Xian-Jun Shao

Bio: Xian-Jun Shao is an academic researcher from Electric Power Research Institute. The author has contributed to research in topics: Partial discharge & Atmospheric-pressure plasma. The author has an hindex of 13, co-authored 36 publications receiving 508 citations. Previous affiliations of Xian-Jun Shao include Xi'an Jiaotong University.

Effect of Low-Temperature Plasma on Microorganism Inactivation and Quality of Freshly Squeezed Orange Juice

Abstract: Dielectric barrier discharge is used to generate low temperature plasma (LTP) for the treatment of freshly squeezed orange juice, which was inoculated with and without three kinds of microorganisms, respectively. Four experiments were designed and conducted: 1) When freshly squeezed orange juice samples inoculated with either Staphylococcus aureus, Escherichia coli, or Candida albicans were treated with LTP for 12,8, and 25 s, respectively, the numbers of each microorganism decreased more than 5 logs; 2) when orange juices without the aforementioned microor ganism inoculation were treated with LTP for inactivating original microorganisms inside and then stored at 4°C refrigeration, the total plate count and the proliferation rate of original microor ganism were both reduced significantly (counting per each 4-d during storage); 3) when orange juice samples without microor ganism inoculation were treated with LTP, the LTP treatment had insignificant effect on the values of vitamin C, total acid, turbidity,°Brix, and pH of orange juice; 4) when orange juice samples were inoculated with S. aureus, E. coli, or C. albicans, respectively, and their pH values were slightly decreased by adding HC1 (similar to that after LTP treatment), there was no obvious inactivation effects due to the reduction of pH values. It was proposed that microorganism inactivation was mainly due to reactive species and charged particles instead of slight pH reduction, and LTP treatment was able to effectively inactivate microbes and maintain the quality of orange juice.

Acoustic localization of partial discharge sources in power transformers using a particle-swarm-optimization-route-searching algorithm

Abstract: Methods to infer the location of partial discharge (PD) in high-power transformers using acoustic emission (AE) data have been extensively studied. The inner complex structure of the transformers is one of the most critical points in localization with AE method. Windings and cores affect acoustic wave propagation by changing the arrival time because of inhomogeneous propagation. A transformer physical model has been established herein by taking these complex factors into consideration. Each node in the model is a potential PD position, and an acoustic wave route comprise a series of nodes. The velocity and propagation factors are set for each node according to its acoustic wave propagation characteristics. A propagation-time estimation algorithm is proposed to calculate the propagation-time. Based on the transformer physical model, a particle-swarm-optimization route-searching (PSORS) algorithm is employed for searching the position of the PD source. By comparing time differences of measured AE signals and the ones estimated by the PSORS algorithm, the velocities and positions of particles are continually adjusted, which can ensure their convergence to the PD source position. Localization experiments were performed in 35 and 110 kV transformers, respectively, to verify the applicability of the proposed algorithm. A protrusion defect is used to trigger PD pulses, and four AE sensors with two different arrangements are employed. The results confirm that the accuracy of proposed localization method is insensitive to the presence of metal structures blocking acoustic wave routes.

Comparative study on the atmospheric pressure plasma jets of helium and argon

Abstract: Formation mechanisms for atmospheric pressure plasma jets (APPJ) of He and Ar are investigated by comparing the discharge current, light emission from jet, and time-resolved image of the discharge. A longer jet of He (Ar) is available with active (ground) electrode sitting at downstream side. The jet of He outside active electrode arises from corona discharge, while that of Ar outside ground electrode results from charge overflow, and can be diffusive or filamentous in different phases of the applied voltage. The underlying mechanisms are discussed. These results can be helpful for the further mechanism investigation and implementation of APPJs.

Localization of multiple partial discharge sources in air-insulated substation using probability-based algorithm

Abstract: Ultra-high-frequency (UHF) sensing technique has been introduced to detect and localize partial discharge (PD) sources in air-insulated substation (AIS). This paper presents a probability-based algorithm to localize multiple PD sources which may occur simultaneously in different power equipment. Assuming that the time difference of arrival (TDOA) between all pairs of antennas in a array are normally distributed, the probability density function (PDF) of PD source coordinates can be obtained by substituting the linearized form of time difference equations into PDFs of TDOAs. When large number of PD signals are recorded, the joint PDF (JPDF) can be calculated from the product of PDF of each TDOA. Then the PD coordinates to be solved are regarded as with highest probability, and can be solved by taking the derivative of JPDF. In the case of multiple PD sources, mixed UHF signals are separated by clustering the TDOA vectors with K Means clustering method. PD experiments are performed to test the presented algorithm, and the localization accuracy of proposed algorithm is compared with other typical methods such as Newton-Raphson, Particle Swarm Optimization and plane intersection method. The results indicate that the probability-based localization algorithm reasonably integrates the TDOAs of continuous signal sequence, which can effectively reduce the influence of TDOA estimation errors and improve the localization accuracy.

Research on Surface Modification of Polytetrafluoroethylene Coupled With Argon Dielectric Barrier Discharge Plasma Jet Characteristics

Abstract: An argon dielectric barrier discharge (DBD) atmospheric-pressure plasma jet (APPJ) is designed and employed for surface modification of polytetrafluoroethylene (PTFE). The plasma diagnostics and dielectric surface analysis are coupled together to investigate the mechanisms of plasma modification. The discharge power is obtained by Lissajous figure, and electron excitation temperature (EET) is measured through an optical emission spectrum and calculated by a Boltzmann diagrammatic method. The surface properties of modified PTFE samples are characterized by the static contact angle, surface resistivity, scanning electron microscope (SEM), and X-ray photoelectron spectroscopy. The results show that the discharge power, EET, and surface wettability increase with the Ar flowing rate, and a slight decrease of surface resistivity is revealed after plasma treatment. The surface roughness of PTFE is enhanced, and the oxygen-containing hydrophilic groups are incorporated by the impacts of APPJ radical species. Moreover, the hydrophilicity of PTFE can be improved by a surface presanding process, particularly after APPJ treatment. Finally, the surface modification mechanisms of APPJ on PTFE are discussed.

Cold Plasma: A novel Non-Thermal Technology for Food Processing

Abstract: In the past cold plasma is used for sterilization of sensitive materials and now it is extended to food industries as a novel technology. For years cold plasma processing has been viewed as useful for microbial inactivation while maintaining quality of fresh produce. However, this process is not effective for in vitro model food systems for inactivation of microbes or enzymes which are present in intact tissues, as it is a surface phenomenon. Cold plasma technology is also used to inactivate endogenous enzymes which are responsible for browning reactions particularly polyphenoloxidase and peroxidases. Several research investigations showed a reduced growth of microorganism via different mode of actions by etching phenomenon, cell disruption by electrophoration etc. Plasma technology is considered as modern non conventional technique which is used for the preparation of modified starches, altering its physical and chemical properties. Overall application of cold plasma for microbial destruction on different food substrates like fruits, meat products, cheese etc. was discussed. Besides this, it is also used to alter the germination rate of seeds. It is an eco-friendly process which is used in the preservation of food and other potential applications as an alternative to common techniques.