In this paper,work was conducted to reveal electrical tree behaviors（initiation and propagation）of silicone rubber（SIR） under an impulse voltage with high temperature.Impulse frequencies ranging from 10 Hz to 1 k ...In this paper,work was conducted to reveal electrical tree behaviors（initiation and propagation）of silicone rubber（SIR） under an impulse voltage with high temperature.Impulse frequencies ranging from 10 Hz to 1 k Hz were applied and the temperature was controlled between 30 °C and 90 °C.Experimental results show that tree initiation voltage decreases with increasing pulse frequency,and the descending amplitude is different in different frequency bands.As the pulse frequency increases,more frequent partial discharges occur in the channel,increasing the tree growth rate and the final shape intensity.As for temperature,the initiation voltage decreases and the tree shape becomes denser as the temperature gets higher.Based on differential scanning calorimetry results,we believe that partial segment relaxation of SIR at high temperature leads to a decrease in the initiation voltage.However,the tree growth rate decreases with increasing temperature.Carbonization deposition in the channel under high temperature was observed under microscope and proven by Raman analysis.Different tree growth models considering tree channel characteristics are proposed.It is believed that increasing the conductivity in the tree channel restrains the partial discharge,holding back the tree growth at high temperature.展开更多
This paper has researched the insulation characteristics of 10% c-C4F8/N2/CO2 mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of ...This paper has researched the insulation characteristics of 10% c-C4F8/N2/CO2 mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C4F8/N2/CO2 gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF6 and the comprehensive GWP is about 5% of SF6, and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF6, 10%c-C4F8/N2/CO2 gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.展开更多
In modern power transmission systems,AC cables are increasingly integrated with overhead lines,forming hybrid networks.These cables are frequently exposed to repeated impulse voltages from the overhead lines.While sur...In modern power transmission systems,AC cables are increasingly integrated with overhead lines,forming hybrid networks.These cables are frequently exposed to repeated impulse voltages from the overhead lines.While surge arresters offer partial protection,the long-term effects of these impulses on polypropylene(PP)insulation remain unclear.This study systematically investigates the cumulative degradation of the electrical breakdown properties of PP insulation under repeated impulse voltage stress.The 50%impulse breakdown voltage(U_(50))was first determined,and a series of impulse tests were conducted at varying voltage levels to assess the number of impulses required for elec-trical breakdown,leading to the construction of an amplitude of impulse voltage(U)and the number of times required for breakdown(N),which is U-N curve.To evaluate the cumulative degradation,impulse voltage at 0.8 U_(50)was applied for 50,100,and 200 cycles,with the electrical conductivity current measured before and after each series of impulses.The results indicate significant degradation in the insulating properties of PP under repeated impulse stress.Mechanisms of cumulative degradation under impulse stress were further explored using isothermal relaxation current and space charge measurements.These findings provide critical insights into the performance of PP in hybrid transmission systems and offer valuable data to inform improved insulation design and protection strategies.展开更多
In recent years,more than 6 million room temperature vulcanized(RTV)silicone rubber coated cap and pin insulators with high mechanical ratings were used in ultra-high voltage transmission lines in China to improve pol...In recent years,more than 6 million room temperature vulcanized(RTV)silicone rubber coated cap and pin insulators with high mechanical ratings were used in ultra-high voltage transmission lines in China to improve pollution performance.However,the unexpected puncture phenomena of RTV coated insulators were exposed during steep-front impulse voltage tests;for instance,the steep-front impulse voltage test pass rate decreased to less than 50% for 550 kN glass insulators with RTV coatings.The steep-front impulse voltage test is the most effective method used to check the insulation quality of cap and pin insulators・This unexpected phenomenon once caused serious concerns to power utilities.In this paper,several possible factors that affect the puncture of insulators were analyzed.Then,the extent of the decline in the breakdown of the 550 kN glass cap and pin insulators with and without RTV coatings were studied.The initial puncture location was then found,and the developmental process of the arc on the insulator surface in steep-front impulse voltage tests was observed with an ultra-high-speed intensified charge coupled device camera.Lastly,a breakdown mechanism is proposed.The puncture phenomena of a RTV coated insulator in a steep-front impulse voltage test is essentially an electrical breakdown of the internal insulation・The RTV coating induces the close adherence of the arc to the surface of the insulator.Such closeness changes the arc development path on the insulator surface and facilitates easy breakdown in the shed weak part.All these factors result in a significant increase in the breakdown probability of RTV coated insulators in steepfront impulse voltage tests.展开更多
With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,a...With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,and interfering with the normal operation of the power grid.Based on the requirements of harmonic suppression and power system protection,a shunt active power filter(SAPF)is proposed as an effective harmonic suppression method.However,there are problems with impulse current and impulse voltage in the starting process of SAPF.Impulse current and impulse voltage cause the power grid and switchgear to bear greater current stress and voltage stress,which seriously affect the security and reliability of the power grid and may damage the switchgear.To effectively solve the problem of impulse current and impulse voltage,the starting process of SAPF is divided into the uncontrolled rectification stage and the transition stage.The mathematical model of the DC side of APF is established.The causes of impulse current and impulse voltage in the uncontrolled rectifier and transition phases are analyzed.By introducing voltage square,a new starting impulse suppression strategy of active power filter based on the slow rising curve is proposed,fundamentally solving the problems of impulse current and impulse voltage.Simulation results verify the effectiveness and feasibility of this method.展开更多
The increase of voltage level for AC and DC transmission systems requires some changes in the high voltage testing for Ultra High Voltage(UHV) equipment.After a short description of the coordination work in the standa...The increase of voltage level for AC and DC transmission systems requires some changes in the high voltage testing for Ultra High Voltage(UHV) equipment.After a short description of the coordination work in the standardization bodies the requirements for UHV equipment are mentioned.The main points concerning high voltage testing of UHV equipment are the impulse shape of standard lightning impulse voltage,the evaluation of the test voltage for impulses with oscillations or overshoot near the peak and the time parameter of switching impulses.The linearity check of the measuring devices,the proximity effect,the wet tests and the atmospheric correction factors are further points to be discussed concerning testing of UHV equipment.展开更多
基金supported in part by National Basic Research Program of China(973 Project)(No.2014CB239501)National Natural Science Foundation of China(Nos.51707100,51377089)+1 种基金State Key Laboratory of Electrical Insulation and Power Equipment(No.EIPE16208)China Postdoctoral Science Foundation(No.2016M591176)
文摘In this paper,work was conducted to reveal electrical tree behaviors（initiation and propagation）of silicone rubber（SIR） under an impulse voltage with high temperature.Impulse frequencies ranging from 10 Hz to 1 k Hz were applied and the temperature was controlled between 30 °C and 90 °C.Experimental results show that tree initiation voltage decreases with increasing pulse frequency,and the descending amplitude is different in different frequency bands.As the pulse frequency increases,more frequent partial discharges occur in the channel,increasing the tree growth rate and the final shape intensity.As for temperature,the initiation voltage decreases and the tree shape becomes denser as the temperature gets higher.Based on differential scanning calorimetry results,we believe that partial segment relaxation of SIR at high temperature leads to a decrease in the initiation voltage.However,the tree growth rate decreases with increasing temperature.Carbonization deposition in the channel under high temperature was observed under microscope and proven by Raman analysis.Different tree growth models considering tree channel characteristics are proposed.It is believed that increasing the conductivity in the tree channel restrains the partial discharge,holding back the tree growth at high temperature.
基金supported by National Natural Science Foundation of China (No. 51337006)
文摘This paper has researched the insulation characteristics of 10% c-C4F8/N2/CO2 mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C4F8/N2/CO2 gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF6 and the comprehensive GWP is about 5% of SF6, and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF6, 10%c-C4F8/N2/CO2 gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.
基金China Southern Power Grid Company Limited,Grant/Award Number:ZBKJXM20220101National Natural Science Foundation of China,Grant/Award Number:52107019。
文摘In modern power transmission systems,AC cables are increasingly integrated with overhead lines,forming hybrid networks.These cables are frequently exposed to repeated impulse voltages from the overhead lines.While surge arresters offer partial protection,the long-term effects of these impulses on polypropylene(PP)insulation remain unclear.This study systematically investigates the cumulative degradation of the electrical breakdown properties of PP insulation under repeated impulse voltage stress.The 50%impulse breakdown voltage(U_(50))was first determined,and a series of impulse tests were conducted at varying voltage levels to assess the number of impulses required for elec-trical breakdown,leading to the construction of an amplitude of impulse voltage(U)and the number of times required for breakdown(N),which is U-N curve.To evaluate the cumulative degradation,impulse voltage at 0.8 U_(50)was applied for 50,100,and 200 cycles,with the electrical conductivity current measured before and after each series of impulses.The results indicate significant degradation in the insulating properties of PP under repeated impulse stress.Mechanisms of cumulative degradation under impulse stress were further explored using isothermal relaxation current and space charge measurements.These findings provide critical insights into the performance of PP in hybrid transmission systems and offer valuable data to inform improved insulation design and protection strategies.
基金supported by the National Natural Science Foundation of China(51577099).
文摘In recent years,more than 6 million room temperature vulcanized(RTV)silicone rubber coated cap and pin insulators with high mechanical ratings were used in ultra-high voltage transmission lines in China to improve pollution performance.However,the unexpected puncture phenomena of RTV coated insulators were exposed during steep-front impulse voltage tests;for instance,the steep-front impulse voltage test pass rate decreased to less than 50% for 550 kN glass insulators with RTV coatings.The steep-front impulse voltage test is the most effective method used to check the insulation quality of cap and pin insulators・This unexpected phenomenon once caused serious concerns to power utilities.In this paper,several possible factors that affect the puncture of insulators were analyzed.Then,the extent of the decline in the breakdown of the 550 kN glass cap and pin insulators with and without RTV coatings were studied.The initial puncture location was then found,and the developmental process of the arc on the insulator surface in steep-front impulse voltage tests was observed with an ultra-high-speed intensified charge coupled device camera.Lastly,a breakdown mechanism is proposed.The puncture phenomena of a RTV coated insulator in a steep-front impulse voltage test is essentially an electrical breakdown of the internal insulation・The RTV coating induces the close adherence of the arc to the surface of the insulator.Such closeness changes the arc development path on the insulator surface and facilitates easy breakdown in the shed weak part.All these factors result in a significant increase in the breakdown probability of RTV coated insulators in steepfront impulse voltage tests.
基金supported by the National Natural Science Foundation of China under Grant 61863023.
文摘With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,and interfering with the normal operation of the power grid.Based on the requirements of harmonic suppression and power system protection,a shunt active power filter(SAPF)is proposed as an effective harmonic suppression method.However,there are problems with impulse current and impulse voltage in the starting process of SAPF.Impulse current and impulse voltage cause the power grid and switchgear to bear greater current stress and voltage stress,which seriously affect the security and reliability of the power grid and may damage the switchgear.To effectively solve the problem of impulse current and impulse voltage,the starting process of SAPF is divided into the uncontrolled rectification stage and the transition stage.The mathematical model of the DC side of APF is established.The causes of impulse current and impulse voltage in the uncontrolled rectifier and transition phases are analyzed.By introducing voltage square,a new starting impulse suppression strategy of active power filter based on the slow rising curve is proposed,fundamentally solving the problems of impulse current and impulse voltage.Simulation results verify the effectiveness and feasibility of this method.
文摘The increase of voltage level for AC and DC transmission systems requires some changes in the high voltage testing for Ultra High Voltage(UHV) equipment.After a short description of the coordination work in the standardization bodies the requirements for UHV equipment are mentioned.The main points concerning high voltage testing of UHV equipment are the impulse shape of standard lightning impulse voltage,the evaluation of the test voltage for impulses with oscillations or overshoot near the peak and the time parameter of switching impulses.The linearity check of the measuring devices,the proximity effect,the wet tests and the atmospheric correction factors are further points to be discussed concerning testing of UHV equipment.
