| 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: Electromagnetic design considerations for fast acting controllers in a power system is introduced and defined. A distinction is made in relation to the more commonly understood system control design necessary for damping electromechanical oscillations using stability programs and eigenanalysis. Electromagnetic eigenanalysis tools have limited availability and are consequently rarely used. Electromagnetic transients programs (EMTP) on the other hand are widely used and a procedure for undertaking electromagnetic control design of fast acting controllers in a power system using emtp is presented |
| Abstract: not available |
| Abstract: This paper investigates the dynamic performance of the advanced static VAr compensator or STATCON at a HVDC converter terminal where the ac system has a very low short circuit ratio (SCR). This STATCON is based on a nine-level GTO thyristor inverter. The studies include operating characteristics of the STATCON under various ac and dc disturbances. The simulation results are compared with other types of reactive power compensation options available for such applications. It is shown that the STATCON has clear advantages over the other compensators, in areas such as fault response time, voltage support ability, and dc recovery, while operating with very weak ac systems. |
| Abstract: Direct connection schemes have been a subject of recent investigation, offering operational flexibility and substantial reductions in ac components. In these schemes the use of active dc filters has been suggested to replace the conventional tuned passive filter design. This paper presents the smoothing transformer as a new means for reducing dc harmonics at characteristic and non-characteristic frequencies using only passive components. A realistic smoothing transformer design is examined using the New Zealand HVdc system operating in the direct connection mode. The steady-state and transient performance of the smoothing transformer design is compared with that of the existing dc smoothing reactor and filter bank. |
| Abstract: When a dc link feeds into an ac system where the short circuit ratio is low or very low, the ac voltage requires some form of supplementary control. The concept of a series capacitor located between the ac system and the dc link has been an attractive consideration but is susceptible to ferroresonance between the series capacitor and the converter transformers. Using dc link controls judiciously, it is shown that any onset of ferroresonance can be eliminated. Benefits to series compensating a dc converter are presented. |
| Abstract: The conventional means for the reduction of dc side harmonics from HVdc converters is the passive filter, an expensive solution, and therefore normally restricted to the elimination of the twelfth harmonic. However, higher order harmonics can still be a source of electromagnetic interference and often need to be filtered. A novel scheme to remove the higher order harmonics has been recently implemented in the form of a combined passive-active filter configuration. This paper describes an alternative solution to passive and active filter arrangements on the dc side of the converter. It is based on the principle of active current harmonic cancellation. The concept proposed here, however, is considerably simpler than the filtering of other thyristor driven dc ripple reinjection schemes, since it does not involve any switching devices. |
| Abstract: This paper presents a validation of a real-time digital simulation of a transmission line model with frequency dependent parameters. 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. 41 microsecond and 71 microsecond time steps are readily achieved in real time with the new line model for three phase and double circuit (6 conductors) transmission lines respectively. The new line model is now installed in a Real-Time Digital Simulator (RTDS). Field test results are presented in this paper for validating the new line model. |
| Abstract: The recent availability of Electromagnetic Transient Programs with graphical front ends now makes it possible to put together models for circuits and systems in a manner similar to the connection of components in a laboratory. In the past, the non-graphical EMT Programs required considerable expertise in their use and thus distracted the students into the details of simulation. The introduction of a graphical simulation based laboratory into Undergraduate and Graduate Engineering Programs is presented, based on the PSCAD/EMTDC program. The philosophy behind the design of suitable example cases is presented with the framework of an Undergraduate Power Electronics Course, an HVdc Transmission Course and a course on Power System Protection. |
| Abstract: Core saturation instability has occurred on several HVDC schemes resulting from interactions between second harmonic and dc voltages and currents on the ac side of the converter and fundamental frequency voltages and currents on the dc side of the converter. The instability, reinforced by unbalanced saturation of the converter transformer, has been solved by suitable use of low order non-characteristic harmonic filters and by hvdc control modifications. While the phenomena has been simulated and observed during switching and fault conditions, time domain simulation of steady state core-saturation instability is difficult because of the extremely long time constants associated with transformer saturation due to the low levels of dc current in the valve windings of the converter transformers. The paper presents an analytical method which can be used to quickly screen ac and dc system operating conditions to predict where core saturation instability is likely to occur. Analytical results have been confirmed using the digital transients simulation program PSCAD/EMTDC. |
| Abstract: not available |
| Abstract: A steady-state, phasor-type solution is developed for the interaction of a 12-pulse controlled rectifier with an accurate three-phase representation of a weak ac system. The solution is validated against a time domain simulation of a test system that contains an excited composite ac/dc resonance, and unbalance in the star-delta converter transformer. A solution is then obtained for a balanced converter attached to a three-phase 138-bus harmonic model of the New Zealand South Island system. |
| Abstract: A steady-state, phasor-type solution is developed for the interaction of a 12-pulse controlled rectifier with an accurate three-phase representation of a weak ac system. The solution is validated against a time domain simulation of a test system that contains an excited composite ac/dc resonance, and unbalance in the star-delta converter transformer. A solution is then obtained for a balanced converter attached to a three-phase 138-bus harmonic model of the New Zealand South Island system. |
| Abstract: not available |
| Abstract: The ferroresonant behaviour of a nonlinear system circuit is examined using the diagnostic tools of deterministic chaos. An electromagnetic-transients simulation program is used to retain the component nature of the system and allow metering as for a real system. The information from state space trajectories, Poincare maps and bifurcation diagrams is compared to that normally available from time and frequency domain analyses. They reveal the global behaviour of the system and the particular points of behavioral change. |
| Abstract: The steady state equations that describe the converter and dc system in the harmonic domain are solved by means of Newton's method, in a manner suitable for embedding in an iterative harmonic analysis of the complete power system. The solution includes the interaction of the converter with the dc system, and the effect of variation in the firing and end of commutation angles caused by ac voltage and dc current harmonics. The convergence of Newton's method is investigated, and methods for accelerating the solution are implemented. Finally, the solution obtained is validated by means of time domain simulation. |
| Abstract: The steady-state interaction of a six-pulse converter with a Thevenin equivalent of the three-phase ac and dc systems is solved. The converter is represented by harmonic phasor mismatch equations, and the interaction between the converter and ac and dc systems is embodied in the solution of harmonic mismatch equations for the converter terminal conditions. Since there are a large number of simultaneous nonlinear equations to be solved, a sparse Newton-type solution is developed that exploits the harmonic three-port nature of the converter, and the relatively weak interaction between switching angles and terminal harmonics. The resulting solution is fast, and closely matches a time domain simulation of the test system. |
| Abstract: not available |
| Abstract: The interaction between an HVDC converter and the saturation characteristic of a converter transformer can lead to a type of harmonic instability widely known as converter transformer core saturation instability. The paper presents a linearized direct frequency domain analysis of the mechanism behind this instability. Using linearized converter transfer functions and transformer saturation characteristics on ac and dc system equivalents, the system equations are solved to describe the phenomenon. A measure of the level of stability, saturation stability factor, is derived and utilized to predict the system dynamics. The analysis is verified by dynamic simulation of several systems. |
