Yu Qinxue

Resistivity of pressboard immersed in mineral insulation oil

The pressboard is an important solid insulation dielectric in AC-DC converter transformers. Thus, it is very significant to understand the dielectric properties of the oil-impregnated pressboard. In this paper, the volume resistivities of oil-impregnated pressboard under different conditions have been systematically investigated. The pressboard was immersed in two kinds of mineral insulation oil, respectively. The measuring device of resistivity was full of oil and isolated from outside. All samples were measured at temperature range of 25-80°C under the field strength range of 1-30kV/mm. The influences of the temperature and the field strength on the resistivity of oil-impregnated pressboard have been investigated. The results of the volume resistivity of oil-impregnated pressboard showed that the resistivity of oil-impregnated pressboard decreased with the increase of temperature, and the activation eneregy increased with the increase of field strength. Meanwhile, with the increase of field strength, the resistivity changed slightly at first and then decreased significantly.

Temperature dependence of AC / DC breakdown strength of HVDC XLPE cable slices

Crosslinked polyethylene (XLPE) has been used for nearly sixty years for its high breakdown strength, low dielectric loss, good thermal stability and excellent mechanical performance. Since the good performances provided by HVAC polymeric cables, related research on HVDC XLPE cables has attracted much attention. In this paper, the temperature dependence of DC breakdown characteristics and AC breakdown characteristics of HVDC XLPE cable insulation are investigated by using column-column electrode system. The XLPE slices are cut spirally from the ±160kV extruded HVDC XLPE cable insulation with a thickness of 16mm. It is found that the DC breakdown strength decreases exponentially with the increasing of temperature, and the AC breakdown strength first increases slightly and then decreases and the maximum value appears in the vicinity of 70°C. And the DC breakdown strength of HVDC XLPE cable insulation is 1.3~3.5 times of its AC breakdown strength.

The DC breakdown of mineral insulating oil and oil-pressboard

AC-DC converter transformer is one of the most important equipments in the high-voltage D.C. transmission system. And the mineral insulating oil and pressboard immersing in oil are important insulation dielectrics used in AC-DC converter transformers. Thus, it is very significant to understand the dielectric properties of the mineral insulating oil and oil-pressboard. In this paper, the DC breakdown of two new mineral insulating oils and a pressboard immersing in these oils under different temperature has been systematically investigated. The oil and oil-pressboard was degassed and dehydrated before the test. In the testing progress, the test device of breakdown strength was protected by nitrogen and isolated from outside. The breakdown strength of two kinds of mineral insulating oil were tested at five temperatures with the range of 25-80°C, and the breakdown strength of pressboard immersed in both oil were also tested at three temperature with the same range. From the results, it can be obtained that the breakdown strength of oil increased with the increase of temperature, whereas the oil-pressboard showed opposite tendency. This paper enhanced the understanding of the breakdown strength for mineral insulating oil and pressboard immersed in oil, provided the theoretical and test basis to expand the engineering application of this mineral insulating oil and pressboard.

Effects of 1.8GHz electromagnetic radiation on dielectric properties of SD Rat's typical tissues

With the progress of modern science and technology, the impact of electromagnetic radiation on biological health condition is increasing. The influence and the mechanism of interactions between electromagnetic radiation and biological tissues are urgently to be studied. In this paper, the variation of dielectric properties of 4 typical SD rat tissues (muscle, liver, kidney, heart) with irradiation of fixed parameters and without irradiation was investigated. For the test group, SD rats were irradiated 8 hours per day for 1–3 days, by a 200W radiation source of 1.8GHz, while the control group was under the same condition except irradiation. The experimental results show that, comparing with the control group, dielectric parameters of the test group produced certain changes, and effect of different radiation dose varies. Meanwhile, blood routine test results of SD rats for both groups were in normal physiological index. After irradiation process, the normal physiological activity of SD rats in both groups could be recovered in a short time. In a high-power radiation condition, the dielectric properties of SD rat tissues would be changed depending on the irradiation time of occurrence and its physiological characteristics like blood also had an abnormal indicator. The results of dielectric properties after irradiation can be used for further study of health effects of electromagnetic radiation on organisms, and provide theoretical analysis and experimental basis for understanding the relationship between electromagnetic environment and human health.

Research on propagation characteristics of high frequency signal in high voltage cable

The relative permittivity and conductivity of the semi-conductive layer and semi-conducting resistance water layer of the high voltage cable were measured by the broadband dielectric spectrometer in the frequency range of 1-100MHz. Based on the measured results, the transmission characteristics of the partial discharge signal of the high voltage XLPE cable were simulated and calculated and finally the theoretical models were obtained. Besides, sinusoidal signal measurement experiment was done on cables of 110kV and 220kV with different lengths and types. It is found that attenuation degree of signal propagation becomes serious with the increase of cables length and signal frequency, which verifies the effectiveness of high-voltage cable partial discharge propagation model. It is the semi-conducting layer that has serious attenuation characteristic to high frequency signal.

Suppressive effect of metal deactivator on the corrosion sulfur of wrapped copper immersed in mineral insulation oil

It has been found that the presence of corrosive sulfur species in mineral insulation oil leads to a large number of failures in power transformers and shunt reactors. The method of adding metal deactivators particularly Irgamet 39TM into insulating oil is widely used to prevent the reaction of corrosive sulfur with copper by forming a passive film on the copper surface. Nevertheless, the influences of paper layers and atmospheric conditions on suppressive effect of metal deactivator are not clear. In this paper, the thermal aging tests in hermetic air and nitrogen conditions are separately designed to investigate the suppressive effect of Irgamet 39TM. Copper plates wrapped up in different number of paper layers are immersed in mineral oil samples with different Irgamet 39TM concentrations and aged at 150°C for 72 hours. the effectiveness of forming passivation layers is evaluated by analyzing the atomic concentration of nitrogen, oxygen and sulfur on copper surface using an X-ray photoelectron spectroscopy (XPS). It has been found that under nitrogen condition, the content of sulfur on copper surface increases with the number of paper layers, and the nitrogen content on the samples wrapped in paper is less than the ones unwrapped. While under air condition, compared to nitrogen condition, the content of sulfur on copper surface is greater. The results show that paper layers and atmosphere conditions have significant influence on the formation of passivation film.

Relaxation polarization model of SD rat tissues at frequency range 42Hz–5MHz

With the increasing recognition of electromagnetic radiation to human health and environment, research on the dielectric phenomenon and the explanation on polarization theory of biological tissues has become an important part of biological dielectric. Our recent study about low-frequency polarization characteristics of SD (Sprague & Dawley) rat tissues found that the polarization characteristic of tissues is consistent with CS (Curie-von Schweidler) polarization theory in α and β relaxation polarization frequency band. In this paper, a designed electrode system was used to test the dielectric parameters of typical SD rat tissues (liver, etc.) by LCR impedance analyzer in-vitro at room temperature. According to related Cole-Cole plot, polarization model of SD rat liver at this range is not a single Debye polarization, but an intricate model accompanied with multiple polarization processes where Debye and CS polarization theory have different proportions at this frequency range. Meanwhile, polarizations of other typical tissues (lung, kidney) are also in line with the theory of CS polarization. With the variation of the imaginary part and the dielectric modulus, the CS polarization model of SD rat in this frequency range was obtained, and the application value of CS polarization theory in the phenomenon of biological tissue polarization was verified. Therefore, at this frequency range, CS polarization model of the biological tissues can be used for further study on the biological dielectric polarization.

The influence of ultrasonic electrokinetic polarization on the dielectric constant of erythrocyte suspension

High-precision measurement of charging properties at cellular level in biological system is quite an important and difficult issue in bio-electromagnetic field. Electrokinetic method based on ultrasonic pulses and traditional dielectric method are two effective ways to solve this problem. Their theoretical similarities make them possible to characterize each other. In this paper, the feasibility of dielectric characterization of electrokinetic polarization was studied; the relevant measurement system was designed and set up, by which the electrokinetic polarization of erythrocyte suspension were characterized. The reliability of the dielectric characterization of electrokinetic polarization was studied by analyzing the experimental results obtained by this method with the dielectric theories and electrokinetic theories. Meanwhile, the electrokinetic mechanism of erythrocyte suspension in different concentrations was considered. This method provides a new way for the study of the charging properties of cells and provides a new method for the interpretation of the characteristics of cell electrokinetic polarization and dielectric properties.

Slow-freezing cryopreservation of red blood cells under the control of an AC elecric field

It is well known that amorphous ice can be used to cryopreserve biomaterials for transplantation. The main issue in this process is that liquid-solid phase transition of water. Due to the polarization of water, amorphous ice may be induced by AC electric filed. In this paper, AC electric field was applied to cryopreserve red blood cells (RBCs) to improve their viability. First, an electro-controlling apparatus for slow-freezing was established. Chicken RBCs were chosen as the sample because it is nucleated cell and it is convenient to estimate the cell viability. RBCs were cryopreserved under the control of an AC electric field at -30 °C for 24h and cell viability after thawing in a thermostatic waterbath at 37±0.5°C was determined by microscope. The result shows that the survival RBCs maintained the integrity of morphological. In the presence of AC electric field (Emax=1.63×105V/m, f=1MHz), the survival rate is 23.4±1.41%, lower than the effect of cryoprotectant (dimethyl sulfoxide, 3.3wt.%), that is, 33.2%±2.57%. the highest cell viability up to 48.4±1.54% was obtained under the above two conditions together. These results indicate that AC electric field can contribute to the success of slow-freezing cryopreservation.

Effects of AC electric fields on the cryopreservation of SD rat liver tissues

The cryopreservation, which refers to preserve the cells or tissues at the subzero temperatures, will inevitably face the problem of cryoinjury caused by the ice crystallization. The application of external field during the freezing process of specimen provides a promising approach to avoid the injury and thus promote the efficiency of the preservation. In the present work, we froze the SD rat liver tissues accompanied with the AC electric field (with field strength E=0.125kV/m~1.0kV/m, frequency f=100kHz~10MHz). The cryopreservation efficiency of the approach has been evaluated by the dielectric properties and the microstructure studies of tissues after frozen for 5h and thawed. We compared the dielectric frequency spectra and the transmission electron microscopic (TEM) images of the following three groups: a) fresh tissues; b) thawed tissues after normally freezing; c) thawed tissues after freezing with AC field. The dielectric frequency spectra results suggest that some curves in group c) to group a). Furthermore, TEM images indicate that the cellular structures in group c) are less severely injured than group b). The phenomena may result from the fact that the AC electric fields affect the formation and growth of the ice crystal during the liquid-solid phase transition, and thus inhibit the cryo-injury.