Rigid Bus Research Articles

Seismic performance of UHV composite post electrical equipment interconnected using a rigid bus with a sliding fitting

To evaluate the influence of a rigid bus on the interconnected post electrical equipment with a sliding fitting, this article conducted shaking table tests on two full-scaled ±800 kV ultra-high voltage post insulators. Simplifying the rigid bus with a sliding fitting serving as a linear spring and damper allowed us to create a dynamic model of the stand-alone insulators and establish advanced two-piece interconnected post electrical equipment. Later, parametric analyses were carried out on the dynamic model. The results showed that the frequencies of the interconnected system were similar to those of the stand-alone counterparts if the dynamic characteristics of the two interconnected items were similar. The seismic responses of the interconnected system generally decrease compared with those of the stand-alone insulators. Thus, the seismic performance of the rigid bus interconnected electrical equipment system could qualify as having a stand-alone status if the dynamic characteristics of the equipment items are similar. The connection stiffness greatly affects the seismic responses of UHV composite post electrical equipment.

Robust Collocated Control of Large Flexible Space Structures

Agile maneuvering and precise pointing control require special attention for spacecraft equipped with large flexible appendages. A joint academia-industry research involving Sapienza University of Rome, Thales Alenia Space in France and the European Space Agency (ESA), investigates the use of innovative solutions to counteract the deterioration in pointing accuracy stemming from interactions between a rigid bus and the flexible structures during operations. Specifically, this paper aims at presenting the design of an attitude/vibration control architecture in a μ-synthesis framework. The architecture consists of an attitude control system combined with a distributed network of actuators/sensors at structural level for active vibration control purposes. A spacecraft equipped with an interferometric Ka-band SAR payload and two solar arrays is considered as a useful and challenging benchmark problem to assess the proposed methodology. The numerical simulations, carried out via both a linearized setting and a nonlinear simulator, have proved the effectiveness of the robust collocated control in comparison with a baseline PID controller.

Theoretical and Experimental Researches of Spring Damping Flexural Oscillations for Beam Structures

One of the main problems in the design of rigid bus in open switchgears is the problem of structural stabilization under the action of various dynamic loads. The implementation of rigid bus with large spans of tube showed a real risk of wind resonance for cylindrical tube structures (aeroelastic self-oscillations). This phenomenon is dangerous due to the fact that at low speeds of the wind flow, intensive oscillations of the tubes occur in the vertical plane, adding to the static loads an essential dynamic component. Its level is comparable with loads from its own weight of structures and can, in combination with other loads, will be the cause of stresses close to the limiting ones by the 1st group of limiting states. The problem of reducing the level of structural oscillations in many cases is associated with the need to increase rigidity and reduce the material consumption of structures, however, it is important to fulfil the technological requirements of the operating conditions and protect people from the harmful effects of oscillations. The article highlights some of the main ways to damp oscillations of rigid bus structures. Is given a mathematical model of the simplest single-mass spring inertial dynamic oscillation damper. Experimental studies have been carried out on the joint work of the rigid bus structure with the spring damper. Has been confirmed the effectiveness of spring dampers using, both outside and inside the tube-bus.

Effects of rigid bus conductors on seismic fragility of electrical substation equipment

The present paper studies the impact of dynamic interaction between high-voltage substation equipment on the response and vulnerability of substation equipment. The 3D numerical model is developed for four types of vulnerable equipment in the both unconnected and connected conditions. The bus slider-rigid bus assembly is utilized to establish the connection between the equipment. The incremental dynamic analysis is carried out in the developed systems to produce the fragility function for each equipment. Also, the Monte Carlo approach is employed to evaluate the accuracy of the generated functions. It is concluded that the incorporation of connection parts in the model can significantly alter the fragility of equipment and the relative performance of vulnerable equipment. Moreover, it is found that when more than two equipment are connected, the effect of indirectly connected equipment can be neglected if the contribution of higher modes to its response is small. The fragility functions for which the interaction effects are accounted can be used to reliably assess the seismic risk of substations.

Damper as a Rigid Insert for Rigid Bus Structures Oscillation Damping

One of the main problems in a design of rigid bus structures in open switchgears devices is a structural stabilization under the influence of various dynamic loads. The implementation of rigid bus structures with large spans of pipe-bus showed a real danger of the wind resonance for cylindrical pipe-bus structures (aeroelastic oscillations). This phenomenon is dangerous in that at low wind speeds there are intense pipe's oscillations in vertical plane, adding to the static loads an essential dynamic component. Its level is comparable with the loads from the weight of the structures and can, in combination with the rest loads, cause stresses close to the maximum admissible for the 1stgroup of limit states. The problem of reducing the level of structural oscillations in many cases is associated with the need to increase the rigidity and reduce the material consumption, but it's important to meet the technological requirements imposed by operating conditions and protect people from harmful vibration. In a paper are considering a new method for damping oscillations for rigid bus structures under the action of a wind vortex excitation – damper as a rigid insert. Is presented a mathematical model of the joint work of the rigid bus structure with the damper as the rigid insert. Have carried out analytical researches of the joint work of the rigid bus structure with the damper as the rigid insert.

Operational modal analysis via image based technique of very flexible space structures

Vibrations represent one of the most important topics of the engineering design relevant to flexible structures. The importance of this problem increases when a very flexible system is considered, and this is often the case of space structures. In order to identify the modal characteristics, in terms of natural frequencies and relevant modal parameters, ground tests are performed. However, these parameters could vary due to the operative conditions of the system. In order to continuously monitor the modal characteristics during the satellite lifetime, an operational modal analysis is mandatory. This kind of analysis is usually performed by using classical accelerometers or strain gauges and by properly analyzing the acquired output. In this paper a different approach for the vibrations data acquisition will be performed via image-based technique. In order to simulate a flexible satellite, a free flying platform is used; the problem is furthermore complicated by the fact that the overall system, constituted by a highly rigid bus and very flexible panels, must necessarily be modeled as a multibody system. In the experimental campaign, the camera, placed on the bus, will be used to identify the eigenfrequencies of the vibrating structure; in this case aluminum thin plates simulate very flexible solar panels. The structure is excited by a hammer or studied during a fast attitude maneuver. The results of the experimental activity will be investigated and compared with respect to the numerical simulation obtained via a FEM-multibody software and the relevant results will be proposed and discussed.

The Visual Extent of an Object

The visual extent of an object reaches beyond the object itself. This is a long standing fact in psychology and is reflected in image retrieval techniques which aggregate statistics from the whole image in order to identify the object within. However, it is unclear to what degree and how the visual extent of an object affects classification performance. In this paper we investigate the visual extent of an object on the Pascal VOC dataset using a Bag-of-Words implementation with (colour) SIFT descriptors. Our analysis is performed from two angles. (a) Not knowing the object location, we determine where in the image the support for object classification resides. We call this the normal situation. (b) Assuming that the object location is known, we evaluate the relative potential of the object and its surround, and of the object border and object interior. We call this the ideal situation. Our most important discoveries are: (i) Surroundings can adequately distinguish between groups of classes: furniture, animals, and land-vehicles. For distinguishing categories within one group the surroundings become a source of confusion. (ii) The physically rigid plane, bike, bus, car, and train classes are recognised by interior boundaries and shape, not by texture. The non-rigid animals dog, cat, cow, and sheep are recognised primarily by texture, i.e. fur, as their projected shape varies greatly. (iii) We confirm an early observation from human psychology (Biederman in Perceptual Organization, pp. 213–263, 1981): in the ideal situation with known object locations, recognition is no longer improved by considering surroundings. In contrast, in the normal situation with unknown object locations, the surroundings significantly contribute to the recognition of most classes.

Seismic interaction in electrical substation equipment connected by non‐linear rigid bus conductors

AbstractAn important element within the power transmission lifeline is the electrical substation that typically consists of a complex set of equipment items interconnected through conductor buses or cables. If the connections are not sufficiently flexible, significant dynamic interaction may occur between the connected equipment items during a seismic event, which may result in damage and loss of the equipment. This paper investigates the interaction effect between electrical substation equipment items connected by non‐linear rigid bus conductors. The equipment items are modelled as single‐degree‐of‐freedom oscillators by use of appropriate shape functions. The hysteretic behaviours of rigid bus connectors are described by differential equation models fitted to experimental data. An efficient non‐linear random vibration method is used to quantify the seismic interaction effect of the connected equipment items. Based on the developed analytical models and method, the effect of interaction in the connected equipment system is investigated through extensive parametric studies. The results lead to practical charts and guidelines for the seismic design of interconnected electrical substation equipment. Copyright © 2006 John Wiley & Sons, Ltd.

Seismic Interaction of Interconnected Electrical Substation Equipment

This paper investigates experimentally the dynamic interaction between components of electrical substation equipment interconnected by rigid bus conductors. Specific tests conducted in this study were (1) quasi-static tests of three different types of rigid bus with spring connectors; (2) quasi-static tests of one rigid bus slider; and (3) shake table tests of five different pairs of generic substation equipment specimens interconnected by three different rigid bus assemblies. All connectors tested exhibit stable hysteretic behavior with various degrees of energy dissipation capacity. The spring connectors dissipate energy through yielding and generated the highest forces among the connector tested and generally caused an amplification of the dynamic response of one of the interconnected equipment components. The bus slider dissipated energy through friction and generated lower forces than those of the spring connectors. Its high damping capacity, however, systematically reduced the dynamic response of interconnected equipment components. Finally, a special seismic connector that incorporates three flexural vertical aluminum cables generated the lowest forces. Its minimal damping capacity, however, resulted in higher equipment dynamic response than with the bus slider.

The effect of magnetic field on optimal design of a rigid-bus substation

Substation rigid-bus design involves electrical, mechanical, and structural considerations. In order to integrate these considerations into one document, IEEE in cooperation with ANSI has issued a comprehensive guide for design of substation rigid-bus systems. The design process based on this guide involves substantial manual effort to integrate all types of calculations. This is particularly evident when the computations have to be repeated several times in order to arrive at a more economic design. In an earlier paper the authors presented a mathematical model and computer program which automates the design process. There has been concern expressed about the possible biological effects of low level magnetic fields. In view of this, a new design constraint taking into account the limits imposed on the magnitude of the magnetic field can be added to the design guidelines. In this paper the authors introduce such a constraint and show how the magnitude of allowable magnetic field at a specified distance from the station buses affects the optimal design of a rigid bus substation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimization of tubular rigid bus design (substations)

The authors summarize a rigid-bus design procedure and present a model for optimization of the rigid-bus design process. The computer program BUSOPT (developed by Ontario Hydro) can perform an optimal selection of conductor parameters, interphase spacing, and span length. The buses can be selected either from the set of standard sizes stored in the program's library or the program can compute the optimal bus dimensions. A calculator mode allows quick analysis of various aspects of the design process. The program has a user-friendly format with context-sensitive help and can be executed on IBM-compatible personal computers. The station design process is complex, and the resulting optimization problem is highly nonlinear. An efficient and robust optimization algorithm has been developed to perform the calculations. In the calculator mode, existing station designs can be checked and the parameters requiring improvements or modifications can be easily identified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimal control of large space structures governed by a coupled system of ordinary and partial differential equations

In this paper we consider the problem of optimal regulation of large space structures in the presence of flexible appendages. For simplicity of presentation, we consider a spacecraft consisting of a rigid bus and a flexible beam. The complete dynamics of the system is given by a coupled set of ordinary and partial differential equations. We show that the solution of this hybrid system is defined in a product space of appropriate finite- and infinite-dimensional spaces. We develop necessary conditions for determining the control torque and forces for optimal regulation of attitude maneuvers of the satellite along with simultaneous suppression of elastic vibrations of the flexible beam.

Mathematical modelling and stabilization of large flexible spacecraft subject to orbital perturbation

In this paper the problem of modelling of large flexible spacecraft and their stabilization under the influence of orbital (radial) perturbation is considered. A complete dynamics of the spacecraft consisting of a rigid bus and a flexible beam is derived using Hamilton's principle. The equations of motion consist of a coupled system of partial differential equations governing the vibration of the flexible beam and ordinary differential equations describing the translational and rotational motions of the rigid bus. The asymptotic stability of the system is proved using Lyapunov's approach. Simple feedback controls are suggested for the stabilization of the system. For illustration, numerical simulations are carried out, giving interesting results.

Mathematical modeling and control of large space structures with multiple appendages

We consider the problem of rigorous modeling and stabilization of large satellites with several flexible appendages, such as a boom, tower, solar panel etc., all located arbitrarily on the rigid bus. The complete dynamics of the system is described by a set of hyperbolic partial differential equations coupled with a set of ordinary differential equations. These two sets of equations are very strongly coupled and describe the interaction among the rigid and the flexible members of the spacecraft. We propose feedback control schemes that make the system asymptotically stable in the sense that all the bus angular motions and the vibrations of the elastic members eventually decay to zero. We also present simulation results illustrating stabilization of the spacecraft by the feedback controls.

Behavior of Air Insulating GAPS of DC Systems Under Impulse, DC and Composite Voltages

This paper deals with the behavior of air insulating gaps of direct current (dc) transmission systems in the voltage range of ±600 kV to ±1 200 kV. The gaps studied were simulating either a bipolar dc tower or a bipolar rigid bus system. The influence of the terminations of the two ends of the insulator supporting the bus was investigated by using a single bus supported at one end. The breakdown voltage of the gaps was determined for a pure impulse, pure dc voltage or composite voltage formed by a dc on which an impulse was superimposed. The proximity effect of one pole on the pole-to-ground breakdown voltage of the other was also investigated.

Short Circuit Tests on a 3o, 230kV Rigid Bus Assembly

This paper describes the results of full scale, 3-phase short-circuit tests on a rigid bus assembly designed for 230kV operation. An investigation was conducted into the momentary withstand capabilities of the installation under actual short circuit conditions. A comparison of test results was made with methods proposed in the literature for the structural design of substation bus systems to withstand short circuit loads. Results indicate that existing design procedures are conservative.

Thermal considerations for outdoor bus conductor design

Outdoor rigid bus design is based on several limiting criteria. This paper brings to a single source the thermal considerations of rigid bus design namely, transfer of heat and properties of material. It concerns itself with aluminum alloys, copper and copper alloys and the currently acceptable shapes. Historically thermal designs have been conservative. This paper will allow the engineer to re-examine the factors involved in increased current loadings of rigid bus and possibly determine new thermal limits.

Waltz Mill 1100-kV Station: Conductor Selection and Laboratory Verification

The 1100-kV Waltz Mill project is a research center being constructed to permit life testing of underground transmission systems. The selection and high-voltage laboratory verification of the 1100-kV bus conductors are described. A six-conductor bundle with a 2.5-inch subconductor was selected for the upper strain bus, and a four-conductor bundle having a 5-inch (IPS) subconductor was chosen for the lower rigid bus. Laboratory radio influence tests show the validity of radio influence selection techniques. Laboratory measurements of audible noise due to conductor corona in heavy rain indicate the audible noise of 1100-kV lines may be in excess of that experienced on 500-kV lines.

An Analysis for Dynamic Behaviour of the Rigid Bus under Electro-Magnetic Force

An Analysis for Dynamic Behaviour of the Rigid Bus under Electro-Magnetic Force