Theoretical Study of Potential Manufacturing Insulation Defects in Medium–Voltage Traction Motors

Medium-voltage motors dedicated to the applications of traction operate in an environment with strong multi-physics constraints. Electrical insulation of these engines is a complex multi-layered impregnated system which requires a given number of steps during the manufacturing process. In the present study, we theoretically investigated the potential manufacturing insulation defects of traction motors in low frequency domain. The aim is to assess the theoretical ability of dielectric spectroscopy method for the detection of these defects and the extension of the method to others insulation systems. The theoretical study is based on numerical modelling and simulation achieved by using Comsol Multiphysics software. In our numerical modelling the properties of the main dielectric elementary materials are frequency–dependent. The identification of each potential defect is carried out by comparing its equivalent capacitance and dissipation loss spectra with the characteristics of insulation without defect. As the results, all artificial defects are identifiable with a specific relative deviation. The detection of all the defects analysed will need a measuring device with resolution of 0.4%. Keywords—AC electric motors, Capacitance, dielectric, dissipation factor, composite insulation, numerical modelling.

Investigation on the Dielectric Properties of Palm Oil with Silicon Carbide Doping for Transformer Application

The dielectric strength of insulating liquids of transformer acts an important parameter in the operation of transformer. Thus, great interest and many studies have been extensively done to improve the dielectric strength. One of study is the introduction of nanoparticle in the transformer oils. Study of the nanoparticles for the last few years had been found that, it can be dispersed in the transformers oils to be nanofluids and directly enhance the transformer performance. In this study, an investigation has been carried out to focus on the effect of silicon carbide (SiC) nanoparticle to AC (alternating current) breakdown voltage of the Refined, Bleached, and Deodorized Palm Oil (RBDPO). AC breakdown test have been conduct according to the standard of the IEC 60156. Besides that, a number of parameters will be evaluated such as dielectric dissipation factor (tan δ), relative permittivity (ε), and resistivity (ρ). Based on the results of the experiment, the electrode gap at 2.5 mm having the highest AC breakdown voltage compared to the other electrode gap which are 1.0 mm, 1.5 mm and 2.0 mm. Furthermore, doping with different concentrations of the silicon carbide (SiC) in Refined, Bleached, and Deodorized Palm Oil (RBDPO) found decreasing of AC breakdown voltage from 52.09 kV (without SiC) to 45.3 kV for 0.001 g/L, 43.2 kV for 0.003 g/L and 40.1 kV for 0.005 g/L respectively.

Photoluminescence Spectroscopy Measurements for Effective Condition Assessment of Transformer Insulating Oil

Condition assessment of insulating oil is crucial for the reliable long-term operation of power equipment, especially power transformers. Under thermal aging, critical degradation in oil properties, including chemical, physical, and dielectric properties, occurs due to the generation of aging byproducts. Ultraviolet-visible (UV-Vis) spectroscopy was recently proposed for the condition assessment of mineral oil. However, this absorption technique may involve all electronic states of the investigated material which typically yield a broad spectrum, and thus cannot precisely reflect the electronic structure of aged oil samples. It also cannot be implemented as an online sensor of oil degradation. In this paper, photoluminescence (PL) spectroscopy is introduced, for the first time, for effective condition assessment of insulating oil. The PL technique involves emission processes that only occur between a narrow band of electronic states that are occupied by thermalized electrons and consequently yields a spectrum that is much narrower than that of the absorption spectrum. Aged oil samples with different aging extents were prepared in the laboratory using accelerated aging tests at 120 °C, under which 1 day of laboratory aging is equivalent to approximately 1 year of aging in the field. These aged samples were then tested using PL spectroscopy with a wavelength ranging from 150 nm to 1500 nm. Two main parameters were evaluated for quantitative analysis of PL spectra: The full width at half-maximum and the enclosed area under the PL spectra. These parameters were correlated to the aging extent. In conjunction with PL spectroscopy, the aged oil samples were tested for the dielectric dissipation factor as an indication of the number of aging byproducts. Interestingly, we find a correlation between the PL spectra and the dielectric dissipation factor. The results of PL spectroscopy were compared to those of UV-Vis spectroscopy for the same samples and the parameters extracted from PL spectra were compared to the aging b-products extracted from UV-Vis spectra. Finally, the corresponding physical mechanisms were discussed considering the obtained results and the spectral shift for each spectrum. It was proved that PL spectroscopy is a promising technique for the condition assessment of insulating oil when compared to conventional transformer oil assessment measuring techniques and even to other optical absorption techniques.