Environmentally Friendly Compact Air-Insulated High-Voltage Substations

Derivative Probes Signal Integration Techniques for High Energy Pulses Measurements

The paper presents problems related to the processing of signals recorded with differential field probes E and H. The fundamental problem to which special attention has been paid is the result of the integration operation. Due to the presence of constant/slowly-varying components in the raw signal, there is a drift present in the outcome of integration. This line wander can be enormous. This is particularly evident if the integration is performed in a standard manner, uniformly over the entire recorded waveform. The paper contains the Authors’ proposition to segment the signal and perform the integration independently in each of the sub-regions. This approach is based on the assumption of a local mean value instead of its global character for the recorded waveform. Although this leads to more complex signal processing, it gives significantly better results as it is suppressing the deterioration drift in the integrated signal more than 400 times. The results are presented on laboratory recordings and outdoor tests. In the first case, voltage pulses with durations of about 50 ns and rise times in the range of single ns were recorded. In the second case, high-energy electromagnetic pulse signals were used. It was formed by sinusoidal waveforms packets of 3 GHz frequency with a single packet duration of 5 μs and packet repetition frequency f ≤ 300 Hz.

Dielectric Surface Flashover under Long-Term Repetitive Microsecond Pulses in Compressed Gas Environment

As a key component of a high-power microwave (HPM) system, a multi-gap gas switch (MGS) has recently developed insulation failure due to surface flashover. Although design criteria for surface insulation have been put forward, it is still not clear how the insulation in this case deteriorated under long-term repetitive microsecond pulses (RMPs). In this paper, flashover experiments under RMPs were carried out on various dielectric surfaces between parallel-plane electrodes in SF₆ and air atmospheres, respectively. Based on tests of the surface insulation lifetime (SIL), an empirical formula for SIL prediction is proposed with variations of insulator work coefficient λ, which is a more suitable parameter to characterize SIL under RMPs. Due of the accumulation effect, the relationship between E/p and pt_delay varies with the pulse repetitive frequency (PRF) and SIL recovery capability decreases with an increase in PRF and surface deterioration is exacerbated during successive flashovers. It is concluded that the flashover path plays a crucial role in surface insulation performance under RMPs due to the photoemission induced by ultraviolet (UV) radiation, signifying the necessity of reducing surface paths in future designs as well as the improvement of surface insulation.

Analysis of Metal Oxide Varistor Arresters for Protection of Multiconductor Transmission Lines Using Unconditionally-Stable Crank–Nicolson FDTD

Surge arresters may represent an efficient choice for limiting lightning surge effects, significantly reducing the outage rate of power lines. The present work firstly presents an efficient numerical approach suitable for insulation coordination studies based on an implicit Crank–Nicolson finite difference time domain method; then, the IEEE recommended surge arrester model is reviewed and implemented by means of a local implicit scheme, based on a set of non-linear equations, that are recast in a suitable form for efficient solution. The model is proven to ensure robustness and second-order accuracy. The implementation of the arrester model in the implicit Crank–Nicolson scheme represents the added value brought by the present study. Indeed, its preserved stability for larger time steps allows reducing running time by more than 60 % compared to the well-known finite difference time domain method based on the explicit leap-frog scheme. The reduced computation time allows faster repeated solutions, which need to be looked for on assessing the lightning performance (randomly changing, parameters such as peak current, rise time, tail time, location of the vertical leader channel, phase conductor voltages, footing resistance, insulator strength, etc. would need to be changed thousands of times).

Decomposition Characteristics of SF6 under Flashover Discharge on the Epoxy Resin Surface

In this paper, the flashover discharging experiment was carried out on epoxy resin surface in an SF₆ atmosphere under pin-plate electrodes, with the electrodes distance from 5 mm to 9 mm. The concentration of seven characteristic gases was detected, indicating that the concentration of SOF₂ and CF₄ was the two highest, followed by SO₂, CO₂, SO₂F₂, CS₂, and H₂S. Based on the changes in the concentration of the characteristic gases, a preliminary rule was proposed to predict the occurrence of flashover discharge on epoxy resin: When the concentration of SOF₂ reaches twice of CF₄ concentration, and the total concentration of both SOF₂ and CF₄ is much higher than that of H₂S, a possible flashover discharge on the epoxy resin surface in SF₆-infused electrical equipment occurs. Through the simulation of decomposition of epoxy resin, it has been revealed that H₂O has different generation paths that can facilitate the formation of SOF₂, finally influencing the concentration variation of the seven characteristic gases.

Thermal Decomposition Properties of Epoxy Resin in SF₆/N₂ Mixture

As a promising alternative for pure SF₆, the mixture of SF₆/N₂ appears to be more economic and environment-friendly on the premise of maintaining similar dielectric properties with pure SF₆. But less attention has been paid to the thermal properties of an SF₆/N₂ mixture, especially with insulation materials overheating happening simultaneously. In this paper, thermal decomposition properties of epoxy resin in SF₆/N₂ mixture with different SF₆ volume rates were studied, and the concentrations of characteristic decomposition components were detected based on concentrations change of some characteristic gas components such as CO₂, SO₂, H₂S, SOF₂, and CF₄. The results showed that thermal properties of 20% SF₆/N₂ (volume fraction of SF₆ is 20%) mixture has faster degradation than 40% SF₆/N₂ mixture. As ratio of SF₆ content decreases, thermal stability of the system decreases, and the decomposition process of SF₆ is exacerbated. Moreover, a mathematical model was established to determine happening of partial overheating faults on the epoxy resin surface in SF₆/N₂ mixture. Also thermal decomposition process of epoxy resin was simulated by the ReaxFF force field to reveal basic chemical reactions in terms of bond-breaking order, which further verified that CO₂ and H₂O produced during thermal decomposition of epoxy resin can intensify degradation of SF₆ dielectric property.