Variable-speed generation units have widely been used in pumped storage hydropower plants. Nevertheless, conventional hydropower plants can also benefit from variable speed operation to compensate for efficiency loss when the hydro turbines work at a water head different from the nominal. When the units are connected to the grid through a DC link, some flexibility in the speed of operation is expected, as the generated AC power will be converted into DC power. This work presents the initial considerations for this operation, including estimating the efficiency achieved for revenue evaluation purposes. The case of the Itaipu Power Plant's 50 Hz units connected to a 60 Hz power system through a DC link will be presented as an example of an application.

The definition of the rated voltage of a hydropower generator is a difficult task that depends on several electrical, mechanical, and construction features. Naturally, the trade-off between influence variables must be solved to reach a minimum cost. This work contributes to analyzing the most critical constraints, exposing the authors' experience in solving this trade-off, and proposing an expedited formulation for defining the rated voltage of a generator based on successfully constructed generators deployed worldwide.

This paper presents the application of Infrared Thermography to measure distribution transformer efficiency. The method is very intuitive, practical, and easy to use. The results obtained with the proposed method are compared to those obtained by the standard procedure, showing excellent agreement with them. The paper presents the nature of the losses in energy transformation, the theoretical basis of the proposed method, and the comparison of its results with those obtained from the standard procedure.