There has been a lot of discussion about the atmospheric heat source over the Tibetan Plateau(TP)and the low-frequency oscillation of atmospheric circulation.However,the research on low-frequency oscillation of heat s...There has been a lot of discussion about the atmospheric heat source over the Tibetan Plateau(TP)and the low-frequency oscillation of atmospheric circulation.However,the research on low-frequency oscillation of heat source over TP and its impact on atmospheric circulation are not fully carried out.By using the vertically integrated apparent heat source which is calculated by the derivation method,main oscillation periods and propagation features of the summer apparent heat source over the eastern TP(Q1ETP)are diagnosed and analyzed from 1981 to 2000.The results are as follows:(1)Summer Q1ETP has two significant oscillation periods:one is 10-20d(BWO,Quasi-Biweekly Oscillation)and the other is 30-60d(LFO,Low-frequency Oscillation).(2)A significant correlation is found between Q1ETP and rainfall over the eastern TP in 1985 and 1992,showing that the low-frequency oscillation of heat source is likely to be stimulated by oscillation of latent heat.(3)The oscillation of heat source on the plateau mainly generates locally but sometimes originates from elsewhere.The BWO of Q1ETP mainly exhibits stationary wave,sometimes moves out(mainly eastward),and has a close relationship with the BWO from the Bay of Bengal.Showing the same characteristics as BWO,the LFO mainly shows local oscillation,occasionally propagates(mainly westward),and connects with the LFO from East China.In summary,more attention should be paid to the study on BWO of Q1ETP.展开更多
Considering the multiscale character of LFO effects of SST on LFO in the tropical atmosphere （low-frequency oscillation） in the tropical atmosphere, the are discussed by using an absolute ageostrophic, baroclinic mo...Considering the multiscale character of LFO effects of SST on LFO in the tropical atmosphere （low-frequency oscillation） in the tropical atmosphere, the are discussed by using an absolute ageostrophic, baroclinic model. Here, SST effects include sea surface heating and forcing of SST anomalies （SSTAs）. Studies of the influences of sea surface heating on LFO frequency and stability show that sea surface heating can slow the speed of waves and lower their frequency when SST is comparatively low; while higher SST leads to unstable waves and less periods of LFO. Since the impact of a SSTA on ultra-long waves is more evident than that on kilometer-scale waves, long-wave approximation is used when we continue to study the effect of SSTAs. Results indicate that SSTAs can lead to a longer period of LFO, and make waves unstable. In other words, positive （negative） SSTAs can make waves decay （grow）.展开更多
与传统的滤油机热油循环方法相比,短路法具有热量从绝缘内部产生、加热效率高、干燥处理效果理想等优势,适用于特高压换流变等大型变压器的现场加热。但工频电流短路加热装置工作电压高、组成设备多、体积重量大,运输、安装、布置复杂,...与传统的滤油机热油循环方法相比,短路法具有热量从绝缘内部产生、加热效率高、干燥处理效果理想等优势,适用于特高压换流变等大型变压器的现场加热。但工频电流短路加热装置工作电压高、组成设备多、体积重量大,运输、安装、布置复杂,在变电站现场使用极不方便。为充分发挥短路法加热变压器高效、快速的优势,研制了基于超低频正弦波脉宽调制技术的低频电流短路加热装置。该装置通过降低电源频率减小变压器绕组的感抗,降低了短路加热过程的工作电压,减小了所需电源容量,使得装置构成简单、体积小、重量轻。该装置已成功应用于±800 k V特高压换流变压器的现场加热干燥处理,应用结果表明:低频电流短路法加热装置能够实现大型变压器现场快速均匀加热,并且使用方便、安全,便于现场应用。展开更多
青藏高原的大气热源及其影响以及环流的低频振荡已有很多探讨,但有关高原大气热源低频振荡及其对环流影响的研究目前尚未充分开展。利用倒算法计算得到的大气热源总量(Q1),诊断和分析1981—2000年夏季青藏高原东部逐日大气热源(Q1ETP,Q1...青藏高原的大气热源及其影响以及环流的低频振荡已有很多探讨,但有关高原大气热源低频振荡及其对环流影响的研究目前尚未充分开展。利用倒算法计算得到的大气热源总量(Q1),诊断和分析1981—2000年夏季青藏高原东部逐日大气热源(Q1ETP,Q1 of the eastern Tibetan Plateau)的主要振荡周期及其对应的传播特征,并取其中1985、1992年进行更详细的分析。结果表明:(1)夏季高原东部大气热源存在两种低频振荡,主要为10～20 d振荡(BWO,Quasi-Biweekly Oscillation),其次为30～60 d振荡(LFO,Low Frequency Oscillation)。(2)在1985、1992年中,高原热源低频振荡与当地降水低频振荡有很好的同位相谱相关,表明热源低频振荡很可能由凝结潜热的振荡激发的,这证明了本文热源数据的可靠性。(3)高原在夏季主要是振荡源地,但也接受外来影响。高原热源BWO生成后主要在原地维持振荡,并受来自孟加拉湾的热源BWO影响,有时部分振荡向外(主要向东)传播;热源LFO情况与BWO类似,以本地振荡为主但也受来自东部大陆LFO的影响,外传时则主要向西。所以研究高原热源低频振荡需要特别注意热源BWO。展开更多
针对目前大型变压器加热干燥方法存在的受热不均、绝缘受损等缺点,设计了一种应用于大型变压器干燥的低频加热电源装置,能够在电压等级较低的情况下,为待干燥的负载变压器提供较高的低频加热电流。该低频加热电源采用交-直-交变换原理,...针对目前大型变压器加热干燥方法存在的受热不均、绝缘受损等缺点,设计了一种应用于大型变压器干燥的低频加热电源装置,能够在电压等级较低的情况下,为待干燥的负载变压器提供较高的低频加热电流。该低频加热电源采用交-直-交变换原理,整流侧为2个不控整流桥,逆变侧采用中性点箝位三电平结构;计算偏差中线电流以达到直流电容电压均衡控制,采用无源性控制理论,构建无源性控制模型,确定无源性控制比率,确保了对指令低频电流的渐近跟踪;通过给定的较大指令低频电流,保证负载变压器的加热效果。仿真结果表明,所提控制算法能够在输出低频电流的同时实现直流电压的均衡控制,且稳态特性好、响应速度快、算法实现简单、鲁棒性强。380 V、700 k V·A的工程实际应用表明低频加热电源具有良好的加热效果。展开更多
基金General Program from National Natural Science Foundation of China(40475029)Key Projects of the National Natural Science Foundation of China(40633018,90711003)
文摘There has been a lot of discussion about the atmospheric heat source over the Tibetan Plateau(TP)and the low-frequency oscillation of atmospheric circulation.However,the research on low-frequency oscillation of heat source over TP and its impact on atmospheric circulation are not fully carried out.By using the vertically integrated apparent heat source which is calculated by the derivation method,main oscillation periods and propagation features of the summer apparent heat source over the eastern TP(Q1ETP)are diagnosed and analyzed from 1981 to 2000.The results are as follows:(1)Summer Q1ETP has two significant oscillation periods:one is 10-20d(BWO,Quasi-Biweekly Oscillation)and the other is 30-60d(LFO,Low-frequency Oscillation).(2)A significant correlation is found between Q1ETP and rainfall over the eastern TP in 1985 and 1992,showing that the low-frequency oscillation of heat source is likely to be stimulated by oscillation of latent heat.(3)The oscillation of heat source on the plateau mainly generates locally but sometimes originates from elsewhere.The BWO of Q1ETP mainly exhibits stationary wave,sometimes moves out(mainly eastward),and has a close relationship with the BWO from the Bay of Bengal.Showing the same characteristics as BWO,the LFO mainly shows local oscillation,occasionally propagates(mainly westward),and connects with the LFO from East China.In summary,more attention should be paid to the study on BWO of Q1ETP.
基金supported by the National Basic Research Program of China under No.2006CB403607State Key Project(Grant No.40633018)+1 种基金National Natural Science Foundation of China(Grant No.90211011)the Key National Project"SCSMES".
文摘Considering the multiscale character of LFO effects of SST on LFO in the tropical atmosphere （low-frequency oscillation） in the tropical atmosphere, the are discussed by using an absolute ageostrophic, baroclinic model. Here, SST effects include sea surface heating and forcing of SST anomalies （SSTAs）. Studies of the influences of sea surface heating on LFO frequency and stability show that sea surface heating can slow the speed of waves and lower their frequency when SST is comparatively low; while higher SST leads to unstable waves and less periods of LFO. Since the impact of a SSTA on ultra-long waves is more evident than that on kilometer-scale waves, long-wave approximation is used when we continue to study the effect of SSTAs. Results indicate that SSTAs can lead to a longer period of LFO, and make waves unstable. In other words, positive （negative） SSTAs can make waves decay （grow）.
文摘与传统的滤油机热油循环方法相比,短路法具有热量从绝缘内部产生、加热效率高、干燥处理效果理想等优势,适用于特高压换流变等大型变压器的现场加热。但工频电流短路加热装置工作电压高、组成设备多、体积重量大,运输、安装、布置复杂,在变电站现场使用极不方便。为充分发挥短路法加热变压器高效、快速的优势,研制了基于超低频正弦波脉宽调制技术的低频电流短路加热装置。该装置通过降低电源频率减小变压器绕组的感抗,降低了短路加热过程的工作电压,减小了所需电源容量,使得装置构成简单、体积小、重量轻。该装置已成功应用于±800 k V特高压换流变压器的现场加热干燥处理,应用结果表明:低频电流短路法加热装置能够实现大型变压器现场快速均匀加热,并且使用方便、安全,便于现场应用。
文摘青藏高原的大气热源及其影响以及环流的低频振荡已有很多探讨,但有关高原大气热源低频振荡及其对环流影响的研究目前尚未充分开展。利用倒算法计算得到的大气热源总量(Q1),诊断和分析1981—2000年夏季青藏高原东部逐日大气热源(Q1ETP,Q1 of the eastern Tibetan Plateau)的主要振荡周期及其对应的传播特征,并取其中1985、1992年进行更详细的分析。结果表明:(1)夏季高原东部大气热源存在两种低频振荡,主要为10～20 d振荡(BWO,Quasi-Biweekly Oscillation),其次为30～60 d振荡(LFO,Low Frequency Oscillation)。(2)在1985、1992年中,高原热源低频振荡与当地降水低频振荡有很好的同位相谱相关,表明热源低频振荡很可能由凝结潜热的振荡激发的,这证明了本文热源数据的可靠性。(3)高原在夏季主要是振荡源地,但也接受外来影响。高原热源BWO生成后主要在原地维持振荡,并受来自孟加拉湾的热源BWO影响,有时部分振荡向外(主要向东)传播;热源LFO情况与BWO类似,以本地振荡为主但也受来自东部大陆LFO的影响,外传时则主要向西。所以研究高原热源低频振荡需要特别注意热源BWO。
文摘针对目前大型变压器加热干燥方法存在的受热不均、绝缘受损等缺点,设计了一种应用于大型变压器干燥的低频加热电源装置,能够在电压等级较低的情况下,为待干燥的负载变压器提供较高的低频加热电流。该低频加热电源采用交-直-交变换原理,整流侧为2个不控整流桥,逆变侧采用中性点箝位三电平结构;计算偏差中线电流以达到直流电容电压均衡控制,采用无源性控制理论,构建无源性控制模型,确定无源性控制比率,确保了对指令低频电流的渐近跟踪;通过给定的较大指令低频电流,保证负载变压器的加热效果。仿真结果表明,所提控制算法能够在输出低频电流的同时实现直流电压的均衡控制,且稳态特性好、响应速度快、算法实现简单、鲁棒性强。380 V、700 k V·A的工程实际应用表明低频加热电源具有良好的加热效果。
