Reactive power capability of large hydro generators and the European grid code requirements with respect to voltage stability

IEC 60034-3 and IEEE C50.13 and C50.12 standards state that the manufacturer shall supply the reactive power capability diagram (also known as P-Q capability diagram). The reactive power capability diagram provides the active and reactive power capabilities at rated conditions. IEC 60034-1 standard only mentions the ‘rated power factor” of AC generators.
IEEE C50.13standard states that “For an air-cooled generator, the power factor at output rating is typically set at 0.90, 0.85, or 0.80 overexcited. For a hydrogen-cooled generator, the power factor at output rating is typically set at 0.90 or 0.85 overexcited. If not specified by the purchaser, the rated power factor shall be 0.90. For both air-cooled and hydrogen-cooled generators it is recommended that the generator should be capable of providing 0.95 underexcited power factor at rated MW”. IEEE C50.12 standard states that “the power factor at output rating is typically set at 0.90, 0.85, or 0.80 overexcited”.
Recently approved European grid code has introduced requirements with respect to voltage stability
formulated as the upper bound of v-qpmax region at pmax at the point of connection. The European grid code has to be implemented at national level by corresponding TSOs.
This paper reports an investigation on the ability of a large hydro generator to meet the upper bound of
European grid code requirement and the sensitivity with respect to several factors.