Showing papers on "Electrical network published in 1994"

Addressing substrate coupling in mixed-mode ICs: simulation and power distribution synthesis

Abstract: This paper describes new techniques for the simulation and power distribution synthesis of mixed analog/digital integrated circuits considering the parasitic coupling of noise through the common substrate. By spatially discretizing a simplified form of Maxwell's equations, a three-dimensional linear mesh model of the substrate is developed. For simulation, a macromodel of the fine substrate mesh is formulated and a modified version of SPICE3 is used to simulate the electrical circuit coupled with the macromodel. For synthesis, a coarse substrate mesh, and interconnect models are used to couple linear macromodels of circuit functional blocks. Asymptotic Waveform Evaluation (AWE) is used to evaluate the electrical behavior of the network at every iteration in the synthesis process. Macromodel simulations are significantly faster than device level simulations and compare accurately to measured results. Synthesis results demonstrate the critical need to constrain substrate noise and simultaneously optimize power bus geometry and pad assignment to meet performance targets. >

Transient stability index from conventional time domain simulation

Abstract: This paper presents a practical and efficient method to incorporate energy analysis into conventional power system time domain transient stability simulation for producing a first swing stability index. The proposed method is a variation of the potential energy boundary source approach, utilizing a numerical transient energy function and a pseudo-fault-on trajectory starting from the dominant potential energy peak point of the postfault system trajectory. The transient stability index not only provides additional insight into the stability studies, but also has the potential of speeding up the stability limit derivation process by reducing the number of program runs. >

Dynamic performance of static and synchronous compensators at an HVDC inverter bus in a very weak AC system

Abstract: This paper discusses the performance of dynamic voltage control devices at the inverters of very weak AC power systems The types of compensation considered are: (a) static VAr compensators (SVC); (b) synchronous compensators (SC); (c) a mix of the two; and (d) fixed capacitors Although the primary purpose of these compensators is to control voltage at the AC bus, their dynamic performance during system disturbances is a very important factor The investigation includes the behavior of the various voltage control options under AC and DC disturbances The paper shows that the SVC has the fastest response for load rejection type of overvoltages, but can cause serious problems with recovery during undervoltages caused by single phase faults The CIGRE benchmark model for HVDC control studies has been modified and used in this study In particular the effect of local load has been included >

On the resistance between two points on a grid

Abstract: The resistance between two adjacent nodes on an infinite square grid of equal resistors can easily be found by superposition. This paper addresses the corresponding problem for two arbitrary nodes. A solution is found by exploiting the symmetry of the grid and using the method of superposition. The mathematical problem involves the solution of an infinite set of linear, inhomogeneous difference equations which are solved by the method of separation of variables.

Voltage correction power flow

Abstract: A method for power flow solution of weakly meshed distribution and transmission networks is presented. It is based on oriented ordering of network elements. That allows an efficient construction of the loop impedance matrix and rational organization of the processes such as: power summation (backward sweep), current summation (backward sweep) and node voltage calculation (forward sweep). The first step of the algorithm is calculation of node voltages on the radial part of the network. The second step is calculation of the breakpoint currents. Then, the procedure continues with the first step, which is preceded by voltage correction. It is illustrated that by using the voltage correction approach, the iterative process of weakly meshed network voltage calculation is faster and more reliable. >

Applications of static phase shifters in power systems

Abstract: This paper examines various functions that can be assigned to a static phase shifter (SPS) to enhance the performance of a power system during steady-state conditions, small-signal dynamics, and large-signal dynamics. The investigations are conducted on four test systems which exhibit typical power system operational problems, e.g. torsional oscillations, inter-area oscillations, transient instability, transient mechanical torques and loop-flow phenomenon. An AC-DC power flow program, an eigenvalue analysis program, an AC-DC transient stability program, and the EMTP are used as the study tools. The investigations show that depending upon the type and the location of an SPS, it may be utilized for mitigation of small-signal oscillations and/or enhancement of transient stability, in addition to steady-state power flow regulation. The studies also reveal that most dynamic characteristics of an SPS can be achieved by augmenting an existing conventional (mechanical) phase-angle regulator with a relatively small size static power converter. >

Development of a frequency-dependent composite load model using the measurement approach

Abstract: In control and stability studies, load models should realistically represent the aggregate load behavior of all kinds of individual components. In this paper, the development of a composite load model, where the load is represented as a combination of an RC circuit in parallel with an induction motor equivalent circuit, is presented. A procedure is developed for identifying a frequency-dependent composite load model using digital measurements from an on-line transient recording system, taking account of system frequency variation. A nonlinear model parameter estimation technique is described to derive the frequency-dependent load model. A computer program called LMSP has been developed. The program consists of five major phases: user-interface, data manipulation, load model identification; model conversion and system model response evaluation. A case study is presented to illustrate, in particular, the accuracy of the developed model for the representation of dynamic load behaviors of an actual power system. >

Series connected voltage-source converter modules for force-commutated SVC and DC-transmission

Abstract: In force-commutated SVC and DC transmission stations, series-connected, multi-converter modules are necessary to build up the DC link voltage rating. Based on digital simulations of 8 modules, it is shown that the total harmonic distortion (THD) of 5% can be achieved from harmonic cancellations by using phase shifting of the triangular carriers in the sinusoidal pulse width modulation technique. The requirement of the DC link capacitor size to ensure ripple-free DC voltage is studied. The 8-module case-study points to the ability to achieve 1% THD for higher voltage rating by increasing the number of modules connected in series. >

Application of GTO voltage source inverter in a hybrid HVDC link

Abstract: This paper investigates the application of a GTO voltage source inverter in a two-terminal HVDC link, which is fed at the sending end by a line-commutated rectifier. This type of HVDC link may be applied when power transfer is predominantly unidirectional, especially to a weak AC system. The investigations are based on analytical studies and digital time-domain simulations with the Electromagnetic Transient program for DC systems (EMTDC). Control method and protection requirements are studied, together with dynamic behavior of the system following disturbances, e.g. DC fault, AC fault, start-up etc. The studies are aimed at exhibiting the technical feasibility of the proposed HVDC scheme. Need for further studies is pointed out when necessary. >

Determination of current distribution in energized conductors for the computation of electromagnetic fields

Abstract: Current distributions in networks of overhead and buried conductors, energized by current injections at arbitrary locations, are computed by two approaches. The first approach solves electric field point matching equations in a weighted least square formulation with linear constraints on the currents. The second approach, specialized to the low frequency range and lossy media, employs a power minimization algorithm. Both approaches lead to geometrically invariant, linearly constrained, quadratic minimization problems. At low frequencies, induced loop currents are determined by explicitly imposing Faraday's law as a linear constraint. Computation results compare well with measurements and with results of other algorithms. At high frequencies, the computation results match those published in the antenna literature. At low frequencies, they are essentially identical to published measurements and to computations based on grounding and quasi-static techniques. >

A fast active power filter to correct line voltage sags

Abstract: An active power filter for compensating voltage sags that occur on a weak AC power system is described. The proposed active power filter is especially suitable in situations where sensitive data processing and other critical loads are to be operated on a weak AC system. The proposed filter is fast acting and simple in design. A design procedure based on IEEE/ANSI voltage withstand tolerance (IEEE standard 446-1987) is proposed. Laboratory tests on a prototype filter show fast response and linear correction characteristics. >

Adequacy assessment of composite power systems with HVDC links using Monte Carlo simulation

Abstract: Direct current (DC) links are finding increasing use throughout the world in the form of long distance transmission and asynchronous interconnections. System reliability studies of a composite generation and transmission system containing a DC link involve modelling the DC transmission line and then analysing the overall composite system with the DC link forming an integral part. This paper illustrates a technique for DC system reliability analysis using the Monte Carlo simulation approach. The procedure developed was tested on a model DC system and the results are presented. The basic MECORE program was extended to include a DC link within composite generation-transmission system adequacy assessment. This paper also presents the Monte Carlo techniques employed for the composite system study and the results obtained for the modified IEEE-RTS (Reliability Test System). >

Resolution and stability analysis of an inverse problem in electrical impedance tomography: dependence on the input current patterns

Abstract: Electrical impedance tomography is a procedure by which one finds the conductivity distribution inside a domain from measurements of voltages and currents at the boundary. This work addresses the i...

Application of multi-variable control for automatic frequency controller of HVDC transmission system

Abstract: In an HVDC transmission system that links two AC power systems, the automatic frequency controller (AFC) calculates power to be interchanged between the two AC systems according to their frequencies thereby improving the frequency characteristics of the two power systems. This paper introduces a newly developed DC AFC system, which applies a multi-variable control to the DC system-based frequency control. It is capable of controlling the frequencies of the two AC systems optimumly while maintaining their stability. This system was developed for one of Japan's HVDC transmission facilities and produced good results in a combined test using a power system simulator. The field installation will be completed in March 1993, when the AFC system will enter service. >

A robust co-ordinated control scheme for HVDC transmission with parallel AC systems

Abstract: This paper introduces a practical control philosophy for HVDC transmission in parallel operation to an AC system with particular emphasis on coordination of both transient and dynamic stability. Systematic development of the control scheme on the basis of on-line identification, optimal control and rule-based bang-optimal co-ordination principles is presented. Verification tests of the scheme on a physical HVDC/AC system simulator show that the simple control computer algorithm is practical and robust. The controller can successfully distinguish between different system fault severities and adapts its output signals to provide maximum synchronising torque and ensure optimal damping of power oscillations. >

Voltage distortion in distribution feeders with nonlinear loads

Abstract: The voltage of three real-life 13.8 kV feeders supplying customers with nonlinear loads was analyzed by means of computer simulations. Three classes of nonlinear loads were considered. Each class is characteristic for different types of AC to DC converters such as the input DC supply used for adjustable-speed-drives, battery chargers, PCs, TVs and electronically ballasted lights. The analysis is based on the determination of the most harmonic susceptible busses and their response to each harmonic frequency. A new expeditive method that takes into account the background harmonic voltage phasor, and an equivalent bus impedance was developed and used to compute the maximum nonlinear loads that yields VTHD=5%, (voltage total harmonic distortion). The main conclusion of this work is that when mitigation methods are not used, for a 15 kV class feeder with a maximum 10 MVA installed load, the total nonlinear residential load should not exceed 300 kW if the ITHD 100%. >

Reconstructable interconnect structure for electronic circuits

Abstract: A reconstructible electrical circuit module includes a substrate, at least one electrical circuit component and an electrical interconnection structure. The electrical interconnection structure includes at least one multiple ply sequence stacked over the component and substrate in which the portion of the module underlying a ply in the electrical interconnection structure is substantially unimpairable by a process for removing that ply.

A power sensitivity model for electromechanical oscillation studies

Abstract: This paper describes the derivation of a power sensitivity model for dynamic studies of power systems, subjected to normal operation disturbances. The need of an infinite bus representation is avoided with the linearized nodal power balance approach. This permits the model to be easily extended to any number of network buses. In the linearized form, the resulting power sensitivity model (PSM), presents some interesting features, such as decoupled modelling and time scale decomposition properties. For presentation reasons, the PSM is first derived for a single generator connected to an infinite bus. Its performance is then compared with the classical Heffron-Phillips Model, as described by de Mello and Concordia (1969). Finally, it is extended for multinodal networks. >

Method and apparatus for insulation monitoring in unearthed DC and AC networks

Abstract: The invention relates to a method for insulation monitoring of unearthed electrical DC networks (mains) and AC networks having an unavoidable ohmic and capacitive insulation impedance between network and earth, in particular such networks with connected rectifiers or other current converters. This method includes a AC pulse voltage which has alternately different pulse voltage values and is applied as measurement voltage via an ohmic network coupling between network and earth to the network to be monitored. The measurement current flowing between network and earth for each pulse voltage value of the transient oscillation of the network at this pulse voltage value, which current is dependent on the magnitude of the insulation impedance between the network and earth and on the pulse voltage value, is detected directly or indirectly as measured-current measured-value, and the measurement-value difference between two sequential measured-current measured-values is used to determine the ohmic insulation impedance between network and earth. In this case it is proposed according to the invention, in order to reduce the measurement times, to observe for each pulse voltage value of the measurement voltage the time response of the instantaneous-network-dependent transient oscillation process of the measurement current, or a quantity such as a voltage derived therefrom, until reaching the transient oscillation state, and to detect the associated measured-current measured-values directly after reaching the transient oscillation states and to switch over the respective pulse voltage value of the AC pulse voltage immediately to its next pulse voltage value. The invention furthermore relates to a device suitable for carrying out this method, with an AC pulse voltage source (20) which generates a measurement pulse and can be connected via an ohmic measurement resistor (Rm; 22) and an ohmic network coupling (24) between an unearthed electrical network (12) to be monitored and earth (E), and further having an evaluation unit which is connected to the measurement resistor and detects the measured-current measured-value (Um1, Um2) occurring respectively at the end of the transient oscillation process of one of each of the measurement pulses at the measurement resistor and it determines the ohmic insulation impedance (Re) between the network to be monitored and earth from the measured-value difference (Um1-Um2) of two sequential measured-current measured-values respectively. In this case it is proposed, according to the invention, for the AC pulse voltage source to be designed as a switchable voltage source (20) which can in each case generate one of a plurality, in particular two, different DC voltage values as a function of a control signal (S; 36), and for the evaluation unit (28, 34) to be designed such that it detects the electrical transient oscillation process from a DC voltage value across the measurement resistor (Rm; 22) and switches the switchable voltage source to the other DC voltage value at the end of each transient oscillation process.

Parallel-in-time implementation of transient stability simulations on a transputer network

Abstract: The most time consuming computer simulation in power system studies is the transient stability analysis. Parallel processing has been applied for time domain simulations of power system transient behavior. In this paper, a parallel implementation of an algorithm based on Shifted-Picard dynamic iterations is presented. The main idea is that a set of nonlinear Differential Algebraic Equations (DAEs), which describes the system, can be solved by the iterative solution of a linear set of DAEs. The time behavior of the linear set of differential equations can be obtained by the evaluation of the convolution integral. In the parallel-in-time implementation of the proposed algorithm, each processor is devoted to the evaluation of the complete set of variables relative to each time step. The quadrature formula, adopted for the integral evaluation, can be easily parallelized by using a number of processors equal to the number of time steps. The algorithm, implemented on a transputer network with 32 Inmos T800/20 adopting a uni-directional ring topology, has been tested on standard power systems. >

Predicting voltage distortion in a system with multiple random harmonic sources

Abstract: A method for statistically describing power system harmonic voltages in terms of the parameters of the harmonic current sources is presented. It is shown that for a large enough number of sources, a complete probabilistic characterization of the harmonic voltages can be found in terms of the second order moments of each current phasor's rectangular components. The method is tested on an existing distribution system by using both simulation and field measurements. >

Accurate voltage phasor measurement in a series-compensated network

Abstract: This paper describes the feasibility studies concerning an accurate voltage phasor measurement in a series-compensated network undergoing large disturbances. The principal modes of distortions in such a network are described. Some of these modes are changing with the fundamental frequency. The phasor evaluation is based on a new digital filter approach in which the fundamental frequency is estimated using a least-square algorithm. The need to have special potential (voltage) transformers is also discussed. This approach would be used in a shunt reactor switching scheme for an overall voltage control of a transmission network. >

System and 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.

A new method for calculating loss coefficients [of power systems]

Abstract: A method is proposed which avoids many limitations associated with traditional B-coefficient loss coefficient calculation. The proposed method, unlike the traditional B-coefficient method, is very fast and can handle line outages. The method utilizes network sensitivity factors which are established from DC load flow solutions, Line outage distribution factors (ODFs) are formulated using changes in network power generations to simulate the outaged line from the network. The method avoids the use of complicated reference frame transformations based upon Kron's tenser analysis. The necessity of data normalization used in least squares and the evaluation of the slope of /spl theta//sub j/ versus PG/sub n/ is not necessary with the proposed method. Using IEEE standard 14-bus and 30-bus systems, the method's results are compared against results obtained from an AC load flow program (LFED). The method's solution speed is compared to that of the LFED method, the base case database method and the conventional B-coefficient method based on A/sub jn/-factor. The proposed method is easy to implement and, when compared to other methods, has exhibited good accuracy and rapid execution times. The method is well suited to online dispatch applications. >

Engine wiring system

Abstract: A wiring system for use with an engine or power module having a number of electrical systems includes a first electrical device of an electrical system, a second electrical device of the electrical system, and an electrical connector connected between the first and the second electrical devices to define an electrical circuit. The electrical connector includes alpha-numeric indicia identifying the electrical circuit. The alpha-numeric indicia include a first alpha-numeric indicium corresponding to the electrical system, a second alpha-numeric indicium corresponding to the first electrical device and a third alpha-numeric indicium corresponding to the second electrical device. The wiring system can also include a connection terminal disposed between the first and second electrical devices, wherein the electrical connector includes both first alpha-numeric indicia identifying the electrical circuit and second alpha-numeric identifying the connection terminal.

Junction box for quick release mounting of electrical circuit components

Abstract: Improvements in wiring assemblies using an electrical junction box assembly having preset electrical terminals. Such present terminals are hard-wired to certain electrical connection devices near the outer periphery of the box. Electrical components, such as a switch, a receptacle and the like can be quickly and easily mounted in place in the box in electrical contact with respective preset terminals. The selective electrical component can be provided with a number of pins at predetermined locations for electrical contact with certain of the preset terminals. One or more power-receiving members, such as a light fixture, can be coupled to respective outer peripheral electrical connection devices for receiving the three or four individual wires of an electrical line from each power-receiving member. The terminals in the box and the electrical connection devices represent an assembly with a quick release fastening capability which adapts the box for connection between a circuit component, such as a switch or an electrical power-receiving member. The electrical components are predetermined as to how they are to be used in a circuit. In this way, the time required to wire a house or building will be reduced and labor costs would be correspondingly lowered. Two or more boxes of the present invention can be ganged to make them suitable for use where, for instance, switches are to be placed side by side to each other, as well as to mount female receptacles adjacent to each other.

Electrical circuit identification means

Abstract: A hand-held electronic receiver for detecting pulses of high magnitude and short duration in an electrical circuit, including an inductive pick-up coil, an electrical signaller, an electrical power supply for the signaller, and an electronic trigger responsive to electrical pulses induced in the pick-up coil for effecting energization of the signaller from the power supply. There is a manually-adjustable control including a circuit responsive to pulsed energy, bridging the pick-up coil for bleeding off portions of induced pulses from the coil, thereby to enable a selective control of resultant output from the coil to be had.