Provide review of power system stability principles and the functionality of the key components for its frequency regulation. Review and describe fundamentals of hydroelectric generators excitation systems and their impact on the power system frequency and voltage stability. Provide in-depth review of power system stabilizers, their interface and integration with generator excitation control systems, including PSS modeling and methodology for establishment of their settings. Discuss proper approach and best practices in PSS testing and commissioning. Provide guidance for proper PSS maintenance and effective monitoring practices, including examples of anecdotal case studies and practical experiences.