Abstract-This paper presents the remaining lifetime calculation of power transformers paper insulation and consequently of power transformers. The calculations are performed based on two models, which are related to the thermal degradation of the cellulose winding paper insulation: the common IEC loading guide and a paper degradation model. The paper insulation model's prediction can be improved by involving data from furfural analysis. The remaining lifetime is extracted from the fault probability (reliability) of the paper insulation. The two models are brought together, to aid the asset manager in the decision making process. A probabilistic approach is used, which can be coupled to analysis in terms of risks, benefits, costs, and availability by the asset manager.

No abstract

No abstract

In countries with a high ambient temperature and strong solar irradiation, transformer winding hot-spot temperature may increase over its maximum permissible limit. This can considerably reduce the insulation life of the transformer by enhanced degradation of the paper insulation. According to current loading guides, for each 6 K increase in working temperature, the ageing rate increases with approximately a factor two. Therefore, it is important to take into consideration the impact of the sun on the power transformer thermal behavior. In this paper, a modified hot-spot temperature model is presented to account for the effect of transformer winding temperature rise by solar irradiation. The effects of solar irradiation on transformer winding paper insulation are shown by comparing the degree of polymerisation (DP), the fault probability and the remaining life. Here, the fault probability is defined as the probability that the estimated DP-value at a certain moment in time is below a certain end-of-life criterion (threshold value). An additional winding hot-spot temperature rise of 9 K during the summer and a temperature rise of 6 K during the winter may occur in countries with strong solar irradiation. This may result in a reduction of the remaining lifetime by up to 40%.

No abstract

PV Plants connected to the medium voltage grid do not contribute to the grid stability. In order to prevent grid instability, directives (codes) for connecting PV plants to the medium voltage power grid have been released. The supply and control of the reactive power from the renewable generation plants are becoming important issues to be studied, because they can facilitate the integration of PV in power grids. In this paper, two new models of a 6.09 MW PV plant, used to analyze its grid integration according to the grid code, are presented. The first is a simplified model, without taking into account transformers and cables, while the second one is a more complex model which includes these components. The model was developed using PSCAD-EMTDC software. The final part of the paper presents the active-reactive power (P-Q) charts, calculated at the common coupling point (CCP), for different levels of solar radiation (0% to 100%). Based on these charts, it is determined the maximum output power level which can be generated by the plant, according to the current grid code.

No abstract

No abstract