pa fan high vibrations

PA FAN HIGH VIBRATIONSBOILERPA FAN

Knowledge Management SystemSIMHADRI

Document Submitted by: D.S.G.S.S.Babji, DGM (BMD),

Emp. No.003937,

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Emp. No.003937,Mobile: 09440918484

E-mail: [email protected]

Date of submission: 11/08/2009

1.ABSTRACT OF THE CASE STUDY1. Equipment Type: Axial Profile Fan2. Equipment Specification: AP-2 20/123. Type of failure : High Vibrations in Axial direction4. Summary of Failure Analysis: Power Point Presentation enclosed

PA fan of Unit#2 at NTPC-Simhadri was having high axial vibrationproblem since commissioning i.e. year 2002.

Since, opportunity to repair comes only during unit overhauls,repeated attempts were made jointly by BHEL and NTPC duringannual overhauls.

PAFan-2A High Vibrations problem

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Finally problem could be solved during overhaul of 2007.

The presentation covers various activities carried at in chronologicalorder.

Commissioned on 04.09.02:Vibrations ontrial run at 50% B.P. / 77 A. at Table-1

Fan vibrations increased

19.02.2003: M/s BHEL Suspected looseness or misalignment. Total rotor assembly and blades were replaced. Vibrations at

Table-1 H V A

M-DE 1.0 1.4 2.1

M-NDE 1.3 1.3 1.9

FAN DE 3.6 2.3 5.5

FAN NDE 2.6 3.0 5.3

Table-2 H V A

M-DE 2.96 3.01 5.11


and blades were replaced. Vibrations at 32% B.P. & 62 A - Table-2

27.04.2003: To reduce unbalance, BHEL carried out alignment and dynamic balancing at site No improvement in vibrations - 52% B.P. Table-3

19.06.2003: Complete rotor assembly was replaced .Vibrations at 65% B.P Table-4

F-DE 8.92 5.4 13.6

F-NDE 7.67 5.35 13.3

Table-3 H V A

F-DE 8.5 5.8 10.2

F-NDE 8.5 4.5 10.5

Table-4 H V A

F-DE 5.9 3.0 8.0

F-NDE 3.8 2.4 8.2

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During Overhaul dt.20.05.2004: Complete Rotor Dismantled. Trial Run Taken.Vibrations in Fig-5 at 55% B.P.-Table-5

During overhaul dt.11.07.2005: Complete servicing of rotor assembly done all bearings, springs , INA ring and Rigiflex coupling were replaced. No improvement.Vibrations at 57% B.P. - Table-6

Table-5 H V A

F-DE 3.3 3.9 7.8

F-NDE 3.3 2.6 8.0

Table-6 H V A

F-DE 2.9 2.6 11.3


During Overhaul of 2006 : BHEL sought for trail run and analyzed. Readings at 49% B.P., 73 A- Table-7

BHEL Suggested the following:� Alignment of Diffuser With Uniform Axial Gap

Of 10 Mm W.R.T Impeller housing � Spring Back Check On The Impeller Housing

And Correction if required, � Alignment Of OGV Core Seal� Vibrations could be flow induced-check ducts

F-NDE 2.4 3.0 11.3

Table-7 H V A

F-DE 3.0 2.0 7.4

F-NDE 3.4 2.0 7.3

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Work Done during Unit Overhaul of 2007 with BHEL supervision

Re-alignment of diffuser w.r.t. impeller housing by adjusting diffusersoft foot. Spring back check done on impeller housing foot.

(Please refer to pic.-1 in the following slide)

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Diffuser Assembly Soft Foot Adjustment (Pic.1)

Correction

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� Metal interference observed between OGV core sealing ring and OGV(Impeller Housing) transmitting strain up to rotor.

� Trial run taken without OGV core sealing ring to confirm the same.

� The diameter of OGV core sealing ring reduced by 2 mm on outer


� The diameter of OGV core sealing ring reduced by 2 mm on outercircumference to relieve strain.(Please refer to fig.-1, fig.-2 and pic.-2 in the following slides)

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Complete PA Fan Assembly (Fig.-1)

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Arrangement of impeller housing/ OGV (Fig.-2)

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OGV Core Sealing Ring (Pic.-2)

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� PA fan Blades at Simhadri are showing symptoms of pitting/flaking andsubsequent metal loss.

� The metal loss problem is referred to CC/OS and is under study by corporateR&D to ascertain root cause and to provide a solution to the problem.


� The pitted/corroded blades were replaced with new sets.(Please refer to pic.-3 in the following slide)

� Fan Motor Alignment Done.

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PA Fan Blades Metal Loss Problem (Pic.-3)

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After completing all the works on PA Fan-2A,

� Vibration Readings were measured after overhaul at unit full load (i.e. 500MW) and were found Within Permissible Limits as given at Table-8

� Vibration measured at 60% B.P. and 97 Amps current.


� Vibration measured at 60% B.P. and 97 Amps current.

Table-8 H V A

F-DE 3.1 0.9 2.5

F-NDE 3.1 0.8 2.5

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pa fan high vibrations

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