hydromotor not able to rotate turbine-may10

7/28/2019 Hydromotor Not Able to Rotate Turbine-MAY10

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PROBLEM: HYDROMOTOR NOT ABLE TO ROTATE TURBINE

PROJECT: NALCO CCP UNIT 10. 120 MW

INTRODUCTIONThe turning gear for 120 MW design of steam turbine is a hydromotor withover running clutch, which is assembled at factory, at the front end of the front

bearing pedestal of the HP cylinder. The hydromotor uses high pressure shaft lift oil,

when turbine is in lifted condition, to rotate the turbine shaft system at slow speed

before start up, and after shut down for cooling down, as required for safe operation

of the turbine.

PROBLEMAt Nalco unit 10 the hydromotor was assembled with steam turbine with all fittings

and connections as in Unit 9, but when the Turning Gear Solenoid valve was opened, to

operate with shaft lift oil arrangement, the hydro motor was not able to rotate the

turbine shaft system.

ANALYSISTo analyze the causes for this fault, the following checks were carried out:

1. After dismantling the hydromotor from the HP front pedestal the Hydro motorwas checked with compressed service air for free rotation. It was found

rotating freely.

HYDROMOTOR


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2. The rotor lift at all the bearings was rechecked and found to be normalbetween 0.05 to 0.1 mm. The turbine was rotating freely with manual barring.

3. The over running clutch direction was confirmed as OK . (In unit 9 it wasreversed and was corrected at site).

4. When the hydromotor solenoid valve was opened pressure dropped from 150KSC to 135 KSC in jacking lift oil pressure. The pressure recovered to 150 KSC

when the solenoid valve was closed.

As a first step, to determine where this pressure drop was occurring, a dummy was

provided in the Hydro-motor inlet after the solenoid block. Then when the hydromotor

inlet solenoid valve was opened, pressure drop was observed exactly as before.

Therefore it could be concluded that this drop was occurring in the solenoid block.Further checks were done to locate the loss as follows:

1. Leakage of the O ring between solenoid and block was suspected, but that hadalready been attended and checks ensured it was OK, with oil pressure and

after dismantling the block.

2. Excess oil flow was observed from bearing lubricating line of over-runningclutch when jacking oil alone was in service. (See fig 6.)

3. By running the jacking oil pump with heated oil in MOT, it was found that thelube oil supply line coming into the FBP is getting hot, so it was suspected that

jacking oil is entering the lube supply line of clutch and hydro-motor.

4. On checking the schematic of oil lines in drawing it was seen that an NRV insidethe block in the lube oil path to hydromotor is meant to allow the hydro-motor

to be lubricated by lub oil when solenoid valve is closed. No oil should go to lub

oil from jacking oil because the NRV blocks this. Normally this NRV will be

provided in the block which is connected to turning solenoid valve. Here it was

suspected to be missed. See figure and pics below for details.


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Fig 1. LIFTING OIL SCHEME : DRG NO. 2-131-00-62253

Fig 2. SOLENOID AND SOLENOID BLOCK ARRANGEMENT


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Fig 3. SCHEMATIC REPRESENTATION OF SOLENOID AND BLOCK

Orifices are supplied separately for fitting in unions at locations shown in figure above.

Fig 4. ACTUAL ARRANGEMENT IN FRONT BEARING PEDESTAL


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So the solenoid valve block, jacking oil , lub oil and drain connection unions for

the hydromotor motor were dismantled. There was no NRV inside the block at

the location as indicated in the schematic drawing no. 2-131-00-62253. Fig 3shows internal details.

This was reported to BHEL/Hyderabad. Immediately, a new spring loaded NRV

was supplied to site which was then assembled in the block. In addition 2 and

2.5 mm orifices which were supplied with the material for hydromotor were

also assembled in the union assemblies as indicated in Fig 3 & 4 above.

Summary of hydromotor checks:

1. Hydromotor freeness can be checked with compressed air. Thehydromotor can rotate either way depending on which side air is given.

2. The clutch assembly is to be ensured as in Fig 5 . The 20 bar lift settingfor the clutch is done with high pressure gauge mounted as shown. This

gauge is removed after the pressure setting is done and the pressure

tapping point is plugged for regular use. See pictures below for details.

Fig 5. CLUTCH LIFT SETTING ARRANAGEMENT


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Fig6:CROSS

SECTIONALVIEWO

FOVERT\RUNNING

CLUTCHASSEMBLY

CLUTCH

LIFTSETTING


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3. The correctness of over running clutch direction is to be confirmed byrotating the splined gear shaft as follows: with turbine at rest, without

hydromotor assembled, the splined shaft will rotate clockwise because

the clutch permits this rotation. Anticlockwise rotation causes

engagement and the clutch will not rotate. Turbine is meant to rotateanticlockwise when viewed from FBP towards generator.

4. Orifices of 2 mm and 2.5 mm are to be assembled in the union connectorsin the lines to lub oil & hydromotor inlet as shown in Fig 3.

5. Healthiness of solenoid is to be established by checking oil entry and cut-off to the hydromotor when open and close commands are given. The

solenoid feeds jacking oil only in the forward direction.

6. The manual isolation valve in the solenoid block must be checked to verifythat it is isolating completely for maintenance and safety.

Note: At the time of manual barring for alignment of turbine, JOP is

in service. To prevent accidental rotation of the turbine with bearing

covers open and no lub oil, a temporary dummy was provided (see pics in

fig 7 below) in the hydromotor inlet. (The solenoid is energized to close

and is normally open without electric supply !)

Fig 7:DUMMY IN JACKING OIL SUPPLY FOR HYDROMOTOR AND ISOLATION VALVE

CONCLUSION

After above checks were completed and the turning gear system was

assembled, the turbine rotated freely without any manual assistance as soon as

solenoid was operated. This time, and during repeated trials later also, the drop

in lift oil pressure was only 2 ksc .

hydromotor not able to rotate turbine-may10

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