Abstract: It is challenging to accurately assess the stability and regulation performance of a hydroelectric unit taking part in automatic generation control (AGC) regulation, since substantial nonlinearity arises from the power regulation dead zone specified in the power mode of its governor. This paper establishes a new formula for stability domain calculation by using the describing function method, deriving the system's stability criterion based on the Nyquist theory, and develops a time-domain simulation-based method for determining the operational zone for power regulation quality. Numerical calculations indicate the derived nonlinear stability domain accurately reflects the stability of the turbine governor’s power regulation transients with a dead zone. Based on regulation quality variations, the stability domain can be divided into five zones, with Zone III identified as the optimal operating domain, where the overshoot and number of oscillations are both zero and the power adjustment speed is fast, meeting the requirements for no oscillation and certain adjustment speed. This study would help optimization and adjustment of a hydropower unit’s power regulation parameters for better stability and regulation quality.

Key words: turbine governor, power regulation, power dead zones, nonlinear stability, regulation quality, operational domains