Turbine Operation (TO) flashcards

35 cards. Read the term and the definition here. The deck at the top of this page is optional.

Isentropic efficiency

Ratio of actual enthalpy drop across a turbine stage or cylinder to the ideal isentropic enthalpy drop for the same inlet and outlet pressures; typically 80-90% for large steam turbines.

Rankine cycle

Ideal steam power cycle with pump, boiler, turbine, and condenser; efficiency improves with higher steam temperature and pressure and with lower condenser pressure.

Nozzle choking

Condition where steam velocity reaches sonic at the nozzle throat; further downstream pressure reduction does not increase mass flow, which then depends only on upstream conditions.

Degree of reaction

Fraction of stage enthalpy drop occurring in the rotor; a 50% reaction stage has equal enthalpy drops in stator and rotor and symmetrical velocity triangles.

Heat rate

Thermal energy input per unit electrical output, usually kJ/kWh; lower heat rate means higher efficiency and is calculated as 3600 divided by thermal efficiency.

Fir-tree blade root

Serrated root profile that transmits centrifugal load to the rotor disc through multiple contact surfaces; used on long blades and inspected for fretting and cracking.

Gland steam system

Supplies low-pressure steam to shaft-end labyrinth seals to prevent air ingress into the condenser vacuum and steam escape into the turbine hall.

Kingsbury thrust bearing

Tilting-pad thrust bearing that carries residual axial thrust not balanced by the dummy piston; pad temperature and oil flow are monitored during operation.

Surface condenser

Shell-and-tube heat exchanger that condenses exhaust steam on the shell side using cooling water in tubes; maintains vacuum and returns condensate to the feedwater system.

Turning gear

Low-speed barring device that rotates the rotor after shutdown to prevent thermal bowing from uneven cooling; interlocked against engagement at high shaft speed.

Differential expansion

Difference in thermal growth between rotor and casing along the axis; excessive positive or negative values cause axial rubs and are a key startup and trip parameter.

Critical speed

Shaft rotational speed at which a natural frequency of the rotor-bearing system is excited; speeds must be passed rapidly during startup and never held.

Cold start

Startup where turbine metal temperatures are near ambient, requiring slow steam admission and gradual loading to limit thermal stress and differential expansion.

Water induction

Entry of water into the turbine from drains, attemperation, or boiler carryover; causes thermal shock, water hammer, and blade damage, requiring immediate trip.

Speed droop

Governor characteristic where a frequency change of a set percentage (typically 4-5%) causes output to change from zero to full load; supports load sharing among units.

Overspeed trip

Independent protection that closes main stop and control valves when speed reaches about 110-111% of rated; tested periodically by mechanical or electronic means.

Fail-safe trip design

Protection philosophy where loss of control power or hydraulic pressure causes valves to close and the unit to trip, so failures default to a safe state.

First-out indication

Control system function that identifies the first trip signal in a sequence, helping operators determine the initiating cause among multiple subsequent alarms.

Proximity probes

Eddy-current sensors mounted on bearing housings that measure shaft-relative vibration and axial position, feeding protection and diagnostic systems.

Load rejection

Sudden loss of electrical load while the unit is running; bypass valves and speed control act to prevent overspeed, and the unit may run back to house load.

Reverse power protection

Relay that trips the generator breaker when power flows into the generator from the grid, preventing turbine blade overheating from motoring and windage.

Bearing metal temperature

Temperature measured by embedded RTDs in bearing pads; rising values indicate oil starvation, misalignment, or overload and lead to alarm or trip.

Condenser vacuum loss

Rise in exhaust pressure from air in-leakage, cooling-water loss, or fouling; raises exhaust hood temperature and risks LP blade overheating, requiring load reduction or trip.

Non-destructive examination

Inspection methods such as dye penetrant, magnetic particle, ultrasonic, and eddy current used to detect cracks and defects without damaging turbine components.

Overspeed test

Periodic verification that the overspeed trip operates at its setpoint, performed by actual overspeed or by a test device that simulates trip conditions.

Valve stroke test

Scheduled test that moves main stop and control valves through full travel to verify freedom of movement and closing time, often done before startup.

Oil analysis

Laboratory testing of lube oil for water content, particle count, acidity, and varnish potential to detect contamination and degradation before bearing damage occurs.

Lockout/tagout

Energy isolation procedure that de-energizes and locks steam, water, oil, and electrical sources before maintenance, with verification of zero energy state.

Confined space permit

Authorization required before entering condensers, drums, or vessels; includes atmosphere testing, ventilation, an attendant, and rescue provisions.

Thermal discharge limits

Regulatory limits on cooling-water return temperature and temperature rise to protect aquatic ecosystems; compliance monitored by discharge temperature records.

Cation conductivity

Conductivity measured after passing a sample through cation resin; sensitive indicator of dissolved ionic impurities such as chloride and sulfate in steam and condensate.

Hydrogen purity

Percentage of hydrogen in generator cooling gas; maintained above a set minimum, with oxygen and moisture limited to prevent arcing and corrosion of windings.

Synchronization conditions

Before breaker closure, generator voltage magnitude, frequency, phase angle, and phase sequence must match the grid within specified tolerances to avoid damaging transients.

Primary frequency response

Automatic governor response to grid frequency deviation, changing output according to droop setting to help restore system frequency within seconds.

Loss-of-field protection

Relay scheme that detects loss of generator excitation and trips or alarms, preventing stator overheating and unstable operation from reduced reactive support.