Multiple strokes are the main factors affecting the safe and stable operation of power equipment. As the core lightning protection equipment, arresters are also frequently thermally collapsed due to multiple strokes. This paper investigates thermal effects of polymer-housed metal-oxide surge arrester (PMOSA) under multiple strokes. The comparative experiments of PMOSA lightning impulse are carried out through multiple strokes of experiment platform, including continuous lightning stroke and multiple strokes. Furthermore, the temperature distribution of the housing surface is obtained by infrared imager for thermal effect analysis. Subsequently, some typical DC parameters are tested to explore the association of impulse aging and thermal effects of the arrester under multiple strokes. Finally, a thermal-electric coupling model (TECM) is constructed to investigate the influence of some factors on the temperature of PMOSA from the perspective of materials and structure. The research in this paper can provide a theory reference and brief data support for improving the heat dissipation performance of arresters under multiple strokes based on structural optimization design and material modification.

Using the dry-type on-board traction transformer cooled by train-induced wind is an effective way to realize the lightweight of on-board equipment. However, the existing small capacity fan cooled dry-type on-board traction transformer cannot meet the power requirements of the high-speed electric multiple unit. For the large capacity dry-type on-board traction transformer, the lack of mathematical models that can reflect the relationship between hotspot temperature and design parameters limits its development. This paper aims to propose an optimization method for large capacity dry-type on-board traction transformer. First, the user-defined function based computational fluid dynamics modelling method for dry-type on-board traction transformer is proposed and validated to accurately obtain the winding hotspot temperature. Then, the response surface models of winding hotspot temperature are firstly proposed based on the response surface methodology. Finally, the lightweight optimization of a 6.3 MVA dry-type on-board traction transformer is completed, and the influence of design parameters on the weight reduction is studied. Under the conservative optimization strategy, the total weight of dry-type on-board traction transformer is reduced to 3650.40 kg, which is reduced by 38.55% compared with the oil cooled on-board traction transformer with the same rated capacity. This paper provides an efficient and feasible method and regular guidance for the lightweight optimal design of dry-type on-board traction transformer, and the obtained response surface models can be used for the optimization of similar dry-type on-board traction transformer under different specific needs.

Multiple strokes (MS) is the primary factor leading to the failure of electrical equipment. Arrester, as the critical lightning protective instrument, its service status is directly relevant to the stability of transmission system operation. Meanwhile, MS also significantly accelerates the impulse aging of arresters and ultimately causes malfunction. This paper proposes a method to evaluate the impulse aging of arresters under MS based on frequency domain dielectric spectroscopy (FDS). Firstly, MS experiments are performed, and then the FDS parameters of arresters are measured. Subsequently, the improved Havriliak–Negami equation (IHNE) is developed to explicitly analyze the dielectric relaxation process of arresters. Additionally, an improved metaheuristic algorithm is presented to identify the parameters in IHNE based on FDS, which has significant parameter identification. Eventually, the impulse aging evaluation model is established. Simultaneously, the condition of two types of arresters (including new and used arrester in service on transmission lines) are estimated based on the evaluation method presented in this paper. The maximum absolute errors are 0.73 times and 1.2 times, respectively, fully validating the effectiveness of the presented method. The investigation of this paper can provide a direct foundation for the replacement and overhaul of line arresters.

On-board arrester (OBA) is an essential equipment of electric multiple units (EMU), and its working condition will directly affect the reliable operation of EMU. Simultaneously, owing to frequent multiple strokes (MS), OBA suffers from accelerated impulse deterioration and serious life threatening. Thus, this paper extracts the feature parameters for degraded OBA under effects of MS. Firstly, an experiment platform is established to perform the MS experiment. The DC parameters and frequency-domain dielectric spectroscopy (FDS) parameters of OBA are then measured. Subsequently, the measured data and the reliability of experimental results are discussed. Finally, microscopic feature parameters (i.e. barrier height (BH) and depletion layer width (DLW)) and dielectric feature parameters of OBA are extracted, and their effectiveness is verified (the maximum and mean of absolute relative error are merely 5.14% and 2.76%, respectively). The results demonstrate that: 1) With increasing MS aging, DLW and BH descend gradually. After 30 MS, the maximum decreases are 64.5% and 82.28%, respectively; 2) The geometric capacitance and third polarized-branch capacitance ascends exponentially with the deepening of impulse aging, while the insulation resistance and relaxation time constants drop exponentially; 3) Several microscopic and dielectric feature parameters are extracted to effectively evaluate the degradation state of OBA.

Overvoltage protection technology is critical to the safe and stable operation of power electronics equipment and power systems. In this article, based on the characteristics of lightning traveling waves, a novel lightning overvoltage protection scheme was proposed using magnetic rings (MRs) for transmission line systems (TLSs). First, the dynamic inductance of the lightning protection scheme using MRs was theoretically derived by combining the ampere loop law and the infinitesimal method. The finite-element method was then used to verify the theoretical derivation of dynamic inductance (TDDI) of the lightning protection scheme. Furthermore, the TDDI was integrated into the electromagnetic transient program, and the electromagnetic transient model (ETM) of the TLS with the lightning protection scheme was established. Subsequently, the effects of MR characteristics under the influence of various factors on the protection performance of the lightning protection scheme were investigated. Finally, the MR string in the lightning overvoltage protection scheme with optimal physical structure was used for field application. The results confirmed the feasibility of the lightning overvoltage protection scheme and ETM accuracy.

The transient grounding resistance of a grounding device may change rapidly when a power transmission line is struck by lightning. The value of the grounding resistance can affect the simulation results of lightning response in power transmission lines, which can create difficulties in lightning protection design. This paper proposes an Electro-Magnetic Transient Program (EMTP) modeling method that considers transient grounding resistance. Firstly, an initial EMTP model of the power transmission line is established. Then, the critical breakdown field strength of the soil is measured. Next, the measurement results are incorporated into a finite element simulation model of the grounding device. Finally, a particle swarm optimization (PSO) algorithm is used to fit the formula for calculating the transient grounding resistance, and it is incorporated into the initial model. Additionally, the accuracy of the proposed simulation model was validated through multiple on-site experiments, with errors within 5%, which is better than conventional modeling methods. Furthermore, based on the proposed simulation model, an analysis of different soil critical breakdown field strengths and grounding device types was conducted, and a comparison of the calculation results between this paper’s method and conventional methods was made. The research results of this paper can provide a reference for high-precision modeling of power transmission lines and guide lightning protection design.