Abnormal Conditions, Trips, and Emergency Response
Core concepts
Candidates must diagnose abnormal conditions by pattern: rising vibration with stable load suggests rub, imbalance, or bearing wear; rising axial displacement suggests thrust failure; falling vacuum with rising exhaust temperature suggests condenser air in-leakage or cooling-water loss; sudden load rejection produces overspeed. Know the immediate response to a trip: verify the trip, ensure steam or fuel is isolated, maintain lube oil and turning gear, and investigate before restart. Understand water induction, steam hammer, and the danger of admitting water to a hot turbine.
Traps
Questions often test whether to trip or to reduce load. A slow trend may allow controlled unloading; a fast trend or protective limit requires immediate trip. Another trap is the post-trip priority: lube oil must continue until the rotor stops and cools, even though the unit is offline. Do not confuse a load rejection (grid loss) with a turbine trip; the unit may survive load rejection if bypass and governor respond.
Worked rule of thumb
If load rejection occurs, expect speed to rise until the governor closes the valves; overspeed trip should be the backup, not the primary response. If speed approaches the trip setpoint and valves have not closed, the correct action is to trip manually and investigate the control system.
Exam focus
Be ready to match symptoms to causes and to sequence emergency actions: protect personnel, isolate energy, preserve lubrication, then diagnose.