With the development of intelligent sensing technology, a large amount of partial discharge (PD) time-domain waveform images are generated in the on-site detection of gas insulated switchgear (GIS) partial discharge. Traditional pattern recognition methods are mostly aimed at structured data and cannot directly identify defect types of such data.At the same time, the deep learning method for GIS PD pattern recognition is generally faced with the problem of small samples.In order to solve the above problems, this paper proposes a PD pattern recognition method based on transfer learning and DenseNet model.Firstly, the time-domain waveform images are processed by image enhancement, normalization, image compression and other image processing techniques.The FDTD method was used to simulate GIS PD, and the time domain waveform image database of four PD defects are established.Using CNN and transfer learning, the recognition accuracy of the model is increased to 95%, with better robustness.The recognition performance of different CNN structures is studied. The results show that DenseNet model has higher accuracy than other structures and shorter training time. This study can be used to diagnose the insulation status of GIS equipment in-site.

Investigations into alternative gases to reduce the usage of SF ₆ have great benefits on global warming issues and the health of maintenance personnel. C ₄ F ₇ N is one of the most remarkable replacements for SF ₆ owing to its good insulating performance, low global warming potential and non-toxicity. The decomposition mechanism of C ₄ F ₇ N is important in evaluating the insulation performance but it is still not clear. Therefore, the B3LYP/6-311G(d,p) method in conjunction with transition state theory is used to study the decomposition mechanism of C ₄ F ₇ N. Sixteen reactions are found in the decomposition pathways of C ₄ F ₇ N. The optimized configurations and harmonic vibrational frequencies of selected species are very consistent with experimental data to verify the method adopted in this paper. The potential energy surface of these reactions are obtained and the reaction mechanisms are analyzed. The rate constants over 300 K–3500 K relevant to the insulation breakdown temperature are computed based on the above quantum chemistry calculations and dominant reactions in different temperature regions are selected. For example, reaction R 5 (C ₄ F ₇ N → TS2 → FCN + CF ₂ CFCF ₃ ) is the most important reaction leading to the dissociation of C ₄ F ₇ N below 600 K, while reaction R 2 (C ₄ F ₇ N → C ₂ F ₄ CN + CF ₃ ) takes the place of reaction R 5 over 600 K to 3300 K and reaction R 3 (C ₄ F ₇ N → TS1 → CF ₂ CFCN + CF ₄ ) becomes dominant above 700 K; reaction R 15 (CF ₂ CFCNCF ₃ → CF ₂ CFCN + CF ₃ ) plays the major role in the generation of CF ₃ with the overwhelming contribution rate. The results obtained here are expected to construct a relatively complete C ₄ F ₇ N decomposition scheme, including the main byproduct formation processes and to lay a theoretical basis for the investigation of its insulation performance.

Five-carbon perfluorinated ketone (C ₅ F ₁₀ O) has been reported as a remarkable eco-efficient replacement for SF ₆ . To investigate its dielectric strength, thermodynamic properties and decomposition characteristics, accurate compositions of C ₅ F ₁₀ O discharge plasma are a prerequisite and can be studied by a chemical kinetic model considering non-equilibrium effects. Rate constants of C ₅ F ₁₀ O decomposition reactions are the basis for this model but have not been reported yet. Therefore, this paper is devoted to investigating the rate constants of C ₅ F ₁₀ O decomposition reactions at temperatures of 300–3500 K, relevant to electrical breakdown and arc-quenching in high-voltage electrical equipment. The rate constants and equilibrium constants as the function of temperature are computed using the transition state theory on the basis of energies and vibrational frequencies, calculated by the B3LYP/6-311G(d,p) method. The dominant reactions generating and/or consuming the species in C ₅ F ₁₀ O decomposition are also selected by contributions higher than 1%. The results in this paper show that (1) C ₅ F ₁₀ O decomposition reactions (except for R7) are endothermic and rate constants differ significantly between different reactions, mainly caused by activation energies; (2) at 1500 K and above, most rate constants fall in the region from 10 ⁻¹⁵ to 10 ³⁰ cm ³ mole ⁻¹ s ⁻¹ or s ⁻¹ , making it so that the corresponding reactions cannot be neglected in C ₅ F ₁₀ O plasma models; (3) reactions R5, R11, R12, R14, R29, R32, R33 and R36 mainly contribute to the degradation of the insulating and arc-quenching performance of C ₅ F ₁₀ O; (4) reaction R2 plays the major role in C ₅ F ₁₀ O dissociation with the contribution more than 72.2% at temperatures of 300–3500 K. To verify the method adopted, thermodynamic properties (entropy, enthalpy and specific heat) of CF ₂ , CF ₂ CF ₂ , CF ₃ , CF–CF ₂ and CO are compared with those from NIST-JANAF tables and a good agreement is obtained. This work is expected to provide the input data for the calculation of non-equilibrium C ₅ F ₁₀ O discharge plasma compositions employing a chemical kinetic model.

C ₄ F ₇ N is one of the promising candidates to replace SF ₆ as insulating medium in power equipment. Meanwhile, the effect of an O atom on C ₄ F ₇ N decomposition is still unclear but it greatly influences the decomposition mechanism and insulating properties of C ₄ F ₇ N. In this paper, the B3LYP method, in conjunction with 6-311G(d,p) basis set, is used to study the decomposition mechanism of C ₄ F ₇ N with an O atom. The molecular structures of reactants, products and transition states (TS) in the C ₄ F ₇ N decomposition pathway, which consists of 25 reactions, are optimized. The potential energy surface of each reaction and the vibrational frequencies of each molecule or TS are studied with same method as the prerequisite for rate constant calculations using transition state theory. The results show that the CN bond breaks with the highest energy of 321.91 kcal mol ⁻¹ , so reaction (R21) (C ₄ F ₇ NO → C ₄ F ₇ O + N) plays a less important role than (R2) (C ₄ F ₇ NO → C ₃ F ₄ NO + CF ₃ ), (R5) (C ₄ F ₇ NO → C ₃ F ₇ O + CN), (R11) (C ₄ F ₇ NO → TS1 → C ₃ F ₅ N + CF ₂ O) and (R15) (C ₄ F ₇ NO → TS2 → C ₃ F ₃ NO + CF ₄ ) in the decomposition of C ₄ F ₇ NO. CF ₂ O and CF ₄ , characteristic decomposition products of C ₄ F ₇ N + O which have negative impacts on the insulating gas, are generated in reactions (R11) and (R15) with a higher rate constant at 1500 K above, respectively. CF ₃ and F ₃ C–O are important in C ₄ F ₇ N with O decomposition because of the high overall-generation rate constants. This work is expected to provide a theoretical basis to evaluate the insulation performance of C ₄ F ₇ N-insulated power equipment and develop novel gas sensors for insulating condition monitoring.

C₄F₇N is one of the most remarkable replacements for SF₆, and its decomposition mechanism has a great influence on insulating performance and environmental properties. It is noteworthy that discharges or high temperature also evaporates metal electrodes (e.g., Cu) in the equipment, and the generated metal gases interact with C₄F₇N and thus affect the C₄F₇N decomposition mechanism, but the decomposition mechanism is still not clear. In this paper, therefore, the B3LYP method in conjunction with 6-311G(d, p) basis set (for C, N, and F atoms) and Lanl2DZ basis set (for Cu atom) combining transition state theory is used to study the decomposition mechanism of C₄F₇N-Cu mixtures. 31 reactions are determined in decomposition pathways of C₄F₇N-Cu mixtures, and their potential energy surface as well as reaction mechanisms are obtained. The rate constants over 300 K–3500 K relevant to the insulation breakdown temperature are calculated based on the above calculations, and dominant reactions in different temperature regions are selected. The results show that (R14) C₄F₇N + Cu → CF₃CFCN + CF₂CuF plays a major role in the decomposition of C₄F₇N-Cu mixtures below 1500 K, while (R1) C₄F₇N + Cu → TS_a1 → CuCN + C₃F₇ and (R21) C₄F₇N + Cu → TS_c1 → CF₃CF(CN)CF₂ + CuF are dominant above 1500 K; (R23) CF₃CF(CN)CF₂ + Cu → CF₂(Cu)C(F)CN + CF₃ is the most important reaction leading to the generation of CF₃ below 1500 K with the overwhelming rate constant, but other reactions also generating CF₃ are dominant above 1500 K.

The variation characteristics of C₅F₁₀O decomposition components at 300 K – 3500 K are studied with a chemical kinetic model considering neutral reactions. Three chemical kinetic models of SF₆ breakdown are built to verify the model adopted (model C) and the results show that ion/electron participated reactions slightly change the molar fractions, which are lower than 10^-14 with little influence on the insulating performance of SF₆. Therefore, model C is reasonable to study the varying characteristics of C₅F₁₀O decomposition components and thus the molar fractions of C₅F₁₀O decomposition products under different temperature decreasing curves and pressures are calculated. The results show that the molar fraction of C₅F₁₀O grows to approximately one as temperature declining to 1,500 K and the temperature decreasing rates have similar affects on the relaxation time of the reactions generating C₅F₁₀O. And high pressure promotes species recombining to C₅F₁₀O by increasing the molar fractions of C₅F₁₀O decomposition components. The results can be used to evaluate C₅F₁₀O insulating performance.