Extra High Voltage Systems Research Articles

Passive Power Filter Optimization Problem Based on Adaptive Multipopulation NSGA-II and CRITIC-TOPSIS

The best configuration of passive filters in extra-high voltage systems is investigated in this study using a two-stage multiobjective decision-making (MODM) framework. A collection of Pareto solutions is found using an adaptive multipopulation-modified nondominated ranking genetic algorithm (AMP NSGA-II) in the first stage. The goals taken into account include the least fundamental reactive power compensation losses, overall cost and maintenance cost, and simultaneous minimum harmonic current distortion rate. The objective weights are determined and the optimum solution is chosen in the second stage using the criteria importance interrelationship (CRITIC) and similarity ranking preference technique (TOPSIS). A number of examples show how the suggested method performs more effectively than the conventional and well-known algorithm and can identify the relationship between the objective functions, indicating that the suggested scheme has better superiority in filters and has a promising future in the solution of multiobjective problems.

Fifth Harmonic Spectral Voltage Components in EHV Power Transmission Systems

Fifth harmonic voltages and currents have been measured in some extra high voltage (EHV) power transmission systems. This paper contains a discussion and explanation of this phenomenon. The emphasis is on the impact of overexcitation of power transformers in EHV systems. Examples of measurements taken in 500 kV substations are illustrated and representative data collected are shown.

A Study on the Harmonic Resonance during Energizing Primary Restorative Transmission Systems: Korean Power System Case

In this paper, a power system restoration study following a massive or complete blackout was performed. The power system restoration process from a complete shutdown system without the operating generation and load starts with energizing primary restorative transmission systems. During this primary restoration process, unexpected over-voltage may occur due to nonlinear interaction between the unloaded transformer and the transmission system. This is known as the harmonic resonance phenomenon that may cause the burning out of a transformer or other devices. So far, harmonic resonances have been reported in some extra-high voltage systems around the world. Since the harmonic resonance originates from the nonlinear characteristics of the power system components, it is very difficult to predict the occurrence of this phenomenon. This paper reports the analyses of the harmonic resonance that can occur in the Korean power system. In addition, through calculating the required buffer load compared to the length of the line, a solution that changes the length of the restoration path impedance considering the specificity of the Korean system was presented. The various analyses of harmonic overvoltage, including methodologies that are used internationally as comparison groups, are provided based on PSCAD/EMTDC simulations.

Análisis de sensibilidad para la determinación de curvas características de tiempos muertos vs potencia de transferencia aplicados a líneas de transmisión

Para la transmisión de grandes bloques de energía eléctrica a grandes longitudes, sistemas de Extra Alto Voltaje constituyen una buena alternativa, donde los elementos que conforman el sistema de transmisión deben ser diseñados de tal manera que ofrezcan una alta confiabilidad y disponibilidad durante su operación. En este sentido, es necesario realizar un adecuado autorecierre monofásico, determinando la capacidad de transmisión de potencia eléctrica y el tiempo muerto de recierre ante eventos de falla monofásica línea – tierra considerando un esquema de apertura y recierre monofásico y la estabilidad transitoria del sistema. Este trabajo propone una metodología para determinar curvas características correspondientes a tiempo muerto vs potencia activa de transferencia que garanticen una máxima trasferencia de potencia activa a través de las líneas de transmisión, y estabilidad transitoria ante eventos de falla, apertura y recierre monofásico. Estas curvas características permitirán decidir, desde el punto de vista de estabilidad transitoria, el valor más adecuado de ajuste del tiempo muerto de recierre monofásico y la potencia de despacho de la central de generación

Secondary Arc Extinction in Extra High Voltage Systems Using Grounding Switches

Long Extra High Voltage (EHV) transmission systems tend to bring a pronounced state of secondary arcing. Therefore, an essential pre-requisite for single-phase-switching application, is the possibility and speed of secondary arc final extinction during suitably short dead-time. During the past several decades, many techniques had been proposed and implemented in order to ensure fast secondary arc extinction. Among these was the use of High Speed Grounding Switches (HSGS’s). In such technique, the faulted phase is grounded via special switches; one at each end of the EHV line after the fault is cleared by both line ends circuit breakers. The primary advantage of grounding the faulted phase is the reduction of the fault point recovery voltage to a very low value. This, coupled with the circulation of opposite loop currents in the fault path, reduces the secondary arc current and lead to a fast secondary arc extinction. A sample 500kV, 300km transmission system equipped with High Speed Grounding Switches is modeled as a test system. The modified Fourier transform is used to calculate the system response through, fault, fault clearance, HSGS’s operation, and line restoration. The non-linearity of the secondary arcing state is also accounted for. The paper concludes with a presentation of some computational results related to the above mentioned EHV system showing that HSGS’s greatly improves the single-phase-switching performance.

Development and hardware implementation of a reliable protective relay data acquisition system

This paper proposes an intelligence based protective relay data acquisition system to correct current transformers and capacitive voltage transformers secondary waveform distortions. The protective relay data acquisition system receives voltage and current signals from current transformers and capacitive voltage transformers and prepares the inputs to the main board after some pre-processing. Current transformers and capacitive voltage transformers provide instrument level current and voltage signals to meters and protective relays in high voltage and extra high voltage systems. The accuracy and performance of protective relays in high voltage and extra high voltage systems are directly related to steady state and transient performance of current transformers and capacitive voltage transformers. Current transformers saturation and capacitive voltage transformers transient could lead to protective relay mal-operation or even prevent tripping. The key of the proposed scheme is to use artificial neural network to achieve the inverse transfer functions of current transformers and capacitive voltage transformers. Simulation studies are preformed and the impacts of changing different parameters are studied. Performance study results show that the proposed scheme is accurate and reliable. The proposed algorithm has also been implemented and tested on a digital signal processor board. Details of the implementation and experimental studies are provided in the paper.

Depressing Turbine-Generator Supersynchronous Torsional Torques by Using Virtual Inertia

Single-pole switching scheme is widely used in the Extra High Voltage system. However, the substantial negativesequence current injected to the turbine-generators imposes the electromagnetic (E/M) torque of double systemfrequency components during the dead time (between single-pole clearing and line reclosing). This would induce supersynchronous resonance (SPSR) torque amplifications on low pressure turbine generator blades and even lead to fatigue damage. This paper proposes the design of a mechanical filter (MF) with natural frequency close to double-system frequency. From the simulation results, it is found that such a filter not only successfully damps the resonant effect, but also has the characteristics of feasibility and compact. Keywords—Single-pole, Supersynchronous, Blade, Unbalance, filter.

Practical Application of a New Feeding Transformer for AC Electric Railway Substations

Most Shinkansen substations in Japan receive their electric power supply for traction from extra-high voltage systems. Modified-Woodbridge transformers have been used for this since 1972; however, these have a rather complicated structure. As such, studies were carried out to develop a new type of transformer, which had the same functions, but was simpler. The transformer has been coined the transformer since it has both roof and delta windings. Test results from a prototype of this transformer revealed that it could be used in AC traction feeding systems. This paper describes the fundamental characteristics of the roof-delta connection transformer and results from tests.

Dynamic investigation of network restoration by the pumped-storage plant Markersbach in Germany

Abstract To restore a transmission network after blackout without predetermined voltage by neighbouring transmission systems, the restoration has to proceed from power-station units within the own network area. In small separate networks connecting electrical equipment and consumers can result in unstable operating conditions. Possibly tripped protective measures can cause the breakdown of the restored transmission system in the end. To investigate network restoration, a realistic dynamic model of the extra-high voltage system is needed on a simulation platform. In this way different scenarios of restoration can be analysed from technical points of view. Creating a complete dynamic network model, the dynamic models of the most significant supplying power plants are necessary. The paper presents the results of modelling the black-start capable pumped-storage plant (PSP) Markersbach that is located in eastern part of Germany. Basing on measurements in the PSP Markersbach a dynamic power-station model was developed and its parameters were identified. With the model of the power plant several restoration scenarios proceeding from PSP Markersbach can be investigated regarding their feasibility. This project is a part of cooperation between Vattenfall Europe Transmission GmbH (VE-T) and University of Rostock. The determined possibilities of a successful network restoration are going to be involved in a conception concerning the restoration of VE-T transmission system. This conception will also be used as instruction manual for employee training.

Analysis of Dynamic Instability in Series Compensated Power Systems

Series compensation has been considered as a powerful alternative based on economic and technical considerations for increasing effectively the power transfer capability and improving the stability of extra high voltage systems. The application of series capacitors to compensate long distance EHV transmission lines, however, introduces three possible potential modes of dynamic instability, namely, the steady state instability, electrical self excitation and mode interaction. This paper provides the necessary an alytical basis for investigating these three modes of instability. The effect of inclusion of network transients and turbine-generator shaft torsional dynamics on stability region in the P - Q plane is discussed. The influence of shaft torsional modes on the dynamic performance of the generator for different degrees of series compensation is studied in greater detail. The introduction of fast acting static excitation systems with purely proportional control for a possible improvement in the stability region is explored. Finally, the voltage profile across series capacitor as function of generator power is included. These aspects, in the opinion of the author, will give an insight into the design and operational requirements of series compensated power systems.

Digital Simulation of Power Distribances and Protective Relaying

This paper describes simulation of power system disturbances and protective relaying performance by means of a digital computer. Line-to-line faults, faults involving ground and open conductors in a power system including both of single-and parallel double-circuit lines are dealt with, that is, voltage distribution under independent or simultaneous occurrence of such faults are calculated. The protective relaying can optionally be simulated by adding or modifying its own subprograms, and the following relayings are herewith detailed as examples: a) Combined phase and directional comparison carrier relaying for extra high voltage system. b) Out-of-step system-split relaying with distance relay of rectangular characteristics. c) Single-and three-phase reclosing systems.

The Use of Series Capacitors to Obtain Maximum EHV Transmission Capability

Series compensation can substantially increase the transmission capability of EHV (extra-high-voltage) systems, permitting a higher loading per right of way. Several of the possible circuit arrangements that can be used for insertion of series capacitors into a transmission system are cited in this paper. Certain technical problems of using series capacitors are analyzed. The effects of fault switching time on stability limit for series-compensated circuits and of delaying reinsertion of series capacitors after fault clearing are indicated for particular configurations. The relative economics of various degrees of series compensation and number of intermediate switching stations for 500 kv and distances up to 400 miles are also shown.

Progress in Extra-High-Voltage Power Transmission

In Part I of this paper a review is presented of the present status of extrahigh-voltage (EHV) power transmission (275 kv and higher) in this country and abroad. A forecast is made of the future requirements and developments of EHV transmission in the United States for the next 20 years, to 1977. It is concluded that: 1. there will be continued and rapid expansion of EHV systems at the highest voltage presently used, 345 kv; 2. that a higher voltage of the order of 460 kv will be introduced probably about 1962 in this country, and 3. a still higher voltage of the order of 650 kv may possibly be introduced about 1975. In Part II the problems are reviewed which must be solved by the utilities and manufacturers in this country in order to transmit power at these higher voltages reliably and economically. Areas of technical work are identified and the problems of EHIV technology are classified accordingly. The means which are available for the solution of these problems are then reviewed: analytical work, laboratory investigations, experimental lines, prototype EHV systems, and, of course, tests on the actual systems. It is concluded that all these means are necessary to obtain a proved solution. There is no doubt that the American electrical industry will continue to meet successfully the challenges presented by the ever-increasing requirements for electric power at a reasonable cost.

Countermeasure for Salt Contamination of Insulators in Chiba Thermal Power Extra High Voltage System

Countermeasure for Salt Contamination of Insulators in Chiba Thermal Power Extra High Voltage System