Crustal movement and land subsidence will cause tower foundation settlement, which seriously affects the safety of transmission line operation. This paper proposed a short-term failure warning method for transmission tower under land subsidence condition based on finite element method, strain monitoring and time series prediction. By simulating the stress distribution of the tower in actual foundation settlement, the weak components of the settlement tower were founded. Combined with the finite element simulation results in various conditions, the reliability of simulation results is verified, and the strain variation range of the corresponding measuring point is obtained. By installing the real-time strain monitoring system and establishing the autoregressive integrated moving average (ARIMA) time series forecast model, warning of the failure of the tower can be sounded in short time according to the strain monitoring and forecasting results. The field results show that the tower is in good condition and with no risk in short term. The method proposed by this paper is economical and easy to operate, which can be used to conduct the emergency treatment of the dangerous tower under land subsidence condition.

In order to improve the performance of a coil launcher, various cores and shells are considered in the structure design in this paper. Different geometry shapes and materials are loaded on the cores and the shells. A single-stage coaxial induction coil launcher is analyzed for simplicity based on Ansoft 2-D simulations. The conclusion can be summarized as follows. A magnetic core will improve the performance of a coil launcher greatly. Coil current and resistance loss of the system will be reduced while kinetic energy conversion rate and efficiency will be increased. A conductive core will reduce the performance because of eddy-current effect. A magnetic conductive core combines magnetization and eddy-current effect. Geometry of a core will also influence the performance of a coil launcher. In general, the greater the cross-sectional area and the length is, the better the performance. A shell takes little effect on the performance of a coil launcher, no matter what material and geometry is used. A magnetic nonconductive core with large cross-sectional area and enough length is suggested to be used in a coil launcher design. A detailed study will be presented in this paper.

The resistivity of oil impregnated paper will decrease during its aging process. This paper takes paper resistivity as an assessment index to evaluate the insulation condition of oil impregnated paper in power transformer. The feasibility of this method are discussed in two aspects: reliability and sensitivity. Iterative inversion of paper resistivity was combined with finite element simulation. Both the bisection method and Newton’s method were used as iterative methods. After the analysis and comparison, Newton’s method was selected as the first option of paper resistivity iteration for its faster convergence. In order to consider the spatial distribution characteristic of paper aging and enhance the calculation accuracy, the resistivity calculation is expanded to a multivariate iteration based on Newton’s method, in order to consider the spatial distribution characteristic of paper aging and improve the calculation accuracy. This paper presents an exploratory research on condition assessment of oil impregnated paper insulation, and provides some reference to the security and economy operation of power transformers.

The fast and accurate solution of the total electric field and ion current density is crucial for the electromagnetic environment of ultra high voltage direct current (UHVDC) transmission lines. In this article, an improved method based on Newton–Raphson method (NRM) and upstream finite element method (UFEM) is proposed to calculate the ion flow field under complex conditions. According to the gas motion theory, the corona-onset electric field, ion mobility, and recombination coefficient are obtained at high altitude and put into the ion flow field model in this article. Subsequently, the charge density is used to solve Poisson’s equation, and the current continuity equations are calculated by UFEM. After that, the charge density of the conductor surface is updated based on NRM. These three parts are iterated repeatedly until the convergence conditions are met. According to the test results of $\pm$ 800-kV UHVDC transmission line at high altitude, the validity and rationality of the proposed method are verified. The result demonstrates that due to the reduction of atmospheric pressure at the high altitude, the corona-onset electric field decreases, and the ion mobility and recombination coefficient increase, which makes the total electric field and ion current density at ground level increase. Compared with the traditional methods, the improved method is insensitive to the initial value of the surface charge density. Moreover, this proposed method can effectively improve the convergence ability and achieve the stable and fast calculation of the ion flow field at high altitude.

An experimental scale-down model of ultra high voltage direct current converter transformer is designed and manufactured to study the wave process in the winding under impulse voltage. Nine outgoing lines are configured on different winding coils of the scale-down model. The voltage waveforms of different outgoing lines are obtained by the lightning impulse voltage. The simulation model of scale-down transformer is established to calculate the distributed parameter matrices through the finite-element method. The equivalent circuit of the transformer winding is proposed to calculate the voltage waveforms and the potential gradient distribution. The comparative analysis of test and simulation results shows that the oscillating voltage occurs in the winding, and the simulation results can reflect the wave process characteristics.