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An asset management tool using a simple technique for determination of maintenance priority level of medium voltage transformers is presented in this paper. Case studies during implementation of the decision tool on transformers with a decreased in oil quality are also discussed in this paper. Among the investigated cases, a transformer with a declined breakdown voltage and an excessive production...
This paper presents a new approach for the determination of buried cable ampacity, considering the humidity migration in soil caused by the temperature rising around cables, and compares calculated results with migrationless considerations. To optimize the utilization of current carrying capacity, accurate calculation of real-time ampacity is needed in case of buried cable transmission systems, which...
Most of the methods available for the resistive current of metal oxide surge arrester are based on a simplified equivalent model, which consists of a nonlinear resistance in parallel with a constant capacitance, and there always exists a phase discrepancy between the resistive current and the applied voltage, it may be caused by the nonlinearity of the equivalent capacitance. In this paper, an improved...
Natural and synthetic esters are considered as potential candidates to replace mineral oil in power transformers. However, there is comparatively less experience on usage of ester-based insulating liquids in large power transformers. The high reliability and safety level required for large power transformers lead to careful assessment of the use of ester as the insulating liquid in these units. Therefore,...
High potential (Hipot) tests have long been used by many on machine stator windings to assess the integrity of electrical insulation system in question. Most industrial standards limit those recommended test values on completed new machines ready for service or existing machines under service/maintenance conditions. There is only limited information available in the literature regarding tests done...
Among all the types of transformer insulation deterioration, partial discharge is relatively a direct one that may lead to carbon traces which have negative effect on insulation. We believe that the relationship between the trace length and total appearance charge of partial discharges is a key to diagnose the oil paper insulation's remained life, even though the carbon trace in paper or pressboard...
A fast, non-destructive, and accurate technique has been introduced more than 30 years ago and industrialized since the last decade to recognize the transformer mechanical defect. This method called Frequency Response Analysis (FRA) and implemented as an off-line technique. Nowadays, transformer researchers as well as experts showing significant interest in real-time application of diagnosis methods...
In recent years, some composite hollow core insulators of current transformers used in China Ningxia Power Grid have showed different levels of degradation and cracking phenomena, especially electrical tracking and erosion. After 10 years operation in a quite dry area, the liquid silicone rubber kept a good state of hydrophobicity and hardness. It seemed the transformer jacket erosion phenomenon cannot...
Electrical partial discharge measurement has been investigated as a nondestructive test method to evaluate the mechanical reliability of piezoelectric ceramics. In order to understand the factors affecting partial discharge in piezoelectric ceramics, the effect of electric loading conditions is investigated. In this work, electrical partial discharge tests have been carried out on piezoelectric bulk...
Pulse oscillation overvoltage arises during the switching process of dry-type air-core reactor. In order to evaluate the destructive effect of impulse oscillation overvoltage on turn-to-turn insulation, a high voltage experimental system of impulse oscillation is designed in this paper, and partial discharge test on inter-turn insulation samples with different sizes of air gap under high frequency...
Cavities are one of the typical defects resulting in partial discharges (PDs) in extruded power cables. This paper focuses on studying the PD characteristics of arbitrary dielectric bounded cavities and electrode bounded cavities embedded in EPR insulation, such as PD distribution, PD inception and extinction voltage, under different type of testing voltage. During the experiment, the applied voltage...
The propagation characteristics of water trees at different temperatures were investigated, and the effect of chain orientation on water tree morphologies was revealed. Accelerated water tree aging experiment was performed respectively at 0°C, 20°C, 40°C and 60°C for XLPE specimens. The morphologies of water trees were observed by an optical microscope, and the sizes of water trees were counted. The...
The introduction of nano technology gives many benefits to the consumers and industries especially in cable insulators fabrication. This technology offers better cable life time and better cable resistance to face the cable failure. With the inclusion of nano filler in unfilled polymer, it shows that the nano filler has the ability in refining the electrical, mechanical and thermal properties compared...
Flashover of contaminated insulators is one of the major problems for the power distribution, especially in high altitude area. Laboratory experiments have shown that low pressure have great influences on the flashover performance of outdoor insulators. In order to investigate the influence of low pressure on the characteristics of AC partial arc, an experimental system was designed in this paper...
The effect of voltage ramp rate on the short-term dielectric breakdown strength of polymer nanocomposites is not well-documented. In this paper, the effect of DC field ramp rate on the large-area breakdown performance of melt-extruded bi-axially oriented polypropylene (BOPP) films incorporating 4.5 wt-% of nano-silica is studied. By utilizing a self-healing multi-breakdown measurement method with...
The pulsed electroacoustic (PEA) method is a useful electrical insulation evaluation technology, which visualizes the space charge in the bulk material using an acoustic pressure wave. Several methods to correct the space charge distribution due to the attenuation and dispersion of the pressure wave have been proposed. However, to improve the precision of the PEA method, herein the appearance acoustic...
The inter-turn insulation of stator winding for wind turbine generator (WTG) usually suffers the repetitive impulse over-voltages when the converter is connected to the winding terminals. The long-term effect of repetitive impulse over-voltages may lead to the development of inter-turn insulation defects and/or the occurrence of inter-turn insulation fault due to partial discharge (PD) activity. In...
We investigated the relationship between the space charge accumulation characteristics and the breakdown in a single layer and double layered polyimide films under dc stress using the pulsed electro acoustic (PEA) method. In recent years, there are many examples of multilayered polyimide film is used as the flexible Printed-Circuit Board (PCB) inside an advanced electronic devices. Therefore, it is...
In this paper, conductance characteristics of the two kinds of XLPE materials such as XLPE and XLPE/SiO2 nano-composite were measured under high stresses (2–70kV/mm) and under different temperatures (e.g. 20°C, 50°C and 80°C), after both XLPE were treated through different thermal treatment methods including thermal treatment and thermal poling treatment. The test results show that nanodoped XLPE...
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