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The epoxy resin insulation in saturable reactors in a HVDC transmission converter valve is subjected to a bipolar exponential decay pulse voltages under normal operating conditions and its aging mechanism is still unclear. In this paper, an electrothermal aging experiment of epoxy resin was carried out under bipolar exponential decay pulse voltages at high temperature. The dielectric properties of epoxy resin before and after aging were measured using frequency-domain spectroscopy. To quantitatively study the aging characteristics, the double-relaxation Cole-Cole model was used to fit the dielectric spectra. As a result, an exponential function relationship between the relaxation time constant and the aging time of epoxy resin under various aging conditions was obtained. This relationship can be used as an empirical formula to evaluate the degree of aging. Furthermore, a comparison of the aging life characteristics of epoxy resin under pulse and sinusoidal voltages with the same peak value was performed. The results show that the electrothermal aging rate of epoxy resin under a pulse voltage is lower than under a sinusoidal voltage. The effect of the measurement temperature on the insulation life evaluation of epoxy resin was also analyzed. [ABSTRACT FROM AUTHOR]

The rise/fall time of a high-voltage nanosecond pulse affects the application effect of the pulse; therefore, it is of great significance to study the adjustment of the rise/fall time. In this paper, a new type of generator topology based on a half-bridge modular multilevel converter (HB-MMC) is proposed that uses MOSFETs as solid-state switches to produce a unipolar/bipolar high-voltage nanosecond pulse with an adjustable rise/fall time. The proposed topology consists of 2 arms, each of which contains several HB-MMC submodules. The capacitors of each arm are charged with a positive voltage and negative voltage in parallel. By controlling the discharging sequence of the two arms, a unipolar or bipolar pulse can be generated. For each arm, by setting the switching sequence of the MOSFETs, the number of capacitors inserted into the discharging circuit can be controlled to allow a multilevel pulse to be generated. The rise/fall time of the output pulse can be adjusted by changing the number of levels and the duration of each level. Detailed illustrations of the proposed configuration and its operational concept are presented. Experimental results for a scaled-down prototype are presented to validate the concept. [ABSTRACT FROM AUTHOR]

This paper considers the electroporation characteristics of a cell under high-frequency nanosecond pulse bursts. A typical two-dimensional cell system, including an organelle membrane, was discretized into nodes using MATLAB, and the mesh transport network method model was established after the bidirectional coupling properties of electrical transport and pore transport were assigned to the nodes within this model. The dynamic process in single-cell electroporation under the application of 10 unipolar high-frequency nanosecond pulse bursts at 1 Hz to the target system was simulated and analyzed. The electroporation characteristics of a single pulse burst and multiple pulse bursts were evaluated. Particularly, the effect of intra-burst frequency on the average pore radius was examined. For the plasma membrane, when multiple pulses were applied, the pore number remained unchanged while the pore radius at the transition region exhibited a more obvious cumulative effect at higher intra-burst frequencies. For the organelle membrane, the number of pores significantly increased when the intra-burst frequency was high (1 MHz). Repetitive pulse bursts expanded the pore radius but do not change the pore number. The results of the present study further enrich our understanding of the electroporation mechanism of a pulsed electric field acting on biological cells. [ABSTRACT FROM AUTHOR]

Nanosecond pulsed electric fields (nsPEFs) with higher repetition frequency presents potential better clinic applicability for tumor treatment. However, the biophysical mechanisms of high-frequency multi-pulse protocols are currently unclear. In this study, a multicellular model with scale of 131 × 121 μm was used to evaluate the accumulation of pore number and pore radius with increasing numbers of pulses. This multicellular system was established based on the transport lattice model combined with the Smoluchowski equation (SE) electroporation model and solved using Pspice and Matlab. The transient and spatial responses of the system under 10 unipolar high-frequency 500 ns pulses with different field intensities (3 kV/cm, 5 kV/cm and 10 kV/cm) and different frequencies (100 kHz, 500 kHz and 1 MHz) were then analyzed. The results show that with increasing numbers of pulses, the pore number remained basically the same but its value was larger when a higher intensity field was applied. The pore evolutions were similar at different field intensities. However, pulse frequency had a significant influence on the changes of pore radius. Pore radius growth effects were more obvious with higher frequency because of its shorter pulse intervals. The results presented here provide theoretical support for mechanism of tumor treatment with high-frequency nanosecond pulses. [ABSTRACT FROM AUTHOR]

A high pulse repetition frequency (PRF) nanosecond pulse generator based on Blumlein pulse forming line (BPFL) and transmission line transformer (TLT) is proposed in this paper. The generator combines the BPFL characteristic, which is used to generate a narrow, high PRF pulse, with the excellent performance at high frequency of a transmission line transformer. A modular structure was adopted for this design. The primary pulse produced by the BPFL in each module will output to the load through the TLT amplifier; further, the output of multiple modules can be cascaded to improve the load voltage and output power. Moreover, this reduces the ratio of the output impedance and the input impedance of the TLT, making the generator more suitable for light loads. A microstrip line was used for the transmission line, which makes it possible to match random loads. Additionally, the size of generator was greatly reduced to realize a compact design. MOSFETs were used in the generator to facilitate the control of both the amplitude and PRF of the output. A two-stage laboratory prototype was fabricated to verify the performance of the proposed topology. As a result, the generator produced pulses for matched loads with amplitudes of 0?2.5 kV, pulse width of 20 ns, and repetition frequencies of 0?10 kHz. The generator can be used as a hardware foundation for research on the biomedical effects of exposure to high PRF nanosecond pulse electric fields. [ABSTRACT FROM AUTHOR]

For non-invasive treatments in the biomedical field, sub-nanosecond pulse electric field matching ultra-wideband antennas have aroused great interest for their excellent directivity and targeted treatment. Sub-nanosecond pulse generators have proved difficult to control in pulsed power technologies despite many studies of pulse generators based on avalanche transistor theory and the Marx circuit. However, no solution exists to the problems of non-ideal waveform of the output sub-nanosecond pulse and the relatively low effectiveness of the Marx circuit. To resolve these problems, the paper describes a sub-nanosecond pulse generator simulation model based on gradient transmission line theory in PSPICE simulation software and the development of a compact solid-state sub-nanosecond pulse generator (18 cm?18 cm?4 cm). From experimental tests, trigger signals of 5-V amplitude, 5-ns rise and fall times (pulse-width 10 ns-50 ns) were generated by Field-Programmable Gate Array (FPGA). A pulse with 1600-V voltage amplitude, 300-ps full width at half maximum, 150-ps rise time, and 10-kHz high-stability repetition rate was generated in an attenuator load with high-bandwidth (8 GHz, 50 ?). The effectiveness (Output pulse voltage amplitude / Charge voltage ? Stages) of this Marx circuit reached to 41.7%, improving considerably on previous efforts. [ABSTRACT FROM AUTHOR]

Applying high-frequency pulses to animals for tissue ablation can reduce the number and intensity of muscle contractions. Hence, developing a composite pulse generator is necessary to investigate the mechanism of tumor ablation under high-frequency composite pulses. In this study, a high-frequency and high-voltage composite pulse generator is proposed for such application. This generator combines the technology of full-bridge soft-switching circuit, MOSFET series, and RCD equalization circuit. This generator has the capability of producing composite pulses, in which the center frequencies of the bursts are up to 2 MHz, the inter-burst delay is 0.1?10 s, the pulse width is from 100 ns to 100 μs, the pulse amplitude is ±3 kV, and the rise time is around 30 ns. The parameters satisfy the requirements of the experiments for studying muscle contraction under high-frequency pulses and tumor ablation. The details of the generator?s production of high-frequency composite pulses are provided. An all-solid-state modular design makes the generator compact and reliable. Initial experiments are then conducted to verify the performances of the proposed generator. [ABSTRACT FROM PUBLISHER]

Lightning current has abundant parameter information, including waveform, rise time, and peak value, which are the foundation of lightning protection research. However, the measured data are usually affected by multi-shunt and multi-reflection; hence, they cannot be utilized directly in lightning protection. Therefore, establishing an inversion method to obtain the original lightning current waveform at the lightning strike point through the use of measured data is necessary. In this paper, the lightning current monitoring system based on differential-integral loop is briefly explained first. Second, to explore the inversion method, the simulation model introduced by Electromagnetic Transients Program-Alternative Transients Program software, including the corona model, is established. Third, the full-waveform inversion method, including its waveform inversion and peak value inversion parts, is presented. Finally, the inversion method is applied to invert two simulated lightning current examples to test the method's effectiveness. Comparison results show that this preliminary full-waveform inversion of lightning current is feasible. [ABSTRACT FROM PUBLISHER]

Direct lightning strike is one major cause of transmission line outage. A study on identification of direct lightning strike faults is beneficial for efficient and relevant repair, which is meaningful to lightning protection. In this paper, the reason for focusing on the lightning current of phase wires at the observation points is briefly explained first. Second, the simulation model by Alternative Transients Program- Electromagnetic Transients Program software (ATP-EMTP software), including the corona model, is established and its validity is proved. Third, the characteristic quantities based on Mahalanobis distance and S-Transform are deduced and presented, respectively. The accuracy rate of this identification method using simulation data is then obtained. Finally, to test its effectiveness, the identification method is applied to identify three actual lightning current examples. And the results from this identification method are reasonable and verifiable by time-domain characteristics from literature and the data acquired by Lightning Location System. This identification method is built on the measurement of the lightning current monitoring system based on differential-integral loop. In addition, this method is applicable to the identification of lightning current on phase wires. [ABSTRACT FROM PUBLISHER]

The measurement of lightning current plays an important role in the identification of lightning strikes fault and location. However, measuring the lightning current directly, accurately, and safely is difficult. This paper presents an improved contactless measuring method by using a differential loop made of a printed circuit board with a numerical integral program. This differential loop is used to obtain the differential signals of the measured lightning current and consists of a planar circular spiral coil, a coaxial fitting, and an aluminous shielding shell. MATLAB numerical integral program is used to integrate the differential signal to reproduce lightning-current waveforms. Measurement theory, equivalent circuit, frequency analysis, and design of this improved contactless measurement are described. In the laboratory, experiments with three types of impact currents (24/42, 8/20, and 7/20 μs) were adopted to calibrate this improved measurement compared with Pearson coil. The results of the experiments show the following: 1) for a certain measuring distance, the differential loop with a numerical integral program can reproduce the waveform of 24/42, 8/20, and 7/20 ?s accurately and completely under an appropriate design; 2) the differential loop retains the advantages of safety, strong anti-interference ability, good linearity and accuracy compared with the differential-integral loop; 3) the improved measurement facilitates the easy unification of stray parameters and breaks the contradiction between sensitivity and low cut-off frequency, which is beneficial in acquiring lightning-current waveforms with low amplitudes. [ABSTRACT FROM PUBLISHER]

Lightning flashes on high voltage transmission lines are quite common and often lead to insulation breakdown which can cause outages in supply. The traditional way to locate the lightning fault on the line artificially is time-consuming. An accurate lightning location will result in faster maintenance and restoration of supply. In this paper, a novel distributed lightning fault location method for transmission line mainly for the shielding failure is proposed based on the non-contact lightning current monitoring system. First of all, according to the transient current wave polarity differences of three phases, the types of lightning are recognized, such as shielding failure, lightning striking the tower and striking the ground wire. Secondly, for the shielding failure, whether the flashover occurs or not is judged based on the timewindow energy ratio of the traveling wave. Thirdly, the lightning striking range in which interval of the line is determined by comparing the signals from all the detection points. Furthermore, the sides of lightning and flashover are distinguished. At last, combing the travelling wave method and wavelet packet transform (WPT), the arrival time of wave head is extracted. The specific locations of lightning and flashover are both calculated by using the signals from the two nearest detection points. By using EMTP-ATP software, a model of lightning striking at different points on a 110 kV transmission line with five detection points is established. The simulation results indicate that the proposed scheme is very effective in locating the lightning on the transmission line with reasonable accuracy, which has important application value. [ABSTRACT FROM AUTHOR]

The design of a spherical coil system for pulsed magnetic field (PMF) exposure is presented for in vivo experiments with tumor-bearing animals. The system has greater focusing capability than conventional systems and has advantages in terms of effectiveness and safety. In the simulation part of the study, the magnetic field distribution of two spherical coil systems were studied using a finite element code, where the influences of coil radius and wire diameter were analyzed to optimize the final design. The simulation results indicate that the coil radius has significant effects on the magnetic field distribution, while the effect of wire diameter is negligible. Based on the designed parameters, a coil system was then developed and the magnetic field focusing ability of the system was measured and evaluated. The coil system has a better focusing performance with the central magnetic induction Bm of 1.3×10-4 T and S80% of 2.8×10-3 m2. The spherical coil system contributes to the system's focusing ability, which is expected to help in experiments for tumor treatment in the near future. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 current?s 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. [ABSTRACT FROM AUTHOR]

Tumor cell apoptosis by using nanosecond pulsed electric fields (nsPEF) has a great potential in clinical tumor treatment. It is difficult to find the appropriate parameters of nsPEF which can induce substantial apoptotic tumor cells because of selectivity between apoptosis and parameters of pulse number and pulse duration. To obtain the optimum parameters of nsPEF which can achieve large proportion of apoptotic tumor cells, nsPEF with different parameters (Electric field intensity of 45 kV/cm; pulse durations are 50, 100 and 200 ns respectively; pulse numbers are 10, 30, 60 and 80, respectively; repetition frequency of 1 Hz) were performed on SKOV3 cells. The experimental results of both Annexin-V/PI staining and DNA ladder gel electrophoresis indicated that apoptosis of tumor cells was pulse duration and number-dependent. With constant electric field intensity of 45 kV/cm, nsPEF of 100 ns duration and 30 pulses caused substantial tumor cell apoptosis with few necrotic cells and maximum caspase-3 activation. [ABSTRACT FROM AUTHOR]

In order to research a new tumor treatment method using exponential decay pulsed magnetic fields (EDPMF), we developed a EDPMF generator by means of the integration of pulsed power technology and modern power electronics technology. After charging a capacitor with a high voltage dc power supply, EDPMF was generated inside the Helmholtz coils by means of discharging the capacitor through a switch to the discharge resistor. After a brief introduction of basic principle of EDPMF generator, steep pulse formation circuit and Helmholtz coils, two main parts of EDPMF generator, were discussed in detail, especially on design techniques. A height-adjustable platform was designed inside the Helmholtz coils. Cell solution and little animals could be treated on this platform. The peak value, width and repeat rate of the output EDPMF waveform could be adjusted independently in the range of 0 ? 1 mT, 160 ns - 55 μs and 1 Hz ? 1 kHz, respectively. The rise time of the output EDPMF waveform was shortened to 70-220 ns by means of choosing quickly operating switch and reducing circuit stray inductance. Magnetic field distribution uniformity was improved via designing better geometrical structure of Helmholtz coils. This was proved by finite element simulation and measurement. Cell experiment in vitro was performed by exposing human liver cancer cells (Hep-G2) to pulsed magnetic field (0.8 mT, 55 μs, 15 Hz) using this generator and the result showed that proliferation of cancer cells in treated group was significantly (P<0.01) inhibited. This suggests possible clinical application using this kind of EDPMF for local tumor treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]