A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can i...A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.展开更多
AA 2219-0 Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardn...AA 2219-0 Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardness characteristics which mainly depicted by microhardness and its gradient were investigated systematically. The results show that pulse frequency has a great effect on the hardness characteristics. The weld zone microhardness and its gradient with different pulse frequency present an evident fluctuant trend. The fluctuation of gradient is slight, illustrating that the mierostructure is uniform with pulse frequcncy varied from 35 kHz to 60 kHz. The fusion zone microhardness and its gradient foUow the similar trends but fluetuate greatly. Maximum value of gradient appears around the fusion boundary due to the coarse and non- uniform microstrueture. The maximum gradient at 60 kHz is only 25.5 % of that at 45 kHz. According to the study, the best hardness characteristics are achieved at 60 kHz frequency.展开更多
We focus on the high frequency current method which is widely applied in the partial discharge(PD)detection of cables.Aiming at guaranteeing the accuracy of this method,we study an innovative time-domain technology fo...We focus on the high frequency current method which is widely applied in the partial discharge(PD)detection of cables.Aiming at guaranteeing the accuracy of this method,we study an innovative time-domain technology for effectively measuring the transfer impedance of the high frequency current transformers(HFCTs).The proposed technology called pulse injection method obtains the system response under the excitation of the wide-band instantaneous pulse signal.Firstly,by studying the working principle of HFCTs,we summarize that the bandwidth of the selected signal acquisition device should be at least 100 MHz to ensure measurement accuracy.Secondly,Gauss pulse and square wave pulse are generated to determine the effects of different sources.The measurement results indicate that Gauss pulse is more suitable for pulse injection method,and the rise time should be under 10 ns to improve the starting frequency of oscillation distortion.Finally,the transfer impedance curves of five types of HFCTs are acquired by both pulse injection and traditional point-frequency methods.The measurement results show a remarkable consistency between two methods.However,pulse injection method requires the simpler operation and lias a higher resolution,obviously improving the measurement efficiency and bet ter displaying the details of the transfer impedance curves.展开更多
采用超高频脉冲GTAW(ultra high frequency pulse gas tungsten arc welding,UHFP-GTAW)工艺在占空比20%的条件下完成了Ti-6Al-4V钛合金组织性能试验,以平均晶粒尺寸表征晶粒细化程度,研究了20%占空比条件下,脉冲频率对晶粒细化、组织...采用超高频脉冲GTAW(ultra high frequency pulse gas tungsten arc welding,UHFP-GTAW)工艺在占空比20%的条件下完成了Ti-6Al-4V钛合金组织性能试验,以平均晶粒尺寸表征晶粒细化程度,研究了20%占空比条件下,脉冲频率对晶粒细化、组织特征及接头拉伸性能的影响规律.结果表明,与常规GTAW(conventional gas tungsten arc welding,C-GTAW)相比,UHFP-GTAW焊缝区以网篮状组织为主,热影响区α'相以短针状为主呈现;焊缝区平均晶粒尺寸最大减小了32%,晶粒显著细化;断后伸长率和断面收缩率最大分别提高了140%和275%,接头塑性明显改善.与50%占空比下平均晶粒尺寸减小率16.7%相比,晶粒得到进一步细化,同时平均断后伸长率及断面收缩率分别提高了22%,33%.展开更多
为研究SF6气体绝缘设备在尖端缺陷下局部放电演化特征,模拟GIS中可能出现的尖端缺陷。采用脉冲电流法测量了尖端放电脉冲序列,同时利用局部放电检测仪测得放电的PRPD谱图,分析了SF6气体中尖端放电的演化特征。为进一步确定GIS中尖端放...为研究SF6气体绝缘设备在尖端缺陷下局部放电演化特征,模拟GIS中可能出现的尖端缺陷。采用脉冲电流法测量了尖端放电脉冲序列,同时利用局部放电检测仪测得放电的PRPD谱图,分析了SF6气体中尖端放电的演化特征。为进一步确定GIS中尖端放电的发展过程及危险度,采用内外置特高频传感器采集到局部放电的特高频电磁波信号,获取了放电PRPD谱图,分析了尖端放电演化过程。结果表明,随外施电压增加,尖端放电的正半周幅值明显高于负半周,正、负半周的上升沿和下降沿放电量随外施电压增大而增大。当GIS内存在尖端缺陷时,在外施电压远低于GIS正常运行电压时就已经发生放电,且放电结果和实验室模型中结果一致。因此,可以考虑采用实验室模型来研究220k V GIS中尖端局部放电发展过程。展开更多
针对高氮钢增材制造熔滴过渡过程中氮元素逸出及飞溅问题,进行超音频脉冲熔化极气体保护(Ultrasonic Frequency Pulsed Gas Metal Arc,UFP-GMA)增材制造熔滴过渡试验,研究不同超音频脉冲电流叠加模式和脉冲电流频率对高氮钢熔滴过渡稳...针对高氮钢增材制造熔滴过渡过程中氮元素逸出及飞溅问题,进行超音频脉冲熔化极气体保护(Ultrasonic Frequency Pulsed Gas Metal Arc,UFP-GMA)增材制造熔滴过渡试验,研究不同超音频脉冲电流叠加模式和脉冲电流频率对高氮钢熔滴过渡稳定性的影响,获取能够实现高氮钢增材稳定熔滴过渡的工艺参数。试验结果表明:在脉冲熔化极气体保护(Pulsed Gas Metal Arc,P-GMA)增材工艺条件下可以实现一脉一滴过渡,但是过渡稳定性较差,飞溅明显;在P-GMA基值阶段或基值和峰值阶段都叠加超音频脉冲电流均不利于熔滴过渡,容易出现短路、熔滴爆炸等问题;在P-GMA峰值阶段叠加低频(20 kHz)脉冲电流时,对熔滴过渡影响较弱,叠加中频(40~60 kHz)脉冲电流能抑制高氮钢熔滴过渡中大颗粒飞溅生成,提高熔滴过渡稳定性,但是当频率超过60 kHz时在过渡中会形成许多小飞溅。展开更多
无励磁分接开关出现放电性故障会严重危害变压器安全运行。介绍了一起500 k V变压器交接试验过程中脉冲局部放电试验异常的案例,应用脉冲电流法、特高频法、超声波法等多维局部放电检测技术进行时差定位,成功诊断了变压器无励磁分接开...无励磁分接开关出现放电性故障会严重危害变压器安全运行。介绍了一起500 k V变压器交接试验过程中脉冲局部放电试验异常的案例,应用脉冲电流法、特高频法、超声波法等多维局部放电检测技术进行时差定位,成功诊断了变压器无励磁分接开关内部异物放电故障;通过材质成分分析判断异物为动触头旋转轴压环的机加工碎屑,异物位于无励磁分接开关动触头旋转轴位置,随挡位切换而移动,导致各个挡位均可检测到局部放电,且脉冲局部放电量随挡位变化而变化。展开更多
文摘A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.
基金The research is supported by the National Natural Science Foundation of China （No. 51005011 ） the Fundamental Research Funds for the Central Universities.
文摘AA 2219-0 Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardness characteristics which mainly depicted by microhardness and its gradient were investigated systematically. The results show that pulse frequency has a great effect on the hardness characteristics. The weld zone microhardness and its gradient with different pulse frequency present an evident fluctuant trend. The fluctuation of gradient is slight, illustrating that the mierostructure is uniform with pulse frequcncy varied from 35 kHz to 60 kHz. The fusion zone microhardness and its gradient foUow the similar trends but fluetuate greatly. Maximum value of gradient appears around the fusion boundary due to the coarse and non- uniform microstrueture. The maximum gradient at 60 kHz is only 25.5 % of that at 45 kHz. According to the study, the best hardness characteristics are achieved at 60 kHz frequency.
文摘We focus on the high frequency current method which is widely applied in the partial discharge(PD)detection of cables.Aiming at guaranteeing the accuracy of this method,we study an innovative time-domain technology for effectively measuring the transfer impedance of the high frequency current transformers(HFCTs).The proposed technology called pulse injection method obtains the system response under the excitation of the wide-band instantaneous pulse signal.Firstly,by studying the working principle of HFCTs,we summarize that the bandwidth of the selected signal acquisition device should be at least 100 MHz to ensure measurement accuracy.Secondly,Gauss pulse and square wave pulse are generated to determine the effects of different sources.The measurement results indicate that Gauss pulse is more suitable for pulse injection method,and the rise time should be under 10 ns to improve the starting frequency of oscillation distortion.Finally,the transfer impedance curves of five types of HFCTs are acquired by both pulse injection and traditional point-frequency methods.The measurement results show a remarkable consistency between two methods.However,pulse injection method requires the simpler operation and lias a higher resolution,obviously improving the measurement efficiency and bet ter displaying the details of the transfer impedance curves.
文摘采用超高频脉冲GTAW(ultra high frequency pulse gas tungsten arc welding,UHFP-GTAW)工艺在占空比20%的条件下完成了Ti-6Al-4V钛合金组织性能试验,以平均晶粒尺寸表征晶粒细化程度,研究了20%占空比条件下,脉冲频率对晶粒细化、组织特征及接头拉伸性能的影响规律.结果表明,与常规GTAW(conventional gas tungsten arc welding,C-GTAW)相比,UHFP-GTAW焊缝区以网篮状组织为主,热影响区α'相以短针状为主呈现;焊缝区平均晶粒尺寸最大减小了32%,晶粒显著细化;断后伸长率和断面收缩率最大分别提高了140%和275%,接头塑性明显改善.与50%占空比下平均晶粒尺寸减小率16.7%相比,晶粒得到进一步细化,同时平均断后伸长率及断面收缩率分别提高了22%,33%.
文摘为研究SF6气体绝缘设备在尖端缺陷下局部放电演化特征,模拟GIS中可能出现的尖端缺陷。采用脉冲电流法测量了尖端放电脉冲序列,同时利用局部放电检测仪测得放电的PRPD谱图,分析了SF6气体中尖端放电的演化特征。为进一步确定GIS中尖端放电的发展过程及危险度,采用内外置特高频传感器采集到局部放电的特高频电磁波信号,获取了放电PRPD谱图,分析了尖端放电演化过程。结果表明,随外施电压增加,尖端放电的正半周幅值明显高于负半周,正、负半周的上升沿和下降沿放电量随外施电压增大而增大。当GIS内存在尖端缺陷时,在外施电压远低于GIS正常运行电压时就已经发生放电,且放电结果和实验室模型中结果一致。因此,可以考虑采用实验室模型来研究220k V GIS中尖端局部放电发展过程。
文摘针对高氮钢增材制造熔滴过渡过程中氮元素逸出及飞溅问题,进行超音频脉冲熔化极气体保护(Ultrasonic Frequency Pulsed Gas Metal Arc,UFP-GMA)增材制造熔滴过渡试验,研究不同超音频脉冲电流叠加模式和脉冲电流频率对高氮钢熔滴过渡稳定性的影响,获取能够实现高氮钢增材稳定熔滴过渡的工艺参数。试验结果表明:在脉冲熔化极气体保护(Pulsed Gas Metal Arc,P-GMA)增材工艺条件下可以实现一脉一滴过渡,但是过渡稳定性较差,飞溅明显;在P-GMA基值阶段或基值和峰值阶段都叠加超音频脉冲电流均不利于熔滴过渡,容易出现短路、熔滴爆炸等问题;在P-GMA峰值阶段叠加低频(20 kHz)脉冲电流时,对熔滴过渡影响较弱,叠加中频(40~60 kHz)脉冲电流能抑制高氮钢熔滴过渡中大颗粒飞溅生成,提高熔滴过渡稳定性,但是当频率超过60 kHz时在过渡中会形成许多小飞溅。
文摘无励磁分接开关出现放电性故障会严重危害变压器安全运行。介绍了一起500 k V变压器交接试验过程中脉冲局部放电试验异常的案例,应用脉冲电流法、特高频法、超声波法等多维局部放电检测技术进行时差定位,成功诊断了变压器无励磁分接开关内部异物放电故障;通过材质成分分析判断异物为动触头旋转轴压环的机加工碎屑,异物位于无励磁分接开关动触头旋转轴位置,随挡位切换而移动,导致各个挡位均可检测到局部放电,且脉冲局部放电量随挡位变化而变化。
