Electrohydraulic pulsed discharge has been widely adopted in the industrial field over the decades. The proper description of the plasma channel and the induced shock wave contributes to the development of the technology. Experiments were carried out under different voltages and conductivities. The optical pictures were captured using a high-speed camera. The radii of the plasma channel were calculated using cylindrical approximation and spherical approximation, respectively. The results of the calculation have been verified by comparing the measured and calculated radii. The shock wave intensity can be properly calculated using the piston model in the accelerated expansion phase. It provides a better understanding of energy efficiency under different breakdown voltages. In addition, the oscillation of the cavity under different water conductivities was also recorded and compared. The water conductivity has an obvious effect on the maximum volume by changing energy consumption.

Power transformers are the most expensive and important component in the power system, and may be subjected to breakdown due to mechanical and/or electrical faults. It is difficult to obtain the condition of the power transformer by only one test method, so transformer fault diagnosis based on different experimental and simulation methods is widely recommended. In this paper, the transformer winding faults diagnosis based on FEM simulation and on-site experiments is described. Based on the FEM simulation, it is necessary to analyze the effect of the winding faults on the change of the electrical parameters. The typical types of winding faults, such as axial displacement, and radial deformation, etc. are taken into consideration. Different fault degrees are investigated in the simulation analysis. Using the parameters calculated in the FEM model, an equivalent circuit of the power transformer is present in ATP/EMTP to study the performance of typical on-site experiments, such as frequency response analysis (FRA) and short-circuit impendence (SCI) test. The frequency bands, which might be treated as the diagnostic bands in the FRA, are simulated and compared. It is found that the resonances in the frequency bands of 200-250 kHz and 350-450 kHz are able to describe the situation, where the displacement percentage of the winding is varying from 0% to 9%. The SCI values under different fault severity are also obtained and compared. Therefore, the diagnosis method can directly bridge the types and degrees of the winding faults with the experiment results. The operating states of several 110 kV power transformers are tracked, and it can be found that the simulation results show a better consistency with the on-site experiment results, and the proposed diagnosis method will help to discriminate the winding faults.

The simulation of electrohydraulic shockwaves is the key technology for their application and device design. The analytical approach of underwater pulsed discharge is described using the dimensionless analysis method, which combines energy based hydrodynamic equations and the electrical differential equation describing the discharge characteristics of the circuit. A constant plasma channel impedance model based on the experimental results and an improved time-varying plasma channel impedance model based on the Braginskii equation are proposed and presented. The plasma channel impedance has a great influence on the deposited energy into the plasma channel and then affects the calculation and analysis of the shockwave propagation. The electrical characteristics and fluid physical properties are taken into consideration, and the results are compared. The application range of different impedance models is summarized, and the time-varying impedance model can provide a more accurate result in the simulation of shockwave propagation. The dimensionless analysis method, together with a time-varying impedance model, could be a useful tool for evaluation of the electrohydraulic shockwave in practical applications and applied physics research of underwater spark discharge.

In order to study the difference in energy conversion efficiency of the shockwaves induced by the expansion of the plasma channel generated by underwater metal wire explosion (MWE) and subsonic streamer breakdown discharge (SSBD), a test stand was constructed, and the experimental results were obtained based on the condition that the voltages of the two discharge modes were the same at the time of the formation of plasma channels. The results showed that the peak value of shockwaves induced by the expansion of the channel and the energy conversion efficiency of MWE were much higher than those of SSBD. The reason lies in the difference in the injected power at the formation moment of the plasma channel and the difference in the time distribution of energy deposited into channels.

Electrohydraulic shock wave (EHSW) is seemingly one of the simplest and most common products of microsecond pulsed discharge (μsPD) in water; however, its generation process remains far less clear. To study the influence of current waveforms on the generation of an EHSW, we conducted discharge current interception experiments using a bypass branch in the circuit. The current interception time Δt is properly controlled so that the discharge current through the water gap can be terminated at a chosen time. Results show that the peak pressure P_m is first linearly increasing with Δt, and then P_m reaches a stable value. The expansion of the spark channel with increasing velocities will enhance the peak pressure. This phase can be regarded as the accelerated expansion phase (AEP) of the piston theory. The transition area of the P_m–Δt relationship of this experimental setup shows that the AEP lasts for about t_m = 5 μs. After the AEP, the deposited energy will help to maintain a higher pressure in the falling edge of the pressure waves. The full width at half maximum of the waveforms finally approaches 12.5 μs in our tests. The experimental results provide evidence of the piston theory in interpreting the generation of EHSW induced by μsPD.