Influence of N2 pressure on surface discharge characteristics of PEEK under positive repetitive square voltage

The micron metal particles are inevitably produced in long-term operation condition of high voltage direct current SF6 insulated apparatus, which could frequently cause the surface discharge. Degradation of long-term surface discharge will be a severe threat to the insulation strength. Aiming at this problem, the surface charge accumulation and flashover voltage of epoxy itself before and after discharge degradation by particles were compared in this paper. The composition after degradation was measured by EDS and FTIR. The microstructure was observed by SEM. The roughness was measured as well. The trap distribution was measured by SPD. The mechanism of degradation and its effect on insulation characteristics were analyzed. The results show that the surface charge accumulation increase three times after degradation. Additionally, flashover voltage decreases 19% after degradation. The smoothly surface after degradation decrease the trap energy level for 14%, which might be the change reason of surface charge accumulation and flashover voltage. This paper can offer as a reference for the effect of micron metal particles on insulation degradation in SF6 gas insulated equipment.

Insulation degradation affected by micron metal particles attached on epoxy surface: charge accumulation and flashover voltage

Streamer-to-precursor transition in N2–SF6 mixtures under positive repetitive submicrosecond pulses

The working voltage of the high-voltage high-power electronic devices is the positive periodic square waveform (PPSW) voltage, which is much different from the conventional AC or DC voltage. For the composite insulation structure of devices, it is important to analyse the transient electric field under the PPSW voltage. However, the existing investigations are often conducted under the electrostatic field due to the high frequency of the PPSW voltage. Thus, the transient characteristics of the electric field are missed. To obtain some qualitative conclusions, this paper focusses on the theoretical analysis of the transient characteristics of electric field for the composite insulation structure under the PPSW voltage. First, the formula of the electric field intensity and the interfacial charge density are derived analytically. Second, the influence of the cycle and the duty cycle on the transient characteristics are investigated. Third, the maximum of the electric field intensity and the interfacial charge density in the positive square waveform steady-state are discussed in detail. Besides, the engineering calculation methods for obtaining these maximum values are also suggested. Lastly, an actual model is employed to testify the validity of the analytical analysis. This work is significant for the numerical calculation of the transient electric field of composite insulation structure under the PPSW voltage in engineering. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1049/hve2.12203

Transient electric field of the combined insulation structure under positive periodic square waveform voltage: Analytical analysis and application

DC wall bushing is one of the key equipment in high-voltage direct current (HVDC) transmission project. At present, post insulators based on epoxy composites are widely used for supporting insulation in SF6-insulated apparatus. However, the flashover faults caused by surface charge accumulation can be a severe threat to the long-term operation of the post insulators under dc field. Therefore, the issue of charge accumulation on epoxy post insulators in HVDC wall bushing and its effect on flashover has been widely concerned. Aiming at this problem, the flashover characteristics of epoxy samples in SF6 gas under polarity reversal conditions with dc voltage prestressed for 10–600 min were measured in this article. The flashover process is analyzed through surface charge distribution measurement and electric field computation. The results show that with the increase of prestressed time, the accumulated negative charge density could reach $-14.8\,\,\mu \text{C}/\text{m}^{{2}}$ , which led to a 12% increase in maximum field strength. As a result, the polarity reversal flashover voltage could decrease by 12% and the flashover time delay could decrease by 84.6%. This article can offer as a reference for the effect of surface charge accumulation on flashover in SF6 gas-insulated equipment.

Effect of Different DC Prestressed Time on Flashover Characteristics of Epoxy Resin Under Polarity Reversal Voltage

In this study, the surface discharge current pulses of polyetheretherketone (PEEK) material under positive repetitive square voltage in a nitrogen atmosphere are measured. The influences of different voltage amplitudes and frequencies on the detail parameters of forward discharge and backward discharge current pulses are statistically analysed. The results show that as the square voltage amplitude increases, the current pulse amplitude, fall time and pulse width of both forward and backward discharge current increase, and the rise time does not change significantly. As the voltage frequency increases, current pulse amplitude, fall time and pulse width of both forward and backward discharge current decrease, and the rise time does not change significantly. Due to the independence of the discharge at different repetitive cycles, the specific discharge process in one cycle is analysed in detail to explain the influence mechanism of the voltage amplitude and frequency on the discharge current. By mean of the Richardson–Schottky and the Cavallini relaxation model, the relationship between discharge voltage ratio and surface charge, and the decay process of surface discharge are analysed. Furthermore, the influences of amplitude and frequency of the positive repetitive square voltage on the PEEK surface current pulses are explained qualitatively.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/hve.2019.0292

Influence of frequency on the surface discharge characteristics of PEEK under positive repetitive square voltage

Solar energy is used in buildings worldwide. However, because the efficiency of photovoltaic power generation varies with environmental fluctuations, it is difficult to control. Therefore, electricity generation from photovoltaics is often poorly matched to the electricity load of the house. The use of storage batteries and photovoltaic panels can effectively improve the stability of the energy supply; however, it also introduces the problem of higher initial costs. Generally, a larger photovoltaic area and battery capacity can lead to higher costs and more renewable energy; therefore, to determine a suitable size of photovoltaic and storage battery for a house, the energy demand of the house must also be considered. The traditional method for sizing photovoltaics and storage batteries mainly considers the daily average electricity demand and the useful area for installing photovoltaics. To size the photovoltaic in a more precise manner, we propose a mathematical model (nonlinear programming) for selecting a relatively optimal solution for the photovoltaic area, battery capacity, and photovoltaic installation angle by considering the hourly and annual demands for electricity from the grid. To validate this mathematical method, a detached house in Zhouzhi county, Shaanxi province, China, was selected to size the devices by the proposed method. Results show that the device sizes determined using the proposed mathematical model are significantly smaller than those determined using the traditional method, without suffering a significant increase in the demand for electricity from the grid. According to our economic analysis, although the proposed method for sizing devices reduces the device cost payback period by half compared to that of the traditional method, the payback period for the devices sized using the proposed method is still 10.6 years. The extremely low electricity price in China may contribute to the extended payback period and thus discourage residents from installing renewable energy devices.

Development of a Mathematical Model to Size the Photovoltaic and Storage Battery Based on the Energy Demand Pattern of the House

Tunable structures and magnetic / optical properties of six Cd(II)-based coordination polymers by introducing different para- or dia-magnetic metal ions

Two novel 3D Zn(II)/Cd(II) MOFs with tri- or di-nuclear cluster units for multifunctional sensing applications in aqueous media

The high levels of energy consumption commonly seen today have severe consequences. For example, energy consumption in buildings traditionally takes the form of electricity generated from fossil fuels, which causes serious air pollution. Hence, the efficient application of clean energy systems in buildings is crucial. An increasing number of small-scale apartment buildings, such as single-room apartments and dormitories, have emerged as modern culture, and societal trends have led to a greater number of people living on their own. In this study, two strategies were proposed to improve the efficiency of solid oxide fuel cell co-generation systems (SOFC–CGSs) in small-scale apartments. A small-scale apartment building in Busan, Korea, was selected as the research object to verify the effect of the proposed strategies. One strategy was sharing a single SOFC–CGS among multiple households, and the other was integrating an SOFC–CGS with a photovoltaic (PV) system. The efficiency of the SOFC–CGS is expected to improve under these two operational strategies. In addition, the two proposed operational strategies were combined to improve the efficiency of the SOFC–CGS. To verify the proposed strategies, various simulations were conducted in this study. The simulation results indicate that each of the proposed strategies can improve the efficiency of the SOFC–CGS and save energy to varying degrees.

https://www.frontiersin.org/articles/10.3389/fenrg.2022.788097/pdf

Bin Zhai

Papers

Influence of frequency on the surface discharge characteristics of PEEK under positive repetitive square voltage

Development of a Mathematical Model to Size the Photovoltaic and Storage Battery Based on the Energy Demand Pattern of the House

Tunable structures and magnetic / optical properties of six Cd(II)-based coordination polymers by introducing different para- or dia-magnetic metal ions

Two novel 3D Zn(II)/Cd(II) MOFs with tri- or di-nuclear cluster units for multifunctional sensing applications in aqueous media

Proposing Strategies for Efficiency Improvement by Using a Residential Solid Oxide Fuel Cell Co-Generation System in a Small-Scale Apartment Building