Steam and Gas Turbines, Engines, and Auxiliaries
What the exam tests
This domain covers turbine stage principles, rotors and blades, gland seals, bearings, lube oil, governors, overspeed trips, condenser vacuum, turning gear, gas-turbine sections, reciprocating engines, and supporting auxiliaries. Expect questions that link a symptom to a mechanical or thermodynamic cause.
Core rules
- Impulse stages use pressure drop in stationary nozzles; reaction stages use pressure drop across moving blades as well. Both convert enthalpy into shaft work.
- Lube oil provides film, cooling, and cleaning; low oil pressure or high temperature must trip or alarm before bearing damage.
- Condenser vacuum lowers exhaust pressure and increases available work. Losing vacuum raises exhaust pressure and can overheat the exhaust hood.
- Turning gear prevents rotor bow during warm-up and cooldown. Gland seal steam keeps air out of a condensing turbine.
Worked example
A turbine has rated speed 3,600 rpm and an overspeed trip set at 110% of rated speed. Trip speed = 3,600 x 1.10 = 3,960 rpm. If a test shows trip at 4,120 rpm, the setting is about 114.4% and is too high for a typical 110% design. The reasoning: overspeed protection must act before centrifugal stress on blades and rotor becomes unacceptable; the manufacturer's set point governs.
Traps
Do not roll a turbine before turning gear and oil flow are established; do not confuse gland seal steam with cooling steam; do not ignore rising exhaust-hood temperature when vacuum falls; and do not test overspeed trip without controlled conditions.