To reduce the induction voltage in the metal sheath, cross-bonded grounding is a widely adopted method in long-distance high voltage power cables, but this introduces challenges to the online monitoring and diagnosis of cable insulation. An online monitoring and diagnosis method for cable insulation based on the analysis of resistive current is proposed in this paper. A theoretical formula for the separation between leakage current and sheath current was derived, and a theoretical formula for the separation between resistive current and leakage current was obtained. An equivalent circuit of a three-phase long distance cable was established using the MATLAB/Simulink platform. The simulation was used to model three typical faults: cable insulation deterioration, open sheath circuit faults, and the sheath breakdown of intermediate joint faults. The results show that the method can be used to monitor each cable’s insulation state under metal sheath cross-bonded, and it also can determine the open sheath circuit faults and fault joint location using the measured current values by the corresponding current sensors increases significantly. Based on the analyses, diagnostic criteria are established for different types of cable faults and fault locations.

Traditional thermal sterilization technology is easy to implement and safe, but it will destroy food nutrition and change food taste. Therefore, people began to turn their attention to non-thermal sterilization. High-voltage pulsed electric field sterilization technology is one of them; it has attracted much attention because of its high efficiency and little damage to food. Different types of loads will cause serious trailing of the pulse falling edge. In view of this situation, this paper proposes a new topology circuit that combines a solid-state switch with a half-bridge Marx generator. It can be used for high-voltage pulsed electric field sterilization. By improving the structure of the classical Marx circuit, the high-voltage pulse power supply of the new topology circuit has the characteristics of steep rising edge and short falling edge delay; does not require isolation inductance or isolation resistance, which solves the isolation problem between the DC charging power supply and the high-voltage terminal; and has a good voltage-clamping function and load adaptability. The working process of the topology circuit under resistive, capacitive and inductive loads and the voltage clamping effect when the solid-state switch does not work properly in the discharge process are analyzed in detail. The power supply is composed of an adjustable DC power supply, five-stage half-bridge Marx generator and control protection circuit. A field programmable gate array (FPGA) is used as the controller to generate control signals, and optical fiber isolation is used to provide control signals for the main loop. The power supply can output a high-voltage square wave pulse with a voltage amplitude of 10 kV, maximum pulse number of 1000 per second, maximum pulse width of 20 μs, pulse rise time of smaller than 300 ns and short pulse drop time, and the repeated voltage amplitude, frequency and pulse width are adjustable, which can meet the requirements of a high-voltage pulse sterilization experiment.

Applying organic coating is an important and effective approach for the protection of metal from corrosion. Weathering degradation and under-film corrosion are the two major important factors that cause the failure of organic coatings. In this work, the degradation investigation of two epoxy coatings (clear and pigmented coatings) was carried out under the dry–wet circulation of three different water fog solutions (deionized water, 0.5 wt% NaCl, 0.05 wt% NaCl + 0.35 wt% (NH₄)₂SO₄) in 35 days. The apparent performance (pull-off adhesion and surface potentials) and electrochemical features [electrochemical noise and electrochemical impedance spectroscopy (EIS)] of the coating samples were monitored after dry–wet fog exposure. In our three accelerating systems of the fog atmosphere, the time that the detectable defects appeared on the surface of coating samples was far ahead in the mixed salt solution than that in the deionized water or 0.5 wt% NaCl solution. For a defective or damaged coating surface, the derived results by using the standard deviation method (SDM) or Fourier power spectrum (FPS) were rather higher than those obtained from EIS as a whole, while for the same coating, the degradation trend with time derived from EIS, SDM, FPS, and scanning Kelvin probe was consistent with each other.

In this article, an air discharge experimental platform is built and an air streamer discharge simulation model is constructed. The uniform electric field air streamer discharge at low temperature and subatmospheric pressure is studied. The result shows that the distributions of electron density, positive ion density, electric field, space charge density, and photoionization rate are basically consistent with those under standard conditions. The captured discharge shape is basically consistent with the simulation results, but the simulated propagation velocity is slightly higher than the actual propagation velocity. The streamer radius is positively correlated with the streamer propagation velocity and negatively correlated with the space charge density. The trend of the actual current waveform is basically consistent with the simulation current waveform, but the actual current peak is slightly smaller than the simulation current peak.

To overcome the degradation of insulating properties caused by the water tree aging of cross-linked polyethylene (XLPE), a self-repairing material for XLPE based on a microcapsule system is proposed. Three-layer shell nucleus microcapsules/XLPE composites with different microcapsule doping content are prepared. The water tree aging experiments are carried out using the water-needle electrode method to analyze the ability of microcapsules to repair the damaged areas of water trees. The results show that, compared with the XLPE material without microcapsules, the electrical properties of composites decline significantly when the doping concentration of three-layer shell nucleus microcapsules is large. When the doping concentration is 1.0 wt%, the microcapsule/XLPE composite breakdown strength has no noticeable change, and the dielectric loss factor does not change significantly, the space charge density decreases, and the space charge properties have been improved considerably. When the water tree branch develops to the position where the microcapsules are located, the microcapsules will rupture and release their internal repair materials and catalysts and react with water to produce an organic silicone resin to fill the water tree cavity, which can achieve an excellent self-healing effect. In addition, the nano-SiO₂ on the surface microcapsules can make the microcapsules and matrix better integrated, which avoids the microcapsule accumulation that tends to occur when incorporating microcapsules, thus improving the repair rate.

Based on the plasma-modified model and photoionization optimization model, this article constructs a low temperature and subatmospheric pressure air surface dielectric barrier discharge (SDBD) model with 37 plasma chemical reactions composed of 18 particles. Through the model, the characteristics of air SDBD at low temperature and subatmospheric pressure are studied. Under a dc voltage of 12 kV, with the propagation of the streamer, the parameters, such as electron density, N₂⁺ density, N₂(C) density, O₂⁻ density, electron temperature, space charge density, electric field, and photoionization rate, show a downward trend at an altitude of 11,000 m but always maintain N₂(C) density > electron density > N₂⁺ density > O₂⁻ density. In addition, the propagation velocity of streamer along the surface is positively correlated with altitude. Electron, N₂⁺, N₂(C), and O₂⁻ density are negatively correlated with altitude. Photoionization rate is positively correlated with the altitude in the streamer development stage. In the streamer propagation stage, except for the sudden drop at the altitude of 11,000 m, it is basically consistent at other altitudes.