Grid Stabilization by Preventing Undesired Triggering of the Reverse Power Protection of Steam Turbines at Overfrequency

The turbine governor of a steam power plant is usually equipped with a Reverse Power Protection (RPP), which avoids generator motoring and ventilation by quickly disconnecting the generator from the grid when reverse power is detected. In this paper, we discuss how the RPP can be triggered even though the plant should remain connected to the grid during overfrequency events, and we present a validated solution for the problem. When the grid frequency rises above 50.2 Hz in the Continental European synchonous area, the mechanical power of the turbine is reduced in accordance with the specifications for LFSM-O (Limited Frequency Sensitive Mode at Overfrequency). Especially in part-load operation, large positive frequency deviations can then result in reverse power and the triggering of the RPP. Using validated simulation models, we investigated under which conditions the RPP could be triggered unintentionally, and developed countermeasures for the control system. These measures were implemented in Altbach HKW 2, a 355 MWel coal-fired power plant in Germany, as part of a migration of the power plant control system, and tested with a corresponding test programme at the plant during operation. Further improvements to the control system were developed and tested using Hardware-in-the-Loop simulations.