Name: Ajai Tandon Company Name: NTPC TANDA

Transcription

1 Name: Ajai Tandon Company Name: NTPC TANDA

2 TG are designed by M/S Skoda, supplied and manufactured by BHEL TG set supported by 7 journal bearings and coupled by three rigid couplings, brg no 2 is thrust cum journal bearing HP: Two concentric casing, two curtis wheel and 8 impulse stage wheels MP: Two concentric casing, 12 impulse stages, 8 solid forged and 4 shrunk fit

3 LP: Four reaction stages in double flow direction. All wheels are shrunk fit Middle portion has LP heaters 1,2 mounted on casing Extraction: Eight uncontrolled extraction Barring gear: 62 RPM between LP and Gen. Steam Admission: HP Cyl. through 4 CV and 2 quick closing valves. IP: Through HRH and 2 no interceptor valves LP: Through crossover pipes

4 After restoration of Turbine blades at LP stage 4A in unit-4 at TANDA T.P.S. The Turbine brg no 2 started showing transient vibrations during change in parameters like frequency, load, MS temp etc. The vibrations were such as to steadily increase in occurrence and level. The unit has to be tripped on three occasions in which even reducing the load to considerable amount the transient did not stooped. The Turbine as such was ok during normal Operation without any deviation in Turbine Supervisory parameters

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6 Axial Shift and Exp : HP Ov : 24.4, MP Ov: 15.0 mm Ax shift: , mm Vibration: Brg No. 1 H - 29 to 65 micron ; Brg No. 1V 20 to 55 micron Brg no 2H 24 to 111 micron; Brg no 2V 29 to 58 Rest Brgs No change or marginal change ECC: HP Ecc. 55 to 53 (No change) ; MP Ecc. 93 to 36 (Reduced) ; LP Ecc 86 to 93 (Minor Change) Lub. Oil Pressure was 1.42, DC lub oil was taken which increased oil pr to 1.9 kg/cm2 temp was 39.3 BRG TEMP Brg no ; Brg no (Increased) Brg no (Reduced) Brg No Brg no Brg no Brg no Front Thurst pad Rear Thurst pad

7 The oil Pr was increased from 1.4 to 1.65 and temp of the oil was increased from 39 to 40 Deg C. The FFT signatures of the Turbine were taken to rule out the possibility of oil Whirl or Oil Whip condition. ( No ½ X or 0.47 X component were noticed.) No high freq were present in signatures DC Em. oil p/p was taken in service to take care of these events which some time reversed these events

8 BRG-1-H DISP and Velocity Signatures BRG-2-H DISP and Velocity Signatures

9 BRG-3-H DISP and Velocity Signatures BRG-4-H DISP and Velocity Signatures

10 BRG-5-H DISP and Velocity Signatures BRG-6-H DISP and Velocity Signatures

11 BRG-7-H DISP and Velocity Signatures It was observed that sudden change in Load and sharp rise in Freq lead to these events. It was hence advised to Operation to take necessary care In this regard. Even after these precautions Transient occurrence frequency and level of vibration kept on increasing and it was difficult to run the machine in a safe manner.

12 During no transient ( ) Brg no. H(D/V/A) V(D/V) A(D/V) 18/11/2010 (TSI parameters) / / / /4.4 19/ / / /1.0 35/ mw, 49.9hz, hp/mp Ov.Exp /16.1, HP/MP/LP Diff Exp /1.04/1.65, / /5.0 34/ / /5.8 50/7.8 Axial shift:-0.14/.15/.10, / /5.4 40/ / / /4.6 HP/MP/IP Ecc-49/109/88, lub.oil-1.7/40.5 C, Vacuum=.923, Brg temp-(1)-71, (2)-65, (3)-70, (4)- 72, (5)-74, (6)-50, (7)-46, Thrust pad FR / Re-53/56

13 The OEM (BHEL) suggested a complete stripping of machine and thorough inspection of all the bearings and alignment. The total time for the same was about 60 days Shutdown. The analysis indicated that brg no 3 loading has got reduced, due to misalignment between LP and IP brg no 2 loading has increased to its limits. Any minor fluctuation was causing Brg 2 Vib. to increase and IP Ecc. to reduce.

14 The Phase analysis indicated pattern of residual vibration vectors at brg 2,3,4,5 in one quadrant as seen below. In this case since vibration was normal in all the three directions during normal operation., abnormally high misalignment and Unbalance problems could not be associated with the phenomenon deg deg Position of Horizontal Vib Vectors before Adjusting the Dynamic forces 1 0 deg 6 In order to avoid frequent transient at brg no 2 which was making it difficult to operate, it was suggested to change the dynamic loading pattern of Horizontal vibration phases

15 Limitations: Plane available for introducing dynamic force was Generator rear i.e. (Brg no.7) Any force introduced will disturb brg no. 7 Approval Since, it was getting very difficult to run the machine, and seeing no respite, an approval from OS was taken Before carrying out this exercise.

16 Being it an unusual exercise for changing the Phase angles of residual unbalance vectors, the process of finding weight amount and location was slightly modified The two tasks were: Avoiding unusual changes at brg no 7 (as the effect would be highest over there being nearest to Weight plane) Keeping the vibration level in all directions and at all brgs within limits and if possible to reduce it.

17 Possible location of affect vectors for avoiding increase in brg 7 radial vector To avoid letting brg no 7 vib to increase, we selected an amount, which will create A vector of about half of the existing brg 7 vector value and its angle should be either opposite to existing brg no 7 vector or about 60 deg apart for creating minimum disturbance to it.

18 BRG-7H Vectors BRG-6H Vectors BRG-5H Vectors

19 BRG-4H Vectors BRG-3H Vectors BRG-2H Vectors BRG-1H Vectors

20 Position of Horizontal Vib Vectors Iteration A Position of Horizontal Vib Vectors Iteration B

21 Position of Horizontal Vib Vectors Iteration C Position of Horizontal Vib Vectors Iteration D

22 3 7 Out of these A and B iteration seemed to give the best solutions. B was selected as in case of A 1 vector of brg 3 was getting reduced,which we wanted to increase for increasing the dynamic Loading. In order to create Vectors 2 for B iteration a weight of 250 gm at 240 deg at GEN brg 7 plane was placed. Position of Horizontal Vib Vectors Iteration E

23 In order to change the Brg vibration phasors apart a 250 gm at 240 deg at GEN brg 7 plane was placed at Exciter end using high density weights. (Angles are from ref to Reflective tape)

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25 The gradual increase of Brg no 2 vibration Stopped after this exercise. It has become self controlled, Even in worst cases of external Excitation, it rises up to 30 micron and then dies itself Brg no. Date H(D/V/A) V(D/V) A(D/V) 1 07-Feb /1.1 25/4.2 17/ Feb /25 21/ / Feb / / / Feb / / / Feb / / / Feb / / / Feb / / /5.58

26 The Time taken for the exercise was about 2 hr, in which the first iteration at Location B itself gave the results. The unusual method is a demonstration how controlling dynamic forces externally can control the vibrations problem. Earlier a similar exercise in unit-3 of TANDA, we were able to control Oil whirl phenomenon by increasing dynamic loading. The exercise also emphasizes that keeping influence coefficients of various turbines may save time and can provides methods to control the forces responsible.