电机烧毁原因分析及缺相保护器

一、电动机烧毁的原因分析1、电动机发热电动机烧毁时的主要特征是发热,因此有人认为电动机烧毁的原因是由于定子绕组发热,只要防止电动机的发热,也就保护了电动机。认为只要采取测量定子的温度来进行保护就可以保护电动机不被烧毁,其实不然,电动机的升温和降温是一个相当缓慢的变化过程,因此,只有对大、中型重要的电动机预埋温度传感器,实行有效的过热保护。对于小型电动机则相当不经济。2、电动机过载有些场合使用的电动机负载几乎     

电机烧毁原因及一款缺相保护器设计

一、电动机烧毁的原因分析1、电动机发热电机烧毁时的主要特征是发热,因此有人认为电机烧毁的原因是由于定子绕组发热,认为只要采取测量定子温度来进行保护就可以保护电机不被烧毁。其实不然,电机的升温和降温是一个相当缓慢的变化过程,因此,只有对大、中型重要的电动机预埋温度传感器,才能实行有效的过热保护。对于小型电机则相当不经济。2、电动机过载有些使用场合电机负载几乎恒定不变,似乎没有必要安装过流保护。但有时会发生堵转使电机过载而烧毁。因此需对电机过载实施反时限特性的保护,一般由过流继电器或热继电器完成。     

变电站10kV出线开关柜烧毁故障分析

变电站10kV出线开关柜烧毁可以引起各种严重后果,为在今后工作中避免烧毁故障发生,需要对故障进行分析并改进。基于此,本文对能够导致10kV出线开关柜烧毁的可能原因进行分析,并针对这些原因提出烧毁故障的监测流程和改进措施,降低10kV出线开关柜烧毁故障发生几率。     

三相交流电动机保护电路

<正> 三相交流电动机广泛应用于工矿,企业生产领域,但在使用中由于负载突然加重等原因造成瞬间电流增大,烧毁某相电源保险丝或因外来电源本身突然缺相,     

电工技术问答

<正> 1、电动机的电源电压过高或过低,为什么都能引起电动机的烧毁? 答:①电压过高时,电动机的激磁电流和电源电压是个非线性关系,在某一范围内,可以近似地认为激磁电流与电压的平方成正比,如电压升高5％,而激磁电流则增加12.5％,但当电压过高时,此时的激磁电流剧增,甚至可达到额定电流的     

农用电动机熔断器的选择与维护

许多农村电动机用户,因选择熔断器熔体的额定电流值不正确,不知道怎样使用维护熔断器而造成电动机及控制线路烧毁的事情时有发生。因此,本文介绍了熔断器选择和维护。     

农用三相异步电动机保护装置

针对农用电动机大量烧毁现象，研制了一种集成化电动机保护装置，该装置具有完善的断相，过流，过载等保护功能，同时具有手动故障自诊断功能，实现了对农用电动机的全方位保护。     

基于一线总线的电动机温度监测系统

针对电动机运行异常时其温度会升高的特点,提出了一种基于一线总线的电动机温度监测系统的设计方案;以某公司烟化炉电动机为例,详细介绍了该系统的硬件结构及上位机软件设计,并给出了该系统在安装调试过程中需要注意的问题。实际应用表明,该系统测量精度高,符合工程要求。     

分析一起电压互感器烧毁及一次保险熔断故障特征及起因

电压互感器烧毁与一次保险熔断故障对整个电力系统的顺利运行具有极大的制约作用,停电检修将会对电力系统造成众多不必要的损失。基于此,本文就电压互感器烧毁及一次保险熔断故障展开相关分析,首先对电压互感器烧毁故障的特征和原因进行了有效分析,然后提出了相应的防范方法     

三相电动机缺相报警及自动保护装置

针对三相电动机在运行中缺相问题,研制出一种报警及自动保护装置,防止电机因跑单相而烧毁。     

常用佳能复印机定影温度异常故障代码清除技术

复印机的定影过程,实际就是定影辊内的加热灯来融化复印件上的墨粉,再通过加压使其达到定影的目的。但这个加热区若因故障原因,很容易造成加热灯无限量加热,因此烧坏上下定影辊或整机的线路,甚至造成火灾。所以复印机在设计上就增加了一个防止程序,只要定影系统的检测元件发现该系统温度异常,就停止复印机预热或继续工作。当出现定影温度异常故障自检码出现时,无论怎么开关电源,复印机都不会重新再工作了,必需用代码技术去清除故障代码,才能重新开启复印机。这对复印机使用者和维修人员是很实用。     

三相异步电动机缺相的原因及处理方法

根据三相异步电动机因缺相运行导致烧坏的实例,详细分析了缺相运行时的现象及产生原因。提出了合理的解决方法,取得了良好的效果。     

The collection 5 MODIS burned area product — Global evaluation by comparison with the MODIS active fire product

The results of the first consecutive 12 months of the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) global burned area product are presented. Total annual and monthly area burned statistics and missing data statistics are reported at global and continental scale and with respect to different land cover classes. Globally the total area burned labeled by the MODIS burned area product is 3.66 × 10⁶ km² for July 2001 to June 2002 while the MODIS active fire product detected for the same period a total of 2.78 × 10⁶ km², i.e., 24% less than the area labeled by the burned area product. A spatio-temporal correlation analysis of the two MODIS fire products stratified globally for pre-fire leaf area index (LAI) and percent tree cover ranges indicate that for low percent tree cover and LAI, the MODIS burned area product defines a greater proportion of the landscape as burned than the active fire product; and with increasing tree cover (> 60%) and LAI (> 5) the MODIS active fire product defines a relatively greater proportion. This pattern is generally observed in product comparisons stratified with respect to land cover. Globally, the burned area product reports a smaller amount of area burned than the active fire product in croplands and evergreen forest and deciduous needleleaf forest classes, comparable areas for mixed and deciduous broadleaf forest classes, and a greater amount of area burned for the non-forest classes. The reasons for these product differences are discussed in terms of environmental spatio-temporal fire characteristics and remote sensing factors, and highlight the planning needs for MODIS burned area product validation.     

电机振动的频谱分析

详细介绍了电机振动数据采集系统的构成,实验中采用将电机加速到不同转速,突然切断电源,采集电机急停数据,然后利用NI公司的LabVIEW对电机平稳运行和急停振动数据进行频谱分析,在频率上分析引起电机振动的机械原因和电磁原因,对比总结出电机的振动特征.     

Analysis of the relationship between spatial pattern and spectral detectability of areas burned in southern Africa using satellite data

Fires in Africa affect atmospheric emissions and carbon sequestration, landscape patterns, and regional and global climatic conditions. Studies of these effects require accurate estimation of the extent of measurable fire events. The goal of this study was to assess the influence of burned area spatial patterns on the spectral detectability of burned areas. Six Landsat‐7 ETM+ images from the southern Africa were used for burned area mapping and spatial pattern analysis, while contemporaneous MODIS 500 m spatial resolution images were used to measure the spectral detectability of burned areas. Using a 15 by 15 km sample quadrats analysis, we showed that above a burned area proportion threshold of approximately 0.5 the spectral detectability of burned areas increase due to the decrease in the number of mixed pixels. This was spatially related to the coalescence of burned patches and the decrease in the total burned area perimeter. Simple burned area shapes were found at the Botswana site, where the absence of tree cover and the presence of bright surfaces (soil and dry grass) enhanced the spectral contrast of the burned surfaces, thus enabling better estimates of burned area extent. At the Zambia and Congo sites, landscape fragmentation due to human activity and the presence of a tree vegetation layer, respectively, contribute to the presence of small burned area patches, which may remain undetectable using moderate spatial resolution satellite imagery, leading to less accurate burned area extent estimates.     

Research on Extraction of Burned Area based on Saliency Enhancement

The information of burned area is significant for post disaster assessment，ecosystems protection and restoration.So far，the existing detection methods of burned areas are less practical.Based on the FY\|3C MERSI satellite data，various characteristics of the burned area are fully utilized and a new method of burned area mapping is created through saliency enhancement.Two burned areas in the northwestern United States were selected as research areas.Three burned\|area\|sensitive vegetation indices(NDVI，GEMI and NDVIT) were combined with the saliency features of the images to enhance and extract the burned areas.Visual interpretations are used to evaluate the experimental results of the proposed method，and compared with the results of NBR threshold method.The results show that the kappa coefficient of the saliency enhancement method in the two research areas reaches more than 0.68，0.2 higher than NBR threshold method.Experiments show that the saliency enhancement method for mapping burned area is high，and the influence of vegetation change caused by non\|burned has little influence on it，and the method has a certain stability compared with the NBR threshold method.     

Landsat digital analysis of the initial recovery of burned tundra at Kokolik River, Alaska

During late July and early August 1977, a wildfire burned 48km² of tundra in northwestern Alaska near the Kokolik River. The environmental effects of the fire were studied in the field and from aircraft and Landsat data. Three categories of burn severity were delineated using an August 1977 Landsat scene acquired shortly after the fire stopped. Measurable reflectance increased in all three categories by the following year as determined from a Landsat image acquired in August 1978. Regrowth of vegetation in the year following the fire was measured using Landsat digital data and compared with field measurements from selected portions of the burned area. Live vascular plant cover doubled in one of the severely burned portions of the area and increased 33% in a lightly burned portion as determined from field measurements. Landsat-derived measurements showed an increase of 62.5% in reflectance for the severely burned areas, and 53% for the lightly burned areas, which is attributed to regrowth of vegetation. Within the most severely burned portion, 9.6 out of a total of 13.3 km² showed minimal recovery based on the Landsat-derived spectral data. Within the lightly burned portion, 5.9 out of a total of 13.5 km² showed the same range of spectral values as did the control areas. Prefire terrain and vegetation conditions were found to influence burn severity. The drier high-relief areas generally burned more completely than lower-lying wet areas. Satellite data acquired after the fire confirmed this for much of the burned area.     

Assessing the feasibility of a global model for multi-temporal burned area mapping using SPOT-VEGETATION data

The possibility of using the Syst@me Probatoire de l'Observation de la Terre (SPOT)-VEGETATION (VGT) data for global burned area mapping with a single algorithm was investigated. Using VGT images from south-eastern Africa, the Iberian Peninsula and south-eastern Siberia/north-eastern China, we analysed the variability of the spectral signature of burned areas and its relationship with land cover, and performed the selection of the best variables for burned area mapping. The results show that in grasslands and croplands, near-infrared (NIR) and short-wave infrared (SWIR) reflectance always decreases as a result of fire. In forests and woodlands, there may occur a simultaneous decrease of SWIR and NIR or an increase of SWIR and a decrease of NIR. Burning of green vegetation (high values of the Normalized Difference Vegetation Index (NDVI)) tends to result in an increase of the SWIR. The best variables for burned area mapping are different in each region. Only the NIR allows a good discrimination of burned areas in all study areas. We derived a logistic regression model for multi-temporal burned area mapping in tropical, temperate and boreal regions, which handles the spectral variability of burned areas dependent on the type of vegetation. The results underline the feasibility of a single model for global burned area mapping.     

A MODIS assessment of the summer 2007 extent burned in Greece

Devastating fires affected Greece in the summer 2007, with the loss of more than 60 human lives, the destruction of more than 100 villages and hundreds of square kilometres of forest burned. This Letter presents a map of the extent burned and the approximate day of burning in Greece mapped by the MODIS burned area product for 22 June to 30 August 2007 and the burned areas mapped independently by the European Forest Fires Information Service (EFFIS). The characteristics of the two datasets, and an evaluation of the areas burned comparing the MODIS and EFFIS data for the same temporal interval are described.     

Comparison of burned area estimates derived from SPOT-VEGETATION and Landsat ETM+ data in Africa: Influence of spatial pattern and vegetation type

An algorithm for burned area mapping in Africa based on classification trees was developed using SPOT-VEGETATION (VGT) imagery. The derived 1 km spatial resolution burned area maps were compared with 30 m spatial resolution maps obtained with 13 Landsat ETM+ scenes, through linear regression analysis. The procedure quantifies the bias in burned area estimation present in the low spatial resolution burned area map. Good correspondence was observed for seven sites, with values of the coefficient of determination (R²) ranging from 0.787 to 0.983. Poorer agreement was observed in four sites (R² values between 0.257 and 0.417), and intermediate values of R² (0.670 and 0.613) were obtained for two sites. The observed variation in the level of agreement between the Landsat and VGT estimates of area burned results from differences in the spatial pattern and size distribution of burns in the different fire regimes encompassed by our analysis. Small and fragmented burned areas result in large underestimation at 1 km spatial resolution. When large and compact burned areas dominate the landscape, VGT estimates of burned area are accurate, although in certain situations there is some overestimation. Accuracy of VGT burned area estimates also depends on vegetation type. Results showed that in forest ecosystems VGT maps underestimate substantially the amount of burned area. The most accurate estimates were obtained for woodlands and grasslands. An overall linear regression fitted with the data from the 13 comparison sites revealed that there is a strong relationship between VGT and Landsat estimates of burned area, with a value of R² of 0.754 and a slope of 0.803. Our findings indicate that burned area mapping based on 1 km spatial resolution VGT data provides adequate regional information.