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Polymers are extensively used as insulating material in high voltage devices, such as underground power cables, power capacitors and transformers. During normal operation the polymeric insulation of a power device is not only subjected to electrical stresses, but could also be subjected to thermal, mechanical and environmental stresses. These stresses either acting singly or in combination can cause...
Electrical wiring and interconnected systems (EWIS) have become a major area of research and development for variety of industries. A variety of factors lead to catastrophic failure described. Here partial discharge (PD) analysis methods for diagnosing aircraft wiring faults are explored since PD signals are strongly correlated with the defects that produce them and form an ideal part for prognostic...
Laboratory tests on field aged and unaged cables were performed using DC depolarization current measurements. Aged cables with water trees showed high dielectric losses and depolarization currents as compared with the reference, unaged cable. Both the area under the depolarization current waveform and dielectric loss factor, tandelta, increased with DC poling and the applied AC voltage, respectively...
The electrical degradation of cable insulation in distribution lines is due to the electrical stress caused by switching surges. During the operation, the insulation of power cables will be placed under high electrical stress, including overvoltages caused by switching. The status of power cable insulation aging is evaluated by the measurement of partial discharge level and AC breakdown voltage. The...
Several degradation mechanisms may affect polymeric insulation system reliability. Some authors postulate that, even in a perfect dielectric, nanoscale cavities can enlarge due to various mechanisms (from mechanical fatigue to lowering of the degradation reaction energy barrier) up to a point where highly energetic phenomena, which bring about breakdown, can be incepted. Other authors are more focused...
This paper presents results from laboratory experiments performed in order to evaluate different methods for quality control of polymeric insulated HVDC cables. In this work, we have investigated the effect of short term (24 h) DC stress followed by rapid grounding of the cable. This is comparable to a voltage step of -U0 at the point of grounding ,and depending upon the cable length, a step of up...
Saudi electric Company (SEC), and Petrochemical industries in Saudi Arabia and other plants provide the utilizing location and testing, and also some of the raw insulation materials for cable industries. Major petrochemical producers are striving to improve the quality of the plastic raw materials. On the other hand, cable industry has also made noticeable progress in the production of distribution...
Insulation liquids are mainly used in oil filled transformers for their cooling and insulating properties. Besides a testing of electrical properties, there is also important to monitor oxidation stability and activation energy as the factors which can decide on an application possibility of the insulating liquid. The main aim of this paper is to describe the influence of temperature aging on the...
Power transformers are vital parts of electric energy transmission and generation systems. Numerous power transformers in the European power grid have reached an age of 30 years or even more and are possibly close to their end of life. Because of economic reasons it is demanded to keep current assets as long as possible in service without taking the risk of a failure. The DP (degree of polymerization)...
The stator windings of large air-cooled rotating machines are insulated with mica-glass fabric impregnated with epoxy. These composites are submitted to thermal, mechanical and electrical stresses. A specific aging arrangement has been setup allowing artificial thermo-oxidative aging of dielectric samples thanks to the application of a dry O2 pressure at a controlled temperature. Two different materials...
There is a general agreement that in service conditions the quality of insulating fluids gradually deteriorates under the impact of electrical, thermal and chemical stress. Two ASTM methods are used to monitor the deterioration of liquid insulation step by step. A comparison is made between the performances of a commercial based mineral oil and ester fluids. The results obtained using a laboratory...
Aging of different oil-pressboard insulation ratios was investigated under controlled laboratory conditions. Modern diagnostic tools and techniques were used to assess the degree of influence of the relative amount of cellulosic materials on aged mineral oil decay products. Determination of relative content of dissolved decay products by spectrophotometry, solid suspension by turbidimetry, Fourier...
The study of polymers used in electrical insulation of wiring is important to the aerospace industry due to potential loss of life and aircraft in the event of an electrical fire caused by breakdown of wiring insulation. In this work, the effect of thermal exposure on the permittivity of PTFE is studied in order to examine the feasibility of developing of a capacitive nondestructive testing method...
Technical standards about security and safety in buildings always include strict requirements about the resistance to the ignition and propagation of fire of electrical components. In particular both power distribution and signal transmission cable insulation must often provide the best flame retardancy possible, especially in public places and transportation systems. This paper presents the outcome...
The accelerated thermal experiments at 90degC, 110degC and 130degC are performed, using the samples that Kraft paper or thermally upgraded paper were immersed by mineral oil or nature ester. The results show that the leveling-off degree of polymerization (LODP) for ester-immersed paper insulation is higher than the one for mineral oil-immersed paper insulation, and the time of getting to the LODP...
Since a few years, non-destructive techniques for assessment of power transformer insulation systems have been developed. The dielectric response in time and frequency domain is studied to determine the oil/paper insulation condition. One of the important parameters affecting the dielectric response is the temperature. On real transformer, the temperature of measurement is not controlled and is usually...
Space charge behavior at physical interfaces in cross-linked polyethylene (XLPE) films subjected to a DC field has been investigated as a function of the nature of the interfaces using the pulsed electro-acoustic technique. Aluminum, gold and carbon black-loaded polyethylene were used as electrodes to investigate space charge build-up in a single dielectric layer. A sandwich structure constituted...
This paper presents results of space charge and conduction current measurements performed on ethylene-vinyl-acetate nanofilled by a layered silicate. Large space charge and conduction current magnitude were observed. To clarify this behavior, fast-acquisition space charge measurements were performed using blocking electrode, with the aim of varying the charge injection/extraction barrier at the electrodes...
The paper presents the evaluation on accelerated ageing of non-ceramic insulation used at outdoor substations. The insulation was evaluated inside a salt fog chamber by applying cycles of salt fog, clean fog, drying, UV radiation and constant voltage. The insulation of two polymeric housed surge arresters and two polymeric bushings was evaluated. An arrester and a bushing were polluted with kaolin...
Dielectric properties of electrical insulation materials are needed for low temperature power applications. Performance of materials and their compatibility determine the size of the electrical insulation in power equipment. In this work we report the dielectric properties of some commercially available materials in sheet form. The selected materials are polypropylene laminated paper from Sumitomo...
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