Enhanced partial frequency variation starting of hydroelectric pumping units: Model based design and experimental validation

The hydroelectric pumped storage is one of the most sustainable solutions to store electrical energy for optimizing the grid operation. However, the pump motor starting may constitute a significant issue for the power plant. Indeed, the motor's large power and the long power lines (needed for connecting remotely located plants to the grid) may prevent a direct-on-line start. On the other hand, constraints as spaces availability in the powerhouse, and time and cost availability (especially for revamping projects) limit the feasibility of other starting methods. In this paper, a novel starting method is proposed for the revamping of a hydroelectric power plant (HPP), where a synchronous machine is used to drive the pump. On the basis of the power plant characteristics, an enhanced version of the synchronous starting with partial frequency variation is proposed, leading to the creation of a startup sequence capable of being integrated into the existing excitation control systems’ software (of both the generator and the motor installed in the power plant). Such Enhanced Partial Frequency Variation (EPFV) starting method combines the advantages of back-to-back starting method to the ones of asynchronous starting, without requiring additional equipment in respect to a conventional direct-on-line start solution. This is enabled by the model-based design approach here applied, which allows to determine the correct set of parameters and variables’ thresholds required for the machine startup, taking into account the specific characteristics of the HPP in study. The developed starting sequence, implemented into the real HPP by using the capabilities of the existing digital excitation control systems, allowed the correct starting of the motor. This is demonstrated by experimental data obtained during the 5MVA motor starting tests. The results also prove the effectiveness of the model-based design approach in enabling the definition of the pump starting sequence, as well as validating the mathematical model used for the sequence design.