Transient Network Analyzer Research Articles

Integration of turbo-generator modules in digital transient network analyzer

The behavior of a small power system consisting of two interconnected generators is simulated in real-time by a prototype digital transient network analyzer (TNA). The prototype digital TNA consists of two computational modules and one I/O module. The modules communicate with each other through ribbon cables. Each computational module simulates one turbo-generator, its transformer, its governor, exciter, and power system stabilizer systems. The numerical integration is shared by two TMS320C30 DSPs at a step-size of 100 /spl mu/s in realtime. The I/O module post-processes the state variables and presents selected information for analog display. The paper presents oscillograms from a test program which includes symmetry checks and behavioral checks against well known waveforms of hunting oscillations, synchronization out-of-phase torques, and subsynchronous resonance phenomena. The success of the digital TNA depends on: (a) the theoretical method of decoupled partitioning so that different portions of the power system can be allocated to different DSP-modules, (b) the architecture of the DSP-modules which can communicate the numerical integration results of one module to its contiguous neighbors with minimum delay. >

A microcomputer-based data acquisition system for transient network analyzer operation

The transient network analyzer (TNA) is a collection of miniature models used to simulate the effects of switching events on power systems and to study various electromagnetic transient phenomena. This paper describes how a new microcomputer is used to serve as a high-performance data acquisition system for TNA operations. The system provides high-speed, synchronous acquisition of multi-phase voltage and current waveforms as well as control of circuit breaker closing-angles for statistical analysis. The computer interfaces with the TNA by means of plug-in boards containing analog-to-digital and digital-to-analog converters. The user interface is implemented with a graphical programming environment to provide controls and indicators on a front panel similar to those found on an oscilloscope. The new technology applied to the system make it a compact, highly flexible, and powerful tool.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transient analysis and hazard-free design of exclusive-OR switching networks

Transient analysis for exclusive-OR switching networks is studied. Based on the theorems proved for logic hazards, three methods are developed for hazard detection. The first is a graphical method that applies to functions of no more than six variables. The second method, which is an extension of the graphical method, can be applied to networks with any number of inputs. The third method is based on the compatibility of the product terms of a modulo-2 sum. Both the second and third methods can be implemented on computers. Three methods for synthesising hazard-free exclusive-OR switching networks are also presented. The first method applies to functions that are hazard-free realisable. In case a hazard-free network is not attainable, a simple disjoint decomposition of the function as hazard-free subnetworks is recommended. In the third method, hazards are suppressed by a secondary network. This method is used only when the first two methods fail. All three methods for hazard-free design can also be implemented on computers.

Digital simulation, transient network analyzer and field tests of the closed loop control of the Eddy County SVC

A static VAr compensator (SVC) was installed at the Eddy County substation near Artesia, New Mexico. It was put into commercial operation in April 1992. Before the commissioning period, a phase of extensive testing and analysis of the digital closed loop control was undertaken. This work was done using the actual control hardware and software in conjunction with an analog TNA and with digital simulation models of control and power systems. Results of this work were checked with the power system during field commissioning of the SVC. This paper gives an overview of the closed loop control design. It presents some results from the TNA tests, digital simulation and commissioning field tests of the SVC operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An extensible real-time digital transient network analyzer

The development of a completely digital power system multiprocessor transient network analyzer (TNA) is reported. Generators, loads, transformers and power lines are represented by simple linear electrical equivalents. Results are reported for both single-phase and three-phase networks. Electromagnetic transient phenomena can be modeled with available digital technology to a detail of about 100 mu s, corresponding to frequencies below about 5 kHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transients on lossless exponential transmission lines using Allen's method

Exact analytical expressions for the time-domain step response matrix of the lossless exponential transmission line are developed, thereby extending the range of problems for which Allen's method can be applied for the transient analysis of networks consisting of interconnections of linear distributed elements, lumped linear and/or nonlinear elements, and arbitrary sources. An indication as to the correctness of the expressions is obtained by comparing them to published results, which also helps to give a better physical insight into the step response matrix. The response to a step input and the transient response to a sudden sinusoidal excitation are presented. >

Electronic sectionalizer control methodology for improved distribution system reliability

A new methodology for sectionalizer control has been developed that provides more security for applications where system transient currents may cause actuate pickup. Actuate pickup, particularly on ground sensing, may occur during upline ground faults when the sudden load current imbalance is compounded by the unfaulted phase voltage rise causing magnetizing current inrush into a large amount of distribution transformers downline from the sectionalizer. Also, motor backfeed and nonsimultaneous fault clearing may cause actuate pickup if the load is sufficiently large. The control has five automatic restraint features: inrush restraint, count restraint, time-integrated threshold restraint, response restraint, and ground restraint. The last three are new features. The control logic was tested by connecting a prototype to the transient network analyzer and simulating conditions that were suspected of causing problems. >

Surge analysis of the tank of a gas-insulated line using lumped constant circuits

Surge voltages evaluated by a digital analysis method, for example, electromagnetic transients program (EMTP) and by an analog analysis method (transient network analyzer: TNA) are compared with experimental results on a scaled model of a gas insulated line. From the results, it is confirmed that the analog analysis method has a satisfactory accuracy and its computing speed is quite high. The error caused by the lumped element modeling of the gas insulated line is comparatively small, and the line is not necessary to be treated as a distributed parameter line. The lumped element model is advantageous to understand the mechanism of the transient characteristic of the induced transient voltage. A simple equivalent circuit of the gas insulated line is proposed and its accuracy is confirmed by a comparison with the calculated result obtained by an accurate line method. The transient overvoltages of the tank and across the insulated flange can be analytically calculated using the equivalent model.

Power swing analysis in a future metropolitan electric power system on a contingent trip of cryogenic high-power cables

A cryogenic power cable is expected to be capable of carrying bulk power as a main transmission line in a future metropolitan electric power system. It is important to establish a strategy of how to sustain power supply when such a highly densified power supply route trips from the network due to contingency. It is proposed here that the bulk power transmitted by the cryogenic cable could be distributed into the parallel conventional transmission lines by suitable circuit breaker operations in the system. In this process, power-flow routes are forced to be changed with a remarkable modification in the system configuration. In this paper, the power swings associated with the large power-flow change following contingent faults are analyzed by means of a transient network analyzer. It is found that the proposed system modification could be realized without any harmful power swing if the parameters in generators as well as in control devices have conventional magnitudes. It is shown also by simulations that the margin to occurrence in an unstable power swing is left sufficient even if the parameters deviate somewhat from the present magnitudes.

Detailed modeling of an actual static VAr compensator for electromagnetic transient studies

The authors present a detailed model of a static VAr compensator (SVC) for digital simulation of electromagnetic transients. It is also demonstrated that this model can adequately reproduce SVC transient behavior as verified in transient network analyzer studies carried out with a replica of the SVC control system. The SVC control system is described, with emphasis on some special blocking schemes needed to meet particular requirements of the power system transient performance. The complete system and SVC data are also included. >

TIME-DOMAIN MODELING OF FREQUENCY-DEPENDENT THREE-PHASE TRANSMISSION LINE RESISTANCE

Abstract Time-domain modelling of frequency-dependent line series resistance by a discrete lumped equivalent circuit is useful for simulation, either on a digital computer or on a transient network analyzer. A resistance model that is suggested by Wheeler (1) for resistance of a lossy coaxial communication cable with ideal square-root frequency-dependent losses is adapted to model resistance of a three-phase power line with earth return. The model is solved using the trapezoidal rule with damping, which is accurate and numerically stable even for large values of time step Δt, as used in simulation of power system transients. The model is simple, accurate, computationally fast, and it can be directly interfaced with an electromagnetic transient program.

Designing for Disaster

Electromagnetic transients are the tidal waves of electric power systems. These momentary voltage surges generally lasting only fractions of a second can be powerful enough to disrupt normal operations and even cause serious damage to major pieces of equipment, such as transformers. Created by lightning, line faults, substation switching functions, and other sudden events along a utility network, transients must be taken into account both in choosing equipment ratings for a power system and in setting its operating parameters. Like the builders of a seawall that must withstand the highest expected waves from the ocean, engineers trying to guard against damage from transients face an extraordinary design task. Most of the huge computer simulation codes related to power systems either model steady-state conditions or deal with system stability problems. The analysis of electromagnetic transients, on the other hand, requires a much more detailed examination of how some critical portion of a power system will react to conditions that can change greatly in microseconds. For many years, simulation of transient effects was performed by special-purpose analog computers called transient network analyzers (TNAs). These machines, which are still in use, recreate a portion of the power system in miniature, complete with voltage sources representing generators and various kinds of capacitive or inductive loads. TNAs are generally adequate but relatively inflexible, tedious to set up, and cumbersome to use. Once a system configuration is modeled, many simulations can be performed. Given the need to manually reconfigure TNA circuits to represent changes in a system, however, the analyzers can also be quite expensive to use. During the late 1960s, Herman Dommel of the Bonneville

極低温大容量送電線の事故脱落時における大都市送電系統の電力動揺解析

A cryogenic power cable is expected to be capable of carrying bulk power as a main transmission line in a future metropolitan electric power system. It is important to establish a strategy of how to sustain power supply when such a highly densified power supply route trips from the network due to contingency. It is proposed here that the bulk power transmitted by the cryogenic cable could be distributed into the parallel conventional transmission lines by suitable circuit breaker operations in the system. In this process, power-flow routes are forced to be changed with a remarkable modification in the system configuration. In this paper, the power swings associated with the large power-flow change following contingent faults are analyzed by means of a transient network analyzer. It is found that the proposed system modification could be realized without any harmful power swing if the parameters in generators as well as in control devices have conventional magnitudes. It is shown also by simulations that the margin to occurrence in an unstable power swing is left sufficient even if the parameters deviate somewhat from the present magnitudes.

Theoretical and Experimental Investigations on Circuit Breaker Transient Recovery Voltages

The purpose of this paper is to present the results of theoretical and experimental investigations conducted on the kilometric faults inpower networks and their impact on the electromagnetic transient recovery voltages in the circuit breaker (CB). In the analytical study, an accurate Laplace s-domain distributed parameter analysis used to obtain A,B,C and D constants of two transmission systems before and after CB. Having the input impedances of two line sections derived from network constants and the laplace transform of the interrupted fault current, simulated by injection of a current ramp time function, an s-domain expression for voltage across C.B. is obtained and laplace-inverted using a numerical technique to obtain its corresponding time waveform. In an expeimental study, a Transient Network Analyzer (TNA) was used for simulating two line sections and Current Injection Unit (CIU). Circuit breaker recovery voltage could then be observed and photographed using a cathode ray oscilloscope and a suitable camera. Different fault and breaker locations could be simulated on TNA by changing the place of the CIU. A comparison showing the agreement between analytical and experimental studies will be presented and several case studies will be reported.

Transient analysis of extended distribution networks

An analytical method is presented for the analysis of the transient behavior of extended distribution networks during short-circuits or start-up using interactive, graphical techniques. A fast algorithm is used which exploits the radical nature of the network to calculate the nodal voltages. Two models are available for the transient analysis of the induction motors, which can be used according to the degree of detail desired. Typical load types for each distribution substation are considered, and the parameters of the loads at each node are determined by the relevant composition of the aggregate nodal load. Disturbances provoked by any type of short circuit are considered, and the user can obtain the currents and voltages at any point of the radial network selected. The program is applied to the analysis of the transient behavior of a realistic distribution network during faults on the network. Comparison of the results with those obtained from the standard practice of considering the loads concentrated on the HV busbars of the HV/MV substations has shown differences of more than 150%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Real-time digital simulator of the electromagnetic transients of power transmission lines

The authors present the theory and results of a novel real-time digital simulator of transmission lines. The simulator is based on a time-domain formulation and obtains the electromagnetic transient performance of balanced three-phase lines in real time. Sample results of energizing a transmission line from balanced and unbalanced sources are presented. The real-time digital simulator results are verified for accuracy by simulating the same system, offline, using the EMTP (ElectroMagnetic Transients Program). It is noted that the newly developed real-time digital simulator can readily be incorporated into modern transient network analyzers and HVDC (high-voltage direct current) simulators. Using these in place of a large number of Pi or gamma sections of passive networks is economical, space saving, and accurate.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Real-Time Digital Simulator of the Electromagnetic Transients of Power Transmission Lines

The authors present the theory and results of a novel real-time digital simulator of transmission lines. The simulator is based on a time-domain formulation and obtains the electromagnetic transient performance of balanced three-phase lines in real time. Sample results of energizing a transmission line from balanced and unbalanced sources are presented. The real-time digital simulator results are verified for accuracy by simulating the same system, offline, using the EMTP (ElectroMagnetic Transients Program). It is noted that the newly developed real-time digital simulator can readily be incorporated into modern transient network analyzers and HVDC (high-voltage direct current) simulators. Using these in place of a large number of Pi or gamma sections of passive networks is economical, space saving, and accurate. >

Power System Analog Simulation Enhancement Using a New Programmable Electronic Model

The paper presents a microcomputer-based hybrid model that performs real-time simulation of Power System equipment, such as linear or non-linear resistors and inductors, converter stations, static VAR compensators and other devices. The presented model was designed to be coupled to Power System Analog Simulators (Transient Network Analyser TNA and/or HVDC link Simulator), and it can generate different voltage or current waveforms, store and process simulation results and also perform closed-loop network simulation, working as a Voltage-controlled Current Source or as a Current-controlled Voltage Source. A detailed analysis is developed and demonstrates that the electronic model operates within the tolerance limits allowed for Power System simulators. A prototype has already been implemented in a Power System Simulation Laboratory and it is presently in use, showing its high flexibility and importance for power system planning and operation studies. The authors believe that hybrid simulation will grow very fast during the next few years, fullfilling the gap between digital and analog Power System Simulation, and even acting as an interface between them.

Real time electronic analog simulation of a three-phase transmission line

The authors present a real-time electronic analog simulation of a three-phase transmission line to be used with the electronic generator and the hydraulic turbine of the University of Sherbrooke, Quebec, Canada. It is a true fire Pi -element three-phase simulator in which line length can be adjusted from 20 to 200 miles and ground and skin effects are included in the setting of the line parameters. This instrument: simulates most horizontal line configurations of 200 kV or more; takes into account the real quality factor of inductances through 3 kHz; makes possible the adjustment of line parameters to their proper values including the frequency dependency; tolerates 10 PU of overcurrent and overvoltages; and makes available a nominal power base variation in the ratio of ten to one. Transient studies show that this simulator compares favourably with other transient network analyzers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multiprocessor UHV Line Relay Testing with Transient Network Analyzer

A multiprocessor-based UHV line relay developed at IREQ [1] was tested on a transient network analyzer (TNA). Special hardware and software designed for relay testing on the TNA are presented together with the relay test session results.