| Abstract: A linear and direct method of determining the major components of noncharacteristic waveform distortion at the terminals of an HVDC converter is presented. The method is a development of the frequency-domain transfer function technique, and relates the ac current and dc voltage to distortion in the firing angle, ac voltage and dc current. The consequential effects of the commutation period and its dynamic variation are included. It is demonstrated that the dynamic variation of the commutation period is an important factor. The model is validated for low-order frequencies by comparison with results obtained by dynamic simulation for a simple test case. |
| Abstract: Electromagnetic transient programs are increasingly being used for the simulation of HVDC systems. Several of these programs have models of standard building blocks which can be strung together to simulate controls. This paper shows that a straightforward use of such building blocks results in incorrect modeling of many analog control circuits. A systematic procedure to model such controls is presented and compared with field tests on the actual control of the Nelson River Bipole II dc transmission system. Selected simulation and field test results for the operation of HVDC system are also presented. |
| Abstract: A Frequency Scanning Method is introduced in the paper to obtain a more accurate frequency characteristic for identifying harmonic instability in HVdc systems. An example of the application is used to identify the resonance frequencies in the CIGRE benchmark model. The paper shows that the Benchmark model is not tuned to the resonance frequency that it was designed for. Using the scanning method, the resonance frequency of the Benchmark model may be shifted to demonstrate a simulation of core-saturation type instability. |
| Abstract: not available |
| Abstract: Several methods for modeling dc and Power Electronic Apparatus in electromagnetic transient simulation programs have been developed in recent years. This paper presents their salient features and comments on their applicability to various dynamic phenomena in Ac-Dc Systems. Factors such as modelling detail, interpolation, elimination of chatter are discussed. The required detail of control modeling is also discussed. Sample results from typical studies in which these are used are also presented. |
| Abstract: A recent CIGRE document published in ELECTRA has described the potential benefits of a direct connection of generators of HVdc converters. While many theoretical contributions have been made, no practical test data has become available so far. This paper reports on harmonic tests carried out at the Benmore end of the New Zealand HVdc link operating as a group connected scheme. It was found that the measured harmonic current levels were well below specified generator ratings. Dynamic simulation accurately predicted the harmonic currents whereas the results of a steady state formulation were les reliable. |
| Abstract: In this paper a novel scheme for supplying remote communities with electrical energy is proposed. The scheme uses a controlled rectifier, a monopolar dc transmission line, and a load commutated inverter with a dual wound synchronous machine. The feasibility of the system, including start-up, operation, and the impact of harmonics is presented. It is shown that the system is technically feasible, but will require harmonic filters on the load side and a reliable communications link for control between the converters which may increase the cost of the scheme beyond what is economically feasible. |
| Abstract: Power electronic controllers in power systems are non-linear by nature and are required to operate satisfactorily over a wide range of system conditions. Dc links and static var compensators (SVC's) are the traditional power electronic controllers widely used at the transmission level. At the industrial level, variable speed drives, cycloconverters, dc rectifiers and power supplies are applied. Non-linearities in their performance are due to signal transmission delays, limits and non-linear gains in their controls, discrete firing intervals of diode, thyristor and GTO valves as well as the effects of transformer saturation. The general way of dealing with non-linearities in controller design is to linearize their performance around an operating point and designing controls by usual linear methods. Although a perfectly rational approach, the resulting design must be rigorously tested to ensure satisfactory operation under extreme conditions and large signal disturbances. Electromagnetic transient programs generically designated herein as "emtp" are most suitable for such tests because of the ease and ability to represent large systems with all non-linear functions and features. In fact, emtp can be used as a controller design tool. Use of PSCAD/EMTDC [1] as the example emtp is applied herein to outline power system non-linear controller design. |
| Abstract: In HVDC converter stations built in the recent years gapless ZnO arresters are in operation for overvoltage protection of the individual station components. Tell-Tale spark gaps are often used for monitoring the surge arrester stresses. For the arresters protecting the thyristor valves the steady state voltage stresses are quite different compared to typical arresters stresses in ac systems. In order to provide data of the actual voltage shape a computer simulation on EMTDC was run. The simulation results show that the fast transients occurring during turn-on and turn-off processes of the valves have a significant impact on the steady state power rating of the trigger resistors of the tell-tale spark gaps. |
| Abstract: Conventional stability analysis of ac systems incorporating HVdc links use either steady state or quasi-steady state representations of the HVdc converter. While these programs are entirely adequate for representing the dynamic behaviour of generators, they are compromised by their limited representation of non-linear components. Dynamic electromagnetic solutions such as EMTP and EMTDC can provide detailed elemental analysis of converters but are computationally expensive. In these types of simulations, the ac system representation must be restricted and consequently the ac system dynamic response is limited. A hybrid simulation package takes advantage of the computationally inexpensive dynamic representation of the ac system in a stability program, with the accurate dynamic modelling of non-linearities. The slow dynamics of the ac system are sufficiently represented by the stability program, while at the same time, the fast dynamic response of say an HVdc system, is accurately modelled by electromagnetic means. |
| Abstract: A theoretical development and formulation for the initiation or onset mechanism of commutation failures was previously produced. General validation of the theory and the parametric analysis of the phenomenon is now extended further by simulations on various HVDC systems. |
| Abstract: This paper presents a parametric study of the coupling of fundamental frequency currents into a dc line from neighboring ac lines. The case study is conducted using an electromagnetic transients simulation program and is based on a practical system. The impact on the induced currents due to factors such as conductor separation, variation in earth resistivity and unbalanced operation is examined. The cross-coupling of these currents onto the converter's ac side in the form of dc currents is also investigated with a view to determining the worst case. Wherever possible, a comparison with theoretical calculations is conducted for greater confidence in the results. |
| Abstract: This paper can be conveniently divided to two parts. In the first part, a brief review of the high voltage direct current (hvdc) transmission system, including its historic background and its advantages/disadvantages compared to ac transmission systems, is presented. Three areas in which there are potentials for the application of hvdc transmission in Islamic Republic of Iran are presented and briefly discussed. In the second part of the paper, the problem of small power tapping from hvdc transmission systems is presented, and a practical solution, based on the solid state devices with turn-off capabilities, currently available in the market, is proposed. The proposed scheme, then, is digitally simulated by the aid of the EMTDC/PSCAD software package. Simulation results prove the practicality of the proposed scheme, and the results of the system's performance are as good as anticipated. |
| Abstract: In this paper the problem of small power tapping from hvdc transmission systems is presented, and a practical solution, based on the solid state devices currently available in the market, is proposed. The proposed scheme, then, is digitally simulated by the aid of the EMTDC/PSCAD software package. Simulation results prove the practicality of the proposed scheme, and the results of the system's performance are as good as anticipated. |
| Abstract: Series compensating a dc link is a topic which raises immediate questions. What does it mean to compensate a dc link? J. Vithayathil and V. Koschik independantly suggested the concept of applying a series capacitor between a dc converter and the ac system. It is known that for a conventional dc link, reactive power equal to 50% or more of its real power must be supplied either form ac filters, the ac power system, or some compensator such as a switched capacitor, synchronous condenser, or a static VAr compensator. As dc power increases or falls, so too does the demand for reactive power into the converters, causing sympathetic ac voltage derivations. If the short circuit ratio is low, compensation is needed to counteract this lack of voltage regulation. Figure 1 depicts the concept of using a series capacitor to provide compensation at the dc inverter. With careful design, a series capacitor between the dc inverter and the ac system acts to self-regulate the reactive power deviations demanded by the dc link as power levels fluctuate. Nyati et al reported that a series capacitor device compensating |
| Abstract: This paper describes a new positive sequence directional element for use in numerical distance relays. The element is incorporated in a numerical relay and the relay is tested on an RTDS (Real Time Digital Simulator). Results are also shown from on-line tests in two different locations in the Manitoba Hydro network. Finally an accurate software model of the relay, proved against recorded performance on the RTDS tests, is used in off-line tests on complex system configurations. |
| Abstract: In this paper the problem of small power tapping from HVdc transmission systems is presented, and a practical solution, based on the solid state devices currently available in the market, is proposed. The proposed scheme, then, is digitally simulated by the aid of the EMTDC/PSCAD software package. Simulation results prove the practicality of the proposed scheme. The performance of the control systems, however, needs to be improved. |
| Abstract: A software model of a digital relay is added to an off-line emtp (EMTDC) and is then subjected to the same waveforms as the actual relay. Its performance is measured against the performance of the actual relay and the accuracy of the model is assessed. |
| Abstract: A software model of a digital relay is added to an off-line emtp (EMTDC) and is then subjected to the same waveforms as the actual relay. Its performance is measured against the performance of the actual relay and the accuracy of the model is assessed. |
| Abstract: Accurate estimation of the locations of line faults has been a subject of interest to electric power utility engineers and researchers for over twenty-five years. Almost all the research done so far, has been aimed at finding the locations of transmission line faults. Lately, the location of faults on distribution lines has started receiving some attention because of public pressure on the utilities for improving the reliability of power supply. This paper presents the overview of a technique that estimates the location of a distribution line shunt fault. Some test results are also reported. |
| Abstract: A digital impedance relay designed for use on three-phase single circuit transmission lines is tested an a double circuit line configuration. The problems associated with the operation of the impedance elements are identified. Suitable modifications to the relay are proposed and tested for double circuit application. |
| Abstract: This paper investigates the effect of the dc capacitance of an advanced static var compensator or STATCON on the dynamic performance at a high voltage direct current (HVDC) inverter terminal where the ac system has a very low short circuit ratio (SCR). The simulation results show that the STATCON behaves almost equally well under severe ac disturbance while the dc capacitance of the inverter is varied over a wide range. The studies also examine the operating characteristics of the STATCON corresponding to the low-order harmonic resonances as a function of the dc capacitor size. It can be concluded that the second harmonic of the ac system has little effect on the stable operation of the STATCON. In determining the dc capacitance size of the inverter, the low-order harmonic resonances are not a matter of the concern. |
| Abstract: This paper presents details on the design, architectural features and applications of a real-time digital simulator (RTDS) developed at the Manitoba HVDC Research Centre (Winnipeg, Canada). Custom hardware and software have been developed and collectively applied to the simulation and study of electromagnetic transients phenomenon in power systems in real-time. The combination of real-time operation, flexible I/O, graphical user interface and an extensive library of accurate power system component models make the RTDS an ideal simulation tool with a wide range of applications. |
| Abstract: This paper presents details on the design, architectural features and applications of a real-time digital simulator (RTDS) developed at the Manitoba HVDC Research Centre (Winnipeg, Canada). Custom hardware and software have been developed and collectively applied to the simulation and study of electromagnetic transients phenomenon in power systems in real-time. The combination of real-time operation, flexible I/O, graphical user interface and an extensive library of accurate power system component models make the RTDS an ideal simulation tool with a wide range of applications. |
| Abstract: This paper presents details on the design, architectural features and applications of a real-time digital simulator (RTDS) developed at the Manitoba HVDC Research Centre (Winnipeg, Canada). Custom hardware and software have been developed and collectively applied to the simulation and study of electromagnetic transients phenomenon in power systems in real-time. The combination of real-time operation, flexible I/O, graphical user interface and an extensive library of accurate power system component models make the RTDS an ideal simulation tool with a wide range of applications. |
| Abstract: This paper discusses the modelling aspects of local load at an HVdc converter terminal. In the CIGRE benchmark model [1] for instance, the local load is modelled as part of the Thevenin Equivalent of the ac system. Alternatively, the local load could be modelled explicitly at the converter terminal. The Thevenin equivalent would then include only the remote ac system. This paper presents the simulation results of the dynamic performance of an HVdc system with both representations of the local load. The results indicate that both representations provide similar responses. Thus the former representation as in the Benchmark is sufficient to represent the effect of local loads and is simpler than the latter model. |
| Abstract: The paper describes how an electromagnetic transient simulation program was used in the design of modifications to the controls of an HVDC converter that was experiencing commutation failures from ac voltage disturbances. These events were reviewed by the valve supplier and two control modifications were proposed. The purpose of the simulation study was first to reproduce measurements recorded at site, and then to select the best control strategy to eliminate the problem. |
| Abstract: Zero-sequence harmonic currents are generated in every HVDC transmission system. They appear from three pulse harmonic currents flowing through stray capacitances or capacitive connections to ground. On the DC-side of a converter station these disturbing harmonic currents enter the line and contribute to telephone interference. DC-filter design has to take into account these harmonics to limit their impact. This paper presents an analysis of zero-sequence harmonic currents flowing on the AC- and DC-side of HVDC transmission schemes. It will show from simulation results whether a simple analytical representation is sufficient to include the impact of zero-sequence currents for filter performance and rating calculations or whether a more detailed simulation has to be carried out. |
| Abstract: This paper describes the modelling of Siemens programmable high speed control system (SIMADYN D) for HVdc/SVC systems using a graphical digital electromagnetic transients program (PSCAD/EMTDC). The control system model is created graphically very similar to the graphical programming of the actual control system at a function block level. This model directly executes the same arithmetic and logic functions as used by the actual control system, including the processing time step, giving very high correlation of function behavior. This results in very fast and flexible programming of any control system associated with a HVdc system. This greatly enhances confidence in the model and gives faster study results even for complex systems. The availability of detailed HVdc control and protection models allows a much broader application of digital simulation including design of new project dependent control features, optimization of control performance, protection co-ordination, support during system commissioning among others. |
| Abstract: This paper describes the modelling of Siemens programmable high speed control system (SIMADYN D) for HVdc/SVC systems using a graphical digital electromagnetic transients program (PSCAD/EMTDC). The control system model is created graphically very similar to the graphical programming of the actual control system at a function block level. This model directly executes the same arithmetic and logic functions as used by the actual control system, including the processing time step, giving very high correlation of function behavior. This results in very fast and flexible programming of any control system associated with a HVdc system. This greatly enhances confidence in the model and gives faster study results even for complex systems. The availability of detailed HVdc control and protection models allows a much broader application of digital simulation including design of new project dependent control features, optimization of control performance, protection co-ordination, support during system commissioning among others. |
| Abstract: This paper investigates the possibility of using the multilevel gate turn-off (GTO) thyristor inverter as an advanced static var compensator (ASVC). The studies have shown that the design is feasible and that the fundamental frequency switching of the GTO thyristors is superior to various forms of pulse-width modulation. The main advantages of the multilevel ASVC over the prototype ASVC is that the series connection of GTO thyristors can be avoided and a staircase type of output voltage can be used to reduce the harmonics, the filtering requirements and the switching losses. |
| Abstract: This paper describes the preparation for tests on the relays on a long 500kV ac line carried out on site using the Real Time Digital Simulator developed by the Manitoba HVDC Research Centre. The purpose of the tests was to examine the relay behaviour prior to the insertion of series compensation in 1993. Off-line simulations were used to check the validity of the equivalents used for the real time simulations and the simulator waveforms were compared to staged fault test recordings. Some test waveforms are shown. |
| Abstract: This paper presents a validation of a real-time digital simulator (RTDS) of frequency dependent transmission line model with a published field test. The real-time transmission line model is based on Marti's time domain formulation which is adopted in the EMTP and EMTDC programs. Improvements to speed up the calculation are made in order to realize electromagnetic transient simulation in real-time by parallel processing using two digital signal processors (DSP's) for each line. The Field test is reproduced by RTDS and the simulation results are compared with the published field test results to show a good agreement between the two sets. Details of the system data for the field test are also given. |
| Abstract: This paper reports on a recently completed evaluation study in which physical High Voltage Direct Current (HVDC) controls were interconnected to the Real Time Digital Simulator (RTDS). The study was performed jointly by RTDS Technologies Inc. of Winnipeg, Canada and ABB Power Systems AB of Ludvika, Sweden. In the past such a study could only have been performed sing an analogue HVDC simulator. The recent introduction of an accurate and flexible real-time digital simulator has however made it possible to perform this study, and many others like it, in a new, more efficient manner. |
| Abstract: This paper reports on a study which investigated expanding and enhancing the capabilities of a traditional analogue simulator using a Real-Time Digital Simulator (RTDS). The main thrust of the investigation focused on methods of interfacing the tow simulators. The solution algorithm of the RTDS, a multi-processor device employing parallel processing techniques, proved to be a very important consideration. Of the three methods considered, the one based on a traveling wave transmission line models was found to be the best suited for the task. This method was satisfactorily tested in an integrated ac/dc system. |
| Abstract: A software model of a digital relay is added to an off-line emtp (EMTDC) and is then subjected to the same waveforms as the actual relay. Its performance to the same waveforms is measured against the performance of the actual relay and the accuracy of the model is assessed. |
| Abstract: This paper reports on testing of the Beckwith Electric M-0430 Multifunction Protective Relay using the Real-Time Digital Simulator (RTDS). The M-0430 is capable of performing a number of protection functions related to synchronous generators. During the tests several functions were evaluated including Phase Distance protection and Loss of Field Protection. Phase and neutral voltages and currents at the synchronous machine terminals were connected to the protective relays using the RTDS simulator's on-board digital-to-analogue conversion components. Appropriate amplifier units were connected between analogue output points on the simulator and the input to the protective relays. A detailed discussion of the RTDS simulator M-0430 functions and the test results are included in the paper. |
| Abstract: This paper introduces a new concept of a modular digital simulator design for testing protective relays. A brief discussion of the relay testing requirements leads to the need for the modular design. The basic features of the modular design are outlined. Several digital simulator implementation approaches are presented and their characteristics described. The benefits of such a modular design concept are summarized at the end. |
| Abstract: Variable frequency operation of an HVDC unit-connection scheme may affect the generator winding I2R losses, and may cause harmonic interferences on both the AC and DC system. The purpose of this research is to determine the magnitudes of generator winding I2R losses under a certain frequency range so as to improve the efficiency of the hydro unit operation at non-rated head and output power. the generator winding additional I2R losses and harmonic interference, are investigated by using the EMTDC program and other subordinate programs. The overall study shows that the generator winding power losses will be increased as the operating frequency decreases under the condition of a fixed generator output. The magnitude of increased losses, though, will not exceed 8-10% of generator total winding I2R losses under normal system operating conditions. Harmonic interference, on the other hand, will become more severe in both the AC and DC systems, as compared to fixed frequency operation. Active of on line tuning harmonic filters may be considered for a particular variable frequency operation scheme being implemented. |
| Abstract: A set of equations are developed that describe the 6-pulse converter in the steady-state harmonic domain. The method used is to directly convolve in the harmonic domain the dc voltage in each conduction period, with an appropriate sampling function. This avoids the need to use transfer functions, FFTs, or complicated Fourier transforms. The technique is fast and simple, and is able to model effects that have, until now, been largely ignored (such as the dc-ripple effect on commutation duration). Moreover, the equations are suitable for inclusion in a Newton-type solution method, as the partial derivatives are easily obtained. |
| Abstract: The high pulse naturally commutated static VAr compensator (SVC) is based on the ability of the ac/dc naturally commutated converter to regulate the absorption of reactive power and the use of a dc ripple reinjection scheme to increase the converter pulse number. A computer model of the proposed SVC is implemented using the EMTDC-PSCAD simulation package to demonstrate steady state and dynamic performance. The computer model shows that the unit can operate without harmonic filters and the response time compares favorably with existing alternatives. |
| Abstract: Graphical user interfaces (GUI) are used in electromagnetic transients simulation programs for increased productivity and other benefits. Shortened learning periods and documentation of simulations are additional benefits. The PSCAD GUI is described. Preparation of data files, running of simulation and analysis and documentation of results are presented. |
| Abstract: This working group report presents dc benchmark models tailored to ac/dc interaction. This is to encourage comparisons of the performance of different control strategies or computational tools related to various ac/dc interaction phenomena and system dynamic performance. System data and results are available on diskette or through e-mail. |
| Abstract: not available |
| Abstract: Adding a dc circuit to an existing transmission line is one method of significantly increasing the power transfer capability of a transmission corridor. The resulting hybrid system has significant coupling between the ac and dc circuits, but also from the fact that they may share the same sending end or receiving end ac systems. The resultant interaction produces overvoltages an the dc system which can be somewhat higher than for a conventional dc scheme. This paper presents a study of these overvoltages. |
| Abstract: A method of eliminating dc components of the currents in the transformer windings of a dc converter is presented. The method uses the technique of firing angle modulation. It is shown that merely eliminating the fundamental frequency component on the dc side may not remove this dc component. The impact of such control action at one converter on the other converters in the dc transmission system is also presented. It is also shown that the undesirable side effects of such a scheme include increased generation of non-characteristic harmonics on both ac and dc sides. The study is performed using an electromagnetic transients simulation program and theoretical calculations. |
| Abstract: Using a series capacitor to compensate a dc converter station is an old idea which with the maturing of dc and series compensation technology, can be realistically considered today. The main incentive is to achieve a lower overall cost when the dc converter feeds into an ac system with low short circuit ratio. Series capacitor compensation is an economical means of maintaining ac voltage control wen compared with other traditional methods using synchronous compensators or static var compensators. If the series capacitor is located on the ac system side of the dc converter and ac filters, then it is prone to ferroresonance and may impact damping of subsynchronous oscillations but dc valve voltage rating can be minimized. If located between the converter and the converter transformer, ferroresonance may no longer be a problem but the dc valves may require a higher voltage rating. Protection against ferroresonance and subsynchronous resonance is of greater concern with the case where location of the series capacitor compensation is on the ac system side of the converter transformers and ac filters. Low cost protection against ferroresonance can be achieved with either minimal hardware addition and/or controls design. Protection against decreased damping of subsynchronous oscillations involving nearby thermal generator shaft torsional effects must be applied. |
| Abstract: The "Control Sensitivity Index" or CSI has been used in the past to how the participation of a specific controller in the onset of instability of an HVDC system. Only steady-state relationships were used in the earlier formulation of CSI. This paper extends the concept of CSI to include the dynamics associated with some of the circuit components such as the smoothing reactor and transformer inductance. It then shows how the dynamics inherent in the control system can be included in the formulation to permit a parametric eigenvalue study. The formulation directly yields the time constants and resonant frequencies as a function of controller gains and hence can be used to tune the controller as well as to predict the onset of instability. |
| 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 non-linear 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 lambda control mode. |
| Abstract: The greater use of detailed models and the increasing size and complexity of system studies in power system digital simulation, has resulted in the need to re-examine the ability of digital computations performed at finite time intervals to accurately represent the actual system. These concerns are manifested in two distinct area. The first is the ability to switch elements at a specific point in time. Traditional digital simulation techniques allow switching elements to change state only at discrete computation times, whereas in reality switching can occur at any instant in time. The second area of concern is in the ability to accurately represent detailed control systems. These concerns are of particular importance in simulations containing a large number of controlled switching devices, such as HVdc systems of ac systems containing FACTs devices. This paper presents a discussion of the implementation and effectiveness of linear interpolation techniques in a digital simulation program. The paper addresses interpolation in both the network solution and the control system. The CIGRE HVdc Benchmark Model [1,2] with detailed controls models is implemented and its effectiveness. All simulation results presented were generated using EMTDC [3], but the techniques discussed can be applied to any electromagnetics transients program. |
| Abstract: Control coordination of fast acting voltage devices is considered of great significance in the electric utility industry as the existing transmission systems are expected to operate at higher loadings. Coordination of the controls of static VAR Compensators, dc transmission systems and power system stabilizers will maximize the loading capability of the network. The available study tools are identified along with how they might be applied to coordinate controls. A procedure for coordinating controls for electromechanical and electromagnetic interactions is presented. A "Global Gain Margin" is defined. |
