Showing papers on "Electrical network published in 1988"

Load modeling for power flow and transient stability computer studies

Abstract: A novel method is presented for preparing load models for power flow and stability studies. The LOADSYN load model synthesis software package transforms data on load class mix, composition, and characteristics into the form required for commonly used flow and transient stability simulation programs. Typical default data have been developed for load composition and characteristics. The load-modeling techniques used in this software and results of initial testing are described. Significant improvements in simulation accuracy are demonstrated. >

Practical reactive power allocation/operation planning using successive linear programming

Abstract: A method for reactive power planning is presented that it finds an optimal solution for both allocation and operation planning in large systems using linear programming (LP). The method utilizes calculated linear sensitivities including active power and voltage phase angle in the formulation. Although the overall method includes these relations, the number of constraints and variables are not augmented in its first procedure, APPROACH-1. Its second procedure, APPROACH-2, overcomes numerical problems caused by a dense constraint matrix. This is achieved by retaining untouched sparse sensitivities in the constraint matrix and by eliminating any calculations related to the inverse matrix. The results of applying this method to a practical 224-bus system and the IEEE-30 bus system verify its robustness and fast convergence. >

Efficient bounding method for linear contingency analysis

Abstract: A very efficient contingency analysis method for detecting branch megawatt flow violation is presented. The efficiency stems from the use of a bounding criterion that drastically reduces the number of branch-flow computations and limits checking, and the use of state-of-the-art compensation and sparse matrix/vector methods. The method requires no offline setup, is highly efficient, and can handle contingencies with any time of network topology and load/generation changes. The method is based on the linear incremental-power-flow model and consequently does not consider reactive power. >

Some applications of phasor measurements to adaptive protection

Abstract: The application of microprocessor-based phasor measurements to novel adaptive protection schemes is presented. The concepts of digital adaptive protection in which relay characteristics are modified in response to external signals and conditions in the system, are examined. The importance of real-time phasor measurements in adaptive protection systems is illustrated by two examples. The first involves obtaining synchronizing information about phasor measurements to be used for current differential protection of a multithermal line. By estimating the reference angles for the phasor measurements the effect of synchronized sampling can be obtained without the expense of synchronizing equipment. The second use is the adaptive setting of out-of-step blocking and tripping. Traditional approaches experience problems because the settings are, of necessity, compromises based on offline studies. By reacting to real-time phasor measurements from selected buses in interconnection, it is shown that improved out-of-step blocking and tripping is possible. >

Real-time analytic sensitivity method for transient security assessment and preventive control

Abstract: An analytic sensitivity method is proposed for the transient security assessment of large power systems. It is based on the recently developed ‘extended equal area criterion’, and on a related transient stability margin. It is shown that this margin leads to a simple algebraic formulation of sensitivity coefficients. Particular attention is focused on the sensitivity with respect to generation power, and possible applications to power system planning and online operation are suggested. For example, the computation of generation and load supply limits provides transient stability constraints and thence means of online transient security assessment and preventive control. Within the limits of the simplified electromotive force behind the transient reactance model, the method proves to be accurate, demanding very little with respect to computing time and fairly independent of the system size. The simulation results reported in the paper corroborate these conclusions.

Analysis of transient stability swings in large interconnected power systems by Fourier transformation

Abstract: A novel technique to analyze transient stability program swing curves is developed which uses the Fourier transformation. This approach generalizes the swing characteristics to specific frequency components over the range of time. The frequency components of the power system swings are identified in the frequency spectrum. These components can then be selected for further analysis. The mathematical process to determine the amount of damping in the respective frequency components is outlined. The damping constants can be obtained by comparing the magnitudes of the respective frequency components in different time windows. Good correlations of the results with conventional linear eigenvalue analysis have been observed. Advantages and necessary precautions in applying the method are presented. >

Mixed-Mode PISCES-SPICE Coupled Circuit and Device

Abstract: A computer program has been written to allow simulta- neous solution of an electrical network containing both nonlinear cir- cuit elements and two-dimensional finite element solid-state models. The circuit solver is based upon the popular SPICE-I1 (l) program, while the PISCES-I1 (2) program is used to model the solid-state de- vices. Both steady-state dc and time-dependent solutions are possible. Additional features have also been added to the solid-state model. These include photogeneration and the optional use of cylindrical coordi- nates.

Mixed-mode PISCES-SPICE coupled circuit and device solver

Abstract: A computer program has been written to allow simultaneous solution of an electrical network containing both nonlinear circuit elements and two-dimensional finite-element solid-state models. The circuit solver is based on the popular SPICE-II program, while the PISCES-II program is used to model the solid-state devices. Both steady-state DC and time-dependent solutions are possible. Additional features have also been added to the solid-state model, including photogeneration and the optional use of cylindrical coordinates. >

The incorporation of HVDC equations in optimal power flow methods using sequential quadratic programming techniques

Abstract: The author presents the formulation and solution method of an optimal power flow problem using a sequential quadratic programming technique for an AC-DC power system with one or more multiterminal DC systems. The algorithm developed has been tested on a number of sample AC-DC systems. The convergence characteristics, insofar as the number of the major iteration goes, is comparable with the Newton-Raphson approach. The economic advantage of being able to coordinate the DC system power transfers is illustrated by numerical examples based on the modified IEEE 30 and 118 bus systems. >

Variable, nonlinear tie-line frequency bias for interconnected systems control

Abstract: In February 1984, Union Electric began implementation of a test to identify the improvement to electric system automatic generation and tie-line control that could be achieved by the application of variable nonlinear tie-line frequency bias. Variable, nonlinear tie-line frequency bias is a better simulation of electric system frequency response than fixed straight-line bias because it recognizes the variable nature of a system's reaction to frequency changes. Important components of this response are the deadband in turbine-generator governors, variations in the number of online generators, and variations in load. The test showed that when tie-line frequency bias is better matched to system response, the result will be improved area-control error performance and reduced generating unit regulation. In addition, interconnection reliability is enhanced due to the fact that variable, nonlinear tie-line frequency bias does not inhibit the full governor response during large frequency disturbances, thereby providing better interconnected systems frequency stabilization. >

Modular electrical wiring system

Abstract: A system utilizing modular hardware for residential and commercial buildings. The system includes pre-wired molded plastic hardware and a circuit breaker panel which can be attached to electrical circuits having wire modules, and can be expanded using a circuit breaker panel extension module. It further includes smaller electrical boxes having mounting dovetails including electrical contacts for electrically and supportedly connecting a first electrical box to a second and third. A cavity is centrally disposed in each electrical box for receiving a pre-wired modular function unit and a standard function module, or a single pre-wired standard function module unit. The standard function module can be a standard switch, dual receptacle, lighting fixture, circuit breaker, or junction box and the like.

Optimal daily scheduling of cascaded plants using a new algorithm of nonlinear minimum cost network flow

Abstract: An optimality condition theorem and an algorithm for nonlinear minimum-cost network flow are proposed. A computational network model for optimal daily scheduling of cascaded plants (ODSCP) is established, and an algorithm for searching the minimum-cost flow-augmenting path and the maximum-cost flow-reducing path in the computational network model of ODSCP is described. Digital computations are carried out and the results show that the proposed method is very fast compared to existing methods. >

Power system stabilizers design using optimal reduced order models. II. Design

Abstract: For pt.I see ibid., vol.3, no.4, p.1670-5, 1988. The design of power system stabilizers using an optimal reduced-order model whose state variables are torque angles and speeds is examined. Two systems, a one machine-infinite bus system and a multimachine system, are considered. A controller, which is a linear feedback of these variables only and hence accounts for the realities and constraints of electrical power systems is designed based on the reduced-order model. The results obtained with the study systems demonstrate that the proposed controller is very effective. >

Electrical circuit modeling of reversed field pinches

Abstract: Equations are proposed to describe the radial variation of the magnetic field and current density in a circular, cylindrical reversed field pinch (RFP). These equations are used to derive the electrical circuit parameters (inductance, resistance, and coupling coefficient) for a RFP discharge. The circuit parameters are used to evaluate the flux and energy consumption for various start‐up modes and for steady‐state operation using oscillating field current drive. The results are applied to the MST device [Bull. Am. Phys. Soc. 32, 1830 (1987)].

Optimal active power dispatch by network flow approach

Abstract: An optimal active power dispatch problem is formulated as a nonlinear capacitated network flow problem with additional linear constraints. Transmission flow limits and both Kirchhoff laws are taken into account. The problem is solved by a generalized upper bounding technique that takes advantage of the network flow structure of the problem. The proposed approach has potential applications to power system problems such as economic dispatch, load supplying capability, minimum load shedding and generation-transmission reliability. The authors also review the use of transportation models for power system analysis. A detailed illustrative example is presented. >

Evaluation of a local DC load flow screening method for branch contingency selection of overloads

Abstract: The author presents a novel screening method, involving a local DC solution, for branch flow limit violations (overloads) which, when incorporated with a performance index (PI) method, can greatly enhance the selection capabilities for online as well as study purposes. The local DC screening method and PI method are compared to results obtained from a full-system DC load flow assessment of two cases: a 24-bus system and a 584-bus representation of the Mid-Continent Area Power Pool system. The results indicate that, when these two methods are combined, excellent contingency selection capabilities are produced. The philosophy for this implementation and the details needed to implement the local DC screening method are presented. >

Dual media local area network interfacing

Abstract: A dual media network interface module includes an electrical network interface and an optical network interface each having a transmit port to which signals to be transmitted on the associated network are applied and a receiver port at which signals received on the network are generated. The receiver port of each interface is connected to the transmitter port of the other interface so that signals received on either network are retransmitted on the other network. Blocking circuits block the receiver signal of a LAN which is transmitting during the transmitting interval plus an interval which exceed the worst case propagation time for the associated network to prevent endless repetition of a signal. A preferred form of the module includes a pair of controller interfaces having transmit ports and receiver ports connected to the corresponding ports of the other controller interface and of the electrical and optical network interfaces to provide bidirectional communications between all devices connected to the module. The modules can be used to interface electrical and optical nodes in a network, to expand both electrical and optical networks, and to interconnect various combinations of electrical and optical local area networks.

Development of Piezoelectric Technology for Applications in Control of Intelligent Structures

Abstract: This work presents analytical techniques, with experimental results for use with piezoelectric actuators as elements of intelligent structres. Mechanical models for the interaction of piezoelectrics with one- and two-dimensional structures are derived. In addition, a model coupling the electrical and mechanical properties of the piezoelectric is presented. This model is used to derive optimal resistive and tuned electrical circuits to maximize energy dissipation in the structure. These results are implemented on a prototype space-truss. Finally, a technique for embedding piezoelectrics inside laminated composite structures is presented.

Comparative analysis and study of the dynamic stability of AC/DC systems

Abstract: The authors present an approach for the dynamic stability analysis of power systems possibly including DC facilities and static VAr equipment. To illustrate a typical application of the computer program described, a system is selected which includes a DC tie interconnecting two large networks, and static compensators which are used to regulate AC voltages. Synchronous generators in the network on the inverter side are dedicated to the interconnection. Regulators to damp oscillations of the dedicated generators are investigated with eigenvalue analysis and Bode plots, which are automatically generated by the program on request. >

Buffer system selection of a steady-state external equivalent model for real-time power flow using an automated sensitivity analysis procedure

Abstract: A steady-state external equivalent model of a large interconnected power system for a real-time power flow use, incorporating a properly selected buffer system, is presented. The particular problem of how to select the buffer (or inner external) system is the author's primary focus. The elements of the buffer system selected from the external system by the automated procedure are key transmission lines, transformers, load, and generators. The external equivalent model presented can be described as a modified Ward P2m-V model. The impact of a condition change in each of these elements on the voltage magnitudes and line flows at the boundary is determined by an automated sensitivity method using the decoupled P- theta and Q-V power flow models. The method has the capability of identifying the important elements for the buffer system based upon a normalized level-of-impact index. Tests were performed on specific areas and the equivalent model was found to provide very accurate results. >

New method for transmission planning using mixed-integer programming

Abstract: The authors present a new approach for planning high voltage transmission networks. The simulation model developed takes into account the capital investment cost in its discrete form as well as the cost of transmission losses. The constraint equations include the DC load flow equations and line loading constraints. The voltage loop equations are written in a modified form, such that a close-loop equation will be ineffective if any line of this loop is deleted. The simulation model utilises the mixed-integer linear programming technique to obtain the least-cost network satisfying line loading constraints. Verification of the method is made through a test example.

Power system remedial action methodology

Abstract: The authors address the problem of remedial-action computations for the purpose of alleviating overloads, abnormal voltages, etc. The method is based on a linear programming (LP) approach. Applications for voltage/reactive-power control, discrete capacitor/reactor switching, load transfer, and interchange control are considered. The method is optionally based on a DC or AC network model. It utilizes a number of innovations to yield an efficient computational procedure. The major innovations are: a procedure for determining coherent constraints which results in a fast identification of active constraints, fast linearization procedures for active constraints, procedures to define the region of validity of the linearized model, and a fast sparsity-coded LP algorithm. The performance of the method for large power systems is evaluated. >

An adaptive optimal control strategy for dynamic stability enhancement of AC/DC power systems

Abstract: The authors present an adaptive optimal control strategy for enhancement of the integrated AC/DC power system performance. The system modeling is general and applicable to large-scale power systems with an embedded HVDC link. The control algorithm incorporates the nonlinear power system dynamic equations. A novel feature of this development is the use of real-time system measurements as inputs to the optimal controller. The closed-loop optimal control law consists of both model and measurement-based terms. The effectiveness of the optimal control algorithm in damping the electrochemical oscillations is illustrated with the use of a nine-bus AC/DC system. >

Circuit protection device

Abstract: A circuit protection device for protecting an electrical circuit from a voltage transient, e.g. a voltage transient caused by an electrostatic discharge, lightning or a nuclear electromagnetic pulse, comprises a threshold switching element formed from an amorphous composition comprising germanium, selenium and optionally antimony, and a pair of electrodes in contact with the composition. The devices generally exhibit a good balance of physical properties including switching speed, energy required to latch them in their low resistance state, high resistance state (off) resistance, threshold voltage and capacitance, which enables them to be used successfully to protect electrical circuits from such transients.

Electrical network insulation monitoring and measuring device

Abstract: An insulation monitoring device comprises an input circuit of a reference AC signal, and an electronic detection circuit for discriminating the components of a measurement signal proportional to the ground fault impedance Z formed by a leakage resistor Rf in parallel with a leakage capacitor C. A synchronous detector has a pair of static inverters processing the first component, which is a function of the current IR flowing through the leakage resistor Rf, and of the second component which is a function of the current IC flowing through the capacitor C. A converter cooperates with the generator to deliver two quadrature signals C1 and C2 to respectively control the inverters. A display means accurately displays the value of the leakage resistance Rf.

A framework to predict voltage collapse in power systems

Abstract: A framework based on region-wise partitioning is presented which accounts for several of the mechanisms to predict voltage collapse and can serve as a basis for comparing the effectiveness of performance indices to predict on-line, voltage collapse problems in power systems. The basis of the framework is the voltage stability (VS) region, which accounts for both static and dynamic mechanisms of voltage collapse. Based on the VS region, static and dynamic performance indices, are defined to predict the static mechanisms of voltage collapse in the input or injection space and the dynamic mechanism in the post-contingency state space respectively. >

Negative feedback influence on simultaneous switching CMOS outputs

Abstract: Recent studies indicate that CMOS circuits exhibit nonlinear behavior (due to the negative feedback) of ground noise as a function of the number of signals switching. Electrical network formulation, modeling and simulation of simultaneously switching signals are discussed. Detailed equations, models, and transient characteristics are included. >

Local band shedding

Abstract: An effective local-load-shedding scheme has been developed to alleviate equipment overloads in underground transmission networks. It offers a very fast and reliable algorithm where accuracy and speed are traded, depending on the severity of overload. For overloads greatly in excess of short-time ratings, the speed of removing the overloads within the specified time is given higher priority than the accurate minimization of load curtailments. To provide positive and reliable collective action, overloads are overcorrected by shedding more loads than is absolutely necessary, since the excess loads shed can subsequently be restored by partial restoration. The local shedding scheme has been tested by simulation at the Potomac Electric Power Company for a number of single and multiple outages in the 138 kV underground transmission network with good results. >

An incremental transformer model for the study of harmonic overvoltages in weak AC/DC systems

Abstract: An incremental transformer model suitable for slow transient studies was developed. A typical application is the study of temporary harmonic overvoltages in AC/DC systems caused by transformer saturation. The proposed model represents the nonlinear magnetic circuit of the transformer and is, therefore, more complex that the piecewise-linear models often used to simulate saturation. Despite its complexity, the model formulation is suitable for direct solution at each integration step and this results in reasonable simulation time. The proposed model is particularly suitable for HVDC system studies since only a few elements of the transformer matrix need to be updated at each switching instant to account for the switching action of the converter valves. A study of temporary overvoltages in a weak AC/DC system is presented. Two types of disturbances leading to temporary harmonic overvoltages are simulated using both the piecewise-linear and the proposed incremental transformer model. Comparison of the simulation results indicates that the proposed model can be successfully used for the validation of temporary overvoltage studies conducted with simpler and faster transformer models. >