一种快速可逆的交流调速系统——可控硅串级调速在龙门刨上的应用

绕线式异步甩动机转子可控硅串级无级调速系统已成功地应用于各种容量的电机。 可控硅串级调速具有很多优点:从使用的电机来看,是无整流子的,维护简单,价     

可控硅在矿山的应用(七)——可控硅串级调速

在绕线式异步电动机的转子回路中,串接电阻进行调速,这时转子回路的转差功率完全消耗在回路的电阻上。该调速方式的缺点是:电阻及其开关设备占地面积大、效率低、电动机在低速时的机械特性较软等。而串级调速是将绕线式异步电动机在不同转速下感应的转差电势,经一组三相桥式整流器变为直流电压,此电压再经一组三相全控桥式有源逆变器把电能反馈到交流电网去,改变可控硅的逆变角,就可以实现无级调速。串级调速的优点是不仅设备占地面积小,而且效率高,如某     

绕线式电机恒转矩起动的研究与实践

从分析绕线式交流异步电动机的机械特性着手，讨论了恒转矩负载下的转子串电阻调速特性，进而推导出转子串电阻实现电机恒转矩起动的电阻数学模型。最后介绍实现绕线式异步电动机恒转矩起动的液体电阻起动器。     

串级调速中换相重叠角对转矩的影响

绕线电动机转子回路引入反电势,使滑差功率经整流器、逆变器反馈给电网,这便是可控硅串级调速的简单过程。由于电动机转子接有整流器,就出现产生换流重叠角的问题,因此分析换流重叠角,讨论其对力短的影响,对矿井提升机能否采用可控硅串级调速是十分必要的。 一、换相重叠角的分析 1.转子接整流器的换相过程及重叠角γ的计算 转子侧整流器为三相不控整流桥,如图1。图中e_(2a)、e_(2b)、e_(2c)分别为转子的相电压,L_2、R_2为转子每相电感和电阻,L为直流侧     

可控硅交流串级调速装置在拉丝机上应用小结

“革命在继续,生产在发展”。革命和生产的形势要求我们增加钢丝产量和品种,提高质量。这就迫切需要我们在原有陈旧的设备上革新挖潜,达到连续化,无级调速化,适应各种材质钢线的生产需要。我们组成了工人、干部、技术人员的三结合小组,在原有设备上“开刀”,在定方案时,淘汰了投资大,收效慢的直流调速方案,提出用原来的交流绕线式感应电机,搞可控硅交流串级调速。在各级领导的支持和帮助下,经过群策群力,反复实践,奋战四个月,终于试制成功100马力串级调速中     

1000kW异步电动机串级调速系统的改造

根据生产工艺的要求，φ４００机主电机的调速采用串级调速，其控制方式电机串频敏变阻器起动，经电压检测达到系统最低速时自动投入串级调速装置。通过对串级调速系统的电磁转矩特性分析，采用了三环系统。其速度反馈是通过对转子电压检测、变换而得到与转换变经规律成线性关系的速度信号，以完成系统的闭环。     

异步机串级调速系统静特性等值电路的化简

绕线式异步机串级调速系统，其调速装置的直流回路处于电动机的转子回路中，而且转差率是个变量。所以，计算静态参数时，要采用直流等效电路。本文就其等效电路的化简进行讨论，给出一些简化计算方法。     

20吨抓斗吊绕线电机转子电阻切换方法的改进

针对我厂烧结原料矿槽抓斗吊大功率绕线式电机采用交流接触器进行转子电阻切换存在的问题，我厂用可控硅无触占开关对其进行了改造。改造后运行效果良好。     

变频器在电弧炉电极自动调节器中的应用

本文根据实例对变频调速式和可控硅－交流双电机式电弧炉自动调节器进行了比较，重点叙述了变频调速式电弧炉电极自动调节器的特点和使用后的效果。     

近代交流调速：第七讲 无换向器电动机

无换向器电动机是近年来发展起来的一种新型调速电机,它是由可控硅逆变器、同步电动机和转子位置检测器三者组成的电机系统。其运行原理和特性与直流电动机相似,结构上却没有机械换向器,故称为无换向器直流电动机,简称无换向器电动机。由于它采用可控硅变频器供电,又称为可控硅电动机。它的变频器的频率严格受控于转子位置信号,实质上是同步电动机的自控式变频调速系统。用交-直-交变频器供电的叫直流式无换向器电动机,用交-交变频器供电的则称为交流式无换向器电动机。 无换向器电动机由于它实际上是电子换向式的直流电动机,所以它既有与直流电动机相似的优良     

转炉炉壳热应力分析

根据实际转炉建立实体模型。以有限元为手段,考虑了炉衬和炉壳材料的物性参数随温度变化的特点和炉衬与炉壳之间膨胀间隙,计算了转炉炉壳在温度载荷和炉衬膨胀压力同时作用下的热应力。所得结果可为转炉炉壳设计提供依据。     

焦炭热性能指标意义浅析

通过对焦炭在高炉内的历程及其变化规律的剖析,阐述焦炭热性能指标的意义,形象地把焦炭在高炉内的损耗分为三部分(M1,M2,M3)。指出M2对焦比及焦炭价格有一定的指导作用。     

Results of treatment of cancer of the cardia

Cancer of the cardia is traditionally discussed with cardiac cancer of the lower portion of the esophagus and upper gastric cancer invading the esophagus, and the specific characteristics of cancer of the cardia have never been clearly defined. We reviewed the outcome of 172 patients with adenocarcinoma of the cardia who had undergone radical surgery between 1949 and 1994 in the Division of Gastrointestinal Surgery of the Cancer Institute Hospital. The centers of the tumors were located within 2 cm above and below the boundary between the esophagus and the stomach, and their longitudinal diameter was less than 8 cm. We divided the patients into an early period (1949-1979; n = 79) and a late period (1980-1994; n = 93), and focused on the historical transition. There were no differences in patient gender or histology between the two periods. However, the late period was associated with fewer cases of esophageal invasion and shorter longitudinal diameter, as the age of the population advanced. The number of advanced cancers such as the localized and infiltrative type had decreased, and early cancer and early clinical stage had become more common, but despite the fact that the number of early cancers had increased, extended dissection, such as thoracic and paraaortic lymph node dissection, was performed more frequently. By clinical stage, the long-term outcome markedly improved in Stage I patient in the late period, and tended to improve in Stage II and III patients. This appears to have been attributable to the prevention of micrometastasis by extended dissection, although the number of early cancers is another major potential cause. There were no differences in the outcome of Stage IV patients between the two periods, and further advances in multimodality therapy must be awaited. The range of resection is basically proximal gastrectomy, and if there are adequate indications, the prognosis is favorable. In view of the status of lymphatic flow and lymph node metastasis, and long-term results, lateroaortic lymph node dissection is important. Since the number of early cancer patients has been increasing, if intraabdominal recurrence is prevented, intrathoracic lymph node dissection will contribute greatly to the outcome of such patients.     

The effect of amount of possession of the trait of hostility on accuracy of perception of hostility in others.

Some theories of personality hold that an individual's perception of others is influenced by his own personality characteristics; more specifically, that a trait of low social value will be projected more into others, and that insight into the possession of these characteristics reduces this distortion. These 2 hypotheses were tested by having a group of college students rate each other (including themselves) on degree of friendliness or hostility. Agreement with group rating about self yielded the insight score. In general, the hypotheses were supported; the "friendly" Ss were most accurate in their perception of others, and insight was positively associated with accurate perception. From Psyc Abstracts 36:04:4HL16M. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of antibiotics of chemotaxis of human leukocytes

The effect of 20 different antibiotics on chemotaxis by human neutrophils was studied. Human leukocytes incubated with chloramphenicol, rifampin, sodium fusidate, and tetracyclines in vitro showed markedly depressed migration. The mechanisms by which these antibiotics affect leukotaxis are discussed.     

Quality of life of relatives of mental patients

Usage of quality of life of psychiatric patients' relatives as the parameter of estimation of the quality of psychiatric care is considered. By means of standard questionnaire elaborated by the authors as well as by means of both individual and group conversations the quality of life was analyzed in 40 relatives which lived together with psychiatric patients. Different spheres of their life and difficulties (financial, social-psychologic, production) were examined in families with such patients. The defects of psychiatric care that had direct influence on the quality of life of the psychiatric patients' relatives are outlined.