INVESTIGATING THE MALFUNCTION OF A HYDRO- GENERATOR'S COOLING-SYSTEM
Electro-magnetic losses within a hydro-generator are sources of heat which heat the generator, and then have to be conducted away. This may, however, cause a temperature rise of the stator bars thus reducing the life-span of the insulation materials. Therefore, any temperature rise of the stator windings is limited. In order to inspect the operation of a cooling-system, several temperature sensors have to be integrated into the stator core in order to measure its temperature, which should not exceed 80 0 C. Temperature measurements performed on a generator showed some deviations from the design temperatures, especially at full-power operation. Thus, an attempt was made to analyse the operation of a cooling-system, and to eventually increase its cooling capacity. It was impossible to perform any complex measurements during the generator’s operation, due to safety reasons. Therefore, our work was limited to 3D CFD simulations using ANSYS CFX 11 solver. The simulations were partly supported by the measurements of some main integral parameters, such as mass-flow rate and pressure drop across the cooling ducts and radiators, as performed during generator idling. The results are presented and discussed in this paper.
Heat Transfer Analysis in Cooling System of Hydropower’s Generator
Cooling process of power plant generator is handled via air-cooled radiators in which the cooling water is supplied from lake with its water temperature varies from season to season. In this study, the effect of temperature fluctuations of cooling water entering the cooling system has been examined via analysis of energy (NTU method) and exergy. The exergy analysis has been done by definition of efficiency coefficient for exergy of cooling media (water) and heating media (air). Besides, the effect of changing the cooling water temperature and flow rate entering the radiators on the cooling system performance has been studied. The results revealed the generator cooling system performance level held sufficient till the temperature of inlet water was kept under 293 k (20°C). On one hand, when the temperature of cooling water at the inlet rises to 12°C, the rate of heat exchange at radiators falls up to 34.3%. On the other hand, by water temperature passing the 12°C limit, the efficiency of cooling media exergy falls to 78% leading to efficiency rise in radiators’ heating media exergy level to 61%. According to the results of this study, changing flow rate of cooling media up to 40% gives rise to the efficiency coefficient of radiators’ cooling media exergy level to about 18.7%. While it does not affect the efficiency level of energy at radiators, the flow rate rise of cooling media may not be considered as a way to give rise to efficiency level of radiators.
Integrating Local CNN and Global CNN for Script Identification in Natural Scene Images
Script identification in natural scene images is a key pre-step for text recognition and is also an indispensable condition for automatic text understanding systems that are designed for multi-language environments. In this paper, we present a novel framework integrating Local CNN and Global CNN both of which are based on ResNet-20 for script identification. We first obtain a lot of patches and segmented images based on the aspect ratios of the images. Subsequently, these patches and segmented images are used as inputs to Local CNN and Global CNN for training, respectively. Finally, to get the final results, the Adaboost algorithm is used to combine the results of Local CNN and Global CNN for decision-level fusion. Benefiting from such a strategy, Local CNN fully exploits the local features of the image, effectively revealing subtle differences among the scripts that are difficult to distinguish such as English, Greek, and Russian. Moreover, Global CNN mines the global features of the image to improve the accuracy of script identification. The experimental results demonstrate that our approach has a good performance on four public datasets.