Jiacheng Xie

Insight into the dielectric response of transformer oil-based nanofluids

The oil-based nanofluids with greater dielectric strength have attracted much attention as a crucial insulating materials in high-voltage oil-immersed power equipment. In fact, the different microstructures of the transformer oil-based nanofluids (TNFs) would result in different dielectric properties. In this work, the broadband dielectric spectroscopy measurement was used to establish the linkage between the electric double layer (EDL) and dielectric response properties of TNFs which was performed at 298K temperature and with frequency range from 10-2Hz∼106Hz. The modified Havriliak-Negami (HN) model function was used to analyze the measured results. The results demonstrate that both the real and imaginary parts of dielectric spectra of two kinds of oil are composed of the conductivity and polarization process. Compared with pure oil, two polarization process could be observed for the TNFs, explained by the EDL structure reasonably. The introduction of the EDL structure provides an idea to account for th...

Moisture characteristic parameter extraction and quantitive analysis of oil-paper insulation based on new explanation model of FDS

Frequency domain spectroscopy (FDS) technique is regarded as an effective nondestructive diagnosis method of the insulating state for oil-paper insulation that has been widely researched worldwide. To quantify the dielectrics FDS character, a new explanation model of the dielectric loss with several parameters was first proposed after an in-depth study of the frequency-domain dielectric response theory. H-N function was used to represent the polarization loss while random free-energy barrier model was used to describe the conductance process. The fitted curve based on the proposed model was in good agreement with the measured curve in lab. Then, in order to develop a new method to evaluate the oil-paper insulating systems moisture content, the frequency domain spectroscopy of several oil-immersed paper samples with different moisture contents of 0.5%, 1%, 3%and 6% were measured at 40°C respectively. By analyzing the results, we find that the moisture content significantly affects only the conductance process. Therefore, the extracted characteristic parameter, namely the DC conductivity 00, which is closely related to the conductance process, can be used to quantitatively describe the moisture content of OIP.

Conduction characteristics of transformer oil-based nanofluids

The DC conduction of transformer oil and transformer oil-based nanofluids were investigated with increasing electric field strength in this paper. The results show that entire process of conduction can be divided into three stages, including resistance stage, tunneling stage and space-charge limited stage. Further analysis indicate that the generation and movement mechanism of carriers are different at these three stages. At low electric field stage, the addition of nanoparticles increases the density of carriers. At medium electric field stage, the thickness of the potential barrier is increased after adding nanoparticles and electrons are captured by nanoparticles. At high electric field stage, the electrons produced by ionization are constantly being caught and released by shallow traps.

Research on SF 6 gas decomposition detection method based on electrochemical sensors

SF6 gas-insulated electrical equipment has been widely used in high-voltage and extra-high voltage power system. The electrical equipment could generate partial discharge and local overheating because of the insulation faults, which further results in SF6 gas decompensating and finally generate several kinds of SF6 decomposition products. The SF6 decomposition products can be quantitatively detected by using relevant electrochemical gas sensors, which contributes to deducing the equipment internal faults. A testing platform of electrochemical sensors detecting is established in this paper firstly. Through configuring and detecting SF6 decomposition products in the detection tank, the response characteristics of CO, SO2 and H2S sensors have been achieved. The experiment results show that CO sensor has a negative temperature characteristic, SO2 and H2S sensors have a positive temperature characteristic, and the temperature compensation curves are fitted by using quadratic fitting method. All sensor have a good linear relationship, but SO2 senor has a response to H2S gas, so the sensor data matrix is used to guarantee the measurement accuracy. In the end, the multi-component mixing gas is configured and used to verify the sensor data matrix, and the results show sensor data matrix has high reliability and accuracy.

Aging characteristic parameter extraction of oil-paper insulation based on frequency domain spectroscopy

Oil-paper insulation is widely used in power transformers. Thus, its insulation quality, aging included, has a strong impact on the operation of power transformer. The purpose of this paper is to evaluate oil-paper insulations aging condition more reliably. The frequency domain spectroscopy of several oil-immersed paper samples with different aging conditions were measured at 25°, 60°, 90° and 120°. Some characteristic parameters were extracted based on a proposed dielectric response function model. Results show that reconstructed curves got from the proposed model were in good agreement with measured curves. Aging and temperature can not only make a difference on the polarization process in high frequency domain, but also can influence the conductance process in the low frequency domain. Its concluded that relaxation time t and shape parameters β and γ can be selected to analyze the aging degree of oil-immersed paper, while DC conductivity σ0 and relaxation time t can be modified to eliminate the influence of temperature.