governor system

8/9/2019 Governor System

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GOVERNOR SYSTEM

PRESENTED DURING THEGENERATION MECHANICALPROGRAMME

MODULE 1 STEAM TURBINE TRAININGSAPELE:

BY: ODAFE AKEMUMECHANICAL INSTRUCTOR

COMPILED BY: ENGR. NWANA


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GOVERNOR SYSTEM

TURBINE GOVERNING ANDCONTROL

The function of a governor is tomaintain the shaft speed constant asthe load varies.

The simplest type of governor is thecentrifugal type. The poweravailable at the shaft IS 2 TT TN where

T is the torque and N is in rpm.


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GOVERNOR SYSTEM

As load (torque decreases! speedincrease! with the increase ofcentrifugal force! the "y balls "yapart and raise the sleeve whichoperating through a lever and afulcrum! activate the main valve to

close and reduce the mass "ow ofsteam admitted to the turbine.


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GOVERNOR SYSTEM

The steady state speed regulator %sis given by

%s & No ' N )**

Nr

+here

No & Speed at no load

N & Speed at rated load&


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GOVERNOR SYSTEM

The speed change from full load tono load is limited to ,.- of thespeed of the rated load. If the rated

speed is ,***rpm. The speed at fullload will be 2/-*pm and at no loadwould be ,*0*rpm.

In case %s & ,*0* ' 2/-* )**

,***


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GOVERNOR SYSTEM


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GOVERNOR SYSTEM

THROTTLE GOVERNING

In a governing system as the load

decrease the shaft speed increases. Thestop valve is partially closed to admit lesssteam to the turbine and to produce less

power according to the demand. 1ue tothe restriction of passage in the valve!steam is throttled from $o to $ throttle.


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GOVERNOR SYSTEM

The throttle and stop valves are locatedin the steam supply line to the turbine.

The stop valve is a hydraulically quic

opening and shuttling valve designed tobe either fully open or shut.

The throttle valve is a regulating steam

"ow valve during operation of theturbine.


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GOVERNOR SYSTEM

NOZZLE GOVERNINGIf throttle governing is done at lowloads! the turbine e3ciency is

considerably reduced. The no44le control may be a bettermethod of governing.

The no44les are made up in set! eachbeing controlled by a separate valve.

+ith the decrease of load the requirednumber of no44le may be shut o5.


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GOVERNOR SYSTEM


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GOVERNOR SYSTEM

EMERGENCY GOVERNOR6very turbine is provided with some form ofan emergency governor which trips theturbine i.e. closes the stop valve and stop

the steam supply when• Shaft speed eceeds ))* of its rated value

• 7ubrication system fails

• 8alancing both static and dynamic is notproper

• 9ondenser becomes hot (due to inadequatecooling water circulation or vacuum is less.


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GOVERNOR SYSTEM

:ne common type of over;speed tripemploys a pin or bolt within the turbineshaft. 9entrifugal forces acting on the

pin trying to force it out of the shaft isopposed by a spring until about )* ofover;speed is reached. +hen thecentrifugal force overcomes the spring

force the pin is force out of the shaftand stries a trigger which in turn!releases a spring to close the stop valve

immediately.


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GOVERNOR SYSTEM

SPEED CONTROL GOVERNOR

The control of a turbine with agovernor is essential! as turbinesneed to be run up slowly! to preventdamage while some applications(such as the generation of

alternating current electricity require$recise Speed 9ontrol.


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GOVERNOR SYSTEM


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GOVERNOR SYSTEM

1uring normal operation insynchroni4ation with the electricitynetwor! power plants are governedwith a four percent droop Speed9ontrol.

This means that the full load Speed is)**. This is required for the stable

operation of the networ withouthunting and drop;outs of power plants.

Normally the changes in speed are

minor.


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GOVERNOR SYSTEM

Ad=ustments in power output aremade by slowly raising the droopcurve by increasing the spring

pressure on a centrifugal governor.

>enerally this is a basic systemrequirement for all power plantsbecause the older and newer plants

have to be compatible in response tothe instantaneous changes infrequency without depending on

outside communication.


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GOVERNOR SYSTEM


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GOVERNOR SYSTEM


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GOVERNOR SYSTEM


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GOVERNOR SYSTEM

There are various points which require speciallubrication. ?or eample! the governorcontrol valve and drive linages as well as theturbine front standard and 7$. turbine base

plates and guides require periodic greasing.It is recommended that an adequatelubrication chart be established whereinlocations and schedule for each pointrequiring lubrication are listed! according toplant eperience and manufacturersrecommendations.


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GOVERNOR SYSTEM

ANNUAL INSPECTION

Annual inspection is carried out to #ndabnormal condition at an each stageand to tae necessary counter;measures immediately.

The necessary inspection@ cleaning are

listed below.


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GOVERNOR SYSTEM

() Inspection of service valve #lter

(2 Inspection and cleaning of =acing pumpsuction starting strainer.

(, Inspection of oil pressure and temperaturegauges.

(- Inspection of 7$. turbine last stage bucet

( Inspection and cleaning of condenser waterbo and hot well.

(0 %un;out chec of generator collector ring.(B Cydrogen gas lea test for generator.

(D Inspection of hydraulic control equipmentand linages.

(/ Inspection and test of all protective devices.


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GOVERNOR SYSTEM

In overhaul! usually performed afterabout 2-!*** running hours (or fouryears interval! all the parts which

cannot be eamined in the routinemaintenance@inspection are checed.

The remaining part of this write up will

be devoted to guides in overhaulinspection.


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GOVERNOR SYSTEM

High, I!"#$"%i&!" &% '() P#"**+#"R(!(#

9hec for! crac on shroud rings and tenonElooseness of shroud rings and locing bladesEerosion on tenons and blades.

Sliding "ow and rust on =ournals! warn;out ofrotor shaft crac on coupling stud.

?or the 7$ rotor chec for crac on locing pins

of last stage bucets! the wires of thepenultimate state blades and on erosion;shields of last stage blades.

9racs are checed by red die penetront

method and erosion@wear by visual inspection.


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GOVERNOR SYSTEM

N('" %i&-h#&g$*

9hecs the eit edges of the no44lepartitions for erosion and attachment

of deposits of foreign matters.

Inner and outer rings of the no44lediaphragms and the no44le partitions

for cracs and for bruises caused byforeign matter

(All by visual inspection.


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GOVERNOR SYSTEM

High &% I!"#$"%i&!" P#"**+#" C&*ig*

9hec for erosion and cracs of inner and

outer casings. 9hec for cracs on the inside

and outside of castings! especially at thefollowing locationsF

9orners of inside and outside! weldment of

the steam chest! weldment of the "anges for

main steam inlet! weldment of all pipes! andcorners of the portion #ed at the #rst stageno44le! plates.


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GOVERNOR SYSTEM

HighT"$-"#&!+#" B('!*

Inspect for cracs and carryoutharness test.

9hec bolt elongation prior totightening and con#rm amount ofstretch after tightening (it must be

within limit speci#ed by design.


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GOVERNOR SYSTEM

L() P#"**+#" C&*ig

9hec the inner casing for the followingF

9racs on surface of hori4ontal =oint.

Adhering scales and their places! colourand quantity.

7ooseness of cauling at the centre pin.

9hec for cracs and erosion at weldedparts! %;#nished parts and stay pipes.


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GOVERNOR SYSTEMC#(**O/"# Pi-"

9hec for the followingF

1amage to heat insulation lagging plates.

Steam leaage from "ange =ointing planesE

6rosion on all inner surfaces of the pipeecluding bellowsE

Attachment of foreign matters on the inner

surfaces of the pipeE

Inspect inner surfaces of bellows.

?or the epansion =oint! chec the shape of

bellows convolutions and inspect the innersurfaces of the bellows.


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GOVERNOR SYSTEM

0(+#&' B"ig*

9hec bolts for looseness.

Tights@loose ball seats.

>ap between 8abbitt surface of bearing and =ournalof shaft (bearing oil gap.

$arallel of the 8abbitt surface of bearing with the =ournal of shaft.

?or the 8abbitt metalF chec for wipe or recess!crac! scratch and the contact to =ournal of shaft

both upper and lower bearings.

9hec the contact faces of on liners of bearing ringand pedestal. 9hec the tooth of the oil de"ectorsand gas between the tooth and rotor using gap

guage.


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GOVERNOR SYSTEM

Th#+*! B"ig

9hec the thrust gap (using assemblydrawing and chec the ball seat gaps of

thrust casing and of thrust bearing ring .Inspect bearing surfaces of thrust plate forwipe or recess sliding "ows and contact fromand width. 9hec metal surfaces for crac.

Inspect the contact using red lead on ballseats of thrust casing and thrust bearingring.


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GOVERNOR SYSTEM

R(!(# (+-'ig

9hec diameters of mating rabbet #ts! *.*,to *.*Bmm press #t must eist! with not more

than 2.Do9 temperature di5erence betweenrotor couplings and measuring instruments!when the diameter checs are made.

9hec length of male rabbet and depth of

female rabbet to ascertain that a minimumclearance of *.Dmm eists when coupling ismade up.


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GOVERNOR SYSTEM

8efore dismantling the turbine completely!tae measurement of blade trip clearances C$!I$ and 7$ rotors with turbine inner casings orno44le diaphragm and mar the aial positionsof the blades relative to the no44le partition orstator blade on a plain board.

Geasure aial clearance between movingblades and no44le partition or stator blades.

9arryout these measurements duringassembly and ensure they conform toassembly drawing or manufacturersrecommendation and mae necessaryad=ustment as required.


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GOVERNOR SYSTEM

After dismantling and inspection!carryout necessary cleaning andcorrective action as required and set

the turbine according torecommendation.

6nsue that the rotor couplings are

properly aligned.


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governor system

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