| 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 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: An Energy Recovery type filter has been presented in this paper for mitigating harmonic instabilities in an integrated ac/dc system. The ER-filter effectively emulates a conventional low Q filter at much reduced losses. It is also able to modified as a variable Q filter. The studies are conducted through computer simulation an a base system chosen from CIGRE benchmark model. A frequency scanning method is introduced in the paper to obtain more accurate frequency characteristic in real HVdc systems. |
| Abstract: Conventional HVDC control systems have employed Proportional-Integral (PI) type controllers. These controllers have pre-defined gain and thus do not always work properly for different operating conditions. Self-learning controllers based on Artificial Neural Networks (ANN) with on-line learning can be highly adaptive and operate at various operating points and for various ac system conditions. This paper reports a study of such controllers and verifies their feasibility using an Electromagnetic Transients Program EMTDC. |
| Abstract: Dc transmission systems usually operate asynchronously. There can be benefits having a dc transmission line provide synchronizing capability, particularly when it is to operate in parallel to ac transmission. System strength will be enhanced if the dc transmission line does its part to support synchronism between its sending and receiving end systems, specially when the parallel ac system gets into trouble. The system stability enhancement provided by dc transmission is well known. A simple modification to the dc transmission controls will not only allow its ac system damping capability to be fully retained but continuous synchronization can also be achieved. |
| Abstract: FACTS devices and other fast acting controllers have the potential to respond to higher frequency (above 5 Hz) electromagnetic oscillations. A procedure is presented for use of electromagnetic transients programs (emtp) in undertaking electromagnetic control coordination of FACTS controllers in a power system. A term for measuring the degree of electromagnetic interaction between FACTS controllers, dc links and other fast acting devices such as power system stabilizers is defined and designated as "Global Gain Margin". |
| Abstract: This paper discusses the performance of dynamic voltage control devices at the inverters of very weak ac systems. The types of compensation considered are: a) Static var compensator (SVC), b) Synchronous compensator (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. |
| Abstract: This paper explores the application of the back-to-back dc link as a synchronous link in an ac power system. Through its prime function of dynamic power control, it can be applied to reduce the series impudence of an ac transmission line. As a phase shift device, the full 360 degree steady state phase angle control is achievable together with a wide range for high speed dynamic phase shift. Enhanced ac voltage control at the back-to-back dc link is also possible with the application of GTO's in a bridge configuration for voltage source converters. A novel configuration is presented to eliminate the need for 24 or 48 pulse arrangements considered necessary for harmonic suppression when conventional voltage source GTO converters are applied. The back-to-back dc link offers the potential to directly control substantial levels of real power in the ac system and with a unique application of GTO's, provide a practical method for independent voltage control. The back-to-back dc link when applied with the considerations of this paper in mind, provides an effective option when extraordinary power control is required in the ac power system. |
| Abstract: not available |
| Abstract: An Artificial Neural Network (ANN) is used to derive the chipping angles for a Pulse Width Modulated inverter. The neural network is trained off line and later implemented in the control system. The ac voltage magnitude order is used as the input to the controller. The ANN outputs three firing angles and thus controls the magnitude of the fundamental frequency voltage while eliminating the two lowest order harmonics. The performance of the ANN controlled inverter is studies using an electromagnetic transients simulation program (EMTDC). |
| Abstract: The paper investigates the use of a novel filter arrangement for eliminating harmonic instability. The CIGRE benchmark model is selected as the base system. Presented in the paper is an example of harmonic instability which is first eliminated using a conventional low Q filter. Subsequently an energy recovery filter (ER-filter) replaces the conventional low Q filter. It is shown that the ER-filter provides similar performance with a fraction of the power loss when compared with a low Q filter. The dynamic performance of the ER-filter is also demonstrated via the simulations of system start-up and faults. The tool used for this investigation is an electromagnetic transient simulation program. |
| Abstract: An investigation into a neural network (NN) based controller, comprised of a NN trained off-line in parallel with a NN trained on-line, is described in this paper. This NN controller has the potential of replacing the PI controller traditionally used for HVDC transmission systems. A simplified theoretical basis for the operational behavior of the individual NN controllers is presented. Comparisons between the responses obtained with the NN and PI controllers fr the rectifier of an HVDC transmission system are made under typical system perturbations and faults. |
| Abstract: This paper presents further investigations into using an Energy Recovery (ER) filter for mitigating harmonic instabilities in integrated ac/dc system. For certain system conditions a low quality factor (Q) filter is desirable and for other conditions a high Q is better. This inspired the concept of a "controllable Q filter" in which the power absorbed in the filter is controllable by electronic means. The controllable Q filter uses an energy recovery (ER) link so that this power is recovered. The investigations are conducted through computer simulation using an electromagnetic transient simulation program. The CIGRE benchmark model is selected as the base system. The results show that the controllable Q filter helps the system recover from faults. |
| Abstract: High voltage direct current should be considered as a complement or extension to the ac power system. To be just as comfortable with hvdc technologies as with ac is an essential qualification for today's transmission engineer, particularly since ac transmission can also utilize the complexity of power electronics. |
