A grounding grid is essential to the lightning protection of power systems. This paper presents a modified partial element equivalent circuit method for predicting the transient behavior of the grounding grid. The frequency-dependent parameters of the grounding grid are obtained first by using the image method. Both modified nodal formulation and vector fitting techniques are applied to derive an extended equivalent network for time-domain simulation. In this method, the soil ionization effect is considered using a nonlinear resistance. The proposed method is verified with experimental results available in the literature. Finally, lightning transients in the grounding grid of a radio base station is presented. The ionization and propagation effects on grounding grid performance are discussed.

This paper addresses lightning surges on the transmission systems with a new hybrid method, using a 1D FDTD model for the transmission line and a PEEC model for the tower and lightning channel. Compared with other circuit-based models, mutual coupling between the lightning channel and other parts in the system can be fully considered. This hybrid method has been validated numerically and experimentally, and good agreements are observed. This method then is applied to analyze the lightning surges on a 500 kV double-circuit transmission line system. It is found that the lightning channel has a significant impact on the surge response of the tower struck. Ignoring the coupling from the channel to the tower will weaken the hazard of lightning strikes. However, the influence of its coupling to the transmission line is not critical. The choice of interfacing points between these two models is then suggested. Furthermore, the influence of the tower footing is inves tigated. It is found that the insulator voltage is made of inductive and resistive components. The inductive component becomes dominant in the case of high soil conductivity and low grounding resistance. The voltage generally increases with decreasing soil conductivity and tends to decay slowly with time.

Improving the accuracy of transformer dissolved gas analysis is always an important demand for power companies. However, the requirement for large numbers of fault samples becomes an obstacle to this demand. This article creatively uses a large number of health data, which is much easier to obtain by power companies, to improve diagnosis accuracy. Comprehensive investigations from the view of both data set and methodology to deal with this problem are presented. A data set consists of 9595 health samples and 993 fault samples is used for analysis. The characteristics of the data set and the influence of the health data on diagnostic accuracy are discussed. The performance of many state‐of‐art algorithms that handle the imbalanced problem is evaluated. Meanwhile, an efficient fault diagnosis algorithm named self‐paced ensemble (SPE) is presented. In SPE, classification hardness is proposed to include the data characteristic in the classification. This method can guarantee the diversity of the data set and keep high performance. According to the experiment results, the superior of SPE is confirmed and also proves that involving more health samples can improve transformer diagnosis when fault data are limited.

This paper presents an assessment of lightning protection schemes for overhead lines from two aspects: protection performance and economic cost. Considering the random nature of lightning, the Monte-Carlo method with a heuristic technique is applied in the assessment. The one-dimensional finite-difference time-domain method is adopted to evaluate lightning overvoltages on insulators and lightning currents in surge arresters for failure assessment. The failure rate of an overhead line is addressed under both direct lightning and indirect lightning. A reduced set of design parameters are identified. It is found that the line insulation itself with a critical flashover overvoltage of less than 200 kV is not sufficient for lightning protection, especially against direct strokes. With other protection options, however, increasing the insulation level can greatly improve the protection performance. Installing surge arresters on every pole results in the best protection performance, but could be extremely expensive due to the replacement of failed surge arresters. The shielding wire provides moderate protection performance with a relatively low cost. The combination of the shielding wire and surge arresters provides much better performance under a wide range of soil conductivity with a moderate cost. It is worth mentioning that adopting high insulation strength for overhead lines in the new-line design could lead to significant cost savings for lightning protection. Guidelines for selecting design parameter values and protection schemes are provided, as well as a procedure for performance-cost evaluation.

Photovoltaic (PV) systems are susceptible to lightning strikes. During a lightning strike, an induced overvoltage is generated in the PV system. This overvoltage can damage the inverters connected to the dc cables. In this article, a comprehensive study is presented to address the installation issues that will influence the induced voltage between the +dc and –dc cables in the PV system. By using the partial element equivalent circuit method, the skin effect and ferromagnetic property of the mounting structures are well modeled. The wiring in the PV module is also considered in the simulation. The influences of the mounting systems, lightning protection systems, PV frames, and dc cable arrangements are thoroughly investigated. The simulation results and discussions provide guidance for PV structure design for maximizing lightning protection performance without adding additional protective devices.