High Voltage Stations Research Articles

Quantifying the effect of rock armour scour protection on eigenfrequencies of a monopile supported OHVS

It is common practice to install scour protection systems during the construction of offshore wind farms. This is because the guidelines allow for a more optimal structural design, as the potential effects of scouring may be ignored. However, multiple sources, as well as measurements, suggest that there is an additional gain in stiffness which is not being taken into account by current guidelines. Scour protection has the ability to provide extra foundational stiffness to the monopile, which results in higher natural eigenfrequencies and mode shapes. In this paper the focus will be on an offshore high voltage station (OHVS) located in the North Sea and the impact of a rubble riprap scour protection on the foundational stiffness of the structure. Furthermore, a proposal is made on how to take these effects into account when calculating for design. This site was equipped with a mobile measurement system containing a multi-axial accelerometer, which was active in a period both before and after installation of the scour protection rock armour layer. In case of similar environmental circumstances, the eigenfrequencies of the OHVS were noticeably higher after the scour protection was installed, thus substantiating the claim of increased foundational stiffness. To perform numerical studies on the impact of the scour protection system on structural dynamics, an OHVS support structure finite element model was built. As no formally agreed upon formulation to include scour protection exists, two possible methods are proposed. One is adding a global accretion layer to model the scour protection as an additional soil layer. The other calculates an overburden pressure due to the scour protection weight, which translates to the stiffening of the upper soil layers of the foundation. Both methods have their own strengths and weaknesses, but more research on different locations and offshore structures is needed to formalize the definitive description for modelling scour protection.

In English

In the work, carbon nanostructures (CNS) were synthesized on a plasma chemical plant using graphite electrodes SIGE (Special Impregnated Graphite Electrodes) and FGDG-7 (Fine-grained dense graphite) in a helium environment. In the experiments, it was established that graphite electrodes of the SIGE brand are suitable for the synthesis of CNS by the electric arc plasma chemical method. In addition, the experiments indicate that SIGE graphite in electric arc synthesis in a gas environment allows the creation of centimeter composite rods (deposits), where the core consists of graphene sheets rolled into nanotubes that can withstand extremely high temperatures (>4000 K). Studies using scanning microscopy have shown that the synthetic deposit of SIGE graphite can be divided into blocks, which is important for its use in high voltage stations because it is possible to prepare deposits of the required length without mechanical impact and without violating the integrity of its structure. The structure of the synthesized carbon materials was studied by scanning and transmission electron microscopy and it was shown that carbon nanotubes are formed during the evaporation of SIGE brand graphite even without the use of a catalyst. Experiments have confirmed that the mass yield of wall fullerene-containing carbon black during the evaporation of SIGE grade graphite significantly exceeds the results obtained during the evaporation of FGDG-7 grade graphite electrodes. Such results make SIGE graphite more productive for the synthesis of expensive carbon nanoproducts (fullerenes and fullerene-like structures) by the electric arc method. It was also recorded that during the synthesis of carbon nanostructures, single-walled carbon nanotubes are formed, which have a positive charge and are deposited in the form of a core on the surface of the cathode electrode under the action of an electromagnetic field.

High-Voltage Stations for Electric Vehicle Fast-Charging: Trends, Standards, Charging Modes and Comparison of Unity Power-Factor Rectifiers

Emission of greenhouse gases and scarcity of fossil fuels have put the focus of the scientific community, industry and society on the electric vehicle (EV). In order to reduce CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emissions, cutting-edge policies and regulations are being imposed worldwide, where the use of EVs is being encouraged. In the best of scenarios reaching 245 million EVs by 2030 is expected. Extensive use of EV-s requires the installation of a wide grid of charging stations and it is very important to stablish the best charging power topology in terms of efficiency and impact in the grid. This paper presents a review of the most relevant issues in EV charging station power topologies. This review includes the impact of the battery technology, currently existing standards and proposals for power converters in the charging stations. In this review process, some disadvantages of current chargers have been identified, such as poor efficiency and power factor. To solve these limitations, five unidirectional three-phase rectifier topologies have been proposed for fast EV charging stations that enhance the current situation of chargers. Simulation results show that all the proposed topologies improve the power factor issue without penalizing efficiency. The topologies with the best overall performance are the Vienna 6-switch and the Vienna T-type rectifier. These two converters achieve high efficiency and power factor, and they allow a better distribution of losses among semiconductors, which significantly increase the life-cycle of the semiconductor devices and the reliability of the converter.

Control of synchronous machines set with microprocessorcontrolled excitation units in high-voltage tests station

Control of synchronous machines set with microprocessorcontrolled excitation units in high-voltage tests station

Complex network analysis of the Brazilian power grid

In the last decades, power grids and other energy transmission networks have received attention from the network literature. In this work, we studied one of the most important static features of power grids, their topology, with focus on the Brazilian Power Grid (BPG). We obtained the spatial structure of the BPG from the ONS (Electric System National Operator), consisting of its high-voltage transmission lines, electric stations and substations. Some traits had to be ignored, such as the local low-voltage substations and as well the dynamic features of the network. We analyzed the complex network of the BPG and its statistics, such as the mean degree, the degree distribution, the network size and the clustering coefficient to characterize the complex network. We also detected critical locations in the network and, therefore, points that are more susceptible to cascading failures and even to blackouts. Our results show that the BPG is functional against random failures, regarding random removal of links and connections, in terms of the size of the largest cluster. We observe that when a fraction ρ of the links are randomly removed, the network may break down into smaller, disconnected parts. However, the largest component of the power grid remains connected. We believe that even a static study of the network topology can help to identify the critical situations and also prevent failures and possible blackouts.

A neural network-based estimation of the level of contamination on high-voltage porcelain and glass insulators

In harsh environments, such as those found in Saudi Arabia, the periodic washing of insulators which is a necessity to ensure continuity in a power supply is very expensive. The accurate estimation of the severity of contamination can help electric utilities to properly schedule such washing and thus reduce the expense of washing and prevent insulator flashover. This paper presents a neural network algorithm for detecting the contamination level of high-voltage porcelain and glass insulators. The algorithm is based on images captured using a digital camera. Two types of features are extracted from each image: histogram-based statistical features and linear algebraic features based on singular value decomposition. Using the extracted statistical features, linear algebraic features, or a combination of both, three neural networks scenarios were successfully designed to associate the insulator images with the appropriate contamination levels and thus the possibility of flashover. Tests of the proposed estimation algorithm demonstrated a high success rate in estimating the contamination level of insulators. Finally, the developed algorithm has been deployed at the high-voltage station at King Fahd University (KFUPM). This deployment will eliminate the need for human intervention in determining the timing and location of required insulator cleaning.

Substation Grounding Studies With More Accurate Fault Analysis and Simulation Strategies

This paper describes hands-on modeling and simulation experience for designing substation ground grids. The grounding studies enable an optimized ground grid design to protect utility personnel and the public. These optimized ground grids meet the IEEE-80 standard [1] for safety and have been simulated and designed using more accurate transient and steady-state fault current calculations. The SI and MI methods are used to simulate the actual fault locations and fault currents at a small station and a large extremely high-voltage station, respectively. The simulations primarily focus on substation specific data for the application rather than utilizing predetermined split-factor curves and the decrement-factor table in IEEE-80. In addition, the new clearing time analysis and grounding study safety assessment strategy will be implemented instead of using the widely applied longest clearing time and its corresponding threshold calculation, which could further optimize the ground grid. With AEP's research and applications, the authors hope it can benefit similar industrial substation design projects.

Investigations on the Seismic Responses of Structures with a Suspended Mass

This paper presents the shaking table tests and an analytical study of structures with a suspended mass under coupled horizontal and tilting ground motions (CHT) caused by an earthquake. Shaking table tests of a 1:10 scaled model for a converter valve hall with a suspended mass in a high-voltage direct current electric power transmission station are carried out. The equations of motion for the structure, including the influence of the rotary inertia of the suspended mass, are derived. The responses of the model to different ground motions during an earthquake are investigated. It is found that the tilting ground motion plays a significant role in predicting the seismic response of the structure, and it needs to be considered in association with the horizontal ground motion. The response of the structure with a suspended mass to CHT ground motion is much larger than that to horizontal ground motion. The possibility of replacing the steel cables with springs as the suspending components is also investigated, and the spring is shown not to influence the acceleration and displacement responses greatly, but it significantly reduces the tension in the suspending components. Therefore, when a suspended mass is used as a mass-pendulum mitigation system, it is more advantageous to use springs or members having a low axial rigidity as the suspending components. In addition, the effects of the length of the cables and springs on the seismic response of the model with a suspended mass are also explored. It is found that the shorter the cables (or springs), the better the mitigation effects of the suspended mass on the main structure.

Using IEC 61850 Protocol in Automation Systems of High Voltage

Growing Development of new metric technology, communications on one side, and variety in IT and incremental information on the other side in designing and manufacturing automation station systems make the pioneers of this industry change the system with the aim of creating "a world, a technology, a standard" in this industry. This evolution led to create a new technique for designing automation systems which is called IEC 61850 standard. Considering the agreement on developing and using this standard, applying this in station automation systems was taken into account since 2005. The new technology needs new interfaces to connect the high voltage switchgears such as modern current and voltage measurement transformers to station automation control systems. By introducing the new technology and using IEC 61850 protocols, designing automation systems with decentralized structure is possible and has a lot of advantages, however great care is needed in designing such system so that system reliability will not be impaired. In this thesis, for better understanding, we first explain briefly the old station structures and their transition and then the IEC 61850 standard structure will be investigated and this investigation includes the way of data transfer. Finally we refer to the effect of this standard on the structure of high voltage station automation system. In power distribution systems, IP and IEC-61850 are introduced as a security ring with more importance of communication, that in the meantime, IEC-61850 as the new international standard electrical station, is capable of providing the Integration, protection, control, measurement and monitoring functions within the stations with high-speed. So not only can prove the importance and the need to replace the IEC-61850 standard as the protocol with high speed data transfer capability ,but also we will also see reducing the time and power transmission losses in the automation network

A Computer Program for Fault Diagnosis and Assessment of Quality Insulation Oil in Power Transformer Based Dissolved Gas Analysis

Accurate faults diagnostics and oil insulation evaluation of electrical power transformers for life-long endurance are the key issue. The durability of transformer function is significantly decided by the quality of insulation oil, which deteriorates over time due to temperature fluctuations and moisture contents. Precise determination of faults in early stages and the efficient assessment of oil excellence in protecting transformers from potential failures occur during operation that can avoid sizeable economic losses. A computer program using traditional software play important role in this regard. The dissolved gas analysis in oil is a reliable method in the diagnosis of faults and assessing the insulation oil quality in transformers. The safeguarding teams in high voltage stations often suffer from the occurrence of sudden faults that results severe damage and heavy monetary loss. The oil must be appropriately treated to circumvent such failure. A computer program is performed to diagnose the faults and to assess the status of insulation oil quality in power transformers. A suitable treatment is achieved via Roger’s ratio method, IEC ratio method and doernenburg ratio method depending on the dissolved gas analysis in the oil. The use of the C ++ program and windows easy process to use, and is highly enough for fault diagnosis and oil quality evaluation. The programing is capable of assessing the oil quality as per IEEE standard and C57-104 -1991 and IEC standard 599 specifications.

Finite element analysis of heat transfer in transformers from high voltage stations

This present paper presents the modeling and simulation of the thermal transfer in the transformers from the high electric voltage stations using finite element method. As the transformers are of high power and are inversed in oil, a particular interest represents the maintenance of physical and chemical parameters of oil as long a time during operation. For this, one presents the coupled analysis electromagnetic field and thermal field. The procedure of coupled analysis consists of a quantity of heat release when passing electric current through the coil of transformers. The amount of heat affects the chemical properties of the oil. Because overloads occurring in their operation, the chemical properties of the oils worsen in time and may lead to premature aging and scrapping of them. The simulation is based on the creating of a geometrical model which follows the transformer’s sizes and material properties, real constants are established by standards. After the simulations an optimal solution is obtained regarding the correct usage of the transformers.

Influence of volcanic ash contamination on the flashover voltage of HVAC outdoor suspension insulators

High voltage station and line insulators are vulnerable to volcanic ash-induced flashover, yet little quantitative data exists on the environmental, volcanological and electrical parameters most influential in reducing their flashover voltage. This paper presents the results from clean-fog rapid flashover tests for 5 different suspension insulators of ceramic, non-ceramic, or RTV-coated design under different environmental and volcanic ash contamination scenarios. Results suggest that moderate accumulations (up to 3 mm) of volcanic ash can accumulate on insulator surfaces without critically reducing the flashover voltage, provided >40% of the creepage distance remains clean and dry. Composite polymer insulators have higher dielectric strength than ceramic equivalents under light to heavy pollution severities, however, all insulators tested here perform comparably when critically contaminated (i.e. both top and bottom surfaces coated in ash). Based on these and other findings, some basic discussion of optimal insulator selection in ashy environments is provided.

Study of the soil corrosion of Q235 steel ground grid in Weinan Shaanxi

For the online detection of the corrosion of ground grids, the relationship between the corrosion rate of Q235 steel and electric resistance was studied by the method of accelerated corrosion in the soil taken from the site of construction of a 750 kV high-voltage transformer station. The corrosion products and morphology are characterized by the SEM (scanning electron microscopy) and XRD (X-ray diffraction) methods. The results show that the rusty layer obtained by the accelerated corrosion has the same structure as the layer obtained by the natural corrosion and the corrosion products mainly consist of γ - Fe2O3 and FeO4. The one-year monitoring was realized and the relationship between the corrosion rate (V ) and resistivity ( R) was established. The deviation of the natural corrosion rate from the computed corrosion rate does not exceed 3%.

High-voltage Station Peripheral Equipment

High-voltage Station Peripheral Equipment

Structural Design Of A Cellular ElectricalSubstation For Electrical Arc Blast Loading

A case study of the structural design for a new generation of indoor electrical substation in South Africa is presented. New state-of-the-art switch gear has recently been developed in South Africa, which substantially reduces the cost but increases risk of explosive blast emanating from possible electrical faults in such indoor high voltage stations. The paper describes the concept of a suitable enclosing building structure and explains the analysis which is based on acoustic energy theory and accepted practice of blast resistant design. Structures under Shock & Impact VI, C.A. Brebbia & N. Jones (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-820-1

An overview of the slow-positron beam facility at the photon factory, KEK

The KEK slow-positron source is in the final stage of construction. The beam line comprises a 31 m long vacuum duct within an axial magnetic field and a following electrostatic guided section. In order to vary the energy of a positron beam dedicated to depth-profile measurements, a high voltage station capable of applying 60 kV has been installed in the beam transport system. The target assembly (a water-cooled tantalum rod of 5 radiation lengths and a moderator with multiple tungsten vanes) and the following straight section (8 m; used for positron storage) are under high voltage. The beam duct located downstream is at ground potential. Positron beams passing through this region have a high kinetic energy. A focusing triplet quadrupole lens and a moderator on the retarding electrode are located at the end of the magnetic transport. This beam line has 9 right-angle-curved ducts, comprising a radius of curvature of 40 cm. Positrons with a maximum energy of 60 keV are guided by bending magnets attached to the beam-transport ducts. A transport system to switch from magnetically guided to electrostatically guided has been installed. The design of the brightness-enhancement stage of the positron beam for positron re-emission microscopy is in progress. In a preliminary experiments at 2.0 GeV with a 2 kW primary beam, 4×10 6e +/s of slow positrons were observed by detecting annihilation γ-rays at the end of the magnetic beam-transport line. Further improvements are expected by careful surface and thermal treatments of the moderator.

The Crossed-Ring Arrangement A New Concept for H.V. Switchgear Installations

A new concept for high-voltage switching stations is proposed, which offers advantages compared to the commonly used breaker-and-a-half scheme as regards availability and costs.

Temporary overvoltages due to load rejection on a series-compensated transmission line

A digital computer method is presented for the accurated evaluation of temporary overvoltage transients on a series-compensated transmission line. The synchronous generator is represented by a five-coil dynamic model, and the effect of the excitation control system associated with the generator is included in the analysis. The transmission network is represented by differential equations involving the network state variables. This kind of study is essential in choosing economical voltage ratings for surge arresters protecting high-voltage station equipment, in view of the modern practice of allowing surge diverters to reseal after temporary overvoltages exceeding their voltage ratings for a limited duration of time. These studies, when conducted for the case of series-compensated transmission lines, can reveal the limit of compensation level beyond which the danger of self-excited oscillation can occur in a particular system.

Measurements and Analysis of Electric Fields in HV and EHV Stations

Numerous electric field measurements were made in high and extra-high voltage stations. The location and magnitude of the maximum field strength were recorded in each station. Actual measured data are analyzed and presented together with a comparison of results from other countries. The measurements were found comparable to many published data. However, this work presents an overall description of the maximum field strength as a function of the station voltage level, design and arrangement of bus and station equipment. Cumulative distribution of ground level electric fields in various HV and EHV stations is presented. The information enables one to make observations on station design and operation requirements.

Major Electrical Equipment Proposed for Tidal Power Plants in the Bay of Fundy

The paper discusses general considerations and future possibilities for the design of generating equipment for tidal power plants with particular reference to Bay of Fundy sites. Factors affecting the design of turbines, generators, excitation system, powerhouse layout and the main electrical connections are reviewed. Various alternatives for transmission of power to shore are listed and the choice of SF6 gas insulated bus duct is substantiated by comparative data. Advantages of integrating the high-voltage switching station with the powerhouse, using SF6 gas insulated metal-clad switchgear are discussed. Application of computers and microprocessors is envisaged. The paper concludes that advances in technology can make a significant contribution to economic development of tidal power.