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Turbine Operation (TO) study materials
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Turbine Operation (TO) practice questions

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Question 1Turbine Fundamentals and Thermodynamics

In a simple ideal Rankine cycle, which component raises the pressure of liquid water before it enters the boiler?

  1. The reheater
  2. The condenser
  3. The turbine
  4. The feedwater pump Correct answer.

Explanation

The feedwater pump receives condensate at low pressure and does work on the incompressible liquid to raise it to boiler pressure. The boiler then adds heat at nearly constant pressure. The turbine is the expander and the condenser rejects heat.

Question 2Turbine Fundamentals and Thermodynamics

Which statement correctly describes the energy conversion in a steam turbine stage?

  1. Thermal energy is converted to mechanical shaft work as steam expands Correct answer.
  2. Steam velocity decreases while pressure rises across the nozzles
  3. Steam pressure rises while enthalpy stays constant across the stage
  4. Mechanical work is converted to thermal energy as steam is compressed

Explanation

In a turbine stage the steam expands through nozzles and blades, so enthalpy drops and the energy appears as shaft work. Pressure falls in the direction of flow. Compression and pressure rise are characteristics of compressors and pumps, not turbines.

Question 3Turbine Fundamentals and Thermodynamics

Which temperature scale must be used when applying the ideal-gas relation and the Carnot efficiency formula?

  1. Absolute temperature, such as kelvin Correct answer.
  2. Fahrenheit temperature measured at the outlet
  3. Celsius temperature measured at the inlet
  4. Any scale, provided both values use the same unit

Explanation

Thermodynamic relations such as efficiency equal to one minus the ratio of cold to hot temperature require absolute temperature. Using Celsius or Fahrenheit ratios gives wrong results because the zero points are arbitrary. Kelvin and Rankine are absolute scales and are acceptable.

Question 4Turbine Fundamentals and Thermodynamics

What is the primary purpose of the condenser in a steam power plant?

  1. To superheat steam before it enters the high-pressure turbine
  2. To reject latent heat so exhaust steam returns to liquid for reuse Correct answer.
  3. To increase steam pressure between turbine stages
  4. To remove dissolved gases from boiler feedwater

Explanation

The condenser transfers latent heat from exhaust steam to cooling water, condensing the steam at low pressure. This low back pressure increases the work available from the turbine and recovers condensate for the cycle. Superheating and deaeration are separate functions.

Question 5Turbine Fundamentals and Thermodynamics

A turbine stage in which steam pressure drops across fixed nozzles and moving blades but the steam velocity stays essentially constant through the moving row is best described as which type?

  1. A radial-flow stage
  2. A velocity-compounded stage
  3. A reaction stage
  4. An impulse stage Correct answer.

Explanation

In a pure impulse stage, enthalpy drops only in the stationary nozzles, so pressure falls there while the moving blades see essentially constant pressure and velocity. Reaction stages drop pressure in both the fixed and moving rows. Velocity compounding uses multiple moving rows with fixed guide vanes between them.

Question 6Turbine Fundamentals and Thermodynamics

Which quantity represents the fraction of the total turbine-stage energy drop that occurs in the moving blades?

  1. Stage loading coefficient
  2. Degree of reaction Correct answer.
  3. Diagram efficiency
  4. Flow coefficient

Explanation

The degree of reaction is defined as the static enthalpy drop across the rotor divided by the static enthalpy drop across the whole stage. A value of zero corresponds to a pure impulse stage and a value near one-half is typical of a symmetrical reaction stage. The other named coefficients describe velocity triangles and aerodynamic losses.

Question 7Turbine Fundamentals and Thermodynamics

Which statement about the Carnot efficiency of a heat engine is correct?

  1. It depends on the working fluid selected for the cycle
  2. It equals the actual efficiency of a well-maintained steam turbine
  3. It sets an upper limit that no real engine operating between the same two reservoirs can exceed Correct answer.
  4. It increases as the heat-rejection temperature rises

Explanation

Carnot efficiency depends only on the absolute temperatures of the hot and cold reservoirs and represents the maximum possible efficiency. Real cycles with irreversibilities always fall below it. Raising the cold-reservoir temperature lowers Carnot efficiency, and the fluid identity does not enter the formula.

Question 8Turbine Fundamentals and Thermodynamics

Steam enters a turbine at 500 degrees Celsius and exhausts at 40 degrees Celsius. Using absolute temperatures, what is the Carnot efficiency between these limits?

  1. About 92 percent
  2. About 40 percent
  3. About 8 percent
  4. About 60 percent Correct answer.

Explanation

Convert to kelvin: 773 K and 313 K. Carnot efficiency is one minus 313/773, which equals about 0.595, or roughly 60 percent. Remember to use absolute temperature, not the Celsius values.

Question 9Turbine Fundamentals and Thermodynamics

A turbine expands steam with an actual enthalpy drop of 180 kJ/kg. If the isentropic enthalpy drop for the same inlet and outlet pressure is 200 kJ/kg, what is the stage isentropic efficiency?

  1. 90 percent Correct answer.
  2. 80 percent
  3. 111 percent
  4. 20 percent

Explanation

Isentropic efficiency is the actual enthalpy drop divided by the isentropic enthalpy drop. Here 180 divided by 200 equals 0.90, or 90 percent. The actual drop is always smaller than the ideal drop because of friction and other losses.

Question 10Turbine Fundamentals and Thermodynamics

Why does reheating steam between turbine stages improve cycle performance?

  1. It lowers the condenser pressure below the cooling-water temperature
  2. It removes the irreversibility of the expansion process
  3. It eliminates the need for a feedwater pump
  4. It raises the average temperature of heat addition while limiting exhaust moisture Correct answer.

Explanation

Reheating returns steam to the boiler after partial expansion, adding heat at a relatively high temperature and thereby raising the mean temperature of heat addition. It also reduces the moisture that forms in the later stages. It does not change the condenser limit or remove irreversibility.

Question 11Turbine Fundamentals and Thermodynamics

In a regenerative feedwater heating arrangement, extracted steam is used to warm the feedwater. What is the main thermodynamic benefit?

  1. It raises the average temperature of heat addition in the boiler Correct answer.
  2. It allows the condenser to operate at a higher pressure
  3. It increases the mass flow through the final turbine stages
  4. It lowers the enthalpy of steam entering the high-pressure turbine

Explanation

Bleeding steam to heaters raises the feedwater temperature entering the boiler, so less low-temperature heat addition is needed. This increases the mean temperature of heat addition and improves cycle efficiency. The trade-off is reduced flow through the later turbine stages.

Question 12Turbine Fundamentals and Thermodynamics

A nozzle accelerates steam from negligible velocity to 400 m/s. Neglecting losses, what is the approximate drop in specific kinetic energy, expressed as an enthalpy drop?

  1. 0.8 kJ/kg
  2. 160 kJ/kg
  3. 8 kJ/kg
  4. 80 kJ/kg Correct answer.

Explanation

Specific kinetic energy equals one-half velocity squared. For 400 m/s this is 0.5 times 160000, or 80000 J/kg, which is 80 kJ/kg. In a lossless nozzle this kinetic energy comes from an equal enthalpy drop.

Question 13Turbine Fundamentals and Thermodynamics

What happens to the work output of a turbine stage if the leaving velocity (exit kinetic energy) is large and is not recovered by the next stage?

  1. It is doubled because kinetic energy scales with velocity squared
  2. It is unchanged because kinetic energy is not part of the energy balance
  3. It is increased because exit velocity adds to shaft work
  4. It is reduced because that kinetic energy leaves as a loss Correct answer.

Explanation

Energy that leaves a stage as high exit velocity is not converted to shaft work within that stage. Unless the following stage recovers it, it appears as a leaving-velocity loss and lowers stage efficiency. The steady-flow energy balance includes kinetic energy terms explicitly.

Question 14Turbine Fundamentals and Thermodynamics

Which condition corresponds to choked flow through a turbine nozzle?

  1. The throat velocity reaches the local speed of sound Correct answer.
  2. The exit pressure falls to exactly half the inlet pressure
  3. The nozzle exit area equals the inlet area
  4. The steam becomes saturated liquid at the throat

Explanation

Choking occurs when the mass flow per unit area reaches a maximum at the throat, which happens when throat velocity equals the local sonic velocity. Further lowering the downstream pressure does not increase the mass flow. The critical pressure ratio depends on the fluid and its specific-heat ratio, not on a universal value.

Question 15Turbine Fundamentals and Thermodynamics

Steam at 3 MPa and 400 degrees Celsius enters a turbine and leaves at 10 kPa with a quality of 0.92. Which quantity is most directly needed to compute the actual work per kilogram in a steady-flow analysis?

  1. The inlet and outlet specific volumes only
  2. The inlet and outlet specific enthalpies Correct answer.
  3. The cooling-water flow rate
  4. The inlet and outlet steam velocities only

Explanation

For an adiabatic turbine with negligible changes in kinetic and potential energy, work per unit mass equals the drop in specific enthalpy between inlet and outlet. The outlet enthalpy follows from the pressure and quality. Velocities and cooling-water flow are not needed for this calculation.

Question 16Turbine Fundamentals and Thermodynamics

A turbine stage has a mean blade speed of 150 m/s and an axial steam velocity of 75 m/s. What is the flow coefficient?

  1. 0.5 Correct answer.
  2. 2.0
  3. 1.5
  4. 0.25

Explanation

The flow coefficient is the ratio of axial velocity to blade speed. Dividing 75 by 150 gives 0.5. This parameter, together with the stage loading coefficient, shapes the velocity triangles and stage efficiency.

Question 17Turbine Fundamentals and Thermodynamics

In an ideal Rankine cycle, why is the feedwater pump work usually neglected in approximate efficiency calculations while it matters in detailed ones?

  1. Pump work is small because liquid specific volume is small, but it is not zero Correct answer.
  2. Pump work cancels exactly with condenser heat rejection
  3. Pump work is always larger than turbine work
  4. Pump work is exactly zero for all liquids

Explanation

Pump work is the product of specific volume and pressure rise, and liquid specific volume is small, so the term is often a few percent of turbine work. It is still nonzero and becomes significant in high-pressure or detailed analyses. It does not cancel with condenser heat rejection.

Question 18Turbine Fundamentals and Thermodynamics

A turbine develops 50 MW of shaft power while the steam mass flow is 60 kg/s. What is the approximate specific work output?

  1. 833 kJ/kg Correct answer.
  2. 0.83 kJ/kg
  3. 1.2 kJ/kg
  4. 3000 kJ/kg

Explanation

Specific work is power divided by mass flow. Fifty megawatts is 50000 kJ/s, and dividing by 60 kg/s gives about 833 kJ/kg. This is a typical order of magnitude for a large steam turbine.

Question 19Turbine Fundamentals and Thermodynamics

Which change raises the thermal efficiency of an ideal Rankine cycle while keeping the turbine exhaust moisture acceptable?

  1. Increasing the condenser pressure
  2. Decreasing the boiler pressure at fixed temperature
  3. Adding heat to the feedwater in the condenser
  4. Increasing the boiler pressure with reheat Correct answer.

Explanation

Raising boiler pressure increases the mean temperature of heat addition and thus efficiency, but it also tends to increase exhaust moisture. Reheat counters the moisture rise, so the combination is used in practice. Lowering boiler pressure or raising condenser pressure reduces efficiency.

Question 20Turbine Fundamentals and Thermodynamics

Steam is throttled through a valve from 8 MPa to 1 MPa with negligible heat loss and negligible velocity change. Which property remains essentially constant?

  1. Temperature
  2. Specific enthalpy Correct answer.
  3. Specific volume
  4. Specific entropy

Explanation

A throttling process is adiabatic with no work and negligible kinetic and potential energy changes, so the steady-flow energy balance reduces to constant enthalpy. The process is highly irreversible, so entropy increases and temperature usually drops.

Question 21Turbine Fundamentals and Thermodynamics

A stage has an isentropic efficiency of 85 percent and an ideal enthalpy drop of 120 kJ/kg. What is the actual exit enthalpy if the inlet enthalpy is 3200 kJ/kg?

  1. 3080 kJ/kg
  2. 3200 kJ/kg
  3. 3302 kJ/kg
  4. 3098 kJ/kg Correct answer.

Explanation

The actual enthalpy drop is 0.85 times 120, or 102 kJ/kg. Subtracting this from the inlet enthalpy of 3200 kJ/kg gives 3098 kJ/kg. Actual drop is always smaller than ideal drop for an expander.

Question 22Turbine Fundamentals and Thermodynamics

Why does a reaction turbine typically have a smaller pressure drop per stage than an impulse turbine?

  1. The rotor blades in a reaction stage do no work
  2. Reaction stages cannot be stacked in series on one shaft
  3. The steam velocity in a reaction stage is always supersonic
  4. Part of the enthalpy drop occurs in the moving blades, so each stage carries less drop Correct answer.

Explanation

In a reaction stage, expansion occurs in both the fixed and moving rows, so the pressure drop is shared and each stage carries a smaller drop. This usually means more stages for a given overall pressure ratio. Reaction blading is normally subsonic and is routinely stacked in series.

Question 23Turbine Fundamentals and Thermodynamics

A turbine with inlet steam at 600 degrees Celsius and condenser at 35 degrees Celsius has an actual cycle efficiency of 42 percent. What is the approximate ratio of actual to Carnot efficiency?

  1. About 0.95
  2. About 0.65 Correct answer.
  3. About 0.30
  4. About 0.42

Explanation

Convert to kelvin: 873 K and 308 K. Carnot efficiency is one minus 308/873, about 0.647. Dividing the actual 0.42 by 0.647 gives roughly 0.65, a reasonable second-law efficiency for a modern plant.

Question 24Turbine Fundamentals and Thermodynamics

In a velocity-compounded impulse stage, steam from the nozzles passes through two moving rows separated by a stationary guide row. What is the main purpose of this arrangement?

  1. To eliminate the need for a stationary nozzle
  2. To absorb a large velocity in two steps and reduce leaving-velocity loss Correct answer.
  3. To increase the pressure drop across each moving row
  4. To raise the steam pressure between the moving rows

Explanation

Velocity compounding divides the high nozzle exit velocity between successive moving rows, so the exit velocity from the last row is lower and leaving loss is reduced. Pressure stays essentially constant through the moving and guide rows of an impulse stage. The nozzles still perform the full expansion.

Question 25Turbine Construction, Components, and Auxiliary Systems

In a large steam turbine, what is the primary function of the thrust bearing?

  1. To reduce radial vibration of the shaft at critical speed
  2. To support the full weight of the rotor against gravity
  3. To seal the shaft where it passes through the casing
  4. To absorb the axial force produced by steam pressure acting on the blades and rotor Correct answer.

Explanation

The thrust bearing carries the net axial load created by steam pressure differences across the stages and holds the rotor's axial position within the clearance limits set by the manufacturer. Radial support is the job of the journal bearings, so the thrust bearing is designed for axial force rather than weight or sealing.

Question 26Turbine Construction, Components, and Auxiliary Systems

A turbine rotor spins at 3,000 rpm. What is its rotational frequency in hertz?

  1. 300 Hz
  2. 60 Hz
  3. 30 Hz
  4. 50 Hz Correct answer.

Explanation

Rotational frequency in hertz equals revolutions per second, so 3,000 rpm divided by 60 seconds gives 50 Hz. This value matters because it sets the fundamental excitation frequency for blade vibration and oil whirl analysis.

Question 27Turbine Construction, Components, and Auxiliary Systems

Which component converts the kinetic energy of steam leaving the last stage into a pressure rise before the steam enters the condenser?

  1. The diffuser section of the exhaust hood Correct answer.
  2. The nozzle diaphragm
  3. The gland steam excluder
  4. The extraction non-return valve

Explanation

The exhaust hood diffuser slows the high-velocity leaving steam, converting kinetic energy into a static pressure recovery that improves overall stage efficiency. Nozzles accelerate steam rather than recover pressure, and the other items serve sealing or protection functions.

Question 28Turbine Construction, Components, and Auxiliary Systems

What is the main purpose of the turning gear (barring gear) on a large steam turbine?

  1. To rotate the rotor slowly during shutdown and startup to prevent thermal bowing Correct answer.
  2. To provide overspeed protection during load rejection
  3. To hold the rotor locked while the turbine is on load
  4. To raise rotor speed during a fast start

Explanation

The turning gear rotates the rotor at a few revolutions per minute so that the shaft cools or heats evenly, avoiding a permanent thermal bow and the vibration it causes. It is not used to accelerate the machine or to lock it during normal operation.

Question 29Turbine Construction, Components, and Auxiliary Systems

In a condenser, what is the effect of a rising cooling-water outlet temperature while steam load stays constant?

  1. Condenser pressure rises but turbine output stays constant
  2. Condenser pressure rises and turbine output falls Correct answer.
  3. Condenser pressure falls and turbine output rises
  4. Condenser pressure is unaffected because heat transfer depends only on surface area

Explanation

Higher cooling-water temperature reduces the temperature difference available for condensing, so the saturation pressure in the condenser rises. A higher back pressure reduces the enthalpy drop available across the last stages, lowering turbine output.

Question 30Turbine Construction, Components, and Auxiliary Systems

Why are last-stage blades of a condensing steam turbine often fitted with lacing wires or shrouds?

  1. To damp blade vibration and stiffen the long, flexible blades Correct answer.
  2. To increase the blade chord for greater steam turning angle
  3. To add centrifugal loading for better rotor balance
  4. To improve the seal between the blade tip and the casing

Explanation

Long last-stage blades are flexible and prone to vibration, so lacing wires or integral shrouds tie blades together, adding damping and stiffness. They are not primarily sealing elements, and they do not exist to add mass or alter the turning angle.

Question 31Turbine Construction, Components, and Auxiliary Systems

A journal bearing on a turbine shows a steadily rising oil outlet temperature while inlet pressure and flow remain normal. Which condition is the most likely cause?

  1. Bearing wipe or excessive loading causing increased friction Correct answer.
  2. A blocked oil cooler bypass valve opening fully
  3. Low oil level in the reservoir
  4. Excessive oil viscosity from overheating

Explanation

A bearing whose outlet oil temperature climbs while supply conditions are steady is generating more heat, which points to increased friction from a wiped or overloaded bearing. Supply-side problems would normally show as changes in oil pressure or flow rather than isolated temperature rise.

Question 32Turbine Construction, Components, and Auxiliary Systems

During a hot start, why is the turbine casing warmed with steam before the rotor is accelerated?

  1. To verify that the overspeed trip functions correctly
  2. To limit thermal stress and differential expansion between rotor and casing Correct answer.
  3. To purge the condenser of air
  4. To reduce the steam flow required to reach rated speed

Explanation

Pre-warming the casing and rotor reduces the temperature difference between them, which limits thermal stress and keeps differential expansion within acceptable limits during acceleration. It does not reduce steam demand for acceleration or serve as a purge or trip test.

Question 33Turbine Construction, Components, and Auxiliary Systems

What happens to the axial thrust of a reaction turbine if the balance holes in the rotor discs become blocked?

  1. Axial thrust decreases because steam leakage falls
  2. Axial thrust is unchanged because blade forces dominate
  3. Axial thrust increases and may overload the thrust bearing Correct answer.
  4. Axial thrust reverses direction during normal operation

Explanation

Balance holes equalize pressure on both sides of a disc so that only the intended pressure drop acts on it. If they block, the pressure difference across the disc grows and the net axial thrust rises, risking thrust bearing overload.

Question 34Turbine Construction, Components, and Auxiliary Systems

Which statement best describes the role of the gland steam system on a condensing turbine?

  1. It cools the shaft packing during overspeed events
  2. It removes condensate from the gland seals
  3. It supplies low-pressure steam to the shaft glands to prevent air ingress and steam leakage Correct answer.
  4. It supplies steam to the turbine first stage during startup

Explanation

The gland steam system feeds low-pressure steam to the labyrinth seals at the shaft ends, creating a barrier that keeps air out of the low-pressure casing and keeps steam from escaping to the atmosphere. It does not feed the first stage or remove condensate.

Question 35Turbine Construction, Components, and Auxiliary Systems

A turbine governor valve is found to have a worn valve stem guide, causing slight lateral movement. What is the most direct operational risk?

  1. The valve may stick or fail to close fully on demand Correct answer.
  2. Valve position feedback becomes more accurate
  3. Steam temperature at the inlet drops sharply
  4. Steam leakage past the valve seat increases

Explanation

Lateral movement from a worn guide can cause the valve to bind or seat poorly, which jeopardizes the ability to control steam flow and to close the valve when required. Accurate feedback and steam temperature are not improved by the wear.

Question 36Turbine Construction, Components, and Auxiliary Systems

What is the function of the condenser hotwell level control?

  1. To set the turbine back pressure by venting steam
  2. To maintain sufficient condensate inventory for the feedwater pumps and prevent pump cavitation Correct answer.
  3. To control the condenser vacuum by regulating cooling water
  4. To regulate the gland steam supply pressure

Explanation

Hotwell level control keeps enough condensate in the hotwell so the condensate pumps have adequate net positive suction head and do not cavitate. Vacuum and back pressure are controlled by other systems such as cooling water and air removal.

Question 37Turbine Construction, Components, and Auxiliary Systems

In a turbine with a radial-flow labyrinth seal, what determines the leakage rate for a given clearance?

  1. The oil temperature in the bearing housing
  2. The material of the seal strips
  3. The pressure ratio across the seal and the number of throttling teeth Correct answer.
  4. Only the rotor surface speed

Explanation

Leakage through a labyrinth seal depends on the pressure ratio across it and on how many throttling restrictions the steam passes, since each tooth converts pressure into velocity and then dissipates it. Rotor speed, oil temperature, and strip material have only secondary effects.

Question 38Turbine Construction, Components, and Auxiliary Systems

Why is a differential expansion measurement between rotor and casing important during a cold start?

  1. It measures the rotor's radial vibration amplitude
  2. It determines the condenser vacuum level
  3. It indicates whether the rotor is growing faster than the casing and approaching axial clearance limits Correct answer.
  4. It shows the amount of steam leaking through the gland seals

Explanation

Steam heats the rotor faster than the massive casing, so the rotor can grow axially relative to the casing and close internal clearances. Monitoring differential expansion lets operators limit loading to keep those clearances safe.

Question 39Turbine Construction, Components, and Auxiliary Systems

An operator observes that the oil film pressure in a journal bearing rises above normal while rotor speed and load are steady. Which explanation is most consistent?

  1. The oil supply pressure has increased Correct answer.
  2. The rotor has been dynamically balanced
  3. The bearing clearance has increased due to wear
  4. The bearing is running hotter than normal

Explanation

Oil film pressure in a hydrodynamic bearing is generated by the supply pressure plus the wedge effect; a rise in supply pressure raises film pressure even at steady speed and load. Wear that opens clearance would tend to lower film pressure, and temperature or balancing do not raise it directly.

Question 40Turbine Construction, Components, and Auxiliary Systems

What is the purpose of the extraction non-return valve in a regenerative feedwater heating system?

  1. To regulate the extraction steam temperature to the heater
  2. To prevent steam from the heater or extraction line from flowing back into the turbine after a trip Correct answer.
  3. To drain condensate from the extraction line
  4. To isolate the heater for cleaning during normal operation

Explanation

On a turbine trip, extraction pressure collapses and the non-return valve closes quickly to stop steam or water from the heater flashing back into the turbine casing, which could cause overspeed or damage. It does not regulate temperature, isolate for cleaning during operation, or drain the line.

Question 41Turbine Construction, Components, and Auxiliary Systems

A turbine rotor has a first critical speed of 1,500 rpm. During run-up, what behavior is expected as the machine passes through this speed?

  1. Vibration amplitude peaks and then decreases as speed continues to rise Correct answer.
  2. Vibration amplitude decreases steadily toward zero at the critical speed
  3. Vibration amplitude stays constant through the entire run-up
  4. The rotor locks at the critical speed until oil temperature rises

Explanation

At a critical speed the rotor's unbalance excitation matches a natural frequency, so vibration rises to a peak and then falls again as the machine accelerates past resonance. The rotor does not lock, and amplitude does not stay constant or fall to zero at resonance.

Question 42Turbine Construction, Components, and Auxiliary Systems

Why is the condenser often operated at the lowest practical pressure rather than at atmospheric pressure?

  1. Lower pressure increases the enthalpy drop available across the turbine and improves cycle efficiency Correct answer.
  2. Lower pressure reduces the cooling water flow required
  3. Lower pressure raises the saturation temperature for better heat transfer
  4. Lower pressure prevents air from entering the condenser

Explanation

Expanding steam to a lower back pressure allows more work to be extracted in the last stages, improving the Rankine cycle efficiency. Air ingress and cooling water flow are managed separately, and lower pressure actually lowers the saturation temperature.

Question 43Turbine Construction, Components, and Auxiliary Systems

What is the main function of the labyrinth seal strips fitted to turbine blade tips?

  1. To damp torsional vibration of the rotor
  2. To support the blade against centrifugal load
  3. To increase the steam turning angle in the stage
  4. To reduce tip leakage of steam past the blade and improve stage efficiency Correct answer.

Explanation

Tip seal strips create a small clearance with the casing or shroud so that only a limited amount of steam bypasses the blade path, preserving stage efficiency. They do not carry blade loads or control vibration.

Question 44Turbine Construction, Components, and Auxiliary Systems

Which parameter is most directly used to detect a loss of condenser vacuum during operation?

  1. Feedwater pump discharge pressure
  2. Gland steam supply flow rate
  3. Condenser absolute pressure compared with the expected saturation pressure for the cooling water temperature Correct answer.
  4. Turbine first-stage steam temperature

Explanation

Loss of vacuum shows up as condenser pressure rising above the saturation pressure expected for the cooling water temperature, indicating air ingress or reduced cooling. The other parameters relate to the feedwater and steam systems and do not directly measure vacuum.

Question 45Turbine Construction, Components, and Auxiliary Systems

In a steam turbine with nozzle governing, how is steam flow to the turbine varied as load increases?

  1. By adjusting the condenser cooling water flow
  2. By changing the speed of the boiler feedwater pumps
  3. By opening control valves in sequence to admit steam to successive nozzle groups Correct answer.
  4. By throttling a single main stop valve over its full travel

Explanation

Nozzle governing admits steam through control valves that open in sequence, each feeding a separate arc of nozzles, so partial-load operation keeps throttling losses low. Throttle governing uses one valve, and feedwater or cooling water changes do not set turbine steam flow.

Question 46Turbine Construction, Components, and Auxiliary Systems

A turbine is shut down and the turning gear is kept running. Why must the shaft sealing steam be maintained or the casing kept under vacuum during this period?

  1. To prevent air ingress that could cause corrosion and to keep seals from overheating Correct answer.
  2. To maintain the oil film pressure in the journal bearings
  3. To keep the rotor cool enough to avoid thermal stress
  4. To keep the condenser hotwell level stable

Explanation

With the machine shut down, air entering the hot casing can cause corrosion and, if gland steam is lost while the seals are hot, the seal surfaces can overheat and distort. Maintaining sealing steam or vacuum protects the seals and the internal surfaces.

Question 47Turbine Construction, Components, and Auxiliary Systems

What is the role of the main stop valve in a turbine protection system?

  1. To isolate steam from the turbine quickly when a trip signal is received Correct answer.
  2. To drain steam from the inlet line during startup
  3. To regulate steam flow to match load during normal operation
  4. To control the gland steam supply pressure

Explanation

The main stop valve is a protective isolation valve that closes rapidly on a trip to cut off steam to the turbine. Load regulation is done by control or governor valves, and drains and gland steam have their own valves.

Question 48Turbine Construction, Components, and Auxiliary Systems

A turbine stage has a nozzle that accelerates steam to high velocity before it enters the moving blades. Which energy conversion occurs in the nozzle?

  1. Heat is converted to mechanical work on the shaft
  2. Pressure energy is converted to kinetic energy Correct answer.
  3. Kinetic energy is converted to electrical energy
  4. Kinetic energy is converted to pressure energy

Explanation

In a nozzle, steam expands and its pressure and enthalpy fall while velocity rises, so pressure energy is converted into kinetic energy. The moving blades then convert that kinetic energy into shaft work.

Question 49Startup, Shutdown, and Normal Operation Procedures

During a normal rolling startup of a steam turbine from cold condition, which parameter is normally held constant during the initial low-speed warm-up soak?

  1. Exhaust hood pressure
  2. Lube oil header pressure
  3. Rotor surface temperature
  4. Rotor speed Correct answer.

Explanation

A cold turbine is typically soaked at a low speed, often a few hundred rpm, so that steam flow heats the rotor and casing slowly and evenly before speed is raised. Holding speed constant lets metal temperatures catch up and limits differential expansion between rotor and casing. Raising speed or load too soon can cause excessive thermal stress and rubbing.

Question 50Startup, Shutdown, and Normal Operation Procedures

Which condition must be confirmed before admitting steam to a turbine during startup?

  1. The condenser vacuum pumps have been stopped
  2. The generator has been synchronized to the grid
  3. The overspeed trip has been temporarily bypassed
  4. The turning gear has been disengaged and the rotor is on oil film Correct answer.

Explanation

Steam admission requires the rotor to be lifted on its oil film and the turning gear disengaged, otherwise the rotor can be damaged or the gear can be shock-loaded. Jacking oil and lube oil flow must be established first. Synchronizing and trip bypassing occur later or are prohibited.