Voltage regulation.
Due to the long water diversion pipe of the power plant, when the unit suddenly loses its load and closes the guide vane during operation, there will be a significant water hammer effect due to the inertia of water flow. If there is no pressure regulating well (also called pressure well), water hammer will destroy the water guide vane and other flow passage components.
The function of the pressure regulating well is to provide a water hammer release channel to reduce the pressure of components passing through the flow.