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TTPS Unit# 5 Turbine High Vibrations

By KVK Vishveshwar & UVM Rao AGM,Maint. AGM,TMD NTPC,TTPS 2/18/2013 1

TTPS , UNIT - 5 ( 110MW ) TURBINE HIGH VIBRATIONS

CONTENTS OF CASE STUDY

1.0 : INTRODUCTION 2.0 : MAJOR JOBS CARRIED OUT 3.0 : POST OVERHAUL BEHAVIOUR OF THE MACHINE 4.0 : VIBRATION TRENDS OF BEARINGS 5.0 : DISCUSSIONS WITH BHEL PERSONNEL 6.0 : RUNNING THE UNIT-5 WITH CLOSE OBSERVATION 7.0 : INSPECTION OF LP ROTOR FOR BEARING HIGH VIBRATIONS 8.0 : MAJOR JOBS CARRIED OUT TO CORRECT MISALIGNMENTS & COUPLING FACE RUNOUTS 9.0 : CONCLUSION 2/18/2013 2

1.0 :INTRODUCTION

Project : NTPC ,Talcher Thermal Power Station, ODISHA

Location : Talcher Thermal (150kms from Bhubaneswar )

Capacity : 460 MW ( 4*60 MW+2*110MW)

PLF : 90% + for the Last 5 years

Stage-1 Units (4*60 MW ) running since 45 years

Stage-2 Units ( 2*110 MW ) running since 30 years

Taken over by NTPC in Jun,1995 from OSEB at PLF of about 19.5%

Current FY 2012-13 ,PLF (Apr,12-Jan,13 ) : 95.5%

2.0 :MAJOR JOBS CARRIED OUT

Unit-5 declared for Capital overhauling after 2,00,000 operating hours in Aug,2011.

HP Turbine ,IP Turbine and LP Turbines were dismantled for

the inspection. Based on the RLA Recommendations of the past overhauls,

the broad scope of work is as follows. Refurbished HP rotor used in Unit#5. New LP Rotor procured from BHEL , Hyderabad also replaced

. HP Turbine Nozzle segments were also replaced . HP Turbine Bearing # 1,HP Diaphragm Stage-1 replaced. Diaphragms ( Guide wheels ) of IP Turbine Stage # 11,12

,14,15,16 ,LP Guide wheels 3 , 3A were also replaced .

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All 5 Bearings oil catchers were replaced .

HP & IP Turbines parting plane fasteners were replaced. IP Turbine Front Gland casing replaced due to distortion.

Replacement of HP/IP,IP/LP,LP/Gen coupling bolts with New ones.

Old IP Rotor was balanced at site with in-situ Balancing machine.

NDT of Turbine Bearings , IP Rotor also carried out.

Alumina Blasting of IP Rotor , Diaphragms ( HP,IP& LP ) and Gland casings carried out.

Induction heating of HP/IP Casing studs

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Machining of excess material from the Diaphragm thickness of IP Diaph Stg # 11,12,14,15,16 and LP Guide wheel # 3 , 3A.

Machining of HP Nozzle segments , IP Front Gland casing to suit the site measurements.

Alignment of Rotor train couplings (HP/IP ,IP/LP,LP/Gen couplings ) and coupled runout after Reaming and Honing of couplings .

Oil flushing of Bearing pedestals and Spray insulation of HP & IP Turbines and LP Turbine middle casing.

Establishing TG on Barring Gear and synchronizing the machine with Grid.

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3.0 :POST OVERHAUL BEHAVIOUR OF

THE MACHINE

The Unit-5 Turbines Capital overhauling was carried out from 30/08/11 – 28/10/11 and after overhauling when the machine was loaded to full load , vibrations of Bearing # 4 , 5 on Pedestal & Shaft were found high of the order of 60-70 microns and 200 – 250 microns respectively.

Also while loading the machine to full load , at about 70-80 MW loading has been restricted as the rate of rise of vibrations on Shaft is high , hence it was restricted for slow loading of the machine @ 1 MW/min. The Turbine configuration is as shown in Fig 1.

NTPC ,TTPS ,UNIT-5 ( 110 MW ) TURBINE CONFIGURATION

Brg#1 Brg#2 Brg#3 Brg#4 Brg#5 Brg#6 Brg#7

HP Turbine IP Turbine LP Turbine Generator

Fig 1

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

Brg Vibration , 4H

Brg Vibration , 4V

Brg Vibration , 5H

Brg Vibration , 5V

Brg Vibration , 6H

Brg Vibration , 6V

Brg Vibration , 7H

Brg Vibration , 7V

Brg Vibrn 5H

Brg Vibrn 7H

4.0 : Vibration Trends of Bearings Unit-5 TG Bearing Pedestal Vibrations,Microns

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100

125

150

175

200

225

250

275

300

Absolute Shaft Vibration , 4H

Absolute Shaft Vibration , 4V

Absolute Shaft Vibration , 5H

Absolute Shaft Vibration , 5V

Abs Shaft Vibration 5H

Unit-5 TG absolute Shaft Vibrations ,Microns

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5.0 : DISCUSSIONS WITH BHEL PERSONNEL Since the shaft vibrations of Brg # 4 ,5 were running on higher side of the order of 250 microns , it was decided to call Specialist of 110 MW sets Mr B. Rama Rao (Ex-BHEL ) to study the behavior of the machine . Mr B.Rama Rao has studied the different parameters of the machine in November,11 and made the following recommendations . The unit may be operated on continuous basis in the present condition and if the pedestal vibrations of Bearings increases to 84 microns(Pk-Pk) load may be reduced. When vibration takes on rising trend ,shutdown may be taken to check the following. a) Checking of LP/Gen coupling alignment b) Checking facial runout of LP/Gen coupling c) Checking of Catenary d) Bearing # 4 ,5 ,6 ,7 inspection for any abnormalities e) In-situ balancing if called for thereafter 2/18/2013 11

6.0 : RUNNING THE UNIT-5 WITH CLOSE OBSERVATION

Since Nov,2011 ,Unit-5 continued to run with almost at the same magnitude of 250 microns of the shaft vibrations of Brg# 4,5 upto Feb,2012 and thereafter slightly increased to 275 microns of shaft vibration of Brg#5 . Brg#5 Pedestal vibrations also gone upto 75 microns ,run upto the end of Mar,2012. Every month BHEL ,Kolkata people recorded the turbine vibrations with portable IRD vibration equipment and found that the machine is running steadily at Full load.

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7.0 :INSPECTION OF LP ROTOR FOR BEARING HIGH VIBRATIONS

-As the shaft vibrations of Brg# 4,5 were running at high values , Unit# 5 was shutdown on 03/04/2012 to inspect the Brg # 4 ,5 ,6,7 and the LP Rotor. The Barring Gear was stopped on 07/04/12 and the dismantling of Brg pedestals started . -After LP Turbine dismantled and LP Rotor taken out of the position ,the following observations were made . During Dismantling Alignment readings of IP/LP Coupling are close to limit values ,but LP/Gen Coupling misalignment was observed as Gen up by 0.105 mm in Radial direction. During Dismantling CRO of LP/Gen coupling was observed on LP & Gen couplings as 0.15mm which is very high.

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During dismantling LP/Gen Coupling bolt stretch was observed as not uniform, varying from 0.10 mm – 0.41 mm ,desired 0.25 mm. Gen coupling face runout observed as 0.08 mm as against a normal acceptable value of 0.02 mm ( Max ) .Also same is the case with LP Rotor Rear end(Gen end ) coupling face .

Generator Bearings # 6 , 7 inspected as Brg# 7 was running with high vibrations of the order of 60 microns and found the bearings are in healthy condition wrt DPT & UT .Same bearings were boxed up.

The IR value of the Generator Bearing # 6 , 7 are coming as ZERO which were improved by opening the Bearing pads & cleaning the Insulating sheet & shims.

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8.0 :MAJOR JOBS CARRIED OUT TO CORRECT MISALIGNMENTS & COUPLING FACE RUNOUTS 1. Bearing # 5 replaced . 2.Coupling Face Runout corrections To correct the Coupling Face Runouts of LP Rotor & Generator ,Cast Iron Lapping plate of 900 mm OD , 30mm Thk was procured and made ready with respect to Surface plate and used this plate for coupling faces corrections after manual scraping of the material from the coupling faces. Final coupling face runouts came after manual scraping & lapping with lapping plate to get desired values of 0.02-0.03 mm for Gen Rotor coupling face and LP Rotor coupling face (Gen. end ). Assistance from CC-OS Steam Turbine group was taken during the correction of coupling face errors in this outage. 2/18/2013 15

GENERATOR COUPLING FACE RUN OUT CHECKING

LEFT

RIGHTIN

OUT

INOUT

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Bolt Hole# R L

LEFT(L) Out

LEFT(L) In

RIGHT(R) In

RIGHT(R) Out

RUNOUT (L-R)/2 Out

RUNOUT (L-R)/2 In

01 07 50 50 50 50 0 0

12 06 51 53 52 51.5 1/4 1/2

11 05 58 57.5 54.5 53 2.5 1.5

10 04 60 60 51 47.5 6.25 4.5

09 03 62 61 48 49 6.5 6.5

08 02 59 58 43 43 8 7.5

07 01 59 60 45.5 43 8 7.25

06 12 60 61 48 47 6.5 6.5

05 11 61 62 48 48 6.5 7

04 10 57 58 52 52 2.5 3

03 09 57 55 54 54 1.5 1/2

02 08 53 52 51.5 51 1 1/4

01 07 53 53 53 52.5 0 0

GENERATOR COUPLING FACE RUNOUT – DISMANTLING VALUES

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GENERATOR COUPLING FACE RUNOUT – FINAL VALUES

Bolt Hole# L R

LEFT(L) Out

LEFT(L) In

RIGHT(R) In

RIGHT(R) Out

RUNOUT (L-R)/2 Out

RUNOUT (L-R)/2 In

01 07 50 50 50 50 0 0

12 06 52 51 52 51 1/2 -1/2

11 05 53 51 54 55 -1 -1.5

10 04 52 51 54 55 -1.5 -1.5

09 03 52 50 54 54 -1 -2

08 02 50 45 54 54 -2 -4.5

07 01 48 47 54 53 -2.5 -3.5

06 12 53 51 53 54 -1/2 -1

05 11 56 54 55 56 0 -1/2

04 10 56 55 56 56 0 -1/2

03 09 55 54 56 56 -1/2 -1

02 08 52 53 52 54 -1 +1/2

01 07 54 52 52 52 -1 0 2/18/2013 18

3.MISALIGNMENT CORRECTIONS LP/Gen Coupling misalignment corrected by lowering the Generator Stator as per requirement. IP/LP Coupling misalignment corrected by moving Bearing # 4 down by 0.15 mm. Bearing # 3,4,5 Yoke interference values maintained at 0.07, 0.05, 0.05 mm respectively.

4.COUPLING BOLT STRETCH More important correction was that the Coupling bolts Stretch for IP/LP Coupling maintained at 0.15 mm and for LP/Gen coupling bolt stretch was maintained at 0.22 mm .

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Unequal bolt stretch of the coupling bolts was disturbing the Rotor eccentricity values during each runup. This practice of uniform tightening of coupling bolts is not there with BHEL ,PSER ,Kolkata and insisted by NTPC to do the same during this inspection. During Assy ,CRO of LP/Gen coupling came as 0.10 mm & 0.04 mm on LP Rear end coupling & Gen coupling which are more improved values than the previous values of 0.15 mm each during dismantling.

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9.0 :CONCLUSION After correcting the Coupling Face runouts , Unit# 5 synchronised on 22/04/12 and the shaft vibrations of Brg # 4 , 5 came down considerably to 150 microns and Brg Pedestal vibrations to 45 microns and the unit is running smoothly . The Vibration behaviour of the machine after Apr,12 inspection is as shown in the next page.

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SN Parameter 02/04 25/04 05/05 15/05

1 Ped Vibrn,4H 36 23 18 23

2 Ped Vibrn,4V 22 6 12 12

3 Ped Vibrn,5H 74 47 49 50

4 Ped Vibrn,5V 54 47 40 40

5 Ped Vibrn,6H 33 28 31 33

6 Ped Vibrn,6V 35 23 34 30

7 Ped Vibrn,7H 59 49 42 44

8 Ped Vibrn,7V 35 39 38 32

9 Speed,RPM 2994 2980 2993 2972

10 Load,MW 112.4 112.6 113 112.2

Before After

Vibration Trend of Unit-5 after Apr,12 Inspection

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Vibration Trend of Unit-5 after Apr,12 Inspection

SN Parameter 02/04 25/04 05/05 15/05

1 Abs Shaft Vibrn,4H 200 116 109 107

2 Abs Shaft Vibrn,4V 185 108 105 101

3 Abs Shaft Vibrn,5H 259 132 155 150

4 Abs Shaft Vibrn,5V 210 122 119 121

5 Speed,RPM 2994 2980 2993 2972

6 Load,MW 112.4 112.6 113 112.2

Before Inspection

After Inspection

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Thanks to you all- IPS-2013

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