Chenguo Yao

Transformer winding deformation diagnostic system using online high frequency signal injection by capacitive coupling

Transformer winding deformation is common among all sorts of transformer failures. Cumulative deformation can eventually burgeon into catastrophic faults and result in entire network outage. It is possible to detect the early signs of faults with continuous online monitoring transformer. However, frequency response analysis (FRA) is considered to be a useful and accurate tool for sufficient detection. This paper aims at proposing a novel diagnostic system for online monitoring power transformer winding deformation based on FRA. In order to realize online monitoring transformer winding, the system uses the capacitive coupling method to inject controllable nanosecond pulses, which function as the excitation signal of winding, and to obtain the response signal. This proposed method may extend frequency range for analysis and perhaps could early detect minor winding movement and looseness. Transformer experiments show great prospect in the application of the system.

Low voltage irreversible electroporation induced apoptosis in HeLa cells

BACKGROUNDnHigh-voltage electric field pulses can make cell membrane electroporated irreversibly and eliminate malignant cells via necrosis. However, low-voltage is not efficient as that.nnnAIMSnThis study determined the differential effects of high- and low-voltage electric field pulses on HeLa cells, when the power of low-voltage was enhanced by increasing quantity of pulses.nnnMATERIALS AND METHODSnPulses electric fields with permanent frequency (1 Hz) and pulse length (100 μs) were performed on HeLa cells. Voltage and pulse sets (8 pulses/set) were various during treatment. CCK-8 assay was used to detect cell viability. The quantitative determination of apoptosis and necrosis were performed by flow cytometry with Annexin V and PI staining. Transmission electron microscopy was used to observe the ultrastructure of HeLa cells. Caspase-3 and caspase-8, the enzymes in apoptotic pathway, were determined by western blot.nnnRESULTSnThe data showed that low-voltage electric field pulses also could make cell irreversible electroporation (IRE) and ablate HeLa cells effectively by induction of apoptosis. The ablating effect due to low-voltage treatments delivered with a greater number of pulses may be as satisfactory as high-voltage, or even preferable because it causes less necrosis and more apoptosis.nnnCONCLUSIONSnIRE induced by low voltage with more pulses could ablate HeLa cells effectively as high voltage, and it was preferable that less necrosis and more apoptosis occurred under such condition.

Window effect of pulsed electric field on biological cells

Based on multilayer dielectric model, for the spherical biological cell subjected to pulsed electric field (PEF), an equivalent circuit model is presented. Frequency-domain analysis shows that inner and outer membranes exhibit band-pass and low-pass filter characteristics in response to PEF, respectively. Therefore, different biomedical effects will be induced by the field with different frequency spectrum. The method to calculate the transmembrane potentials induced by time-varying PEF is introduced, and the relationship between rectangular pulse and transmembrane potentials is also discussed. It is found that because of different charging time constants, different durations have selective effects on inner and outer membranes. The analyses in both the frequency-domain and time-domain show a window effect of PEF on biological cells. When duration is reduced from microsecond to submicrosecond, and to nanosecond, the target induced is changed from the outer membrane to the inner membrane gradually. The window effect gives preliminary explanation for various bioelectric effects such as electroporation, intracellular electro manipulation and nanopores, providing help to the applications of PEF in tumor treatment.

FPGA-Controlled All-Solid-State Nanosecond Pulse Generator for Biological Applications

In vivo studies of tumor-cell apoptosis induced by nanosecond pulsed electric field require high-voltage nanosecond pulses delivered to the biological tissues. In this paper, a newly developed all-solid-state nanosecond pulse generator based on the Marx generator concept is proposed for this application. The generator comprises four parts: a dc charging power, a solid-state Marx circuit using metal-oxide-semiconductor field-effect transistors, a control circuit using a field-programmable gate array, and the load. This generator has the capability of producing repetitive pulses with a voltage up to 8 kV, pulsewidth of 200-1000 ns, rise time of 35 ns, and repetition rate of 1-1000 Hz with various resistive loads and 1-kV dc input voltage. The all-solid-state design makes the generator compact and reliable. Initial experiments were carried out to verify the performances of the proposed generator.

Finite difference time domain simulation of lightning transient electromagnetic fields on transmission lines

Lightning parameters measurement of the transmission lines is the foundation of lightning protection research. It plays an important role in supplying the original accurate data to study the lightning characteristics, analyzing the reason for lightning accidents, and designing the insulation of the transmission line. In this paper, the distribution of the lightning transient electromagnetic fields around the tower is simulated by the finite difference time domain (FDTD) method based on a model established with reference to an actual 500 kV transmission tower. The analysis of simulation is used to verify the feasibility of non-contact lightning current measurement based on the differential loop. The obtained results show that when lightning strikes the conductor, the waveforms of magnetic field obtained from the detection points are the same as the lightning currents waveform, and the amplitude of the magnetic field intensity exhibits a stabile linear relationship with the lightning current. All the detection points located around the tower can completely get current waveform flowing on the transmission lines. Moreover, the amplitudes and the polarities of the waveform from the detection points have different characteristics when lightning strikes different conductor. Lastly, a new lightning fault pattern recognition method which can figure out the lightning fault phase accurately is established based on the online monitoring of lightning current on the transmission lines by the differential loop.

Effect of actin cytoskeleton disruption on electric pulse-induced apoptosis and electroporation in tumour cells

Electric pulses are known to affect the outer membrane and intracellular structures of tumour cells. By applying electrical pulses of 450 ns duration with electric field intensity of 8 kV/cm to HepG2 cells for 30 s, electric pulse‐induced changes in the integrity of the plasma membrane, apoptosis, viability and mitochondrial transmembrane potential were investigated. Results demonstrated that electric pulses induced cell apoptosis and necrosis accompanied with the decrease of mitochondrial transmembrane potential and the formation of pores in the membrane. The role of cytoskeleton in cellular response to electric pulses was investigated. We found that the apoptotic and necrosis percentages of cells in response to electric pulses decreased after cytoskeletal disruption. The electroporation of cell was not affected by cytoskeletal disruption. The results suggest that the disruption of actin skeleton is positive in protecting cells from killing by electric pulses, and the skeleton is not involved in the electroporation directly.

Apoptosis induction with electric pulses - a new approach to cancer therapy with drug free.

Electrical pulses have been widely used in biomedical fields, whose applications depend on the parameters such as durations and electric intensity. Conventional electroporation (0.1-1kV/cm, 100micros) has been used in cell fusion, transfection and electrochemotherapy. Recent studies with high-intensity (MV/cm) electric field applications with durations of several tens of nanoseconds can affect intracellular signal transduction and intracellular structures with plasma intact, resulting in an application of intracellular manipulation. The most recent development is the finding that parameters between those two ranges could be used to induce apoptosis of cancer cells. Proposal of apoptosis induction and tumor inhibition has advantages to pursue the treatment of cancer free of cytotoxic drugs.

A novel lightning current monitoring system based on the differential-integral loop

Among the traditional lightning current monitoring systems, it is hard to ensure measuring lightning currents directly, expediently, accurately and safely at the same time. So aiming at solving the problem of measuring the lightning current on the overhead transmission lines, it is necessary to create a novel lightning current monitoring system based on the differential-integral loop which has been widely applied in the pulse power measurement technique to achieve non-contact measurement of the lightning current on the lines under the consideration of the field conditions of lines. In this paper, the method of acquiring the lightning current waveforms and the design of the novel monitoring system are introduced. In the laboratory, the results of the experiments by using the high impulse current generator to simulate the lightning currents show that: for the certain measured distance, through adjusting the sensor parameters and choosing reasonable electromagnetic shielding measures, the lightning current monitoring system can collect the data of the high impulse current accurately and completely, and the monitoring system has the advantages of safety, high EMC performance and accuracy. At last, the field photos of this lightning current monitoring system are shown, and the field data proves that it can effectively meet the requirements of the monitoring system and be very convenient to popularize widely.

Intense picosecond pulsed electric fields induce apoptosis through a mitochondrial-mediated pathway in HeLa cells

The application of pulsed electric fields (PEF) is emerging as a new technique for tumor therapy. Picosecond pulsed electric fields (psPEF) can be transferred to target deep tissue non-invasively and precisely, but the research of the biological effects of psPEF on cells is limited. Electric theory predicts that intense psPEF will target mitochondria and lead to changes in transmembrane potential, therefore, it is hypothesized that it can induce mitochondrial-mediated apoptosis. HeLa cells were exposed to psPEF in this study to investigate this hypothesis. MTT assay demonstrated that intense psPEF significantly inhibited the proliferation of HeLa cells in a dose-dependent manner. Typical characteristics of apoptosis in HeLa cells were observed, using transmission electron microscopy. Loss of mitochondrial transmembrane potential was explored using laser scanning confocal microscopy with Rhodamine-123 (Rh123) staining. Furthermore, the mitochondrial apoptotic events were also confirmed by western blot analysis for the release of cytochrome C and apoptosis-inducing factor from mitochondria into the cytosol. In addition, activation of caspase-3, caspase-9, upregulation of Bax, p53 and downregulation of Bcl-2 were observed in HeLa cells also indicating apoptosis. Taken together, these results demonstrate that intense psPEF induce cell apoptosis through a mitochondrial-mediated pathway.

Contactless measurement of lightning current using self-integrating B-dot probe

Lightning is a form of pulse power in nature. It is a serious threat to the safe operation of power grid. However, in high voltage power systems, it is almost impossible to directly measure the lightning currents accurately and safely. This paper presents a contactless lightning current sensor for transmission tower based on B-dot probe. This sensor consists of a multi-turn loop, a self-integrating resistance and a shielding. In the laboratory, the typical lightning current (8/20 μs) was simulated by a high impulse current generator. The experiment results show that: the sensor can accurately reproduce the waveform and amplitude of the current generated by the high impulse current generator, based on a specific measuring distance under reasonable design. And this sensor has the advantages of safety, strong anti-interference ability, and good linearity and accuracy.