Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are a...Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.展开更多
More and more applications of ZnO arrester in electrical system experienced more problems.One thing,that is still under some investigation,is the effect of multiple lightning strike to the performance of ZnO arrester....More and more applications of ZnO arrester in electrical system experienced more problems.One thing,that is still under some investigation,is the effect of multiple lightning strike to the performance of ZnO arrester.As we know,the design of ZnO arrester for transmission system and for distribution system differs in the point of view of the number of ZnO blocks.Transmission system,due to its higher nominal voltage than distribution system,has more numbers of ZnO blocks inside an arrester tube.In term of the current rating of an arrester,it is found that there is some different value of the current rating.The current rating of an arrester installed closer to electrical substation is higher than that of some further away from the substation.To the respond of a lightning impulse strike,the arrester will let a high value of impulse current flowing.It tends to heat the ZnO material of the arrester.If the number of impulse strike is quite high then it may give the effect to the change of the arrester performance.This condition will endanger the equipment that is protected by the arrester from lightning strikes.During this research,the scope of work is limited to making an impulse current generator toward to one having 8/20 μs wave-shape.This kind of impulse current wave-shape is the one that is used for studying the performance of ZnO block.The effect of the inductance and capacitance of the impulse current generator were also studied.A 10 fused cut out was blown by an impulse having 10321 A of 17.8/37.8 μs.A ZnO arrester block brokendown/allowed large value of current :10982 A flowing under the voltage of 10.5展开更多
Partial discharge(PD) is one of the most important phenomenon in high voltage insulations.In most cases, the appearance of partial discharges is related to insulation defects.Understanding partial discharges is import...Partial discharge(PD) is one of the most important phenomenon in high voltage insulations.In most cases, the appearance of partial discharges is related to insulation defects.Understanding partial discharges is important for diagnosis on insulation condition.Corona discharges appear when extremely high electric field appears on the conductor surface exceeding the electric field strength of the gas.The high electric field may occur at around protrusion with very sharp tip.This paper reported a holistic approach of corona discharge investigation.The needle-plane electrode system was used.The medium between the electrodes was air.The needle was made from steel with radius of curvature of 3μm(Ogura needle).Sinusoidal as well as triangular applied voltages were used.The waveform of the corona discharges was measured using a digital oscilloscope.The corona discharge pulses were measured using a phase-resolved PD measurement system.The system was able to measure the magnitude(q) and phase angle position(φ) of each PD pulses,as well as the number of discharge pulses(n).The role of applied voltage was investigated using phase-resolved analysis of corona discharge pulses through pulse sequence,pulse magnitude and pulse number analysis. Experimental results indicated that corona discharge current waveform was an impulse with rise time of about several ns and the impulse width of about 100 ns.The Fast Fourier Transform analysis indicated that the corona discharge current waveform had several spectrum peaks at frequency of 7.8 MHz,85.9 MHz,109.4 MHz and 195.3 MHz.The experimental results also showed that discharge pulses were concentrated around the peak of applied voltage for both sinusoidal and triangular voltages.The discharge magnitude,as well as its probability of occurrence,was strongly dependent on the instantaneous applied voltage.The shape ofφ-n,as well asφ-q-n PD patterns,were strongly reflected by the shape of applied voltage.In order to get deep understanding of the corona discharge,by utilizing results of the phase-resolved analysis,electrical equivalent circuits of corona discharges were proposed.The electrical equivalent circuit contained capacitances and a spark gap.For deeply understanding of PD phenomenon,computer simulation was done by using the proposed electrical equivalent circuits.The similarity of the measured and simulated PD patterns was assessed by comparing measured and simulated theφ-q-n andφ-n PD patterns.The results indicated that simulated PD patterns similar to those obtained from experiment.展开更多
文摘Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.
文摘More and more applications of ZnO arrester in electrical system experienced more problems.One thing,that is still under some investigation,is the effect of multiple lightning strike to the performance of ZnO arrester.As we know,the design of ZnO arrester for transmission system and for distribution system differs in the point of view of the number of ZnO blocks.Transmission system,due to its higher nominal voltage than distribution system,has more numbers of ZnO blocks inside an arrester tube.In term of the current rating of an arrester,it is found that there is some different value of the current rating.The current rating of an arrester installed closer to electrical substation is higher than that of some further away from the substation.To the respond of a lightning impulse strike,the arrester will let a high value of impulse current flowing.It tends to heat the ZnO material of the arrester.If the number of impulse strike is quite high then it may give the effect to the change of the arrester performance.This condition will endanger the equipment that is protected by the arrester from lightning strikes.During this research,the scope of work is limited to making an impulse current generator toward to one having 8/20 μs wave-shape.This kind of impulse current wave-shape is the one that is used for studying the performance of ZnO block.The effect of the inductance and capacitance of the impulse current generator were also studied.A 10 fused cut out was blown by an impulse having 10321 A of 17.8/37.8 μs.A ZnO arrester block brokendown/allowed large value of current :10982 A flowing under the voltage of 10.5
文摘Partial discharge(PD) is one of the most important phenomenon in high voltage insulations.In most cases, the appearance of partial discharges is related to insulation defects.Understanding partial discharges is important for diagnosis on insulation condition.Corona discharges appear when extremely high electric field appears on the conductor surface exceeding the electric field strength of the gas.The high electric field may occur at around protrusion with very sharp tip.This paper reported a holistic approach of corona discharge investigation.The needle-plane electrode system was used.The medium between the electrodes was air.The needle was made from steel with radius of curvature of 3μm(Ogura needle).Sinusoidal as well as triangular applied voltages were used.The waveform of the corona discharges was measured using a digital oscilloscope.The corona discharge pulses were measured using a phase-resolved PD measurement system.The system was able to measure the magnitude(q) and phase angle position(φ) of each PD pulses,as well as the number of discharge pulses(n).The role of applied voltage was investigated using phase-resolved analysis of corona discharge pulses through pulse sequence,pulse magnitude and pulse number analysis. Experimental results indicated that corona discharge current waveform was an impulse with rise time of about several ns and the impulse width of about 100 ns.The Fast Fourier Transform analysis indicated that the corona discharge current waveform had several spectrum peaks at frequency of 7.8 MHz,85.9 MHz,109.4 MHz and 195.3 MHz.The experimental results also showed that discharge pulses were concentrated around the peak of applied voltage for both sinusoidal and triangular voltages.The discharge magnitude,as well as its probability of occurrence,was strongly dependent on the instantaneous applied voltage.The shape ofφ-n,as well asφ-q-n PD patterns,were strongly reflected by the shape of applied voltage.In order to get deep understanding of the corona discharge,by utilizing results of the phase-resolved analysis,electrical equivalent circuits of corona discharges were proposed.The electrical equivalent circuit contained capacitances and a spark gap.For deeply understanding of PD phenomenon,computer simulation was done by using the proposed electrical equivalent circuits.The similarity of the measured and simulated PD patterns was assessed by comparing measured and simulated theφ-q-n andφ-n PD patterns.The results indicated that simulated PD patterns similar to those obtained from experiment.
