What are the causes of increased axial displacement in steam turbines?
1 Answers
The main causes of increased axial displacement in steam turbines include: (1) Decrease in steam temperature and pressure, overload in the flow passage, and shutdown of regenerative heaters; (2) Increased steam leakage due to wear in the diaphragm shaft seal clearance; (3) Poor steam quality leading to scaling in the flow passage; (4) Water hammer occurrence; (5) Load variations. Generally, the axial thrust of condensing steam turbines increases with load; for extraction or back-pressure turbines, the maximum axial thrust may occur at a certain intermediate load. (6) Damage to thrust bearings; (7) Drop in condenser vacuum; (8) Decrease in grid frequency. Key points for handling increased axial displacement: (1) When increased axial displacement is detected, pay special attention to the temperature of thrust bearing pads and their return oil temperature, monitor turbine vibration, and listen for any abnormal sounds inside the turbine. (2) If axial displacement increases to the alarm value (+1, -1.45 mm), quickly reduce the load to bring it below the alarm value, report to the shift leader to identify the cause and take action, and keep a record. (3) If axial displacement increases to the trip value (+1.2, -1.65 mm) and the protection does not activate, and the thrust bearing pad temperature rises to 95°C, perform an emergency shutdown. (4) If axial displacement increases significantly, vibration rises notably, and bearing return oil temperature increases sharply to 75°C, perform an emergency shutdown. (5) Even if axial displacement has not reached the limit value, but thrust bearing temperature rises significantly and any thrust pad temperature reaches 95°C, and load reduction does not resolve the issue, perform a fault shutdown.
