Repowering and Evaluation of New Power of Synchronous Generators

Useful life of winding insulation is about 30 years. This may be reduced when it is overloaded or when it works in aggressive environments. When retrofitting is undertaken an increase to a higher insulation class is recommendable. So the generator's capacity should be increased, and this will not just more than fully compensate for the investment made it will also result in a more efficient use of the raw materials used and thus contribute to sustainable development. Our Brazilian experience shows that retrofitting with repowering is successful. The objective of this study is to present two cases of repowering, in which the old insulating materials were replaced by other, modem ones. So, eight SG of a Power Plant in Cubatao, S.P and two SG of CEMIG, MG had its power increased up to 40%. The discussion also deals with how to determine the new power obtained after the repowering, before the final load tests. In large machines, the load tests are critical. In order to calculate the field current of the full load SG to determine the temperature rise in field, indirect tests are undertaken. Which are the methods that present reliable results? This study compares three study methods, ASA, IEEE 115, and the General Method with their theoretical analyses. The ASA method is now regarded as normal in many countries. According to Brazilian Standards it is given under NBR-5052. In the IEEE 115, this method is named "Phasor Diagram Analysis-Salient-Pole Machines". The General Method is an academic treatment with a better theoretical basis.