Surface Of Bushing Research Articles

오염물질에 따른 변압기부싱 모델의 기중 코로나 방전 특성

The surface of bushing is contaminated with rain, dust, salt and others. A bushing with contaminations in air is serious problem in insulation. Therefore, it is important to understand the inspection and diagnoses of the safety. The ultra-violet rays(UV) camera has attracted interest from the view point of easy judgement. In this paper, we will report on the corona discharge characteristics of surface flashover model with contaminations in air. Also, UV images of discharge and corona pulse count in air are analyzed using prototype UV camera of Korea and a UV sensor with an optic lens. These results are studied at both AC and DC voltage under a non-uniform field.

Influence of Wear and Backlash on Machined PEEK Polymer Bushes and 7075 Aluminium Alloy Cam Plates Used in Robot Joints

Due to constant exposure to high torque and loads toughness, compressive durability and light weight of joint parts are crucial factors for biped walking humanoid robot parts. When polymer transmission parts are used for the manufacture of humanoid robot joint, wear becomes an important factor in terms of transmission error (backlash) between the input and output axes, ex. between the motor and the robot’s leg joint. In such joint system, a polymer bushes is directly connected to a cam plate, playing an important role in the robot's movement ability. In this work, the influence of wear of reinforced poly-ether-ether-ketone (PEEK) polymer bushes in friction against 7075 aluminium alloy cam plates is investigated in order to establish the application possibilities in transmission parts in humanoid robot’s joint. The PEEK bush surface conditions as well as the input axis-output axis backlash require close examination, so that efficient systems can be built. Sliding wear tests were performed on bushes under 0-50kgfcm loaded torque while the cam plate oscillated. Based on the wear observation, it was found that in a high load range the backlash increased along with number of cycles due to PEEK bush wear. The bush surface roughness also increased during testing. Roughness of PEEK bush surface and the loaded torque for output axis were significantly related to backlash of output axis in robot joint.

Design of hybrid steel-composite interference fitted and adhesively bonded connections

The work deals with the definition of the axial push-out force in hybrid connections realized by means of a carbon-epoxy composite bush which is press fitted into a steel housing and, eventually, supplemented with anaerobic adhesive, in order to obtain an innovative (hybrid) journal bearing. Lamè's solution has been extended to orthotropic material (composite bush) in order to evaluate analytically the coupling pressure due to interference assembly, while experimental campaigns have provided the values of coefficient of friction and of the adhesive shear strength (steel-composite). The mere application of the anaerobic adhesive before the assembly operation does not provide any sensible increase in push out force especially if compared with metal–metal interference connections. In order to take advantage of the adhesive strength, specific hoop channels for the adhesive hosting have been realised on the external surface of the composite bush.

기중 부싱모델의 오염물질에 따른 방전 특성과 자외선 이미지

A bushing is very important because it must supply the high voltage to the power equipment. Generally, the surface of bushing is contaminated with rain, dust, salt and others. A bushing with contaminations at air are serious problem in insulation. Therefore, it is important to understand the inspection and diagnoses of the safety. The ultra-violet rays(UV) camera has attracted interest from the view point of easy judgement. In this paper, we will report on the corona discharge characteristics on bushing model with contaminations. Also, UV images of discharge in air are analyzed using prototype UV camera of Korea. These results are studied at both AC and DC voltage under a non-uniform field.

Diagnosing Shorted Turns on the Windings of Power Transformers Based Upon Online FRA Using Capacitive and Inductive Couplings

Interturn faults are a significant problem in power transformers that can eventually burgeon into catastrophic faults and likely result in an overall network failure. The main problem with SFRA as one of the well-recognized diagnostic tools for detecting winding faults is its restriction to the domain of offline testing since the method requires injection of a test signal into the transformer windings through the high-voltage bushings. To address the difficulties arising from this issue, in this contribution, a new technique for online transfer function monitoring of the power transformers windings through a quite simple, economic, and noninvasive capacitive sensor installed on the surface of the transformer bushing is presented. Interturn faults with various levels of severity were imposed on the winding of a 35-kV/400-V, 100-kVA oil-immersed distribution transformer to evaluate the feasibility and sensitivity of the method. The experimental results proved that the newly developed online monitoring system is feasible and sensitive to detect unambiguously interturn faults even down to 0.2% shorted turns along the winding. As such, the proposed approach in this paper enables timely warning of a rising failure and serves a better purpose in assessing the health of a faulty transformer.

3310 Permeability of Sintered Porous Metal in Finishing Process with Grinding and Electrical Discharge Surface Modification

This paper concerns the machining process of the porous metal bushing for aerostatic bearings. The change in air permeability of the bushing is investigated during the grinding process which is employed to improve the form accuracy, and it is found that the permeability has decreased with the significant fluctuation as the removal volume increases. Then, the electrical discharge surface modification is proposed as a flexible post process to re-increase the permeability. After the process with a small scanning electrode, re-solidified layer has been generated on the surface of bushing and the increase in permeability has been confirmed.

The verification of adiabatic model of a lateral sliding bearing with a floating ring bearing

This research work describes the adiabatic model of a lateral slide bearing with a floating ring bearing. In order to support recommended assumptions for a designed model and for an evaluation accuracy of achieved results, the author developed a verification method which let comparing results received in a numerical way with that of the ones received in experimental tests. The evaluation criteria of a theoretical model were presented in regard to results from empirical studies. These criteria were divided into three groups. As the basic criteria, the author accepted the position of a bearing journal centre towards a fixed bearing bush, also for these positions pressure and temperature distributions in the outer oil film were chosen. In the conclusion, suggestions were made about the comparison of pressure and temperature distributions, frictional moments on a fixed bush surface, and angular velocities of a floating ring bearing towards a fixed bearing bush. The reasons of differences between measured and calculated values were also discussed.

Research on Hole Expanding with Spiral-Fluted Electrode in ECM

A manufacturing technology applying a special spiral-fluted electrode in traditional ECM (Electro-chemical Machining) is introduced, this method is provided with the advantages of both narrow-gap ECM and pulsed current ECM. It is a new technological method for expanding holes in hard metal materials parts. In this paper, a new type ECM electrode is proposed to solve hole expanding problem in carbide drill bush. The machining principles and the influence of some operating parameters of ECM on the machining precision and productivity are described. Experiments results indicate that the accuracy and quality of the machined surface and the machining efficiency could be improved greatly by applying spiral-fluted electrode in ECM. It is also showed that the inner surface of the carbide bush was finished easily by this method with the optimal operating parameters, at the same time, the surface roughness of a machined hole is improved to 1ess than 0.2m Ra, and the dimensional accuracy of hole can reach 0.02mm.

2010年3月30日静岡県牧之原台地周辺における凍霜害時の茶株面気温と典型的被害事例

2010年3月30日静岡県牧之原台地周辺における凍霜害時の茶株面気温と典型的被害事例

Research on elastohydrodynamic lubrication of a crankshaft bearing with a rough surface considering crankshaft deformation

Journal misalignment in bearings caused by crankshaft deformation under load exists generally in internal combustion engines. When serious journal misalignment takes place, the minimum oil-film thickness of bearings is greatly reduced and the maximum oil-film pressure of the bearings increases markedly. Therefore, it is necessary to consider the surface roughness and deformation of bearing surface when analysing the hydrodynamic lubrication characteristics of a misaligned bearing. In this paper, the elastohydrodynamic lubrication properties of crankshaft bearings considering crankshaft deformation under load and the surface roughness for a four-cylinder internal combustion engine were studied. The lubrications of the crankshaft bearings were analysed by the dynamic method. The deformation of the bush surface under the oil-film pressure was calculated by the deformation matrix method. The results show that, when crankshaft deformation is considered, the surface roughness has a marked effect on the orbits of the crankshaft bearings, but deformation of the bearing surface scarcely affects the orbits of the crankshaft bearings. When the surface roughness of a bearing is considered, the maximum oil-film pressure of crankshaft bearings obviously increases, the minimum oil-film thickness decreases markedly, and the end flowrate changes little in most of the engine cycle. When elastic deformation of the bearing surface is considered, the maximum oil-film pressure of bearings decreases to a different extent: elastic deformation of the bearing surface affects the end flowrate, the frictional coefficient of the journal, and the minimum oil-film thickness very little.

On the linear stability analysis of finite-hydrodynamic porous journal bearings under coupled stress lubrication

The objective of the present investigation is to study theoretically, using the finite-difference techniques, the dynamic performance characteristics of finite-hydrodynamic porous journal bearings lubricated with coupled stress fluids. In the analysis based on the Stokes micro-continuum theory of the rheological effects of coupled stress fluids, a modified form of Reynolds equation governing the transient-state hydrodynamic film pressures in porous journal bearings with the effect of slip flow of coupled stress fluid as lubricant is obtained. Moreover, the tangential velocity slip at the surface of porous bush has been considered by using Beavers-Joseph criterion. Using the first-order perturbation of the modified Reynolds equation, the stability characteristics in terms of threshold stability parameter and whirl ratios are obtained for various parameters viz. permeability factor, slip coefficient, bearing feeding parameter, and eccentricity ratio. The results show that the coupled stress fluid exhibits better stability in comparison with Newtonian fluid.

Iron-oxidising microbial biofilms as possible causes of increased friction coefficient in intermediate and lower guide vane bearing bushings at a hydroelectric powerplant in Brazil

Increased coefficient of friction led to malfunction of many and destruction of some maintenance-free bushings of intermediate and lower guide vane bearings at a hydroelectric power plant in Brazil. Analysis of surfaces of failed bushings revealed the presence of three types of deposits. The contact zones between bushings and the guide vane axis were covered with a thin black graphite film. The remaining bushing surface was covered by a mix of yellow-red coloured deposits, which contained a large proportion of iron-oxide-rich microbial biofilms, and green-coloured deposits, which consisted largely of copper oxides. Biofilms sampled from both the inside and the outside of the bearings contained 75% iron oxides by weight. The iron oxide deposits produced by these biofilms were identified as the primary cause of increased friction resistance between the bushing surface and the guide vane axis. Iron deposition within biofilms was made possible by the action of iron-reducing bacteria in the anaerobic zone of the reservoir immediately in front of the turbine intakes. These bacteria enriched the anoxic reservoir water with Fe(II) and the relatively small oxygen concentrations in turbine feedwater prevented the complete oxidation of Fe(II) in the penstock. Water-proofing of the bearing seals would prevent water penetration into the bearings and biofilm formation on the bushing surfaces and thus avoid the type of failure observed at this plant.

Effects of test conditions on the tribological behaviour of a journal bearing in molten zinc

Wear of journal bearings, consisting of cobalt-based Tribaloy T-800 bushings and carbide-coated 316L stainless steel (316L SS) sleeves, was evaluated in a molten zinc–aluminum alloy at different speeds and loads. It was found that these bearings experienced much less wear in comparison with the commonly used Stellite 6 bearings under similar conditions. There appeared to be a threshold load level of about 6.7 kN, below which both the friction and wear of the bearings were low. With the load maintained at a constant level, an increase in the test speed resulted in lower friction and lesser wear. The worn surfaces of both bushings and sleeves were relatively smooth without the appearance of wear grooves. Thorough analyses of the tested samples revealed that both materials have a lesser tendency to react with molten zinc. The binder phases of the carbide coating, however, did react with the test bath. Cracking of the test materials near the contact surfaces indicated that surface fatigue wear was the major wear mechanism affecting the journal bearing sliding in molten zinc.

Corona detection on surfaces of insulators using ultrasound sensors and fibre-optic transmission systems

Progress in the study and modelling of the corona phenomena depends on the availability of experimental techniques. In this paper an experimental method based on acoustic emission techniques for detection of corona discharge on the surfaces of the insulators is presented. Analysis of the received signal is carried out in the time domain and the possibility of using such a system in a high-voltage substation for detecting corona on the surfaces of insulators and bushings is discussed. Copyright © 2005 John Wiley & Sons, Ltd.

Flash-over mechanism of SF/sub 6/-gas type termination for DC power cable

With the development of /spl plusmn/250 kV DC-XLPE power cable and flexible joint so far, there arose a need to develop other components for the construction of DC-power transmission. One of those is SF/sub 6/-gas type, horizontally installed termination. To supply the DC electric power with reliability and stability, we need to clarify the phenomena under DC voltage application in this system. This paper examines the flash-over (FO) phenomena under DC voltage application in the SF/sub 6/-gas type, horizontally installed termination by using the model electrode in which the firefly of metal particle was imitated under the condition of charge accumulation on the epoxy bushing. In this examination, we confirmed experimentally that the behavior of metal particles was affected by the change of a field distribution due to the charge accumulation on the epoxy bushing, on the other hand, the metal particle promoted the charge accumulation on the epoxy bushing. Under these circumstances, FO initiated at the edge of the metal particle showing firefly, developed along the epoxy bushing surface. These seemed to mean that there was a synergetic effect of charges accumulation and behaviors of metal particle to introduce a FO. It was concluded that it was very important to be strongly aware of the existence of metal particles and its behavior in the SF/sub 6/-gas type termination, when it was used under DC voltage application.

An Experimental Investigation of the Effect of Groove Location and Supply Pressure on the THD Performance of a Steadily Loaded Journal Bearing

This paper aims to present the results of parametric experiments carried out in order to study the influence of groove location and supply pressure on the performance of a steadily loaded journal bearing with a single-axial groove. Hydrodynamic pressure and temperature distributions on the bush surface, shaft temperature, flow rate and bush torque were measured at variable supply pressure, using bushes with a single groove located at three different positions. A series of tests were carried out for variable applied load and rotational speed. The experimental evidence shows that some bearing characteristics are significantly sensitive to changes in groove location and supply pressure. One groove located at 30 degrees in relation to the load line, in the direction of shaft rotation, can conduct to reductions in maximum temperature, maximum hydrodynamic pressure and bush torque, with a moderate increase in oil flow rate. [S0742-4787(00)02801-0]

Field Optimization of HighVoltage Bushings

A method is described for optimizing the field stress on HV bushings- penetrating though a flat grounded casing - by modifying their profile, seeking a uniform distribution of the tangential field along the bushing surface. This results in an increase of the inception voltage for surface flashover on the bushing surface. The optimization process was achieved by an algorithm developed for calculating the tangential field component on the bushing surface. The algorithm was based on the charge simulation technique to satisfy the boundary conditions at the electrode, bushing and casing surfaces. The dominant effect in the optimization process is ascribed to the inclination angle and the height of the bushing outside the casing.

Rain and contamination tests on HVDC wall bushings with and without RTV coatings

Results of tests made to determine the ability of room temperature vulcanized (RTV) silicone rubber coatings to improve the performance of HVDC wall bushings are described. The behavior of uncoated full-scale +or-500 kV wall bushings is first determined in wetting conditions consisting of nonuniform rain and fog with various amounts of predeposited surface contamination. Parameters affecting flashover performance, such as polarity, rain conductivity, and contamination severity, are discussed. Results of nonuniform rain tests on an RTV coated wall bushing are reported. Fog tests and in-service experience have demonstrated that RTV coatings improve the HVDC contamination flashover performance of station post insulators; no flashovers occur in laboratory clean fog tests at rated voltage with ESDD levels up to 0.1 mg/cm/sup 2/. The application of RTV, silicone grease, or oily coatings makes the surface of a wall bushing sufficiently hydrophobic to prevent flashovers during nonuniform rain tests without a pre-deposited layer of contamination.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mechanism of HVDC wall bushing flashover in nonuniform rain

A model which assumes a dry zone of changing length is used to determine conditions which may lead to flashover of HVDC wall bushings in nonuniform rain. The key parameter in the proposed mechanism is the ratio of the resistance per unit length of the wet region to the resistance per unit length of the drier region. Measurements of the surface resistivity are presented for horizontal insulators, including wall bushings, with different surface conditions subjected to rain. Such measurements can be utilized to evaluate the potential capability of various materials to prevent wall bushing surface flashover in nonuniform rain.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stock-scion compatibility in tea (Camellia sinensisL.)

SummaryA bud grafting trial was carried out with five clones differing in vigour, using each clone both as rootstock and as scion. The vigour of the clones was assessed in terms of pruning weight per unit area of the pruned bush surface. The magnitude of the difference in vigour between the rootstock and the scion clones was found to be a satisfactory indication of grafting success, provided that the stock was the more vigorous of the two clones. The rootstock influenced the leaf yielding capacity of the scion, but it did not affect the liquor quality of the leaf.