Accurate calculation of short-circuit (SC) dynamic characteristics of power transformer windings is of great significance to the safety of transformers. A 110 kV power transformer model is established, and SC electromagnetic characteristics and dynamic characteristics of the transformer windings are obtained through magnetic-structural coupling analysis by the finite-element method, considering the nonlinear mechanical characteristics of spacers. The distribution of leakage magnetic field and electromagnetic force (EF) and dynamic stress and displacement of windings are calculated due to SC fault. The SC EF of windings decreases exponentially with time. The axial EF of the disks at both ends of the winding is larger, while the radial EF is smaller, compared with that of central disks. The variation law of winding stress and displacement is similar to dynamic EF. The stress and displacement at both ends of the winding are larger while that in the middle part is smaller. The maximum stress and displacement of the end of windings are nearly 60% and 90% higher than that of the middle part, respectively. The axial displacement is the major part of the total displacement. The analysis method can provide a reference for checking the SC strength of the transformer.

A four-stage fast linear transformer driver (LTD) with sharing shell was constructed as a fundamental component of China's next-generation Z-pinch driver CZ34. Separate metal rods replaced conventional independent cavity shells for the ease of installation and maintenance. SF6 was utilized for the first time as insulating medium instead of transformer oil. To investigate the electrical performance of the LTD module, a 3-D full-scale electromagnetic model was developed by field-circuit co-simulation method in Computer Simulation Technology Studio Suite. Fundamental discharging brick was modeled as a conductive current path in 3-D model, excitation was employed through exterior circuits coupled to the field model. The applicability of the simulation model was validated by primary experiments. Compared to circuit simulation, the field-circuit co-simulation modeled the impedances of transmission lines and load impedance accurately since specific structures were included. Annular liquid resistor in experiment configurations brought in extra load inductance, which influenced greatly on output voltage fluctuations in each stage due to the mismatch of load impedance. Simulation results were in good agreement with experiments, except that the switch performances were not entirely up to expectations. It was indicated that several switches showed notable delays according to calculations, leading to voltage and current loss in measurements.

In this paper, a low kilo-volt-ampere rating zigzag connected autotransformer based 36-pulse rectifier system supplying vector controlled induction motor drives (VCIMD) is designed, modeled and simulated. Detailed design procedure and magnetic rating calculation of the proposed autotransformer and interphase reactor is studied. Moreover, the design process of the autotransformer is modified to make it suitable for retrofit applications. Simulation results confirm that the proposed 36-pulse rectifier system is able to suppress less than 35^thharmonics in the utility line current. The influence of load variation and load character is also studied to demonstrate the performance and effectiveness of the proposed 36-pulse rectifiers. A set of power quality indices at AC mains and DC link are presented to compare the performance of 6-, 24- and 36-pulse AC-DC converters.

Previous research showed that pulsed functional magnetic stimulation can activate brain tissue with optimum intensity and frequency. Conventional stimulation coils are always set as a figure-8 type or Helmholtz. However, the magnetic fields generated by these coils are uniform around the target, and their magnetic stimulation performance still needs improvement. In this paper, a novel type of stimulation coil is proposed to shrink the irritative zone and strengthen the stimulation intensity. Furthermore, the electromagnetic field distribution is calculated and measured. Based on numerical simulations, the proposed coil is compared to traditional coil types. Moreover, the influential factors, such as the diameter and the intersection angle, are also analyzed. It was demonstrated that the proposed coil has a better performance in comparison with the figure-8 coil. Thus, this work suggests a new way to design stimulation coils for transcranial magnetic stimulation.

The aim of this contribution is the first numerical investigation on the electromagnetic (EM), thermal, and mechanical coupled fields of a newly developed single-stage fast linear transformer driver (FLTD) with 24-separate columns in the China Z-pinch driver CZ34. Considering the mutual influences of the EM, thermal, and mechanical fields during a pulsed current discharging process of the FLTD, the proposed numerical model is calculated using the field-circuit coupled time-domain finite integration technique (TD-FIT). By making reference to Tonti’s classification diagram, integral form state variables in the transient thermal field and mechanical field can be defined similar to those of the EM field. With appropriate time integration schemes, governing equations of different physical fields can be transformed to corresponding algebraic time-updating equations. The two-way interplays of the EM, thermal, and mechanical fields is performed with predefined coupling terms and time steps. The simulated results indicate that, during one current discharging process, the temperature rise is less than 1 K and the maximum deformation generated by the Lorentz force is less than 0.1 mm.