Converter Terminals Research Articles

On Line Stabilization of the large HV-AC-DC Power System BY Using Observation Decoupled Reference as a System-Wide Target

The concept of the Observation Decoupled Reference vector was introduced earlier [1] by the Washington University research group. It was demonstrated [2] [3] that effective system stabilization can be accomplished based on this new concept using purely local information and local action at the generating stations provided control means such as damping resistors or load skipping are available at each generating station. In this paper the Observation Decoupled Reference vector is considered as a systemwide target to be tracked and approached using a limited number of contr-l devices such as the converter terminals of an overlying HV-DC system. The tradeoff is that fast reliable communication between the generating stations and the Control Center are needed. Computations of moderate size are carried out both at the local units and at the Control Center. Very effective system stabilization is demonstrated by large scale simulation. It is believed that this represents the first real solution for using the (multiterminal) HV-DC system to stabilize an associated AC system.

Effects of Geomagnetically-Induced Currents on HVDC Converter Operation

Electrons and protons emitted by a solar flare can be captured by the Earth's magnetic field. The resulting transient in the geomagnetic field can produce quasi-dc currents in electric power systems. These geomagnetically-induced currents (GIC) in excess of 100 amps have been measured in the transformer neutral leads. With the practice of using EHV and UHV lines for transmitting ac power over long distances and because the systems are more solidly grounded, the problems posed by GIC have become more severe. This paper presents the consequences of transformer half- cycle saturation on the operation of HVDC converter terminals. A detailed computer simulation of the Square Butte HVDC system reveals that the large values of GIC can cause enough distortion in the ac system voltage at the inverter end to prevent normal system operation. Moreover, the amount of harmonics generated could overload the ac as well as the dc-side filters.

AC Power Flow Control with a Multiterminal DC System

The scheduling of the power transfers of a multiterminaL dc network to control the power distribution in certain ac lines of an ac-dc system requires coordination. With the new method presented in this paper, the coordination of the dc network's power transfers is simplified considerably to that of solving a linear matrix equation of order one Less than the number of converter terminals. The Losses, as well as the power limits of the converters, in the dc network are considered in the method of coordination. This method of coordination is combined with a standard ac-dc load-fLow, whose purpose is to estabLish the resuLtant operating point of the ac-dc system, to form an algorithm for scheduling the dc network's power transfers to control the power distribution in certain ac lines of an ac-dc system. The tests performed on a 5 dc terminaL, 30 ac bus, sample system showed that the power flows, close to the desired values, in a number of the ac Lines could be simultaneously obtained with just one iteration of the proposed algorithm. The algorithm proved to be efficient and effective in these tests. The algorithm can be used to plan dc network reinforcements to an ac network and is potentially suitable for the on-line application of networK flow control.

Insulation Coordination Designs of HVDC Converter Installations

There have been as many insulation coordination schemes as there exits HVDC transmission systems throughout the world due to the complexity and variety of terminal arrangements. This paper presents the first consolidated treatise with heretofore needed completeness and a significant amount of previously unpublished data obtained from surveys. It furnishes a comprehensive digest of tried schemes from which new HVDC converter terminals can be designed. Included are equipment insulation levels, arrester protective characteristics, and even protective margins where possible on each of the varied schemes.

Damping of Power Swings in AC Tie Lines Using a Parallel DC Link Operating at Constant Reactive Power Control

This paper presents a method for the damping of power swings in the ac lines interconnecting two power systems, utilising the fast electronic power flow control characteristics of a parallel dc link. The basic principle of the method is that the dc link is operated in order to maintain constant active power flow in the ac tie lines and constant reactive power consumption at the converter terminals. The proposed control strategy was tested using dynamic simulation techniques and the results obtained show that, under certain conditions, the contribution of a parallel dc link to the stability the ac system can be significant.

Hybrid Computer Simulation of Multiterminal DC Power Transmission Systems

Techniques are developed for the hybrid computer simulation of multiterminal dc power transmission systems with two- or three-conductor transmission lines. The switching of the static converters as well as the attenuation and transport delay of a distortionless transmission line are represented in detail. An example study is performed using a hybrid simulation of a singlepole three-terminal system, wherein the converter terminals are represented on the analog portion and the transmission line is represented on the digital portion of the hybrid computer. Results include waveforms for the transient behavior of the system during line faults on each of the three transmission branches.

Solid-state HV dc transmission technology

Studies have been made during the past few years to determine the feasibility of employing thyristors in high-voltage dc converter terminals. Overall objectives have also included the integration of solid-state circuitry in order to take advantage of the fast response times associated with thyristors. Because of their advantages over mercury valves, from the point of view of economy as well as performance, a bright future is seen for these solid-state devices in the dc power field.