Vibration studies and on-site balancing of GT-1 assembly

Transcription

1 Page 1 of 32 Fig-1 showing the bump test measurements made on exciter rear end. A predominant frequency at 220 Hz was seen in the spectrum

2 Page 2 of 32 Fig-2 showing bump test measurements made on generator NDE fan blade showing predominant frequencies at 338 Hz and 414 Hz which are quite far away from operating speeds

3 Page 3 of 32 Fig-3 showing bump test measurements made on generator NDE fan showing predominant frequencies at 414 Hz which are quite far away from operating speeds

4 Page 4 of 32 The above snap showing the existing balancing correction mass provided initially by the manufacturer on the generator rear fan assembly

5 Page 5 of 32 Picture-1 Picture-2 Picture-1 and 2 shows the mass correction provided on the exciter rear end. This might have been added on the exciter assembly during static balancing (slow speed balancing) at shop conditions.

6 Page 6 of 32 The above snaps showing dial gauge being used on the low speed coupling to check the run outs and was found to be within limits. The above snap showing physical inspection of the outer surface of the low speed coupling which was carried out at site conditions

7 Page 7 of 32 The above snaps showing oil inlets for low speed side gear coupling. It showed that on the left hand side of the gear coupling the oil supply was limited since there is no separate oil nozzle to supply oil to the meshing teeth, while on the right hand side the oil supply was adequate to the meshing teeth.

8 Page 8 of 32 Table-1 showing overall vibration levels recorded on GT-1 train before and after balancing at no load Location Horizontal Vertical Axial Before After Before After Before After Turbine front Turbine rear Generator front Generator rear Table-2 showing vibration levels recorded on gearbox input and output bearing after balancing Location Horizontal Vertical Axial Gearbox input Gearbox output Table-3 showing vibration levels recorded on Generator front and Generator Rear bearing after balancing and the set loaded to 12 MW Location Horizontal Vertical Axial Gearbox input Gearbox output Comparative casing vibration levels of Turbine front before and after balancing Vibration levels in mm/sec RMS Before balancing After balancing Horizontal Vertical Axial Direction of measurement

9 Page 9 of 32 Comparative casing vibration levels of Turbine rear before and after balancing Vibration levels in mm/sec RMS Before balancing After balancing Horizontal Vertical Axial Direction of measurement Vibration levels in mm/sec RMS Comparative casing vibration levels of Generator front before and after balancing Before balancing After balancing Horizontal Vertical Axial Direction of measurement Vibration levels in mm/sec RMS Comparative casing vibration levels of Generator rear before and after balancing Before balancing After balancing Horizontal Vertical Axial Direction of measurement

10 Page 10 of 32 Horizontal Vertical Axial Fig-4 showing comparative frequency spectrum of turbine front in HVA direction after balancing, all vibrations are in mm/sec RMS

11 Page 11 of 32 Horizontal Vertical Axial Fig-5 showing comparative time plots of turbine front in HVA direction, all vibrations is in mm/sec RMS

12 Page 12 of 32 Horizontal Vertical Axial Fig-6 showing comparative frequency spectrum of turbine rear in HVA direction, all vibrations are in mm/sec RMS

13 Page 13 of 32 Horizontal Vertical Axial Fig-7 showing comparative frequency spectrum of gearbox input in HVA direction, all vibrations are in mm/sec RMS

14 Page 14 of 32 Horizontal Vertical Axial Fig-8 showing comparative frequency spectrum of gearbox output in HVA direction, all vibrations is in mm/sec RMS

15 Page 15 of 32 Before Balancing After Balancing Fig-9 showing comparative frequency spectrum of generator front in horizontal direction before and after balancing, all vibrations are in mm/sec RMS

16 Page 16 of 32 After Balancing Before Balancing Fig-10 showing comparative frequency spectrum of generator front in vertical direction before and after balancing, all vibrations are in mm/sec RMS

17 Page 17 of 32 After Balancing Before Balancing Fig-11 showing comparative frequency spectrum of generator front in axial direction before and after balancing, all vibrations are in mm/sec RMS

18 Page 18 of 32 After Balancing Before Balancing Fig-12 showing comparative frequency spectrum of generator rear in horizontal direction before and after balancing, all vibrations are in mm/sec RMS

19 Page 19 of 32 After Balancing Before Balancing Fig-13 showing comparative frequency spectrum of generator rear in vertical direction before and after balancing, all vibrations are in mm/sec RMS

20 Page 20 of 32 After Balancing Before Balancing Fig-14 showing comparative frequency spectrum of generator rear in axial direction before and after balancing, all vibrations are in mm/sec RMS

21 Page 21 of 32 Horizontal Vertical Axial Fig-15 showing comparative frequency spectrum of generator front bearing in HVA directions after balancing and at 12 MW load

22 Page 22 of 32 Horizontal Vertical Axial Fig-16 showing comparative frequency spectrum of generator rear bearing in HVA directions after balancing and at 12 MW load

23 Page 23 of 32 On-site balancing protocol: The above snap showing the correction mass of 154 gm was added at 55 deg on the Generator front in the direction of rotating from the reflecting sticker which is being the 0 deg reference. It was ensured that all the allen bolts with split mass was tightened with metal lock. 1. A 2-plane balancing was attempted on the generator assembly by taking generator front as plane-1 and generator rear as plane-2 2. Based on the correction mass as shown by the balancing software a correction mass of 550 gm at 355 deg was added on generator front fan assembly and 300 gm at 55 deg on generator rear fan assembly 3. The train was rolled to FSNL, but there was increase in vibrations on generator front. 4. Hence a calculated mass of 154 gm was added on generator front at 55 deg while the above masses were removed 5. With 154 gm there was a considerable decrease in vibration levels on both generator front and rear in HVA directions and hence this mass was retained on the assembly

24 Page 24 of 32 Comparison of panel vibration readings with DI 440 FFT analyser The above snap showing the vibration junction box from where the vibration readings were recorded. The settings of DI 440 were made as per the parameters shown on the panel box Frequency band width: Hz Sensitivity: 200 mv/unit Measuring parameter: Peak Table-4 showing comparative vibration levels recorded directly from the vibration panel and also from DI 440 FFT vibration analyzer, GT-1 at FSNL Turbine front Turbine rear Gen front Gen rear All vibrations are in inch/sec (ips), pk Panel DI All vibrations are in mm/sec, pk Panel DI All vibrations are in mm/sec, RMS DI

25 Page 25 of 32 Comparative vibration levels recorded from the vibration panel and DI 440 FFT analyser Vibration levels in mm/sec Peak Panel DI 440 Turbine front Turbine rear Gen front Gen rear Bearing locations Comparative vibration levels recorded from the vibration panel and DI 440 FFT analyser Vibration levels in inch/sec Peak Panel DI 440 Turbine front Turbine rear Gen front Gen rear Bearing locations

26 Page 26 of 32 Fig-16 showing frequency spectrum recorded from the vibration junction box of GT-1 at FSNL, top: Turbine front, bottom: Turbine rear, the red circled peak is at a frequency of 30 Hz (1800 rpm).

27 Page 27 of 32 Fig-17 showing frequency spectrum recorded from the vibration junction box of GT-1 at FSNL, top: Gen front, bottom: Gen rear, the red circled peak is at a frequency of 15 Hz (900 rpm). Also this 15 Hz frequency was not seen on the Gen rear data.

28 Page 28 of 32 High temperatures in the Gen front and Gen rear bearing assembly area The above snap showing the poor ventilation and it is suspected that the hot air may have a churning action heating the generator front bearing as well as the vibration probe assembly It is recommended to have a better cooling system for the generator rear bearing assembly area as here also the hot air is being circulated during full speed which may be over heating the vibration probe. Needs to be studied.

29 Page 29 of 32 Observations and Conclusive Remarks: 1. The vibration levels recorded from the vibration panel was high as compared to the data recorded using DI 440 FFT vibration analyzer. 2. All the vibration probes mounted on the train needs calibration 3. Inspection and replacement of electronic vibration panels if required 4. All the couplings can be changed to diaphragm flexible couplings for better reliability and maintenance free operation 5. For the time being it is recommended to check the physical condition of the gear coupling for any dust accumulation or muck formation or deposits 6. Based on the trend data from the panel 960 rpm is the generator critical speed, 2000 rpm is the turbine rotor critical speed 7. The mass addition effected on the generator front fan assembly for the purpose of unbalance correction should not be altered in any manner. Doing so would alter the balance quality achieved. 8. Any change / alteration in the rotating mass of the generator front fan assembly will change the balance quality achieved. 9. The temperatures at generator front and rear are very high and due to this the vibration probe is misbehaving. Proper exhaust facility is to be provided for hot air coming out of generator. It is recommended to design a chimney or exhaust fan, or copy the cooling system of the GT It is recommended to inspect the thermal insulation of the gas turbine exhaust. 11.It is preferable to have new vibration probes which can withstand at least 150 to 200 deg temperatures. 12.A portable handheld vibration meter is recommended to take frequent measurements. Model will be selected and recommended shortly to BAFA. 13.It was observed that there is no any mechanical issues as such for the generator front or rear vibrations to reach 25 or 27 mm/sec as the vibration data from DI 440 were recorded at this location several times which showed no higher vibrations 14.If the spikes still exist before replacing the probes, for the time being it is advisable to disconnect generator bearing probes and take periodic measurements with handheld equipment till the system gets established to avoid unwanted trips. 15.As such with these defects, the machine cannot run with unpredictable trips due to high temperature. 16. The spectrums recorded from the vibration panel box from turbine front and rear showed 1800 rpm (30 Hz) and from generator front showed 900 rpm (15 Hz) frequency components. Mostly likely it is attributed for temperatures or probe fixing related issues. However, if the critical speeds of the respective machines happen to be these components, it will appear if there may be rotating looseness.

30 Page 30 of After taking care of all other corrections, if still this appears, it is advisable to check the health of rotating components and their fitment. For such investigations, detailed rotor dynamic calculations will help. 18. Several failures were recorded earlier at other gas turbine sites. Failures were seen on first two stage blades because of location problems like sea coast. 19. Hence to reduce the extensive damage it is better to install probes near to the tip of the blade to monitor blade crack growth so that the equipment can be stopped and the damaged blade can be replaced to avoid further secondary damages. 20. Whenever there is an opportunity it is advisable to carry out natural frequency tests on all blades to prepare a document and check the structural integrity 21. It is advisable to take each component and prepare manufacturing drawings of all important components like bearings, couplings etc. 22. A few balance masses that can be fit into the fan slot of generator front and rear assembly are to be made ready for any field balancing activity in future. 23. It can be in the range of 20, 30, 40, 50 and 60 gm. >>>>BAFA<<<<