steam turbine question answers

7/25/2019 Steam Turbine Question Answers

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What basic governor troubles are apt to occur?Answers:

Hunting-alternate speeding and slowing of the engine, which means thatthe governor is too sensitive to load changes.Sticking-failure to control speed, allowing the engine to run awa orslow down-which means that the governor is not sensitive to loadchanges or parts are binding or worn.

What is a governor safet stop?Answers:!n throttling-tpe governors, the safet stop is a weighted arm thatneeds the support of a governor belt. "f the belt breaks, the idler arm

drops and shuts the steam suppl valve to the engine. !n #orliss units,the flballs fall to the lowest position and knock off the safet cams$ thecams disengage the catch blocks on the steam intake valves so that nosteam is admitted to the engine.

Wh is condensation or e%cessive carrover dangerous to reciprocatingengines?Answer:&ecause water is non-compressible. "f an e%cessive amount of watergets into the clinder, it will wreck the engine.

Wh should a steam or moisture separator be installed in the steam linene%t to a steam turbine?Answer:All multistage turbines, low-pressure turbines, and turbines operating athigh pressure with saturated steam should have a moisture separator inorder to prevent rapid blade wear from water erosion.

'nder what conditions ma a relief valve not be re(uired on the e%haustend of a turbine?Answer:"f the manufacturer has provided that the turbine shells are constructedfor full-inlet steam pressure for the entire length of the shell. "t isabsolutel essential to have a relief valve to protect the shell in theevent an e%haust valve is closed and high-pressure steam is admitted tothe shell on the front end of the machine. )%plosions have occurredwhen this happened.

What are some conditions that ma prevent a turbine from developingfull power?


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Answers:*he machine is overloaded.*he initial steam pressure and temperature are not up to designconditions.*he e%haust pressure is too high.

*he governor is set too low.*he steam strainer is clogged.*urbine no++les are clogged with deposits."nternal wear on no++les and blades.

Wh is it necessar to open casing drains and drains on the steam linegoing to the turbine when a turbine is to be started?.Answers:*o avoid slugging no++les and blades inside the turbine with condensateon start-up$ this can break these components from impact. *he blades

were designed to handle steam, not water.

What three methods are used to restore casing surfaces that aree%cessivel eroded?Answers:etal-spraing.Welding."nsertion of filler strips or patch plates. *he manufacturer should beconsulted on the metallurg involved so that the best method can beselected.

What is steam rate as applied to turbo-generators?Answer:*he steam rate is the pounds of steam that must be supplied perkilowatt-hour of generator output at the steam turbine inlet.

What is the most prevalent source of water induction into a steam turbo-generator?

Answer:eaking water tubes in feedwater heaters, which have steam on the shellside supplied from turbine e%traction lines. *he water at higher pressurecan flow back into the turbine because the e%traction steam is at a lowerpressure. #heck valves are needed on the steam e%traction line toprevent the back-flow of water into the turbine.

What is a regenerative ccle?Answer:"n the regenerative ccle, feedwater is passed through a series of feed-

water heaters and is heated b steam e%tracted from stages of a steamturbine. *his raises the feedwater to near the temperature of boiler


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water, thus increasing the thermal efficienc of the ccle.What is the re-heating ccle?Answer:"n the re-heating ccle, superheated steam is e%panded in a high-

pressure turbine and then returned to the boilers re-heater to raise thetemperature of the steam to the inlet temperature, usuall to around/012#$ it is then returned to the turbine to be e%panded throughintermediate-pressure turbines. "n some cases, the steam is againreturned for re-heating in the boiler and then e%panded in the lower-pressure sections of the turbine. *he main purpose of re-heating thesteam on large turbo-generators is to avoid condensation in the lower-pressure sections of the turbine, which can rapidl cause blade erosionproblems from wet steam.

What does the Willans line show?Answer:*he Willians line is a plot of throttle flow versus the load, usualle%pressed in kilowatts$ generall it is a straight line e%cept for low andhigh loads. *he Willians line is used to show steam rates at differentloads on the turbine.

What are topping and superposed turbines?Answer:*opping and superposed turbines arc high-pressure, non-condensingunits that can be added to an older, moderate-pressure plant. *oppingturbines receive high-pressure steam from new high-pressure boilers.*he e%haust steam of the new turbine has the same pressure as the oldboilers and is used to suppl the old turbines.

What is an e%traction turbine?Answer:"n an e%traction turbine, steam is withdrawn from one or more stages, atone or more pressures, for heating, plant process, or feedwater heaterneeds. *he are often called 3bleeder turbines.3

What are four tpes of thrust hearings?Answer:&abbitt-faced collar bearings.*ilting pivotal pads.*apered land bearings.4olling-contact 5roller or ball6 bearings.

What is the function of a thrust bearing?Answer:

*hrust bearings keep the rotor in its correct a%ial position.


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What is a balance piston?Answer:4eaction turbines have a%ial thrust because pressure on the enteringside is greater than pressure on the leaving side of each stage. *ocounteract this force, steam is admitted to a dumm 5balance6 piston

chamber at the low-pressure end of the rotor. Some designers also usea balance piston on impulse turbines that have a high thrust. "nstead ofpiston, seal strips are also used to duplicate a pistons counter force.

What is a combination thrust and radial bearing?Answer:*his unit has the ends of the babbitt bearing e%tended radiall over theend of the shell. #ollars on the rotor face these thrust pads, and the7ournal is supported in the bearing between the thrust collars.

What is a tapered-land thrust bearing?Answer:*he babbitt face of a tapered-land thrust bearing has a series of fi%edpads divided b radial slots. *he leading edge of each sector is tapered,allowing an oil wedge to build up and carr the thrust between the collarand pad.

What is important to remember about radial bearings?Answer:A turbine rotor is supported b two radial bearings, one on each end ofthe steam clinder. *hese bearings must be accuratel aligned tomaintain the close clearance between the shaft and the shaft seals, andbetween the rotor and the casing. "f e%cessive bearing wear lowers thehe rotor, great harm can be done to the turbine.

What is gland-sealing steam?Answer:"t is the low-pressure steam that is led to a sealing gland. *he steam

seals the gland, which ma be either a carbon ring or labrinth tpeagainst air at the vacuum end of the shaft.

What is the function of a gland drain?Answer:*he function of a gland drain is to draw of water from sealing-glandcavities created b the condensation of sealing steam.

What is an air e7ector?

Answer:


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An air e7ector is a steam siphon that removes non-condensable gasesfrom the condenser.

How man governors are needed for safe turbine operation? Wh?

Answer:*wo independent governors are needed for safe turbine operation. !neis an overspeed or emergenc trip that shuts off the steam at 89 percentabove running speed 5ma%imum speed6. *he second, or main governor,usuall controls speed at a constant rate$ however, man applicationshave variable speed control.

How is a flball governor used with a hdraulic control?Answer:As the turbine speeds up, the weights are moved outward b centrifugal

force, causing linkage to open a pilot valve that admits and releases oilon either side of a piston or on one side of a spring-loaded piston. *hemovement of the piston controls the steam valves.

What is a multi-port governor valve? Wh is it used?Answer:"n large turbines, a valve controls steam flow to groups of no++les. *henumber of open valves controls the number of no++les in use accordingto the load. A bar-lift or cam arrangement operated b the governoropens and closes these valves in se(uence. Such a device is a multi-port valve. 'sing no++les at full steam pressure is more efficient thanthrottling the steam.

What is meant b critical speed?Answer:"t is the speed at which the machine vibrates most violentl. "t is due toman causes, such as imbalance or harmonic vibrations set up b theentire machine. *o minimi+e damage, the turbine should be hurriedthrough the known critical speed as rapidl as possible. 5#aution, be

sure the vibration is caused b critical speed and not b some othertrouble6.

How is oil pressure maintained when starting or stopping a medium-si+ed turbine?Answer:An au%iliar pump is provided to maintain oil pressure. Some au%iliarpumps are turned b a hand crank$ others are motor-driven. *his pumpis used when the integral pump is running too slowl to providepressure, as when starting or securing a medium-si+ed turbine.


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Wh is it poor practice to allow turbine oil to become too cool?Answer:"f a turbine oil is allowed to become too cold, condensation ofatmospheric moisture takes place in the oil and starts rust on the

polished surfaces of the 7ournal bearings. #ondensed moisture minterfere with lubrication.Steam blowing from a turbine gland is wasteful.

Wh else should it be avoided?Answer:"t should be avoided because the steam usuall blows into the bearing,destroing the lubrication oil in the main bearing. Steam blowing from aturbine gland also creates condensate, causing undue moisture in plante(uipment.

&esides lubrication, which are two functions of lubricating oil in someturbines?Answer:"n large units, lube oil cools the bearings b carring off heat to the oilcoolers. ube oil in some turbines also acts as a hdraulic fluid tooperate the governor speed-control sstem.

What is meant b the water rate of a turbine?Answer:"t is the amount of water 5steam6 used b the turbine in pounds perhorsepower per hour or kilowatts per hour.

Wh is there a relief valve on a turbine casing?Answer:*he turbine casing is fitted with spring-loaded relief valves to preventdamage b e%cessive steam pressure at the low-pressure end if thee%haust valve is closed accidentall. Some casings on smaller turbines

are fitted with a sentinel valve, which serves onl to warn the operator ofover-pressure of the e%haust end. A spring-loaded relic valve is neededto relieve high pressure.

Wh must steam turbines be warmed up graduall?Answer:Although it is probable that a turbine can, if its shaft is straight, bestarted from a cold condition without warming up, such operation doesnot contribute to continued successful operation of the unit. *hetemperature strains set up in the casings and rotors b such rapid

heating have a harmful effect. *he turbine, in larger units especiall


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should be warmed slowl b recommended warm-up ramp ratesbecause of close clearances.

What should ou lost vacuum while operating a condensing turbine

plant?Answer:"f vacuum is lost shut down immediatel. *he condenser cannot standsteam pressure, the condenser tubes ma leak from e%cessivetemperature. )%cessive pressure will also damage the shell, the e%haustand the low-pressure parts of the turbine.

What are the main causes of turbine vibration?

Answers:

'nbalanced parts.oor alignment of parts.oose parts.4ubbing parts.ubrication troubles.steam troubles.;oundation troubles.#racked or e%cessivel worn parts.What is the purpose of a turning gear?Answer:Heat must be prevented from warping the rotors of large turbines orhigh-temperature turbines of


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full. *his provides more uniform heating around the high-pressure partof the turbine. ost modern controls start with full-arc and switch topartial arc to reduce throttling losses through the valves.

What are some common troubles in surface-condenser operation?Answer:*he greatest headache to the operator is loss of vacuum caused b airleaking into the surface condenser through the 7oints or packing glands.Another trouble spot is cooling water leaking into the steam spacethrough the ends of the tubes or through tin holes in the tubes. *hetubes ma also become plugged with mud, shells, debris, slime or algae,thus cutting down on the cooling water suppl. #orrosion ma beuniform, or it ma occur in small holes or pits.

Where would ou look for a fault if the air e7ector didnt raise enoughvacuum?Answers:"n this case, the trouble is usuall in the no++le. =ou will probabl findthat the no++le is eroded.*he strainer protecting the no++le is clogged.*he steam pressure to the no++le is too low.

steam turbine question answers

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