Barring Gear Causes and Prevention

7/31/2019 Barring Gear Causes and Prevention

1/27

Barring Gear

Types, Reasons of Stal ling

and Preventive actions

AK Sehgal

Sr. Mgr. COS-ST

[email protected]
http://www.pdfcomplete.com/cms/hppl/tabid/108/Default.aspx?r=q8b3uige22


2/27


3/27

LMZ design, 3.54 rpm

PT IPT LPT Gen.

HPT

IPT

Motorized TurningGear
http://www.pdfcomplete.com/cms/hppl/tabid/108/Default.aspx?r=q8b3uige22http://www.pdfcomplete.com/cms/hppl/tabid/108/Default.aspx?r=q8b3uige22


4/27

Old 210/500 MW Barring Gear in a KWU design Hydraulic Wheel

HPT IPT LPT Gen.


5/27

Front Pedestal new 500 MW BHEL turbine-Hydraulic Wheel

HPT IPT LPT Gen.


6/27

Failure to keep Hot machine on Barring Gear

Because of positive drive and higher torquemargin in case of Motorized ones, Barring gearstalling is hardly a issue. Even if minor touchingof seals is there, it is rubbed off.

Never the less, in old fleet i.e. Pre-Vindhyachalstage-II turbines there is no issue of stalling(Except appropriate auxiliary steam temperaturefree of condensate).

Post vindhyachal, reduced gland clearances,Turbine is extremely sensitive to Auxiliary steamtemperature supply.


7/27

If Turbine fails to rotate freely with one man thenit should not be forced upon. Interstage SealFin and Gland seal fin Wearwill result due toTemporary Rotor Bowing and Casing Hogging

due to Top-Bottom temperature difference. Ifforced rolling, Permanent Rotor Bow may alsoresult.

On the other hand One instance of Barringstalling eats up to 3 days of outage loss, sopreventive actions are must.


8/27

Main Reasons of inability of turbine to sustain onbarring gear and associ ated checks

In case of KWU design 210/500 MW there arenumber of reasons established on the basis ofcases;

Resistance to RotationInadequate LiftMotive Power

During coasting Down, When Turbine Speed reaches 220 rpmTurning valve Opens. After how much time of tripping of turbine,Barring gear is stalling, is very important and helpful in finding out itsreason.
http://www.pdfcomplete.com/cms/hppl/tabid/108/Default.aspx?r=q8b3uige22http://www.pdfcomplete.com/cms/hppl/tabid/108/Default.aspx?r=q8b3uige22http://www.pdfcomplete.com/cms/hppl/tabid/108/Default.aspx?r=q8b3uige22


9/27

Rubbing

due to condensed moisture/liquid.due to air chilling of glandsDeviated mechanical Clearances.

Due to presence of foreign material

Also possible due to Generator seal ring rubbing on shaft.

Rubbing provides resistance to rotation.


10/27

Entry of Wet/ condensed steam into Turbine glands


11/27

Entry of Wet/ condensed steam into Turbine glands

Case: 21.09.2003, 0043 hrs both Units tripped on low condenser vacuum due totripping of CW pumps. after attending the CW pumps problem, boiler lighted up andat the time of charging of aux seal steam for vacuum pulling, turbine speed startedreducing and got stopped at 0900 hrs barring gear stopped.Reason: Wet Steam/Condensate.

Such type of cases including Post trip can be avoided by checking:

Check-1 Open Motorized Warm up valve MAW-10 and see if temperature risesmore than 50C, if So it indicates the presence of Wet Steam/Condnesate.

Check warm Orifice is there in Warm up drain line or not? If yes check size. If No, Getit installed.Check if the location of continuous warm up line/drain is at height than or distantfrom seal steam supply temperature monitoring point, if yes then modify and bring itnearest and to a lower elevation than main seal steam control valve.check whether steam traps provided in aux PRDS are working ?

Check source aux. steam temperature (270 Degree+ for New and 220 Deg+ Forold one.?Check if unit PRDS is charged commonly from farthest unit?

Also Check CRH NRVs for proper seat contact area and full closure (If passing,during initial HPBP opening, low temperature steam with spray is likely todeaccelerate the turbine when on Barring).


12/27

After unit trip: do not keep Gland seal steamcharged for more than 1-2 hours. Unnecessarilypossibilities of change in auxiliary seal steamtemperature .

During Controlled cooling: Ensure seal steamsupply isolating valve is tightly closed and Warmup drain valve i.e MAW-10 and MAL-81 drainvalve is opened to rule out possibility of

condensate remaining entrapped.Also ensure implementation of X-98.


13/27

Air Chilling of Glands

Check: Post Trip vacuum killing Sequence of operation:Stop Vacuum pump

Kill Vacuum by opening Vacuum breaker

Isolate Gland seal steam at Vacuum of 0.2-0.3 Kg/cm2

or Back pressure of 0.7 -0.8 kg/cm2Stop Gland steam Exhauster i mmediately after isolation

of gland seal steam

Case: Talcher # 4, 22.03.2004 ,0016 hrs Turbine trip, Came on Barring gear,

Full vacuum maintained with gland seal steam supply charged. 0615 hrs, Sealsteam isolated, turbine speed subsequently started dropping. 0640 vacuum

breaker opened. (but s peed continued to drop and came to standstill at about0705 hrs. Turbine was left to cool and time was utilized for PG test preparations.

Reason: Air Chilling


14/27


15/27

Disturbed Seal Fin Clearances

LPT Gland Clearance: Check that Gland box is not skewed andkeys are properly set. Ensure at least 0.7 mm radial clearance allaround the front and Rear glands by inserting long feeler (500 mmlong).

Case: Talcher # 5, 13.05.04 0659 hours Turbine manually tripped.

Everything normal. Various checks were done by BHEL and NTPCby finally shifting of HP casing by 0.30 mm on LHS (Looking fromfront pedestal towards generator), turbine came on Barring speed.

Check: Disturbance in Casing position/centering due to pipepush/pull in Turbine area MS ,CRH, HRH, Cross around pipingHangers and Supports. Walk down survey and Healthiness.Checking in Hot (Pre-shut down), Cold (Shut down) and setting andfinal checking in subsequent hot (after shut down) condition .

Case: FSTPS # 5, 500 MW, 2001-02 Barring gear problem and HighVibration . During inspection rubbing marks on shaft under LPT front

gland. Clearances restored. No problem subsequently. Reason :Abnormal LPT gland clearance.


16/27

Case: 02.01.2005, 0100 hrs -Unit shut down for boilertube leakage. Af ter one hour Condenser Pass -B wasdrained to attend debris f ilter choking, and one CWpump was also stopped. At 1100 -1300 hrs Other CW

pump stopped. At 1455 hrs i.e. about 14 hours of unittrip, Barring gear speed came down f rom 75 rpm to 0rpm. No other intervention was made. Reason: CWdraining of Condenser

Check: Till HPT temp


17/27

Rubbing due to Foreign Material

Case: Korba # 3, on four occasions of Unit trip on06/05, 30/07, 29/11/2003 &10/1/2004, T urbine did cameon Barring Gear but after 42.7, 39.5,33 & 32.6 hours

respectively.During O/H axial bump check valure of HPTnot OK. HPT opened. A metallic piece of shape (15*12mm size, 4 mm thick) was f ound stuck in 22nd stagefixed blades of HPT which was rubbing agai nst rotatingblade whenever machi ne speed reduced.


18/27

In sufficient Lift of Rotor Journals

Case : Dadri# 4, During annual shutdown in the year 2000 Turbine

came to standstill after the machine was desynchronized.Jacking oil hose found burst at mid section . Probably vigorousrubbing during trips etc. caused hose to fail. Later site hasproperly routed the hose and clamped it with adjacent pipinginside the pedestal and no failure observed since then.There are number of cases because of jacking oil hosefailure/ Jacking oil Piping.

Checks:Check that no extra pocket is formed near jacking oil recess andproper jacking oil recess is there inside the bearing.Lift Pedestal Covers and see if any abnormality or leakage is there in

hose, joints, pressure gauge etc.Check J.O. Hose of Proper length, routing and flexible clamping with

adjacent oil piping and clamping of metal pipe in each pedestal.

Check and set required bearing l ift by adjusting jacking oil pressurewith one Jacking oil pump and Maintain protocol for Jacking oilheader pressure, bearing lift and jacking oil pressure at each bearing.Checking of J.O. Pipe c lamps/supports from MOT room to Beari ngPedestal for tightness/adequacy by actual shaking of piping. (Toprevent pipe failure due to shaking/vibration during start up and shutdown)


19/27


20/27

Jacking oil Hose replacement to be done whenever bearing isremoved for inspection.

Jacking oil hoses pressure rating and quality to be ensured.Trend monitoring of Jacking oil back pr essure (provided insidein bearing no. 1,2,3,4) at all brgs. Indicates health of Hoses andNRV s.

Check that there are no grooves on journal near the jacking oilpocket 9especially Brg. 6). This will lead to leakage of lifting oil past

the pocket and affect lifting. Take action for Rotorreplacement/correction.Prevention: J.O. Flushing of the system to be done duringoverhauls (whenever bearings are opened) (To prevent scoringmarks in journal and bearing which leads to leakage of liftingpressure).1. Close oil supply to all bearings2. Remove brg. end hoseof brg. 6/7 (whichever applicable) and route to a Drum.3. Run JOP

with brg. 6/7 supply valve partially open for few minutes. 4. Flushthrough Jacking oil header end.


21/27

Ensure that Jacking oil header pressure is maintainingfor a given lift settings. (There are no. of cases whichshow in that header pressure is not consistent-BHEL is developing alternative valve supplier.)

After unit synchronization clean J.O. f ilter. InstallJacking oil header f ilter, wherever not existingMake arrangement for locking/cover ing of J.O.pressure setting val ve for Brg. 5,6, 7 (if applicable)- toprevent accidental disturbance.Check J.O. NRV s (provided inside the pedestal ( brg.

1,2,3,4) (to prevent sticking/passing)During overhauling check there are no grooves onrotor journal nar jacking oil pocket . Take action forrotor replacement or journal machining .


22/27

Precautions

Record and trend coasti ng down time

during each unit tripping-3000 rpm to 200

rpm.

After each unit tripping, when turbine on

Barring gear, Check whether any

abnormal sound is coming near Glands

and bearings or any abnormal vibration.


23/27

Motive Power

Visually Check the condition of Barring Gear Oilsupply isolation valve for actual opening.

Ensure that Pipe f or Manual Barring is al waysavailable at fixed location near the Barring ge ar.

Check condition of Barring gear nozzle and wheel

blades and clearances during Overhauling.There has been issue of inherentl y lesser barring

speed which is giving very-2 less torque margin to

tolerate practical deviations .


24/27

Developments

The reason of lesser speed/torque has

been found due to submergence ofhydraulic wheel in Pedestal Oil. BHEL has

suggested modi fication vide X-99, which

has yielded minor benefit. Further COS-SThas suggested modi fication for completely

coming out of issue.


25/27

Miscellaneous

Covering of Turbine floor Oil pipingtrench with Grilled plate.

Covering of oil piping in Pedestalapproach area wi th removable grilled

plate platform (wherever not provi ded).

In case of Problem Please preserve 1

second trend interval data for Turbo-visory, CW, jacking oil headerpressure .


26/27

Thanks for listening patiently.


27/27

Barring Gear Causes and Prevention

Documents

Transcript of Barring Gear Causes and Prevention