Turbine Operation (TO) key terms

The reduction in a fluid's total heat content as it expands through a turbine stage, representing the energy converted into shaft work plus losses.

The ratio of actual work extracted from a turbine to the work that would be extracted in an ideal, frictionless expansion between the same inlet and outlet pressures.

The amount of thermal energy input required to produce one unit of electrical output, commonly expressed in Btu per kilowatt-hour; lower values indicate better plant efficiency.

A single turbine element consisting of one stationary nozzle row that accelerates the working fluid and one rotating blade row that extracts energy from it.

A turbine design in which pressure and velocity drop occur across both stationary and rotating blade rows, so the rotor is driven partly by pressure forces.

A turbine design in which the full pressure drop occurs in stationary nozzles, and the rotating blades extract energy mainly from the high-velocity jet with little pressure change.

A rotational speed at which a rotor assembly resonates with its own natural frequency, producing amplified vibration that must be passed through quickly during run-up or coastdown.

A cylindrical bearing that supports the rotating shaft on a pressurized film of lubricating oil, carrying radial load while allowing smooth rotation.

A bearing that resists axial forces pushing the rotor along its axis, typically using tilting pads fed with pressurized oil to maintain a load-bearing film.

A clearance-sealing arrangement at the point where the rotor passes through the casing, using steam, air, or labyrinth teeth to limit leakage of working fluid or ingress of air.

A non-contacting seal made of a series of close-clearance ridges and cavities that throttles leakage flow by repeatedly accelerating and dissipating it.

The sub-atmospheric pressure maintained in the exhaust condenser so the turbine can expand steam to a low temperature and extract more work.

The condition in which a rotor's mass is distributed so that centrifugal forces cancel, minimizing vibration; balancing is performed during manufacture and after major repairs.

The controlled acceleration of the turbine from turning gear or barring speed up to synchronous speed, observing hold points, thermal limits, and vibration criteria.

A slow-speed drive that rotates the shaft when the machine is shut down, preventing rotor bowing from uneven cooling and keeping bearing surfaces wetted.

The process of matching generator voltage, frequency, phase angle, and phase sequence to the grid before closing the breaker to connect the unit.

Internal stress produced when temperature differences within thick metal parts cause uneven expansion; rapid heating or cooling raises this stress and can crack components.

The maximum permitted speed of change in turbine output, set to keep thermal stresses and boiler or reactor transients within design limits.

A protective action that rapidly closes the main stop valves when shaft speed exceeds a set limit, typically triggered by a mechanical bolt or redundant electrical sensors.

A control loop that compares actual shaft speed with a setpoint and adjusts valve position to regulate speed or load, including droop and isochronous modes.

The programmed decrease in speed setpoint as generator load increases, allowing multiple units to share load stably in parallel on a grid.

A hardwired or redundant protection circuit that directly de-energizes trip solenoids to close stop valves when any critical parameter exceeds its limit.

Continuous measurement of shaft and bearing vibration, with alarm and trip thresholds, used to detect imbalance, misalignment, rubs, and bearing degradation early.

A pressure surge caused by sudden stopping or reversal of liquid flow in piping, which can rupture lines and damage valves and turbine internals.

A violent shock in steam piping caused by trapped condensate being picked up by high-velocity steam, potentially damaging valves, supports, and blading.

Piping, valves, and traps that remove condensed water from steam lines and turbine casings, preventing erosion, hammer, and thermal shock.

The thin pressurized layer of lubricant separating shaft and bearing surfaces, which must be maintained to prevent metal-to-metal contact and overheating.

Inspection methods such as ultrasonic, magnetic particle, dye penetrant, and radiography that reveal internal or surface defects without damaging the component.

Visual examination of internal turbine passages, blading, and seals using a flexible or rigid optical probe inserted through casing ports, often without full disassembly.

A safety procedure that isolates energy sources and attaches locks and tags so equipment cannot be re-energized or started while personnel work on it.

A formal written authorization that defines the scope, hazards, and controls for a specific maintenance or operational task before work begins.

A regulatory cap on the temperature or heat content of cooling water returned to a river, lake, or estuary, protecting aquatic life from thermal pollution.

The increase in cooling water temperature as it passes through the condenser, which affects vacuum, plant efficiency, and compliance with discharge permits.

A measure of oil's resistance to flow; it must be high enough to form a load-bearing film yet low enough to circulate and cool the bearings.

A chemical additive that forms a protective film or alters water chemistry to slow metal attack in condensers, boilers, and cooling circuits.

A measure of a water sample's ability to carry current, used as an indicator of dissolved ion concentration and contamination in steam, condensate, and cooling water.

The power required by the grid at a given moment, which the unit must follow within its ramp capability while respecting thermal and emission limits.

The ratio of real power to apparent power in an AC circuit; it determines reactive power support and must be managed within generator capability limits.

The system-wide alternating-current frequency, held near its nominal value by balancing generation and demand; it provides a reference for governor response and load shedding.