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In this study, polyaniline (PAni), was used to surround Zinc Oxide (ZnO) nanoparticles to be dispersed in a High Density Polyethylene (HDPE) matrix. The dielectric properties of the composite samples were characterized using dielectric spectroscopy in a wide range of frequencies (10−2 Hz – 1 MHz) at room temperature. Interesting results were found especially for the sample containing 10 wt% of ZnO/PAni...
When an electric machine has an insulation failure in service a decision must be made to rewind or replace it. In addition, depending on the age of the machine, the possibility of uprating the insulation system can be made along with the rewind. This paper will review the areas that need to be addressed in the process of making these assessments.
The main barrier of a dry type transformer is the major insulation between the high voltage and low voltage windings, usually consisting of air and solid in combination, aiming to meet the dielectric requirement. The lightning impulse test is the major driver to the insulation design. The design rule is usually set by a combination of theoretical understanding, previous experience and recommendation...
Under AC/DC combined electric field, the oil-pressboard insulation of the converter transformer accumulates space charges to generate a partially distorted non-uniform field and thus affects the electric strength distribution of the insulation system. The present research uses the needle-plate electrode to simulate the distorted non-uniform electric field fostered by the space charges and adopts the...
Partial discharge (PD) level under the specified AC/DC test voltages, which is one key parameter indicating the insulation reliability of ultra-high voltage direct current (UHVDC) converter transformers, do not often be accurately determined due to the impact of the external electromagnetic interference. To solve this problem, a method that uses the ultra-high frequency (UHF) technology to monitor...
Insulating pipe sections from epoxy and ceramic are presented for use in two-phase cooling systems, where the evaporator is on electric potential whereas the condenser is on ground. For the example of 2 kV system voltage and 12.6 kV impulse voltage, a dimensioning procedure is presented, taking into account air, solid insulation, and refrigerant. The latter must be considered in vapor, liquid and...
International Standard IEC60034-18-41IS was issued in 2014 to qualify Type I insulation systems of inverter-fed-electrical rotating machines. In the next stage, Technical Specification IEC60034-18-42 for Type II insulation systems is currently under discussion. To perform the qualification test, it is desirable to have a repetitive impulse voltage generator that can simulate given waveform parameters...
For water-cooled stator bar of power generator, leaks of water at the copper strand brazing location will reduce dramatically its insulation resistance. Therefore, the insulation resistance measurement is an important and simple test to perform in the periodic maintenance program. The temperature has an important effect on the insulation resistance. To correctly trend the insulation resistance of...
For large high-voltage motors it has been shown that there is a consistent relationship between motor Partial Discharge (PD) measurements recorded in Volts to PD measurements recorded in Coulombs, both measured quickly in succession [6,7,10]. This relationship, the ratio of PD measured in volts to PD measured in Coulombs, is expressed in a transformation factor called the F-factor. It appears that...
Until late 80s, most of the HVDC wall bushings installed, including those at the DC voltage of 600 kV, were provided with porcelain insulators with glazed external surface. During 70s to 80s, large numbers of flashover incidents have been reported on HVDC wall bushings. Many studies have been carried out on this problem. Uneven wetting, as the main cause of those flashovers had been identified and...
In this work, we investigate the possibility of using nano-sized fillers in conventional polymeric insulating materials to obtain a high permittivity nanodielectric in order to mitigate field stress. In this work, Barium titanate (BT) fillers are used in an epoxy (Bisphenol A) polymer matrix. The average BaTiO3 nanoparticle diameter is 90 nm. Specimens with various filler contents up to 5% by volume...
Failure mechanisms and PD (partial discharge) characteristics on rigid polyimide film are revealed under bipolar pulse voltage. Mean discharge quantity of PD under square waveform is measured for pure polyimide (PI) and nano doped PI film. Results of Scanning Electron microscope (SEM) showed that surface discharge (corona) is main reason of PI insulation material failure and nano particles addition...
Dielectric tests performed on live line tools are essential to ensure the safety of the work. This paper shows some possible improvements to the standards defining measurements of insulating sticks and insulated boom aerial devices. Laboratory experiments and simulations were carried out on insulating sticks in order to evaluate various electrode arrangements applied in practice during voltage probe...
In every high voltage grid, the replacement of assets is a slow but steady process that guarantees long-term reliability of the power distribution networks. The prioritisation of such interventions is based on complex rating criteria specifically designed to highlight potential issues of certain machines (or families of machines) in need of care. Given the tremendous costs of operations such as the...
Dynamic Line Rating is an effective way of uprating transmission lines in a cost efficient way, without reconductoring old lines, or building new ones. Uprating of equipment found in power systems has always been an issue. Having higher ampacity rates over a power line due to DLR, increased thermal stress occurs not only on the conductors, but on insulators, and on other pieces of equipment as well...
This article presents considerations and results of practical tests on the use of insulating polyamide monofilament line as the likely replacement for the traditional non-insulating multifilament ropes, employed in online interventions. The use of insulating polyamide monofilament line decreases the necessary time in online interventions, since some safety distances can be reduced. Furthermore, its...
Partial discharge (PD) activity may occur inside power transformers and the existence of this activity produces a negative effect on the transformer until eventually there is catastrophic failure. Therefore, partial discharge detection and measurement within a transformer winding have become an important research area to provide asset health information enabling the maintenance and replacement processes...
It is well known that it is hard for discharge to occur in a small void in solid insulating material, because of lack of initial electrons. For this reason, the discharge occurs after a long delay even at a critical electric field sufficient to initiate discharge. To resolve the problem, supplying initial electron by X-ray irradiation to various defective samples has been attempted over the years...
The cellulose based oil impregnated insulating system of power transformers is exposed to significant aging due to heat, oxygen, moisture and acids during operation time. This degradation affects the mechanical strength of the cellulose. It is generally accepted that a degree of polymerization (DP) below 200 can be defined as the end of life of an insulation system. In literature however there exist...
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