Delay in Opening of LP Bypass Valve

PROJECT: TALCHER/NTPC, STAGE II - 4 X 500 MW PROBLEM: DELAY IN OPENING OF LP BY PASS (LPBP) VALVES CAUSING BOILER TO TRIP ON REHAETER PROTECTION The problem of delayed opening of control valves of LPBP was experienced in 500 MW units of Simhadri and Talcher. Time taken from turbine trip to the LPBP control valves opening was more than 15 seconds, causing re-heater protection to act tripping the boiler. The reasons for the delay are that the control valves can open only after opening of spray injection valves and generation of impulse pressure to reset the protective devices. Also delay is contributed from time taken for increase of signal oil pressure for Stop and control valves. BHEL Hardwar studied the problem at Simhadri units and suggested to carry out modifications in LPBP signal oil system, water injection pressure impulse circuit and change in setting. Following modifications were carried out in Talcher unit 3 during annual overhaul in December 2005, for resolving the problem in line with the suggestions from BHEL,Hardwar.

1. The spray water pressure impulse to the protective devices is provided with the impulse lines drawn upstream and downstream of spray valves with orifices. The impulse signal, when the spray is closed should be positive, thus avoiding air lock in the impulse lines. The orifice sizes (Tag no. MAN91BP001, 2,3 & 4) in the impulse lines ahead of spray valves were increased to 7 mm from earlier values of 4.5 mm. This has improved the impulse pressure to LPBP system from 0 ksc to 2.3 Ksc, when the spray valve is closed. This helps in increasing the impulse pressure quickly to the reset the protective devices.

2. In the LPBP signal fluid line, filling line from control fluid and air

release lines are provided with orifices to maintain positive pressure when no command is available for LPBP. Vent line orifice

(MAX42bp041) was reduced from 2.5 mm to 1.8 mm. This has increased the signal fluid pressure at LPBP control valve servomotor end from 0 Ksc to 0.6 Ksc.

3. The injection water permissive to the protective devices were re-adjusted to reset at 6.5 ksc from earlier design value of 9.5 ksc.

4. Pressure transmitters were provided in LPBP injection water line, Signal fluid for injection water valve and signal fluid for LPBP control valves for recording and analysing the time taken at each stage of LPBP operation.

After carrying out the above modifications, healthiness of the limit pressure controller was checked with 0% and 100% command to the converter. The signal fluid pressure for both Control Valves was observed to be 2.75 ksc with limit controller in lower position and 100 % command to converter, value within the stop valve opening point. The following are the observations.

Parameters Limit controller in lower position and 0 % command to convertor

Limit controller in lower position and 100 % command to convertor

Water injection pressure

2.3 15

Signal fluid pressure to LPBP CV1

0.63 2.75

Signal fluid pressure to LPBP CV 2

0.75 2.75

Signal fluid pressure to WI valve

1.03 7

A 100 % manual command was issued from MMI to LPBP control valves and from analogue and trend data, it was observed that the LPBP control valves starts opening within 4 seconds of issue of command and

fully opens within 5 seconds. This fulfils the requirement of boiler for not tripping on re-heater protection. Lowering of protection setting for spray water pressure protective devices may create conditions, where inadequate spray is fed to quench steam to condenser. This may lead to abnormal operating conditions in the condenser, which may affect vacuum and increase exhaust hood temperature. The performance of the system with these modifications is under observation.

FEED BACK NO. 1

PROJECT: RAMAGUNDAM UNIT-7 PROBLEM: NON-METALLIC EXPANSION JOINT FAILURE Non-metallic expansion joints provided in the left (224B) of HOT AIR DUCT (PA TO BUS) got ruptured and the ruptured portion of the bellow was replaced partly on 10.02.05. Repeatedly in the same NMEJ’s some portion of the bellows got ruptured and replaced during 26/09/05 and 08/02/06. Similarly NMEJs bellows (234 A & B) of HOT AIR DUCT TO MILLs (refer enclosed drawing), small portion of bellows got ruptured and replaced on 07/02/06. The rupturing of bellows of these NMEJs caused shut down of the units each time.

During the month of Sep’05 BHEL (T) representative visited site and suggested certain modifications of the restraints of the duct, which could not be carried out as the customer has not shut down of the unit. During the first week of March’06 a team compromising PSSR TSX, BHEL (T)’s duct design and FES visited the site and analyzed the problem with documents of Simhadri and Talcher. Team observations

1. It NMEJ tag no. 224B (PA interconnecting duct at LHS) was found leaking from the top.

2. NMEJ tag no. 224B (PA interconnecting duct at RHS) a cut on the outer layer to a length of about 300mm was noticed (mechanical damage and no leakage of hot air) on the topside.

3. The supporting arrangements of the hot PA ducts were inspected

and observations were recorded. Sketch enclosed indicates that NMEJs were subjected to tensile force in the joint, which may be the probable cause for repeated failure. The corrective actions along with site installed conditions enclosed here.

Restraints & support to be modified/erected at site during shut down/ corrective actions of agencies.

SL. No

DESCRIPTION SITE ACTION

BHEL (T) ACTON

REMARKS Orientation requirement

1

S7-S7 & S8-S8

Left & right are differently oriented at site

Should be parallel to the axis of the boiler

2 S14-S14 Correct orientation of I-beam foot is not clear in the drawing

The orientation of I-beam foot plate (top plate) and restraints axis are to be clearly given in drawing

The orientation of I-beam foot was parallel to the duct and the restraints were also erected parallel. This obstructs left right moment of the foot of the duct.

The I-beam foot should be perpendicular to boiler axis and the restraints are to be erected parallel to the foot permitting left/right moment of the foot.

3

S-15-S15

It was not

Modification

The

(S15A) erected. It has to be erected.

could not be carried at site as customer had not extended shut down

orientation as per drawing permitting left/right moment

4

S18-18

Supports provided without restraints.

Drawing has to corrected to change the section S6_S6 as S18__S18

Earlier drawing0-00-265-05981/00 shown as S6-S6

Center of PA COMMON DUCT HAS to be anchored as per section S18__S18 of drawing 1-00-265-046776/00

Higher width of fabric is required with the present position of ducting to avoid future failure and BHEL(T) will finalise after discussion with M/S KEB, the original supplier of NMEJs. It was decided to replace the 3 NMEJs with new fabric and bolsters during the next available shut down. SITE ACTION TO AVOID FAILURE OF NMEJs: All the restraints of the ducts should be sketched in a line diagram and proper expansion of the ducts to exert only expected thermal compression over the NMEJs has to be confirmed with required agencies AS A CRITICAL CHECK before actually erecting the NMEJs.

FEED BACK NO.2

PROJECT : VISAHAKAPATNAM STEEL PLANT (VSP)

PROBLEM: LOW VACUUM FOR 7 YEARS IN TG -2,TPP

TG-2, TPP, VSP is a controlled extraction condensing steam turbine of 60 MW rating supplied by BHEL and installed around 1990. A problem of low vacuum has been troubling this unit for last 7 years i.e. vacuum was maintaining at - 0.72 ksc with both main ejectors and one starting ejector in service, at full load and extraction as per design.

Actions taken: Earlier VSP has done all regular checks to resolve the problem since its existence i.e. they have done, at different times,

1. Condenser tubes cleaning (by acid cleaning and bullet cleaning). 2. Water tightness test of steam space (by filling water to turbine rotor axis).

3. Replacing all ejectors with new ones.

In spite of all such efforts condenser vacuum was always low. VSP requested BHEL to find air ingress points to resolve the low vacuum problem, using our Helium detection kit.

During February 2006 BHEL deputed a commissioning engineer from PSSR with a Helium leak detection kit to locate as yet unidentified air ingress points in VSP TG-2.

A special cooling provision was made in a sampling line taken from the main ejector air vent (i.e. the sampled air/vapor was cooled with a temporary arrangement and taken up straight to turbine floor) to prevent moisture entry into the kit. Water vapor from air exhaust in

the ejector can hamper Helium detection by wetting the special purpose membrane of the detection kit.

With this, the total system was checked with Helium detection kit. The complete results list is annexed in a separate table. Major leaks measured were:

1. Vertical parting plane (i.e joint between HP top casing and LP top casing: see annexed figure for detail). ---- 20,000 ppm. (major air ingress point indicated in sketch enclosed).

2. HP flash tank vent bellow near flash tank. ---- 500ppm

3. Starting ejector air isolation valve gland and valve flange.--- 200ppm. VSP took a unit shut down to attend the leak points along with generator pedestal vibration problem. All identified points were attended.

When VSP brought back the unit to full load with extraction, vacuum was significantly improved to -0.83 ksc.

TURBO GENERATOR NO.2

HELIUM LEAKAGE DETECTION TEST

S. NO.

LOCATION LEAKAGE VALUE (ppm)

501 Turbine rear gland bellow 1-4 02 Horizontal parting plane (MER side) 1 03 Vertical parting plane (MER side) 50 (Max.) 04 Both Bursting Diaphragms 0 05 Vertical parting plane (ECR side)

(Leakage is from Horizontal flange to valve block near rib)

20,000

06 Horizontal plane (ECR side) 0 07 Rear bellow (ECR side) 0 08 Vacuum breaker 0 09 HP flash tank bellow near condenser 0 10 LP1 extraction valve bonnet 30 11 HP flash tank bellow near flash tank 500 12 Condenser box 0 13 Hot well manhole cover 0 14 Surge pipe, stand pipe flanges 0 15 HPH-4 Safety valve 0

VACUUM LEAK DETECTION WITH HELIUM DETECTION KIT

Integral top casing of 60 MW Turbine

of Vishakapatnam Steel TPS

FEED BACK NO.3

Project: METTUR UNIT -1

LP Top Casing

Major Air Ingress point (900 portion out of 3600 joint)

HP Top Casing

Shown Portion 20,000 ppm detected.

SUB : CYCLE TIME REDUCTION : The capital overhaul works of unit-1 - 210 MW – LMW TG set of Mettur Thermal Power station was completed in record time of 34 days from de-synchronisation to synchronization inspite of additional works over and above the normal overhauling. To achieve this reduction in cycle time, the following methods and planning were adopted. 1. Established the site before the shut down of TG set and made

available BHEL/SAS personnel, sub-contractor men and T & P at work spot. (Unit was shut down on 03/01/06. Site was fully established by 28/12/05). Temporary shed for sand blasting was prepared and kept ready even before shut down of the unit.

2. All the special tools , fixtures available with customer to be used

during overhaul were brought from the customer stores and kept ready.

3. New bearings for turbine bearing no.6 & 7 were brought to

turbine floor from customer stores before TG shut down. Cleaning, assembly, suitability checking and blue matching were completed in advance, which saved considerable time.

4. About 150 nos. of skilled, semi-skilled and unskilled workers of

sub-contractors were engaged and the work was organized/carried out round the clock.

5. External agencies like M/s Supreme Mannings, Kolkatta for

opening the turbine parting plane bolts and retightening during assembly by induction heating, M/s Power Test Asia for conducting electrical testing of generator and agencies for reaming were engaged well in advance by timely and meticulous planning.

6. Major activities like replacement of all HP, IP & LP sealing rings,

including checking of freeness of all rings, filing, scrapping and grinding of excess fin height were carried out by engaging efficient and experienced Mill Wright fitters around 20 nos. , round the clock using more number of grinding machines, scrappers and files.

7. Cooling of turbine was made faster by removing insulation in time,

as per the maintenance manual practice which has enabled the starting of dismantling works.

8. The introduction of top ripple spring in 60 slots of generator

stator was carried out totally by SAS/Secunderabad Technicians and expert guidance, without waiting for BHEL, Haridwar man power, which has saved lot of time and made the generator ready in time for electrical testing, hydraulic testing, varnishing and finally for threading in of generator rotor.

9. For the additional works allotted by the customer for

rectification of magnetic off-center, the preparatory works like shifting of pedestal, enlarging of stator base holes, getting the required hydraulic jacks for shifting of stator , disconnecting the water, gas piping flanges from stator and also removal of bus duct, etc. were carried out in advance without waiting for the contractual formalities for awarding the job, which has saved seven days

In addition to the above mentioned steps, BHEL /SAS has taken care to maintain utmost quality during dismantling and assembly of TG set, thereby did not encounter any sort of trouble during re-commissioning and could synchronize the unit without loss of time. Reduction in cycle time saved the operating expenses for BHEL and

reaped intangible gains by the way of customer satisfaction, as the customer realized larger benefits by generation and enhanced availability. The above feed back was contributed by SAS/Secunderabad.

FEED BACK NO.1

PROJECT: Ennore TPS Unit 3 - 110 MW

PROBLEM: 110 MW Vacuum System improvement

In Unit 3 - 110 MW of Ennore Thermal Power Station M/s. TNEB had recently replaced the full set of HP, IP, and LP Steam Turbine rotors with new ones. During the shutdown several modifications were initiated outside the main STG rotor system, with a view to improve STG performance. At earlier times, when the unit was running at 70-90 MW after R&M, the vacuum was always poor and affecting the unit output. A comprehensive effort was made with all round focus on the vacuum and related systems. Listed below are the important measures taken:

1. LP Casing parting plane modification:

Grooves were cut in the in LP Casing parting plane and a silicone cord was introduced for sealing against air ingress.

2. LP Casing metal stitching

Metal stitching was done in cracked sections of the LP Casing to seal the steam space from air ingress.

3. Polymer cladding of condenser

Polymer cladding of condenser CW water boxes and parting planes was done to reduce the seawater corrosion of water box material. CW parting plane corrosion has resulted in poor condenser heat transfer because of CW short circuit.

4. Introduction of priming ejector in CW lines

A Priming ejector was introduced for air removal in condenser CW lines and water boxes for achieving full CW flow.

5. Rerouting of LPHs 1&2 drains:

LPHs 1&2 drains were modified in consultation with BHEL (HYD) to route them to condensate pump suction as per original scheme.

6. Segregation of turbine extraction and pipeline drains:

The steam from high pressure MS, CRH and HRH drains, and most other low pressure drains, were earlier connected to Service Condensate tank ( SCT) with a provision to be connected to condenser or to atmosphere. This resulted in additional thermal loading of the condenser, and was an undetectable source of air ingress. The SCT was isolated from the condenser by blanking its vent and drain connections to vacuum system, and converting it to a purely atmospheric pressure vessel for start-ups. Thus high temperature steam has been diverted away from the condenser to reduce thermal loading on it. At the same time the extraction line drains were removed from SCT and connected to HPH Flash Tank.

7. Rerouting of LPH and HPH extraction drains

HPH 7,8 and LPHs 3,4,5 extraction drains from pipelines, downstream of NRVs were routed to HPH Flash tank in consultation with BHEL (HYD). This was required to ensure the drains in the vacuum system were segregated from the SCT.

8. Replacement of Ejectors

New Ejectors were installed with enhanced air handling capacity, considering the age and corrosive atmosphere in these old units at Ennore.

9. LP Gland Steam pressure tapping modification

LP Gland Steam pressure tapping was relocated at the LP front gland seal with NB 65 impulse pipe header for accurate measurement for auto control.

10. HP Gland steam line introduced

HP Gland steam line for HP gland packing was introduced from 11 ata PRDS header since it was not envisaged in earlier SKODA design. It was one of the major reasons for air ingress from HP Gland seals in this steam turbine, that prevented achieving of full vacuum, when there was no self sealing steam while STG on barring gear.

11. Condenser water tightness test

The Condenser tightness test was conducted by filling water upto TG floor (7.9 meters). Water was retained in the condenser for 36 hours and zero drops in level was achieved for this period after attending all the leaks.

12. LP Gland Steam header drain modified.

A drain was introduced in the LP Gland Steam header, with a steam trap and trap bypass to condenser, since it caused hammering in the sealing steam lines every time these lines were charged during vacuum pulling.

With this, most of the air ingress to condenser, and its thermal loading points have been taken care of. The drain modifications were undertaken by TNEB on the request of PSSR, on the original SKODA system, with the support of BHEL Hyderabad T & C Engineering for attaining full load and improved steady state behavior of the machine at higher loads.

The unit was restarted recently in March 2006. During the restart when vacuum was pulled in this modified system, –0.95 ksc (approx 720 mm Hg of mercury) vacuum was achieved with STG on barring gear.

715 mm Hg of vacuum was found to be maintaining stably under steam dumping, rolling, synchronization, and load conditions.

FEED BACK NO.2

PROJECT: EID PARRY, PUDUKKOTTAI - 1x18.55 MW TG

PROBLEM: POOR VACUUM DURING INITIAL COMMISSIONING

STG supplied by BHEL, Hyderabad at EID, Parry, Pudukkottai is having

air cooled condenser, which is supplied by M/s Paharpur Cooling

Towers. Air evacuation system consists of one starting ejector and two

main ejectors.

Vacuum pulling was carried out on 19/03/06. Even after admission of

turbine sealing steam, maximum vacuum of –0.5 kg/cm2 could only be

achieved. Two minor leakages were identified at turbine side and

nothing was reported from air-cooled condenser side. But the air flow

from main ejector exhaust was more than 60 kg/hr. Motive steam

supply pressure at ejector inlet was 5.5 kg/cm2, against design

pressure of 8 kg/cm2. The steam supply line is of 2 inch size. It was

decided to increase to 3 inch size. After increasing the line size, rated

steam pressure at ejector inlet was maintained. The leakages at turbine

side were arrested. Vacuum of –0.8 kg/cm2 was achieved. However the

air exhaust remained high (above 55 kg/cm2).

With condenser vacuum of –0.8 kg/cm2 it was decided to roll the

machine. While rolling to first warming up speed of 1000 RPM, vacuum

has fallen to –0.78 kg/cm2 and stabilised. After two hours of warming

up, speed was raised to second warming up speed of 4000 RPM. While

holding at 4000 RPM, vacuum started deteriorating and within 20

minutes, the vacuum dropped to trip level of –0.55 kg/cm2 and unit

tripped. The air evacuation system and condenser were studied. The

following are the observations made:

1. There are 6 cooling fans in total to cover all the segments of

condensor. The air evacuation lines for the main ejectors are from

the condensor drawn from all segments. All the cooling fans are

necessarily to be run enabling steam entered to get condensed at

all sections. The speed of fan can be adjusted, as they are

variable frequency driven. Earlier they were running only three

fans. It was decided to start all the fans.

2. The air evacuation line for the starting ejector is drawn from the

condensate collecting tank (Hotwell). Condensate collecting tank is

connected to the turbine exhaust with an isolation valve, which was

open. This has caused the exhaust steam to directly flow in to the

condensate tank, thereby heating the condensate. After rolling to

4000 RPM, the condensate temperature was 65 deg C. This high

condensate temperature influenced poor performance of the main

ejectors. Also, the starting ejector removing only the exhaust

steam directly bypassing condensor. Hence it was decided to keep

the valve in the line between turbine exhaust and condensate tank

closed, before rolling.

3. Also, as the temperature of condensate was high, it was decided

to replace the total DM water in the condensate tank with fresh

water. The schematic arrangement of condensor and air evacuation system are

as shown in the enclosed figure.

After carrying out the above changes in the operation of condenser and

air evacuation system, unit was rolled to rated speed of 5650 RPM. It

was running at rated speed for electrical tests for more than 12 hours,

without disturbance in the vacuum. Subsequently, the machine was

loaded upto 2 MW. Vacuum dropped upto 0.77 kg/cm2 on loading the

machine.

Further for improving the vacuum, air ingress in the air-cooled

condenser is to be identified and arrested, which is planned by

customer in the shutdown in first week of April 2006.

EID PARRY CONDENSOR AND AIR EVACUATION SYSTEM

TO GSC

CCT/HOTWELL

CEP

STARTING EJECTOR

MAIN EJECTOR

TURBINE

COOLING FANS

AIR COOLED CONDENSOR

THIS VALVE CLOSED

FEEDBACK NO.1 PROJECT : EID PARRY, PUTUKKOTTAI

CRITICAL IMPROVEMENT IN SWITCHYARD OPERATION. In EID Parry/Pudukkottai site, 110 KV supply is fed from Alangudi Sub station and it is also feeding to Aliyanalli Sub station of load approx 30 MW. This system is loop in and loop out for TNEB, who are controlling the Breaker operations.

ALANGUDI SS 110KV ALIYANALLI SS 110 KV

BREAKER AT SS BREAKER AT SS

SWITCH YARD BREAKER AT EID (A) 110 KV TRANSMISSION BREAKER AT EID (B)

110KV GCB TRANSFORMER TIE AT EID SWITCH BREAKER YARD 11 KV 11 KV DISTRIBUTION TO SUGAR PLANT Whenever Breaker at Alangudi SS trips or Breaker ‘A’ and ‘B’ trips our machine will be suddenly loaded since the load increases to approx. 30 MW + House load and trips on under frequency/voltage. The Breakers at Alangudi SS and Aliyanalli SS are not synchronizing Breakers. The closing risk of Breakers is always there without synchronizing checks, at both Sub Stations, when supply is available at both ends of Breaker, i.e. one end from our machine and the other end from grid supply.

G

The circuit is modified to trip the Tie Breaker, whenever the Breaker at EID Parry Switchyard ‘A’ and ‘B’ trips or breaker opens out, to safeguard the generator with suitable/interlocks i.e. when the Breaker at Alangudi SS or 110 KV Breaker at EID Switchyard ‘A’ is open, the Tie Breaker should also open. Once supply is restored at 110 MV end, the Tie Breaker could be closed, after completion of synchronizing checks.

FEED BACK NO.2

Project : CPCL Frame V GT, units 1 & 2 Problem: Failure of rotary flow dividers of fuel supply line to GT Combustion chamber

The flow dividers of M/s Ropar make supplied to Gas Turbines at CPCL site were not performing well during commissioning phase of the Gas Turbines, due to various reasons. All the four flow dividers supplied in both ‘ On base and Off base ‘ skids have failed. The condition of the flow dividers were such that one or two could not be even rotated slightly. There were no flow dividers available with manufacturing units or with any authorized service agency. Complete commissioning was held up leading to non-completion of contractual obligations. Replacement against insurance will be a long-drawn affair, which will not meet neither BHEL nor CPCL’s requirements. Hence the flow dividers were serviced at site. All the flow dividers have been working satisfactorily since servicing, for around 10000 hours and hence it was strongly felt that servicing would restore the healthiness.

Engineers from hyderabad have also felt that servicing had extended the life of flow dividers beyond the normal 8000 working hours. The entire works were carried out in a controlled, closed and clean environment. Sufficient care was taken to ensure availability of proper tools, required lifting arrangements, etc. Before disassembly, all the components were match marked. The self-locking bolts were replaced in the probe gear wheel. During assembly at every stage of plates assembly, care was taken to check the freeness for rotation, condition of ‘O’ rings, etc. The gears in the gear pumps were very high degree of finish and the clearances were very close, at the order of less than 0.l mm. Even a minor scratch affects the freeness of rotation. The sun gear locks all the planetary gears and does not allow differential flow. All the ring plates are isolated with ‘O’ rings.

Collection of paste like ferrous matter on the needle bearing holding areas was observed. The bearings were soaked in naphtha and the paste like ferrous matter was cleared. The bearings are to be absolutely clean and in good condition, after cleaning. Initially it took 3-4 days to service one flow divider. But later on one flow divider could be easily serviced in a day. By now, the customer & Hyderabad Engineers have been acquainted with the art of servicing after witnessing the servicing of flow dividers carried out by our Engineers. Thus, we could save the total cost of replacements, cost of contract extensions and insurance, etc. The figures in the next few pages explain the various steps in assembly and the construction features

10 NO. OUTLETTO COMB. CHAMBER

1 NO.FUEL OIL INLET

RING TYPESOLID PLATESWITH L IFT ING LUGS, 'O' RINGS FOR ISOLATION

I

I I

I I I

IV

V

A

BBUSH IN ALL HOLES SHALL BE FREE

I TOP PLATE WITH SPEED PICK UP WHEEL II PLATE WITH GEAR PUMP SPINDLE, BUSH AND LOCKING ARRANGEMENT III PLATE HOUSING 10 NO. GEAR PUMPS IV PLATE HOUSING 20 NO.

NEEDLE BEARINGS FOR PUMPS V BOTTOM END PLATE WITH OIL INLET AND OUTLET CONNECTIONS

LIFTING LUG

TOP PLATE

I

I I

I I I

I V

V

RING PLATE WHERENEEDLE BEARINGS LOCATED

'O' RING

GEAR OFONE PUMP

NEEDLE BEARINGS

PLATE HOUSING GEAR PUMPSMESHED WITH PANETARY GEAR

10 NO. GEAR PUMPS

PLANETARY GEAR

The following important precautions to be taken to ensure good servicing of the flow divider. 01. During assembly the bush inserted in all the holes shall go free. 02. All the bolts shall be tightened uniformly. 03. All ‘O’ rings of required dimensions, new and required quality shall

be used. 04. Gear pumps and gear shall be checked for scratches, clearances

are in the order of 0.015 mm. 05. During assembly at every stage check for free rotation of gears.

For this, just if the probe stem is rotated with thumb and finger it shall rotate the gears.

06. In a good serviced divider with the index finger and middle finger in the probe gears, it shall be possible to rotate freely.

07. Ensure the divider is not dummied/blocked in suction and discharge sides.

08. Servicing shall be carried out in a clean and closed environment. 09. Pure naphtha was filled in vessels and bearings were soaked for 24

hours. 10. Plastic toothbrushes were used for removing contaminants. 11. Uniformly free rotation is important than free rotation itself.

FEED BACK NO: 1.

PROJECT: EID PARRY, PUDUKKOTTAI, 1 X 18.55 MW TG PROBLEM: LOAD COULD NOT BE RAISED BEYOND 14 MW

DURING RESTART OF TG AFTER BRIEF COGEN PLANT SHUT DOWN. FURTHER LOAD REDUCED DAY BY DAY TO THE LEVEL OF 7 MW.

ANALYSIS: The above problem of load could not be raised beyond 14 MW, was reported to us, by customer through mail. We requested customer to send the operating parameters. As per the parameters mailed by customer on 14/06/06, the actual load was 13.8 MW with set point of 18 MW. At the same time the HP control valve demand at control room was 100% and valve position at local is also indicated as full open. As per valve flow characteristics, at full open of valve, the inlet steam flow should be 110 tph. But the inlet steam flow was only 80 tph, for which the load of 13.8 MW was approximately matching with the steam map. The steam flow limitation (80 tph) leads to suspicion on restriction at control valve or within turbine. For further analysis, we requested for the parameters from the date of reaching full load along with wheel chamber pressure. Our site engineer furnished the data from 20th may 2006. The following are the observation. The wheel chamber pressure shows increasing trend after restart of the turbine on 11/06/06. The wheel chamber pressure of 65 kg/cm2 at full load and upto 11th June 2006 is almost matching with HP regulation curve.

Also, the secondary oil pressure data indicates the control valve remains partial open till 11/06/2006 and later it became full open.

The excessive wheel chamber pressure indicates the restriction is within turbine. It has lead us to conclude that deposits of salt and silica constricts the passage in the fixed and moving blades, thereby causing drop in efficiency and power output. The only reason for the deposit will be poor steam quality. We requested customer to look into the history of analysis of chemical regime of the steam. After analysis of DM plant, customer confirmed some problem in the RODM plant, which was causing impure water being fed into the boiler.

BHEL/PSSR/TSX department advised Customer to shut down the unit and to clean the scale deposits on moving and fixed blades of turbine. The unit was shut down on 23.06.06. Customer has issued work order to SAS for carrying out the above works. The turbine was opened on 08/07/06, the photographs of turbine deposits is enclosed for reference. The turbine is being cleaned by Alumina blasting.

CONCLUSION:

The problem gives the lesson of how the steam purity affects the performance of Steam Turbine. Hence utmost importance has to be given for boiler water and steam analysis in any power plant of any size.

FEED BACK - 2 PROJECT : RAICHUR – UNIT 3 PROBLEM : BALANCING OF LP ROTOR AT SITE

Generator rotor replacement was carried out on Unit 3 , 210 MW unit (Seimens Turbine – Russian Generator ) of Raichur thermal power station during May 2006 due to rotor earth fault. The IP turbine rear shaft vibrations increased to alarm levels of 120 microns peak from earlier levels of 75 microns peak at rated load parameters. The control room vibration levels are given below as recorded on 06-06-2006. Load: 172 MW Freq : 49.28 Hz

Shaft Vibrations in microns peak(pk)

Bearing Vibrations in microns peak(pk)

HP Front 49.5 2.9

HP Rear 34.0 3.0

IP Rear 119.8 14.9

LP Rear 26.2 10.7

Vibration analysis of bearing and shaft vibrations indicated predominant presence of running speed vibration components. The LP front pedestal vibrations are given below.

The LP front vibrations for Seimens turbine are normally in the range of 25 to 30 microns pk-pk. Here the pedestal vibrations were high and also the phase difference between vertical and horizontal directions were 111 degrees – very near to 90 degrees which results in good vibration reductions to balance correction.

Balance correction was carried out on LP rotor using LP front Plane. A total number of 11 balance weights of 90 grams were added at LP front plane to arrive at satisfactory shaft and pedestal vibration levels on turbine. The LP front pedestal vibrations after balancing are given below.

1X- microns pk-pk

Phase Overall

Vertical 26 58 26

Horizontal 27 283 27

Axial 24 136 25

The control room vibration levels at 180 MW load are given below as recorded on 07-06-2006. Load : 180 MW Freq : 49.42 Hz

1X- microns pk-pk

Phase Overall

Vertical 49 46 49

Horizontal 56 295 56

Axial 57 192 57

Shaft Vibrations in

microns pk Bearing Vibrations in microns pk

HP Front 22 2.8

HP Rear 21 4.5

IP Rear 72 9.2

LP Rear 46 5.2

The IP rear shaft vibrations coast up plots before and after balancing are given in figures 1 & 2. It is observed that there is no critical speed sharply reflected at IP rear . The coast up plot shows considerable reduction in shaft vibration levels after 2700 rpm

0

20

40

60

80

100

120

140

600 900 1200 1500 1800 2100 2400 2700 3000 3300

RPM

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FEED BACK NO.1

PROJECT : NEYVELI THERMAL POWER STATION II, UNIT NUMBER 6, 210 MW. PROBLEM : 1. Starting device not operating from control room.

2. EHTC hunting when changed over to load control at load of 40 MW.

1. Starting device not operating from control room. Problem: The servicing of all the governing system components was carried out during overhaul. There were no problems during checking and setting of governing characteristics. While checking the operation of starting device from control room, it was observed that the device was not operating. The power supply module was checked and found to be healthy. The power supply was getting extended whenever command was given from control desk. But it was noticed that the power supply module was tripping on overload protection within few seconds of command. While giving command, observation was made at local and found that motor was not rotating. Analysis:

The starting device motor is provided with magnetic brake and hence it is not possible to check the freeness of motor by rotating manually. The brake will get released on giving command. The cable terminations of brake system was checked and found healthy. The motor was decoupled and operation of the motor was checked by giving command at control room. It was found that the motor was rotating freely in both directions of commands in decoupled condition. Also, the adjusting gear was rotating freely by hand and starting device was free to operate by hand wheel.

The coupling (part number 25 and 26 in the figure) is within the housing and not visible after assembly of motor. The extended shaft of the motor with coupling hub was rotated during assembly and proper coupling was ensured. The motor is bolted to the housing of the adjusting gear and after tightening the coupling gap (gap between part numbers 25 and 26 in the enclosed figure) should be 0.5 mm. Measurements of length of extended shaft with coupling hub and depth of the other part of coupling in adjusting gear were made and found that there were no gap in coupling. Also, while tightening the motor, the shaft was forcing against the worm wheel of adjusting gear (as the measurements indicated interference at coupling) and motor shaft was getting jammed and unable to rotate by motor, causing the motor to trip on overload. Conclusion: For maintaining coupling gap, 1 mm shim was introduced between motor and the housing of adjusting gear. After assembly it was found that the starting device was operating from control room and the current was normal during operation. It was advised to check the coupling gap, whenever motor was replaced for starting device or speeder gear.

Figure .1 Adjusting gear for starting device

2. EHTC hunting when changed over to load control at load of 40 MW.

Problem: The unit was rolled and synchronized with EHTC in service. During rolling, at warm up speed, rated speed and during synchronization, the behavior of EHTC was smooth. While changing over to load control and loading beyond 40 MW, severe hunting of EHTC and control valves was noticed. The machine was immediately changed over to hydraulic governing and further loading was done. Analysis: The behavior of EHTC and control valves at rolling and speed control mode at low load was smooth. Also, during checking of characteristics the behavior was smooth. Hence it is suspected that the load controller settings might have got disturbed and is to be tuned. But as per C & I engineer, the settings are same as pre-overhaul values. The balance voltage was checked and found to be –3.5 volts, instead of –1 volt. The same was readjusted to –1 volt. With EHTC in isolated position, the speed control loop was checked and found that the feedback was not smooth even after adjustment of balance voltage. It was decided to check the freeness of the pilot valve. The moving coil with sleeve was removed. The pilot valve was observed for its rotation by admitting and isolating the control oil many times. It was found that at times, the pilot valve does not rotate. The pilot valve was removed and serviced again. The holes of oil jet for rotation in the disc of the pilot were thoroughly cleaned and assembled back. The rotation of pilot with admission of control valve was checked many times and the pilot was rotating smoothly. The behavior of the EHTC in isolated condition was checked and found to be smooth. The machine was changed over to EHTC control at load of 150 MW and the behavior was smooth. Conclusion:

While checking the characteristics of EHTC, the behavior was smooth. It is necessary to check the rotation of pilot and its consistency by admitting and isolating control oil many times.

FEEDBACK NO:2

PROJECT : ENNORE THERMAL POWER STATION, 110 MW, UNIT - 3 PROBLEM : FOULING OF COOLING WATER TUBES IN CONDENSER

Unit-3 at Ennore Thermal Power Station was shutdown to inspect and clean the condenser Cooling Water(CW) tubes and water boxes by chemical cleaning. This was required to overcome the choking and fouling of CW tubes that was indicated by the difficulty in maintaining vacuum at higher loads. When the CW water boxes were opened for inspection, large quantity of corroded flake material was found in the MS inlet pipes. Similar debris was found lodged in the inlet sections of the CW tubes. In all passes, these were suspected to be coming out due to the corrosion of CW pipes, from the debris filter to the condenser water box inlet. In ‘D” condenser pass these scales had jammed in the tubes of the condenser. The tubes were first cleaned, by TNEB, with water jets, and the physical blockages at the inlet of the condenser tubes were removed. Then, TNEB adopted a process of chemical cleaning using the services of a consultant from 24th to 29th of June ‘06. During the process, each quarter pass i.e. A, B, C, and D, of the condenser was subjected to circulation with chemicals for a period of 24 hrs. The chemicals added were proprietary preparations i.e 200 Kgs of chemicals made up of polymeric dispersant inclusive of 16 kg ortho-phosphoric acid added to 30 m3 of water. This was circulated for 24 hours in each pass. The circulation was maintained at 90 TPH by a single pump. Finally before completion, the system was drained and rinsed. The chemical cleaning data is tabulated as below:

Chemical cleaning data - Unit-3 - ETPS Sl. No.

Description Condensers

A B C D 1 Starting

time/date 18.30 hrs. 25.06.06

0000 hrs. 27.06.06

20.30 hrs. 25.06.06

0030 hrs. 27.06.06

2 Closing time/data

18.30 hrs. 26.06.06

0400 hrs. 28.06.06

2030 hrs. 25.06.06

0400 hrs. 28.06.06

3 Starting pH 4.5 4.5 4.5 4.5 4 Closing pH 4.0 4.0 4.0 4.0 5 Starting TDS* 4108 4322 5526 5796 6 Final TDS* 22581 18189 19922 20482 7 Increase in

TDS in 24 hrs.

18473 13867 14346 14686

Approximate Calculations for one quarter Condenser – A pass

No. of tubes : 3300 nos Length : 7.5 m Area/Tube : 0.47 m2

Total increase in TDS* x Vol circulated (30 m3) : 540 Kgs-approx. Deposition (Increase in TDS*/Tube) : 158 gms. Estimated Deposit : 337 gms/m2

(*TDS is Total Dissolved Solids. This does not include the scales and corrosion products found in the condenser tubes and water box, because they were removed separately before the chemical cleaning was commenced.)

Condenser performance at Ennore TPS is affected by:

? Poor heat transfer due to a sticky greasy coating that forms, and also binds, the debris and dirt carried by the water to the inside

walls of the tubes. The refineries upstream release the greasy contaminants that are mixing in the CW, because of the opening of gates from the Buckingham Canal into the CW intake at ETPS. The coating thus formed reduces the heat transfer in the tubes.

? Reduced cross section area for flow, which is significantly reducing because the corroded chips are lodging in each tube and preventing adequate CW flow, for heat to be carried away.

The importance of good quality CW, and the prevention of corrosive action on CW pipes in older plants like ETPS, is essential to ensure prevention of fouling of tubes, good condenser heat transfer, good vacuum and good output from unit.

Annexed pages of operation data show clearly the improvement obtained in unit performance. Ennore Unit 3 has recently completed a run generating 63 MU, the highest ever, recorded monthly generation in 30 years, since 1973, for this unit, at 00.00 hrs on 31.07.06. It has sustained this steady generation of 90 – 100 MW continuously from 1.7.06 after the recent R&M works on vacuum system and above chemical cleaning of the condenser.

FEED BACK NO.1

PROJECT : TALCHER UNIT - 6 PROBLEM : HUNTING OF HIGH PRESSURE CONTROL VALVE-2 During first commissioning of turbine, hunting of HPCV –2 was observed. The control valve was hunting to the tune of 20 to 30 mm beyond 40% opening. Hunting stops at valve wide open condition. The auxiliary pilot valve (14), of HPCV-2 (Refer the enclosed drawings) was serviced on few occasions, during available shut down. But the problem could not be resolved. Hunting of HPCV 2 causes load variation and hunting of HPCV 1 also. Hence to avoid load fluctuations and HPCVs hunting, the HPCVs were kept wide open during regular operation of the unit. Trial operation of the unit was conducted with HPCV-2 in wide open position. Site referred the problem to Haridwar. Haridwar has suggested site for dismantling the control valve servo motor and carry out thorough inspection of the internals, i.e. auxiliary pilot valve, pilot piston, feed back linkages, main pilot valve and spring discs of main piston. Customer has not permitted shut down of the unit due to grid demand, to carry out the above works suggested by Haridwar. However, for conducting PG test at rated parameters, BHEL suggested to limit HPCV-2 opening at 40% by using ATT motor and control the load with HPCV-1. NTPC was persuaded to permit BHEL to conduct the PG test. PG test of turbine was completed. The control valve is actually moved by the piston (9) which is loaded on one side by the disc springs(10) and on the other side by hydraulic pressure. The position of the valve is determined by the secondary fluid pressure. The supply of secondary fluid (connection b) controls the auxiliary pilot valve (14) which directs control fluid from connection ‘a1’ to the appropriate side of the pilot piston (4). The pilot piston operates

the main pilot valve (3) through lever (5) so that when the valve is being opened, control fluid from connection ‘a’ is directed to the bottom side of piston (9). When the valve is being closed, fluid drains through the main pilot valve. The auxiliary pilot valve is continuously rotated by the action of fluid jets to ensure that the valve moves freely at all the times. Sticking in any of auxiliary pilot valve, pilot piston, main pilot valve or in any of the feed back linkages/levers can cause hunting or inconsistent behavior of control valves. On 17th May 2006, the unit was shut down. The HPCV-2 was dismantled and all the internals were inspected in the presence of Haridwar technicians. Following observations were made. 1. The auxiliary pilot valve, which is actuated by the secondary fluid,

was found to have scratches over its surface. Rust particles were found in between the pilot valve and its sleeve. Two (out of three) radially drilled holes through which control fluid flows and keeps the pilot valve in rotation were found to be enlarged, because of which the pilot valve could not rotate uniformly, causing erratic valve behaviour. The enlargement of holes observed was a manufacturing defect. The defective auxiliary pilot valve assembly was replaced with a new pilot valve and sleeve from customer spares.

2. The Teflon sealing ring which separates the two ports in the pilot

piston (4) has longitudinal scratches which was suspected to be the reason for not sealing at high pressures. The defective sleeve was replaced.

3. All the feed back linkages were found intact without any

looseness. 4. The main pilot valve was also found to be all right. 5. 3 nos. spring discs, which were found broken, were replaced. Control valve servomotor was assembled and calibrated. While checking control valve characteristics, HPCV-2 was found to behave sluggishly. The pilot piston (4) was adjusted such that at maximum secondary fluid pressure (5 Ksc.), 1 mm travel reserve was maintained. This helps in residual pressure above piston aiding in quick response to varying demand. After this adjustment, the valve characteristics were found in order with slight hunting of 2 to 5 mm at valve stroke of more than 40. The machine was cleared for rolling, as this is a normal behaviour. Turbine was rolled on 30/05/06 and found that during loading (opening of HPCV-2 beyond 40%), there was no hunting in the control valves.

FEED BACK NO:2

PROJECT: EID, PARRY, PUDUKKOTTAI, 1 X 18.55 MW TG PROBLEM: HIGH MAIN STEAM SILICA PROBLEM DURING RESTART

AFTER OVERHAUL OF FOULED TURBINE

During the month of June 2006, it was reported by customer that the machine could not be loaded to rated capacity. The operating parameters of the unit were obtained from the customer and was examined by us. It was concluded that the main cause could be due to fouling of turbine blades, which was caused by impure steam. Based on our advise the unit was shut down and the turbine top casing was dismantled. Heavy scale deposition on the internals of the turbine was observed. The scale deposits were removed by alumina blasting. The damaged components of turbine were sent to Hyderabad works for rectification and were received & installed in the turbine. After completion of the above works, turbine top casing was put back and boxed up. After carrying out oil flushing, turbine was put on barring gear. We advised customer for inspection and cleaning of other areas like boiler, air cooled condenser, etc. The vessels like Boiler drum, Deaerator, Condensate storage tank were inspected, cleaned and boiler was flushed. After completion of assembly of turbine Boiler was restarted on 07/08/06. After nearly 18 hours of venting, the steam through start up vents, steam purity (Silica 0.02 PPM and Iron Nil PPM) was achieved. Consistency in steam quality was ensured for 6 hours and Turbine was rolled, synchronized and loaded to 3 MW on 08/08/2006. After two hours, load was raised to 5 MW. At this load the Main steam silica was found increasing. The Turbine was hand tripped, as the silica level has increased to 0.07 PPM. Boiler was kept in service and steam was vented out through start up vents at boiler and turbine end. Even after two days of venting, the silica level was not dropping below 0.05 PPM. Boiler was boxed up due to shortage of DM water. When the boiler was restarted after 24 hours of cooling, the main steam silica level has increased to the level

of 0.25 to 0.3 PPM . The silica levels of feed water and drum saturated steam were well within limit of 0.02 PPM. Drum water (CBD sample) silica also reduced to the operating level of 0.5 PPM. This indicated that the contamination had been carried over from super heater coils. Hence customer was advised to clear the deposits from super heaters by steam blowing operation. It was decided to carry out steam blowing by continuous blowing method through ESV. ESV was dismantled, Steam blow device and temporary piping to atmosphere were erected. Steam blowing was carried out for three days (total number of blows - 13 ) and silica was monitored. After ensuring steam purity ,Turbine was restarted on 22/08/06. When the deaerator was charged with PRDS steam, Silica level of Feed water and Steam started increasing . Further following precautions were taken to ensure that there were no contamination from other associated system.

1. Deaerator pegging steam line was disconnected and steam blown.

2. CBD vent connection to deaerator was kept isolated and customer was advised to charge this line only after few weeks of stable operation of the unit.

3. The condensate of air cooled condenser outlet was left to the drain till the purity was achieved. On achieving the condensate purity ( less than 0.03 PPM), the condensate was partially put back into the feed water circuit and the feed water purity was monitored. Full recovery of condensate was made after achieving condensate purity of 0.02 PPM.

4. Condensate purity of turbine exhaust condensate collection tank was checked before putting it to CST.

5. After achieving condensate purity, turbine load was gradually raised to maximum load on condensing mode without extraction. Steam purity was monitored and found to be within limit.

6. Turbine LP extraction was charged and process steam was given.

The purity of condensate return from sugar plant was also achieved. After achieving purity of condensate , closed loop was established.

7. Turbine MP Extraction to feed water heater was charged leaving the condensate from feed water heater outside initially. Condensate purity was ensured before putting back into closed loop.

Full load of 18.55 MW with extractions was achieved on 27/08/06. The inlet steam flow at different extraction flows and load are in line with design steam map curves. The wheel chamber pressure matches with the inlet steam flow, as per the design curve. The unit is now operating at full load.

FEED BACK NO.1

RE-COMMISSIONING STEAM TURBINE GOVERNING SYSTEMS: PROBLEMS FACED AFTER OVERHAUL.

PROJECTS:

1. NTPC, RAMAGUNDAM STPP, UNIT - 6, 500 MW

2. NTPC, SIMHADRI TPP, UNIT - 1, 500 MW

3. TNEB, TUTICORIN TPS, UNIT - 4, 210 MW

1. RAMAGUNDAM UNIT 6:

(i) IPSV-1 was tripping while opening with starting device from UCB and

(ii) Turbine was reaching over speed value with speeder gear.

Both these problems were observed during regular operation before planned overhaul. (i) To overcome IPSV-1 tripping, which was suspected to be due to fluid leakage within it’s test valve, customer has replaced the liner of the test valve for IPSV-1. During re-commissioning of the system, the same IPSV servomotor was again tripping while opening from starting device. While observing the local pressures of above and below piston during SV opening, the pressure above piston was reducing to 5 ksc, and the valve was tripping at almost in full open condition. The rate of opening was also found to be faster than other valves. When the IPSV operation was done locally, slowly, by limiting the test valve stroke, the servomotor opened smoothly and did not trip. This indicated that the tripping occurred due to draining of large quantity of trip fluid, during opening. By limiting the stroke of test valve, the draining was controlled and the pressure above piston was kept at more than 6 ksc, while opening of the servomotor. To limit the stroke permanently, the test valve cover was opened for introducing washer / ring (Refer Figure 1) inside the test valve. The test valve drawing was referred, and it was found that the adjustment ring was missing. A ring of 9 mm thickness was introduced. Thereafter, the operation of all stop valves, with starting device, from control room, was found to be normal.

Figure 1

(ii) To over come the problem of over-speeding with speeder gear,

the speeder gear stroke length was reduced to 24 mm from 30 mm by shifting the stopper nut, during overhaul of the governing rack components. For checking the speed regulation with Hydraulic

governing, the machine was changed over to speeder gear. When Hydraulic governing had taken over from Electro Hydraulic Governing ( EHG ) at 3000 RPM, the speeder gear position was reduced from 24 mm to around 8 mm. As with this position the speed could go to more than 3200 RPM, the adjustment with adjusting screw (Refer Figure 2) for speeder gear was made, but only 3 mm could be adjusted and further provision was not available in the adjusting screw. With this limited adjustment, speed was raised with speeder gear up to 3210 RPM. The speeder gear position was around 16 mm at this speed. Hence to achieve speed regulation of 3210 RPM, speeder gear limiter is to be advanced by further 5 mm.

Figure 2

Adjusting screw

2. SIMHADRI UNIT 1:

(i)IP secondary oil pressure not responding to EHC voltage (ii) EHG hunting during rolling

The above mentioned problems were encountered during calibration of governing system after servicing of all control elements in the governing system by BHEL/Hardwar technicians during overhauling of unit by SAS. (i) EHC vs IP secondary fluid pressures were not responding.

The IP secondary fluid pressure is developed as per the required characteristics,

With EHC coil voltage at zero, IP sec. pressure is 2 ksc and With EHC coil voltage at “1.7”, IP sec pressure is 6 ksc

On observation, it was found that the spring of one of the follow up pistons was found to have displaced and defective. The follow up piston was replaced and this problem was resolved. EHC voltage vs IP sec pressures characteristics were taken and found to be alright. (ii) EHC hunting problem during rolling: While rolling the machine, hunting was observed. The following observations were made during the analysis of EHC hunting problem.

i) Hydraulic controller is found to be alright. ii) EHC is hunting (hunting observed from 25% to 35% of command)

other than this range, there is no EHC hunting. iii) Individually EHC & Hydraulic is alright. (Checked by closing both

isolation valves on secondary fluid headers). iv) When the entire system (HP and IP secondary fluid circuits) is in

service, more draining of fluid is taking place, and hunting is

observed especially when the IP secondary fluid circuits are taken into service.

v) IP secondary fluid system was checked but no abnormality was observed.

vi) At EHC positions between 25% and 35% range, while opening extraction NRVs, trip fluid pressure was varying, which was causing secondary fluid pressure fluctuations.

vii) All extraction NRVs openings were adjusted / staggered to open one by one, to avoid variation in trip fluid pressure. But still minor variations were observed both in trip fluid pressure and Secondary fluid pressure.

viii) The trip oil line to extraction relays was inspected for its orifice size. The 5 mm dia orifice in trip fluid line to extraction relay (installed during initial commissioning based on BHEL / Hardwar instructions) was not in position. The desired orifice was introduced and characteristics were retaken. The unit was rolled and synchronized. No further hunting was observed in EHC.

3. TUTICORIN TPS, UNIT 4:

(i) EHC not responding with respect to the feed voltage

(ii) Balance voltage indicates maximum instead of -1.0 ± 0.2 volts.

To analyze, EHC behavior was checked by simulated inputs during shut down. By that it was found that pilot piston was disturbed from its equilibrium position. Inconsistent behavior of IP follow up pistons was also noticed. It was decided to service EHC pilot (item 6 in Fig 3), and do a complete inspection of follow up piston feedback linkages etc.

Figure 3

Accordingly, when the EHC unit was dismantled along with coil, it was noticed that the bottom screw (Refer Figure 3) of pilot valve, which acts as a plug to prevent trip oil draining from the pilot, was found

loose. This probably has caused disturbance to the equilibrium position of the pilot valve. Also the pilot valve was not spinning because of dirt in the assembly and jets. The screw was tightened properly with thread sealing compound. Pilot valve and sleeves were serviced and free rotation of pilot valve was ensured.

While checking the follow up piston behavior by opening the side cover of assembly, it was found that one no. IP follow-up piston control sleeve (Refer Figure 4) got dislodged from the assembly because the cylindrical link pin, with its 2 nos. of locking split pins, were missing and could not be located. Spare cylindrical pin and split pins were assembled and EHC characteristics were corrected. The behavior of EHC was now found satisfactory.

Further, Hydraulic governing HP / IP control valve characteristics were also checked and minor deviations from design value were readjusted. Turbine was rolled on 26-09-06 and behavior of EHC was found to be normal.

Figure 4

CONCLUSION:

The above problems faced in the governing system in three different power stations indicate that a thorough checking of governing system components during every overhaul is essential. Customers are being advised to ascertain the healthiness of the governing system during shut down and overhaul. Unhealthy deviations are to be identified and the critical components that are to be serviced, or replaced, can be decided during the study.

FEED BACK NO. 2

PROJECT : NINL,DUBRI PROBLEMS : ENCOUNTERED DURING PRE COMMISSIONING

OF GAS TURBINE AFTER 6 YEARS AT NINL

DUBRI.

? The Gas Turbine was received at site by Feb. 2000.

? The Gas Turbine erection work started in April 2000.

? The Gas Turbine Train Alignment completed in May 2001.

? The erection work stopped from June 2002 to Sept. 2003 and from May 2004 to Aug. 2004 due to reasons not attributable to BHEL.

? The re-erection work started from Aug 2004 and the following major problems are faced.

1. Lot of GTG enclosure items, Bus duct items from Transformer to GTG, Transformer items, Vent fans, CO2 items, & other items like Push buttons, Contactors, Pressure gauges, Limit switches, Transducers, electronic cards in Digital Voltage Regulator (DVR) as well as Mark-V panels were found missing.

2. Some of the available items were not working due to severe rusting and other mechanical damages.

3. The 125 Volts Batteries were in highly damaged condition and BHEL was forced to purchase new batteries.

4. After arranging the materials, the balance erection/ pre-commissioning works were carried out. Thorough inspection was carried out from inlet plenum to exhaust duct. During inspection of compressor and GT, one no. bolt was found inside the Gas Turbine under 2nd stage blades. (Fig 1).

All efforts to remove the bolt, without resorting to opening of the top half of GT, were not successful. Boroscopic inspection was carried out by representative from BHEL/Hyderabad. One washer like substance was visible during boroscopic inspection. BHEL/Hyderabad proposed to open the top-half of GT casing, as it was suspected that there could be some other foreign objects, which could not be observed by physical as well as boroscopic inspection.

The turbine was opened under the supervision from Hyderabad representative. Along with bolt, one no CS impulse pipe of size 8x300 mm, welding rod cut bits were also found inside the Turbine.(fig2). The washer like substance observed through baroscopic inspection was found to be an integral part of GT.

The timely action of identifying the foreign materials saved the Turbine, as otherwise it could have resulted in major failure, while commissioning the Gas Turbine.

FEED BACK NO.1

PROJECT : NTPC , KAYAMKULAM , UNIT 2 PROBLEM : HIGH VIBRATIONS IN EXCITER OF GAS TURBINE Gas Turbine - 2 was restarted during 2nd week of October 2006,

after a gap of nearly two months. On reaching FSNL, vibration of

Exciter bearing of GT - 2 was increasing . The vibration levels of Gas

Turbine and Generator were steady. The exciter bearing was

monitored with a casing probe mounted at 45 degrees. The alarm limit

is 12.5 mm/sec and trip levels are 25 mm/sec. At FSNL, the exciter

vibration levels were around 6 mm/sec and this progressively increased

to 14 mm/sec within 20 minutes.

Since the unit was at rest for considerable duration of time under

preservation, the customer was asked to soak the unit at cranking

speed of 700 RPM . The soaking time was limited to 1 hour based on

operational confidence arrived from water wash experience . The unit

underwent soaking cycle 4 times before the unit was taken for FSNL.

There was a considerable improvement in exciter vibration behaviour .

The vibration levels once again had increasing tendency but the rate

was very slow. The levels were crossing alarm limit in 2 hours of

operation at FSNL. The Unit was also loaded to 75 MW to check

behaviour on synchronization. The increasing tendency was still

persisting. ( Please refer Fig 1.).

It was recommended to check interference between exciter bearing

shell and Yoke.

On checking it was observed that there was a clearance of 0.07 mm

between shell and yoke, instead of interference of 0.05 mm ( as per

design ) . This was corrected as per design requirement.

The unit was restarted on 28-October-06. The exciter bearing

vibration levels at FSNL were around 5.5 mm/sec and this was observed

to be steady after continuous operation. The Vibration levels remained

below 6 mm/sec on load .

EXCITER BEARING VIBRATIONS TREND AT FSNL AND ON LOAD

Figure 1

FEED BACK NO.1

PROBLEM : RENOVATION WORK CARRIED OUT AT UPPER

KOLAB HEP

HISTORY OF THE MACHINE

Four units of 80 MW capacity each were supplied and erected under the supervision of BHEL at Upper Kolab Power House at Orissa Hydro Power Corporation Limited (OHPC). In all four machines, the turbines were supplied by BHEL, Haridwar and the generators were supplied by BHEL, Bhopal. They were commissioned in a phased manner from 1988 to 1993. Unit no.1 was commissioned on 15.03.1988 Unit no.2 was commissioned on 16.04.1988 Unit no.3 was commissioned on 10.02.1990 Unit no.4 was commissioned on 12.01.1993 The Unit 4 of Upper Kolab Power House tripped at 0730 hrs. on 19.07.2005. Prior to it, the machine was running smoothly. After initial inspection, winding was found damaged and BHEL/SAS was contacted by OHPC. At that stage, the fault was apprehended to be in the windings with minor damages to core. The affected bars were removed, i.e. 34 nos. of Upper bars and 4 nos. of Lower bars. It was observed that extensive damage was observed in the core and the pressing fingers of core pressing plates (portion of pressing fingers in between slot no.43 –44 and 48 – 49 facing lower bars had melted. Immediately a message was sent to BHEL/Haridwar for their advise and comments. BHEL team recommended that the entire core should be removed and replaced with new one.

A number of discussions were held between OHPC, BHEL/Haridwar, BHEL/Bhopal and BHEL/SAS. Considering the long time to get a new stator and availability of resources, it was jointly decided to get the damaged portion of stator rectified locally and run the unit till such time they get a new wound stator from BHEL. An order was given to BHEL/SAS for the repair of Stator core. (LOI no.322,dated 27.01.2006). P.O.No.SGM/UKHEP/OHPC/TECH/FM-94/403/WE dated 31.01.2006. SYNOPSIS OF WORKS CARRIED OUT. The unit was dismantled, the rotor was lifted and kept in service bay. The affected sector of generator stator was dismantled completely. The damaged core punchings were removed. The damaged finger plates were replaced by new finger plates. The finger plates were fabricated locally. The stator core was rebuilt. HV test and ELCID test was carried out on stator. The defective poles were removed and the coil was replaced. The poles were reassembled. HV test and IMPEDANCE test was conducted on rotor. The details of work carried out are given below: A. GENERAOR : 1. Stator :

a. Stator core of affected sector (slot no. 16 – 61) was completely dismantled.

b. Stator bars (Top slot no. 5 – 80 and bottom bars 16 – 65) were removed.

c. Damaged bottom support fingers were removed and replaced by new fingers welded and leveled by grinding.

d. Stator core building, intermediate pressing were carried out at site.

e. Defective winding bars were sent to M/s Abhirami Engg. Works, Chennai for reconditioning.

f. After reconditioning, the bars were reassembled and tested. g. Complete stator was HV tested at 13.5 KV for one minute

and found alright. h. ELCID test was carried out.

2. ROTOR

a. 3 nos. of defective poles were identified. b. Defective pole coils were removed and replaced. c. Insulation packing between pole body and pole coil were

replaced by new packing. d. HV test and IMPEDANCE test was carried out on rotor. e. Rotor was sprayed with insulating air dry varnish.

3. BEARINGS

a. Runner disk insulation surface was blue matched with thrust collar by scrapping.

b. All the thrust pads were blue matched with runner disk mirror surface.

c. All the guide bearing pads were blue matched with respect to journals.

d. Bearing journals were cleaned and polished. e. All guide bearing RTDs were calibrated. f. Bearing oil was centrifuged. g. Dial thermometers, RTDs and TSDs of bearings were

calibrated. 4. TOP BRACKET :

a. Top guide bearing oil coolers and thrust bearing oil coolers were cleaned and hydraulic test carried out.

5. BOTTOM BRACKET :

a. Bottom bracket oil coolers were cleaned and hydraulic test was carried out.

b. Brake jacks were dismantled, cleaned and tested. 6. SLIP RING : a. Slip rings were cleaned and reassembled. 7. PERMANENT MAGNET GENERATOR :

a. Stator and rotor were cleaned and varnished with air drying insulating varnish.

8. AIR COOLERS :

a. Air coolers were dismantled, cleaned and assembled. b. Hydraulic test was carried out.

9. LEVELLING AND ALIGNMENT :

a. Rotor leveling was done to a level of 1 div. using block level of 0.02/m accuracy.

b. Load sharing of thrust pads was done up to 3 div. in static condition and upto 1½ div in dynamic condition.

c. Throw at LGB is 0.06 mm d. Throw at TGB was 0.102 mm e. Bearing clearance at LGB and UGB set as 0.16 mm

10. WORKS CARRIED OUT BY M/S OHPC

a. Fabrication of fingers for pressing plates. b. Repair of stator winding bars. c. Procurement of winding materials.

d. Assistance for testing of stator and rotor e. Calibration of instruments f. All turbine assembly works.

B. COMMISSIONING :

a. The unit was spun on 27.09.2006. b. Pre commissioning checks and Electrical were completed on

05.10.06. c. The unit was synchronized and loaded on 06.10.06. d. 72 hours trial operation was completed on 09.10.06.

MAJOR DEFECTS AND REMEDIAL MEASURES ADOPTED

- Pressing fingers of the pressing plates in the bottom portion of the core in between lower bar no. 43 – 44 and 47 – 48

have melted. Core in the vicinity of these fingers have also got melted.

- The melted copper has also got sprayed in this portion of the core.

- The bottom most stampings in between slot no. 36 – 46 & 46 – 56 are fully charred and have protruded out radially inwards by about 2 – 3 mm.

- The complete bottom stack of glued stampings has moved inwards by about 1 – 2 mm.

- Blacking of core up to 6 – 7 packets was seen. - Some slot wedges in this sector and adjoining stator sector

were found to have shifted down. - Three nos. of poles were found to be defective. Remedial measures - Complete core of the affected sector removed. - The damaged core punchings were replaced by better

punchings. - The glued punchings were repaired and reused at the top.

- All the specified tests were conducted on stator. - The defective pole coils were removed and replaced by new

spare coils. - Tightening of wedges in the remaining part of stator. - This is a unique instance of rehabilitating a damaged core

slated for replacement and making the machine available for operation at full load.

FEED BACK: 2

PROJECT : RAYALASEEMA UNIT: 3 PROBLEM : TROUBLE SHOOTING OF maxDNA NETWORK

COMMUNICATION

During the start up of maxDNA for first commissioning at RTPP Unit 3, it was found the Digital Processing Units (DPUs) were not communicating with max Stations and vice versa thru max Net. Initially the doubt was on the cable crimping. We have checked the continuity of cable and the sequence using network cable tester.

Network cable tester is a device that checks the continuity and sequence of cable in a Un-Shielded Twisted Pair (UTP) cable connection. It has got a transmitter and a receiver. The transmitter sends the signal on one wire at a time and does it cyclically for all eight wires. The receiver on sensing the signal, glows the corresponding LED.

We have decided to check the cable pairing, since it could be a potential cause for communication failure. Though there are four pairs inside the UTP cable, only 2 pairs are used in a straight thru cable. The details are in the figure-1.

Figure - 1

Of this TX+ and TX- uses one pair, which is White/Orange and Orange and RX+ and RX- pair uses the White/Green and Green. On inspection at the network cable connector the connections were found as in figure-2.

Figure-2

The combination used for Receiver was White/Blue for RX+ (pin no:3) and Green for RX-.(pin no:6) since they belong to different pairs, this would have caused cross talk or electrical interference resulting in failure of communication.

This mistake in cable pair was existing in all UTP cable connectors

and the same was corrected by re-crimping the UTP cables as per TIA-EIA 568 B standard (Figure-1). After re-crimping, communication was established in maxNet and the boiler light up was done as per plan from maxStation.

Note: It is not necessary that a transmitter pair should always use

Orange pair or Green pair for Receiver. We can use any other pair for transmitter, like Green for Transmitter and Orange for Receiver or any other combination, provided the same pair is used in the other side of cable also. But as a Standard Orange pair is used for Transmitter and Green pair for Receiver.

More details about network cabling could be found at Z:\Utilities\Switch_Mgmt in the maxDNA installation CD.

FEEDBACK:1 PROJECT : BELLARY TPP PROBLEM : COMMISSIONING OF max DNA SYSTEM When the software *.4F files were loaded into the relevant panels required for boiler light up, it was observed that many signals were already in the simulated mode(called forced signal). This was preventing the proper functioning of the logics. Commissioning Engineers at site have tried to remove the unwanted simulations by un-forcing the same (removing simulated signals). But it was seen that there were many such signals.

Site posed the problem to EDN engineers and received information that the above software *.4F files contains TEST directory, which was used during testing of the software/logics at EDN shop floor, before the panels were dispatched to site. The TEST directory was deleted during commissioning of the panels at site. All *.4F files received for

the BOP and SG max DNA system also contained ‘TEST’ directory. Hence site has to delete all the test software from the program, so that the system operates with actual site conditions. The procedure for deleting the *.4F files, was received over phone and the same is given below:

1. Open “maxtools” and in MaxTOOLS, open configuration (*.4F) of the required Digital Processing Unit (DPU) and delete the “TEST” directory.

2. Right click the “INPUT” menu and select the tabular details from the drop down menu.

3. Select the “DTAG” and also select “show references”. 4. Double click on “forced val” (simulated value), “forced val ref”,

“mode” and “mode ref” on the available attributes. Click OK. 5. All “DTAGS” are displayed showing the above attributes. 6. In the “DTAGS”, change the forced val from ‘1’ to ‘0’ and in the

mode “attribute” change all “forced signals” to “normal”. 7. Remove all simulated signals like “sim1.out”, “sim2.out”, -- --,

etc. and exit. 8. In the file drop down menu, select “validate references”. 9. Deselect “optimized” and “start”.

10.Check for any errors. If present, click on the errors and check for red signals and remove the same if present in “forced ref” and “mode ref”.

11.In the file drop down menu, select “validate references”. Repeat step 9 to 11 till no error message is displayed.

12.Once complete, select “full download” for loading configurations to DPU.

After the above operation, the logics were functioning satisfactorily and connected systems were commissioned successfully.

FEED BACK: 2

PROJECT :20 MW STG AT CPCL,CHENNAI PROBLEM :LIMITATION IN LOADING OF MACHINE DUE TO

ERRATIC BEHAVIOR OF I/H CONVERTERS OF HP,IP AND LP CONTROL VALVES.

Details of problem: The 2 x 20 MW STG at CPCL, Chennai was originally provided with Pro-control Based Electro Hydraulic Turbine Converter (EHTC) for HP,IP and LP control valves and the EHTCs were supplied by BHEL, Hyderabad. M/s CPCL has decided to upgrade the turbine governing system with the latest version, using VOITH make I/H converters. The hydraulic systems were modified to suit the VOITH make I/H converters by BHEL, Hyderabad. The modified oil system was flushed and control valves were stroked manually by BHEL ,Hyderabad Engineers and cleared for commissioning

from EHTC panel. The modification in software as well as Hardware in the EHTC panel was carried out by EDN, Bangalore. During Commissioning by EDN Engineer, it was observed that the characteristics of I/H converters were found to be erratic. The readings are as follows :

Current Signal (ma)

Secondary oil pressure(kg/sq.cm)

4 1.5 8 0.8 12 1.5 20 4.5

As the Power/Steam from this unit for the Refinery is very much critical, GM/Cogen, CPCL has requested the services of PSSR experts to analyse and resolve the problem. PSSR Engineers from Headquarters were deputed immediately to study and resolve the problem. Analysis The I/H converter was mechanically operated and found to be in order.

The correct electrical connection of the I/H converter should be as in figure 1, whereas the actual connections were found as shown in figure 2.

The connections were corrected properly in line with figure 1. The I/H converters of HP, IP and LP turbines were carried out and the characteristics were found to be linear for the input signal of 4 to 20 mA. The machine was rolled, synchronized and extractions were taken into service. The characteristics after correction of connections are shown as below:

D

A

B

C

E

F

+ 24 V

+ 0 V

+ve

-ve

4 to 20 mA I/H Convertor

FIG.1

D

A

B

C

E

F

+ 24 V

+ 0 V

+ve

-ve

4 to 20 mA I/H Convertor

FIG.2

Current Signal (ma)

Secondary oil pressure(kg/sq.cm)

4 1.5 8 2.20 12 2.9 16 3.72 20 4.5

Conclusion: The reversal in the polarity of signal wire and mistake in loop terminations (0 volt) caused the back e.m.f. to the coil and the characteristics were disturbed. The rectification in the termination has resolved the problem.