demand fast computation, and this paper proposes an efficient algorithm for real-time network reconfiguration on large unbalanced distribution networks. A novel formulation of the network reconfiguration to achieve loss minimization and load balancing is given. To reduce computational requirements for the solution algorithm, well justified power flow and loss reduction formulae in terms of the on/off status of network switches are proposed for efficient system updating. The algorithm relies only on a few full power flow studies based on system states attained by explicit expressions using backward-forward sweeps for efficient computation of power system states at the critical system operating points. The solution algorithm runs in an amount of time linearly proportional to the number of tie switches and the number of sectionalizing switches in the system. The solution algorithm has been implemented into a software package and tested on unbalanced distribution systems including a system with 292 buses, 76 laterals, 7 transformers, 45 switches and 255 line sections under diverse system conditions.

A distribution short circuit analysis approach using hybrid compensation method

Abstract: This paper addresses a new approach for real-time short circuit analysis of radial and weakly meshed distribution networks. The approach works based on a well documented radial power flow study method, and uses a hybrid compensation method to account for loops, PV nodes, and fault currents simultaneously. The three-phase short circuit analysis, in its actual a-b-c phase representation, can be applied to balanced or unbalanced distribution systems. A distribution short circuit program which is developed based on this approach, is integrated with a three-phase power flow program to solve various types of single or simultaneous faults, including single-line to ground, three-line to ground, double-line to ground, line-to-line, and double three-line to ground faults. Results of the application of this approach to large-scale distribution networks are also reported in this paper.

Low-order black-box models for control system design in large power systems

Abstract: The paper studies two multi-input multi-output (MIMO) procedures for the identification of low-order state space models of power systems, by probing the network in open loop with low-energy pulses or random signals. Although such data may result from actual measurements, the development assumes simulated responses from a transient stability program, hence benefiting from the existing large base of stability models. While pulse data is processed using the eigensystem realization algorithm, the analysis of random responses is done by means of subspace identification methods. On a prototype Hydro-Quebec power system, including SVCs, DC power lines, series compensation, and more than 1100 buses, it is verified that the two approaches are equivalent only when strict requirements are imposed on the pulse length and magnitude. The 10th-order equivalent models derived by random-signal probing allow for effective tuning of decentralized power system stabilizers (PSSs) able to damp both local and very slow inter-area modes.

Heterogeneous artificial neural network for short term electrical load forecasting

Abstract: Short term electrical load forecasting is a topic of major interest for the planning of energy production and distribution. The use of artificial neural networks has been demonstrated as a valid alternative to classical statistical methods in terms of accuracy of results. However, a common architecture able to forecast the load in different geographical regions, showing different load shape and climate characteristics, is still missing. In this paper we discuss a heterogeneous neural network architecture composed of an unsupervised part, namely a neural gas, which is used to analyze the process in sub models finding local features in the data and suggesting regression variables, and a supervised one, a multilayer perceptron, which performs the approximation of the underlying function. The resulting outputs are then summed by a weighted fuzzy average, allowing a smooth transition between sub models. The effectiveness of the proposed architecture Is demonstrated by two days ahead load forecasting of L'Energie de L'Ouest Suisse (EOS) power system sub areas, corresponding to five different geographical regions, and of its total electrical load.

Value-based transmission planning and the effects of network models

Abstract: A value-based automated transmission system planning model is presented in this paper and the impact of the various network representations on the results of the model is discussed. Value-based integrated resource planning provides a "societal cost" (utility operation and investment costs plus customer outage costs) minimizing composite generation-transmission system expansion plan. The model trades-off and compares the costs and benefits of alternative generation and transmission resources using a consistent economic and engineering criterion in order to determine an "optimal" resource expansion plan. The generalized Benders decomposition algorithm with "importance sampling" used to solve the problem enables the model to estimate certain average information about scenarios or contingencies by examining only a very small fraction of all the scenarios or contingencies. The impacts of system resources upon both real and reactive power can be analyzed when using the AC power flow equations. It is concluded that for transmission system planning where reactive power flows and voltage constraints are important, it is imperative that an AC power flow model be used. The combination of AC power flow and linearized power flow models, with linearization about the solution of the AC power flow model, was found to be a promising compromise between accuracy and computation time.

A time-domain approach to transmission network equivalents via Prony analysis for electromagnetic transients analysis

Abstract: This paper presents a method of obtaining transmission network equivalents from the network's response to a pulse excitation signal. The proposed method is based on modal decomposition representation for the large-scale interconnected system. In this framework we use Prony analysis to identify the network function of the system and to decompose the large system into a parallel combination of simple first-order systems. As a result the network function of the transmission network can be identified easily, and a Thevenin-type of discrete-time filter model can be generated. It can reproduce the driving-point impedance characteristic of the network. Furthermore, the proposed model can be implemented into the EMTP in a direct manner. The simulation results with the full system representation and the developed equivalent system showed a good agreement.

Method and apparatus for locating electrical circuit members

Abstract: Electrical components such as IC modules and printed circuit boards, at least one of which has an array of solder balls or other protruding conductors, are connected quickly, precisely and economically with a component locator having openings adapted to capture the protruding conductors. The locator is aligned with one of the components, and the other component is pressed against the locator. The protruding conductors enter the capture openings and complete electrical circuits with contacts on the other conductor.

Flexible etched circuit assembly

Abstract: An electrical connector assembly (10) is mounted on a printed circuit board (18) and includes a flexible etched circuit (FEC) (15) with electrical traces thereon. The FEC (15) is part of an electrical circuit which includes electrical components (22,24), electrical contacts (23), a ground path (12, 12a), and an electrical connection (90). The FEC can include various electrical components (22,24), for example, in order to filter the electrical circuit.

Precision Tests of a Quantum Hall Effect Device DC Equivalent Circuit Using Double-Series and Triple-Series Connections

Abstract: Precision tests verify the dc equivalent circuit used by Ricketts and Kemeny to describe a quantum Hall effect device in terms of electrical circuit elements. The tests employ the use of cryogenic current comparators and the double-series and triple-series connection techniques of Delahaye. Verification of the dc equivalent circuit in double-series and triple-series connections is a necessary step in developing the ac quantum Hall effect as an intrinsic standard of resistance.

Efficient heuristic partitioning algorithm for parallel processing of large power systems network equations

Abstract: An efficient heuristic algorithm for automatic partitioning of a power system network is presented. The algorithm was designed for use in conjunction with a diakoptics-based coarse grain parallel method for solving large, sparse linear systems arising from network analysis. It exploits the techniques of factorisation path graph partitioning and equivalent post-ordering. Test results for systems up to 811 busbars and 1476 transmission lines are included for comparison purposes. This indicates that the method is able to divide a power system network model into a number of equal sized subnetworks in order to optimise the use of parallel computer systems for network analysis while the resultant number of fill-in elements is kept to a minimum.

Control sensitivity indices for stability analysis of HVDC systems

Abstract: This paper presents a new concept called the "Control Sensitivity Index" or CSI, for the stability analysis of HVDC converters connected to weak AC systems. The CSI for a particular control mode can be defined as the ratio of incremental changes in the two system variables that are most relevant to that control mode. The index provides valuable information on the stability of the system and, unlike other approaches, aids in the design of the controller. It also plays an important role in defining nonlinear gains for the controller. This paper offers a generalized formulation of CSI and demonstrates its application through an analysis of the CSI for three modes of HVDC control. The conclusions drawn from the analysis are confirmed by a detailed electromagnetic transients simulation of the AC/DC system. The paper concludes that the CSI can be used to improve the controller design and, for an inverter in a weak AC system, the conventional voltage control mode is more stable than the conventional /spl gamma/ control mode. >

Composite resonance; a circuit approach to the waveform distortion dynamics of an HVdc converter

Abstract: A frequency domain analysis is applied to a controlled HVDC power converter interconnecting AC and DC power networks. The converter is considered as a three-port network, and described using transfer functions. Using AC and DC power system frequency dependent impedances, an equivalent electrical circuit is constructed. The concept of composite resonance is introduced to emphasise the interaction between the AC and DC systems, and a simplified damping factor derived to predict the dynamics of waveform distortion during transient recovery. The frequency domain analysis is verified by dynamic simulation. >

High fidelity simulation of power system dynamics

Abstract: Detailed assessment of phenomena occurring in a power system remains a major challenge for most utilities. Complex simulations often involve fast and slow phenomena, both of which must be taken into account to obtain a faithful representation of reality. Methods that consist of splitting these phenomena into different classes (transient, mid-, or long-term stability), each corresponding to specialized software and a particular model, are no longer satisfactory. To meet this challenge, EUROSTAG software was developed for the simulation of power system dynamics. It covers the full range of phenomena, from transient to long-term stability, using a single power system model, and its application field is extensive: from the electromechanical oscillations up to the daily load evolution; from the line tripping to the centralized frequency or voltage control; from the generalized blackout to the system restoration procedure; and from tuning the generating unit controller to studying power electronics such as FACTS or HVDC. Thanks to an automatically variable step-size strategy, this single integrated program with single and extended modeling simulates the whole set of phenomena with a high degree of accuracy. Great attention has been paid to user-friendliness. Users are able to design their own process models and build new scenarios interactively, conveniently, and rapidly. >

Measuring Process for Measuring Chargeable Electrical Consumption from an Electrical Network and Electronic Electricity Meter

Abstract: A process is described for the measurement of electricity consumption, that is specially suitable for small consumers, comprising the steps of continuously measuring consumer current, integrating said current with time to obtain a value (A.h) relating to consumption; adjusting the integration in function of the voltage of the network to obtain an adjusted value (Av.h) proportional to a preestablished unit of electricity consumption; and computing the number of preestablished units obtained to provide a value proportional to chargeable electricity consumption. Preferably, the adjustment to the integration is carried out in accordance with four bands of network voltage, in the form of a nominal band on either side of the nominal network voltage, an overvoltage band, an extended voltage band below the nominal band an an undervoltage band. An electricity meter without any power source is also described, comprising a current transformer (TC) having the consumer load line (15) as primary and a secondary generating a current representative of the current in the load line, a circuit connected to the secondary to integrate the value of such current with time, detector means for detecting when the integration circuit reaches a preestablished chargeable unit value of consumption of electricity and counter means associated with the detector means to sum the detected units of consumption. A housing is also described which is a single part and of extremely simple manufacture.

Power failure alarm

Abstract: A combination electrical connector and power failure signal device, comprising a generally box-like housing having a front, a back and a chamber, a male electrical plug on the back, a female electrical plug on the front, an electrical circuit in the housing including conductors connecting the male plug to the female plug, an alarm circuit in the housing responsive to power in the electrical circuit maintaining a stand by condition, the alarm circuit including a sensor for sensing a failure of power in the electrical circuit and initiating a first alarm mode, and responsive to a predetermined time in the first alarm mode to terminate the first alarm mode and initiate a second alarm mode, and a battery for powering the alarm circuit during failure of power in the electrical circuit.

Unified AC/DC power flow for system simulation in DC electrified transit railways

Abstract: The paper presents the improvements of a commercially available train simulator, the Energy Management Model (EMM), to evaluate the power flows in DC electrified transit railways. The sequential Gauss-Seidel power flow program used in EMM has been replaced by a unified Newton-Raphson AC/DC power flow to speed up the calculations. A precise model of the uncontrolled bridge rectifier with commutation impedance has been applied to the power flow formulation. Effects of regenerative braking on rectifier operations are also taken into account. Both the improved and the original train simulators have been tested on the Blue Line of Taipei Rapid Transit System which is under construction. Simulation results show that the proposed power flow program, with excellent convergence characteristics and accuracy, is of great value for train simulation.

Detection of Jacobian singularity and network islanding in power flow computations

Abstract: The paper provides a tool to investigate the occurrence of Jacobian singularities in power flow computations by Newton methods. In particular, a numerical procedure is presented that establishes the rows or columns of the Jacobian matrix that are linearly dependent. The method proposed is straightforward and may be easily implemented as an extension of any existing factorisation routine. Although the results presented are general, attention is focused on the detection of network islanding in the base case power flow or following a branch outage: the buses belonging to an island are identified at the cost of only one backward substitution computation. Examples of application of the procedure are shown with reference to a small network. Tests were successfully carried out using medium and large scale systems.

Simulation of single-phase induction motor by a general method coupling field and circuit equations

Abstract: A general method for coupling field and electrical circuit equations is presented in this work. The external electrical equations associated with the feeding circuit are represented in state space form. To illustrate the proposed methodology the dynamical operation of a single-phase induction motor is carried out. >

Apparatus for stress testing capacitive components

Abstract: A plurality of electrical circuit components having capacitance, e.g. ceramic capacitors, are tested simultaneously in a corresponding plurality of test channels. They are stressed by a variable voltage source that can produce an electrical potential selected from a wide range from low potential to high potential. For example the range of selectable potentials can be 1000 volts with a resolution of 1 volt. The charge current by which a component accumulates a charge is controlled to a selected linear rate by a current controller. Voltage sensors and current sensors measure accumulated charges and leakage current, respectively. The current sensor can be selectively sensitized to a plurality of anticipated leakage current ranges. In addition, the selected potentials can each be applied to the components in a single step or can be applied over time in ramp fashion. A processor can be used for running at least a prescribed test process on components, the processor being operatively coupled to, for controlling and receiving inputs from, the above elements. For example the processor is preferably coupled to the variable voltage source, the current controller, the voltage sensor, the current sensor, and a component discharge circuit, operatively coupled meaning that the processor controls.

Electrical powerway for furniture panel

Abstract: A modular electrical system for mounting on furniture components such as wall panels. The system includes modules which each include at least one power block provides increased electrical circuit capacity, which capacity in the preferred embodiment is at least six electrical circuits. The power block provides different groupings of circuits which are externally accessible, such as for connection to removable receptacle units, on opposite sides thereof. Flexible electrical connectors are provided for connection to and transmitting electrical power between power blocks of adjacent panels. Each connector transmits only one grouping of electrical circuits therethrough, whereby two such connectors are normally utilized for connection between adjacent power blocks of adjacent panels to transmit all electrical circuits therebetween. The individual flexible electrical connectors can be used for transmitting electrical energy into branching panels, which branching panels may be provided with only the selected grouping of circuits.

A New Approach to Calculate the Decaying AC Contributions to Short Circuit: The "Characteristic" Currents Method

Abstract: For the near to generator short-circuit analysis, it is well known that a rigorous calculation procedure requires the use of complex dynamic models of power system components. In most practical cases, however, it is sufficient to adopt simplified and standard based calculation methods. For these cases the paper suggests a new approach of the short-circuit models of power system components based on the "characteristic" currents method [l]. The paper, at first, presents a short overview of the IEC Standard 909, assumed as reference for the proposed approach. The calculation assumptions and the simplifications of the IEC Standard are pointed out in order to evidence how the new approach proposed allows to obtain conservative, but more accurate results. The "characteristic" currents procedure is successively applied to a sample network with external feeder and internal generation and with motor load. The same network is analyzed by means of the IEC procedure and by means of a computer program able to consider dynamic models of electrical equipment. A comparison among these approaches is carried out in order to validate the "characteristic" currents method. Comparisons between the proposed method and recognized IEEE/ANSI standards have not been performed in the paper.

A Mathematical Model of a Tubular Solid Oxide Fuel Cell

Abstract: The solid oxide fuel cell shows great potential as an efficient energy conversion system for use in central power stations. These cells can reform most hydrocarbon fuels with air to produce electricity and provide a heat source at 1,000 C while maintaining an efficiency of 60--75 percent. This paper describes a steady-state model for the prediction of voltage, current, and power from a single-cell tube. The model is a distributed parameter electrical network that includes the effects of mass transfer resistance (concentration polarization), chemical kinetic resistance (activation polarization), as well as relevant electrical resistance (ohmic losses). A finite-difference heat transfer model is also incorporated to allow for radial and axial temperature variations. The model computes the fuel and oxidant stream compositions as functions of axial length from energy and mass balances performed on each cell slice. The model yields results that compare favorably with the published experimental data from Westinghouse.