The accurate identification of the oil-paper insulation state of a transformer is crucial for most maintenance strategies.This paper presents a multi-feature comprehensive evaluation model based on combination weighti...The accurate identification of the oil-paper insulation state of a transformer is crucial for most maintenance strategies.This paper presents a multi-feature comprehensive evaluation model based on combination weighting and an improved technique for order of preference by similarity to ideal solution(TOPSIS)method to perform an objective and scientific evaluation of the transformer oil-paper insulation state.Firstly,multiple aging features are extracted from the recovery voltage polarization spectrum and the extended Debye equivalent circuit owing to the limitations of using a single feature for evaluation.A standard evaluation index system is then established by using the collected time-domain dielectric spectrum data.Secondly,this study implements the per-unit value concept to integrate the dimension of the index matrix and calculates the objective weight by using the random forest algorithm.Furthermore,it combines the weighting model to overcome the drawbacks of the single weighting method by using the indicators and considering the subjective experience of experts and the random forest algorithm.Lastly,the enhanced TOPSIS approach is used to determine the insulation quality of an oil-paper transformer.A verification example demonstrates that the evaluation model developed in this study can efficiently and accurately diagnose the insulation status of transformers.Essentially,this study presents a novel approach for the assessment of transformer oil-paper insulation.展开更多
As an important component of oil-immersed transformers,the bushing's internal insu-lation ageing and dampness after the long-term operation can cause changes in the in-ternal electric and temperature fields,seriou...As an important component of oil-immersed transformers,the bushing's internal insu-lation ageing and dampness after the long-term operation can cause changes in the in-ternal electric and temperature fields,seriously threatening its safe operation.This paper tested the power frequency permittivity and direct current conductivity of aged and damp oil-paper insulation samples at different testing temperatures,and constructed a dynamic dielectric parameter calculation model.Meanwhile,a simulation model was established based on the actual structure of the 252 kV/1250 A bushing which is mainly used for the oil-immersed high-voltage bushings of 110 kV and above.The electric-magnetic-thermal multi-physical fields were used for simulation analysis.The influence of ageing/moisture(different degrees of dampness in the upper and lower regions)on the electric field distribution in the bushing was obtained.During the initial to steady-state process,the electric field distribution at the zero and end shield shows a reversal phenomenon.When the capacitor core has different degrees of dampness in the upper and lower regions,the impedance distribution of the capacitor core is non-uniform.This phenomenon will lead to an increase in the radial electric field gradient at the end shield of the capacitor core,which is prone to the risk of slip-flashing discharge.In summary,this paper adopts the field-induced dynamic parameters method to analyse the changes of multi-physical fields in the bushing.This can provide theoretical guidance for optimising the bushing structure and on-site maintenance.展开更多
The±200 kV direct current(DC)cables of the Zhoushan Transmission Project were targeted,and crosslinked polyethylene(XLPE)insulation samples were prepared from faulty and spare cables.Samples were tested for oxida...The±200 kV direct current(DC)cables of the Zhoushan Transmission Project were targeted,and crosslinked polyethylene(XLPE)insulation samples were prepared from faulty and spare cables.Samples were tested for oxidation induction period,Fourier transform infrared spectroscopy,differential scanning calorimetry,thermally stimulated depolarisation current,space charge and DC dielectric strength.The evolution of performance parameters was analysed,and the insulation ageing characteristics of onsite operating DC cables were deduced.The results show that compared with spare cables,the carbonyl index of operating cables decreases,the crystallinity increases and DC dielectric strength increases slightly.It is inferred being related to the reduced content of antioxidants and crosslinking by-products and improved molecular chain and crystal microstructure of XLPE insulation.It is suggested that the insulation ageing of high voltage DC XLPE cable is divided into two stages.In the early stage,the secondary crosslinking and recrystallisation processes are dominant,and the thermal and electric effects make the material properties basically stable or even slightly improved.In the middle and later stage,the thermal oxygen reaction is dominant,the microstructure of the material is destroyed,with a large number of macromolecular chains broken and some crystalline regions transformed into amorphous ones,and the insulation properties degraded significantly.展开更多
基金supported by the Natural Science Foundation of the Fujian Province(2021J01109).
文摘The accurate identification of the oil-paper insulation state of a transformer is crucial for most maintenance strategies.This paper presents a multi-feature comprehensive evaluation model based on combination weighting and an improved technique for order of preference by similarity to ideal solution(TOPSIS)method to perform an objective and scientific evaluation of the transformer oil-paper insulation state.Firstly,multiple aging features are extracted from the recovery voltage polarization spectrum and the extended Debye equivalent circuit owing to the limitations of using a single feature for evaluation.A standard evaluation index system is then established by using the collected time-domain dielectric spectrum data.Secondly,this study implements the per-unit value concept to integrate the dimension of the index matrix and calculates the objective weight by using the random forest algorithm.Furthermore,it combines the weighting model to overcome the drawbacks of the single weighting method by using the indicators and considering the subjective experience of experts and the random forest algorithm.Lastly,the enhanced TOPSIS approach is used to determine the insulation quality of an oil-paper transformer.A verification example demonstrates that the evaluation model developed in this study can efficiently and accurately diagnose the insulation status of transformers.Essentially,this study presents a novel approach for the assessment of transformer oil-paper insulation.
基金National Natural Science Foundation of China,Grant/Award Number:52307164Heilongjiang Provincial Natural Science Foundation of China,Grant/Award Number:YQ2024E044。
文摘As an important component of oil-immersed transformers,the bushing's internal insu-lation ageing and dampness after the long-term operation can cause changes in the in-ternal electric and temperature fields,seriously threatening its safe operation.This paper tested the power frequency permittivity and direct current conductivity of aged and damp oil-paper insulation samples at different testing temperatures,and constructed a dynamic dielectric parameter calculation model.Meanwhile,a simulation model was established based on the actual structure of the 252 kV/1250 A bushing which is mainly used for the oil-immersed high-voltage bushings of 110 kV and above.The electric-magnetic-thermal multi-physical fields were used for simulation analysis.The influence of ageing/moisture(different degrees of dampness in the upper and lower regions)on the electric field distribution in the bushing was obtained.During the initial to steady-state process,the electric field distribution at the zero and end shield shows a reversal phenomenon.When the capacitor core has different degrees of dampness in the upper and lower regions,the impedance distribution of the capacitor core is non-uniform.This phenomenon will lead to an increase in the radial electric field gradient at the end shield of the capacitor core,which is prone to the risk of slip-flashing discharge.In summary,this paper adopts the field-induced dynamic parameters method to analyse the changes of multi-physical fields in the bushing.This can provide theoretical guidance for optimising the bushing structure and on-site maintenance.
文摘The±200 kV direct current(DC)cables of the Zhoushan Transmission Project were targeted,and crosslinked polyethylene(XLPE)insulation samples were prepared from faulty and spare cables.Samples were tested for oxidation induction period,Fourier transform infrared spectroscopy,differential scanning calorimetry,thermally stimulated depolarisation current,space charge and DC dielectric strength.The evolution of performance parameters was analysed,and the insulation ageing characteristics of onsite operating DC cables were deduced.The results show that compared with spare cables,the carbonyl index of operating cables decreases,the crystallinity increases and DC dielectric strength increases slightly.It is inferred being related to the reduced content of antioxidants and crosslinking by-products and improved molecular chain and crystal microstructure of XLPE insulation.It is suggested that the insulation ageing of high voltage DC XLPE cable is divided into two stages.In the early stage,the secondary crosslinking and recrystallisation processes are dominant,and the thermal and electric effects make the material properties basically stable or even slightly improved.In the middle and later stage,the thermal oxygen reaction is dominant,the microstructure of the material is destroyed,with a large number of macromolecular chains broken and some crystalline regions transformed into amorphous ones,and the insulation properties degraded significantly.
