About 30 percent of all overhead power distribution outages are caused by failing electrical equipment. Arc and partial-arc sources predict an eventual outage. Replacing failing equipment reduces all reliability index figures. The novel sensing device discussed accurately determines the Global Positioning System (GPS) location of an arc source from moving vehicles. It can be called an outage-avoidance system.
The transmission capacity of overhead transmission lines is limited largely by its operation temperature, which is determined by the competition between the heat generation by load current and the heat dissipation into the environment. The ohmic heat generation is a function of the conductor resistivity, which is a function of its temperature and current distribution inside the conductor, taking the skin effect into account. The heat dissipation is influenced by the temperature of the conductor and the air, the surface condition of the conductor, the wind, the sunshine, and the humidity of air, etc. Finite Element Analyses are carried out in this paper to calculate the thermal dynamics by coupling the thermal field and the fluid mechanical models. The results show the temperature distribution and the evolution history in the conductor - air system under various environment conditions. Thus the maximal load level can be defined accordingly. The calculation also gives the time required for the conductor to reach equilibrium with load and environment changing. This information can help the grid operators to decide how to dispatch the loads among multiple transmission lines, either as a temporary routing or as a steady state solution.
Material's micromechanism determines its property, therefore we should research on polymer material's micromechanism so as to further explain its insulation characteristic. From material's infrared spectrum, main function groups can be found through the wave numbers of absorption peaks. In the experiment five kinds of polymer materials, which are kraft paper, PC, PET, PTFE and PPS, are aged in the condition of high temperature and high electric intensity. Polymer materials before aging and under aging for one to three months are tested for infrared spectra. The absorption peaks of polymer materials' infrared spectra respectively reflect their main function groups. From the comparison of infrared spectra of the polymer materials before and after aging, we can find transformation of characteristic function groups of the polymer materials under aging. In this paper the infrared spectral characteristics of mineral oil impregnated polymer materials under electro-thermal aging are preliminarily analyzed.
The electric performance of the one kind of hydrogenated transformer oil and three kinds of naphthenic transformer oil had been tested by using the experimental methods specified in the GB/T7595-2008. A series of experiments, including dielectric dissipation factor, volume resistivity, dielectric constant, breakdown voltage and electrostatic charging tendency, mechanical impurities, corrosive sulfur and sulfur content had been conducted. Compared with the other three naphthenic transformer oil, the hydrogenated transformer oil performed the best electrical properties.
Power transformers are supposed to be and remain in service in various environmental circumstances under different electrical and mechanical stresses. Base on failure history in power transformers obtained from four corners of the globe one of the major problems in transformers is mechanical defect. A number of monitoring and diagnostic methods have been introduced to recognize transformer active part displacement and winding deformation. Frequency response analyses and short circuit impedance measurement have been employed as two common diagnosis methods in large power transformer winding deformation recognition. On the other hand, researchers are expressing an increased concern about power transformer condition monitoring in the smart grid context. Hence, all of off-line methods need to move towards on-line applications. One of the challenges is finding reasonably accurate method which can provide sufficient information about transformer winding condition. In this study, mechanical defects of windings and their causes are investigated in detail. Frequency response analyses and short circuit impedance measurement as two popular methods in transformer winding deformation diagnosis will be employed to get insight into transformer active part condition. A large power transformer has been taken as a case in order to put the capability and sensitivity of abovementioned methods into test. Onsite test results on this giant transformer winding show that frequency response analyses method is capable to provide far more information as to the healthy or defected condition and physical movements of the transformer's windings and core compared to the other method.
The purpose of this work was to study the effect of hydrostatic pressure on the initiation and growth of electrical trees in a silicone insulation material for electrical apparatus. In this study a commercial available light transparent silicone material was subjected to a hydrostatic pressure in the range 1 to 100 bar at 30°C. The test objects were concentric cylinders with a tinned copper conductor as a high voltage electrode. The insulation thickness was 4 mm and stainless steel needles with tip radius of 4 μm were inserted in the conductor with a distance of 2 and 3 mm from the insulation surface. The joints were submerged in water which also acted as a ground electrode. During the high pressure tests the samples were placed in a stainless steel vessel with optical windows. High voltage was fed into the vessel by using specially designed miniature cable penetrators. In order to avoid partial discharges at the cable ends outside the vessel, silicone oil filled cable terminations were installed. The tree growth was monitored by measuring partial discharges (pd), together with recording of light emission from the discharge channel. The results show that tree growth in silicone rubber rapidly leads to breakdown. Pd inception is suppressed with increasing hydrostatic pressure, while the tree growth rate is slightly increased.
We recognize the increased availability of environmentally friendly thermoplastics on the market today. Besides pure bio-based materials like Poly(lactic acid) (PLA) and Polyethylene (PE), there are also engineering plastics available which are partially derived from renewable resources. For example many Polyamide grades can be found that are partially based on castor oil. The use renewable resources is believed to lower the carbon footprint of these materials compared to their crude oil based counterparts. As a result the use of bio-based engineering plastics can help us to obtain sustainable growth. We have investigated the performance of two bio-based Polyamides, both compounds contain 30 wt% glass fibres and halogen free flame retardant. The first material was a PA 4.10, where 49% of the resin was bio-based. The second compound was a PA 6.10, with 31% renewable content. Housings for a low voltage DIN-Rail product was produced by injection moulding. The selected product was a Residual Current Operated Circuit-Breaker (RCBO) with over current protection. The assembled prototypes were tested according to IEC-Standards. As reference a standard glass fibre filled PA 6 material was used. The bio-based compounds showed outstanding results. For example the moisture absorption of the two grades was at least 50 % lower compared to the standard PA 6. Both materials also reached a CTI value of 600V and passed the glow wire test at 960°C. The prototypes containing the bio-based compounds passed the required type testing, which indicates that there is no problem using engineering thermoplastics that are partially based on renewable resources in low voltage applications.
In this paper, the variation of the resistivity of SiC powder at low and high voltage as a function of milling time was investigated by controlling the particle size, morphology and compactness (applied pressure). The particle shape and size of commercially available SiC powders were altered by ball milling. The electrical properties of the various SiC powders were characterized at low voltage by using a pressure controlled ohmmeter and frequency-domain spectroscopy. A resistivity increase from 7 to 54 MΩ.cm was observed when the grinding time increased from 5 to 30 minutes, which corresponded to a decrease of the particle size from 54 μm to ~4.5 μm. The nonlinear characterization I-V for high electrical field was investigated. X-ray diffraction and scanning electron microscopy have been carried out to highlight the size decreasing and crystalline structure of the milled powder.
This paper deals with hybrid organic-inorganic coatings having the purpose to improve the electrical properties of host insulating materials. In particular, space charge behavior of coated XLPE specimens is investigated here as a function of temperature. Three different nanocoating designs are tested, showing promising results in terms of space charge reduction with respect to uncoated XLPE specimens. This improvement has been associated with the increase of the injection barrier at the electrode/insulation interface provided by the nanocoating layer which acts as a partially-blocking electrode.
This paper presents a three dimensional, full parameterized numerical model based on finite-element-method (FEM) to determine transient temperature distributions on real stator bar geometries. The model allows calculating the resulting timedomain thermal gradient across the insulation for internal (current) as well as external heating (oven) and therefore the comparison with measurements provided by thermal cycling tests (IEEE 1310-1990 / IEC 60034-18.34). FEM-results for simplified models of stator bar geometry are compared with the analytical results of the describing partial differential equations and advanced thermal lumped models. A detailed geometry of an exemplary generator stator bar (20 kV, 450 MVA) is modeled. This model takes several temperature depending material parameters into account. Furthermore the resulting convection, depending on cooling gas flow velocity, dynamic viscosity and temperature distribution on the stator surface, is calculated within this transient model. Finally several measurements are performed on two test-setups of generator stator bars for both situations, an internal current heating in the copper bar and external heating in an oven. The measurement and calculation results are evaluated and compared. As a result a very good correlation is obtained between theoretical and experimental investigations, which show the capability of the new developed numerical calculation model.
Dissolved gas in oil analysis (DGA) has been used for many years successfully for diagnosis and condition monitoring of mineral oil filled transformers. Due to the usage of alternative dielectric liquids, for example natural and synthetic esters, it is necessary to investigate if and how this diagnostic method can be applied to these insulating systems. This contribution presents the gassing behavior of different insulating liquids from experiments, which represent electrical and thermal faults. Also the suitability of existing mineral oil interpretation methods for DGA is considered. One mainly investigated fluid is Envirotemp FR3™. Where possible the amount and relation of gases are compared to mineral oil and other synthetic esters' gassing behavior.
The subject of this study is dielectric properties of a four-component casting epoxy resin containing TiO2, Al2O3, WO3 and SiO2 nanofillers over the frequency range 20 Hz - 1 MHz with the aim to investigate the possibilities of using dielectric spectroscopy for diagnostics of such nanocomposites or structures constructed of them. Both positive and negative features of nanofillers in the epoxy resin are examined. The paper explains how to prepare samples for dielectric measurements, then proceeds with the presentation of results themselves before arriving to interpretations.
Rotating electrical machines must be designed for the environment in which they operate. High voltage generators and larger motors are normally designed to run under standard environmental air pressure and humidity. Machines running in special conditions such as close to the sea, in underground caverns, under water or in high humidity require special designs. The specific conditions have to be considered from the beginning as they can influence the size, the sealing, the covering and several other components of the machine. The main influence of operating machines at higher altitudes is the reduced air density. This air density influences the cooling efficiency and the dielectric strength of the air. These two effects have a direct influence on the design of electric machines. The influence of air density on the dielectric strength of air gaps is investigated and described in this paper.
Through the ongoing miniaturization of electric components, insulation systems with microscopic dimensions become more significant. Furthermore, the increasing use of HVDC and power electronics in energy distribution and transport results in a varied electrical stress situation for the used insulation materials composed of AC-, DCand mixed voltages. In this context, the paper contains experimental examinations analyzing the dielectric properties and the conducting behavior of unfilled, unsaturated polyester resin with thicknesses s≈3 .. 1000 μm at electric field strengths E≈1 .. 9 kV/mm. For the realization of test specimens a vacuum process and an optimized micro-milling process are used. This enables the production of samples with insulation thicknesses in the lower μm-range and surface roughnesses of a few nanometers. According to IEC 60250 and IEC 60093 the test specimens are equipped with a three-electrode system. The dielectric properties, relative permittivity and dissipation factor, are measured at frequencies f = 20 Hz .. 20 kHz and different sample thicknesses. The apparent conductivity is determined by polarization and depolarization current analyses. All measurements are carried out at a controlled temperature ϑ = 20°C± 2°C. As a result, the electric properties of unfilled, unsaturated polyester resin show significant thickness dependencies as they are known for polymer's permeability and breakdown strength. The measured relative permittivity, dissipation factor and apparent conductivity decrease with decreasing sample thickness. For the interpretation of this behavior a model based on space charges in microscopic areas close to the electrodes is proposed.
Implementation of cable system aging management is progressing rapidly in the nuclear industry. This paper describes the scope of the aging management system, the tactics, assessments, and tests being applied to in-plant and underground cable systems. Progress to date on medium-voltage cable testing and assessments of low-voltage power and instrument and control cable is discussed as are failure mechanisms and test methodology for the types of medium voltage cable used in nuclear plants.
The water absorption characteristics of a HTV silicone rubber material were investigated at different relative air humidity (RH). The two-sided water absorption process into disc-like HTV samples at different RH can be described by a Langmuir type diffusion model. The permeation process of water vapor through HTV discs was quantified by adjusting different constant RH at both sides of the discs. The permeation coefficient of the HTV discs amounts to an almost constant value of 10 -7 g cm -1 s -1 cmHg -1 at RH higher than 60%. Finally, a simplified model is introduced by what the water vapor permeation process into an air filled interface defect inside a composite insulator can be simulated.
Nanotechnology is a general term covering a wide range of many fields. It deals with characteristics in nanometer size and/or microscopic regions on materials and functional devices. Adding small amount of nanofillers to epoxy resins can lead to electrical, mechanical and chemical improvements. To evaluate the influence of the nanofillers on the partial discharge inception voltage and breakdown voltage, the measurements of the specimens were carried out under homogeneous (plane-plane) and inhomogeneous (rod-plane) electrical field configurations at temperatures from 23 °C up to 180 °C. In this study, host material, namely bisphenol-A epoxy resin, and related micro filler are the same basic components for all produced samples and TiO2 nanofillers were considered at different percentages up to 10% by weight (pbw). Then nanofillers were mixed with the host material using high speed mechanical mixer and ultrasound device simultaneously to make sure, that they are mixed with the host material homogeneously and in nanoscale, too. Regarding the importance of a homogeneous distribution of nanofillers, an even distribution of them was validated by means of transmission electron microscopy. The results show, that adding nanofillers can increase the PD inception voltage of the specimens up to around 15% above glass transition temperature (Tg) under inhomogeneous field and around 25% above Tg under homogeneous field. The breakdown voltages increased under inhomogeneous field at some concentrations of nanofillers, but the changes are not considerable. Under homogeneous field, the results show, that nanocomposites have higher breakdown voltage up to Tg than the conventional composites. Mechanical and thermal results show also considerable improvements.
The main objective of this study is to investigate the feasibility of using an RF antenna to detect partial discharges in outdoor insulators. Moreover, the study focuses on identifying the sources of partial discharge using artificial neural networks. In outdoor insulators, partial discharges could be initiated either from surface discharge due to pollution and/or from corona discharges from energized ends. Both statistical and spectral features have been used as an input vector to a feed forward neural network with back propagation training algorithm. The proposed method is found to be successful in classifying different types of partial discharge with a recognition accuracy of 93%. The proposed method can be used during overhead line inspection to assess the status of outdoor non-ceramic insulators.
Partial Discharge (PD) measurements are considered as a very powerful technique for testing and monitoring the condition of high-voltage (HV) insulations. PD activity is generally accepted as an early breakdown indicator, which is also reflected in numerous standards. In the present contribution, the authors describe the fundamentally different propagation mechanisms of electrical impulses in the conventional (according IEC 60270) and the ultra-high frequency (UHF) range. The low-frequency components of the PD signals propagate mainly via the conductor, whereas the high-frequency components (UHF signals) are radiated as electromagnetic waves. The sensitivity and spectrum of the measurement depends strongly on the geometric position of the PD, damping and resonances of the propagation path, and the frequency response of the receiver. Field simulation has been used as an appropriate tool for calculating PD signal propagation in HV apparatus.
