Blade Casing Vibration

1. By
Corporate R&D BHEL
Blade Vibration Monitoring System
&
Casing Vibration Monitoring System

3. Interface Unit
Data acquisition System
BVMS
What is Blade Vibration Monitoring (BVMS)?
Blade vibration monitoring system (BVMS) monitors the vibration behavior
of all the number of blades in a stage during actual running of the
turbine.

4. Rotor blade rotation
Rotor blade
Tip Timing sensors
mounted to case
(optical line probe)
1 2 3 Nr
1/Rev Shaft Pulses
Rotor Blade Pulses
1 2 3 Nr
TOA1
TOA2
TOANr
TOA1
TOA2
TOANr
Rotor with Nr blades
1 2
TOA1
TOA2
time
reference
Non contact Eddy
Current probe
1/Rev sensor
gives reference
TOA calculated
relative to ref.
Principle of BVMS –Time of Arrival Measurements
(TOA)

5. Eddy Current Sensors: Principle of Operation
S
N
Losses in engine and sensor
case create Low Pass effect
Conductive and/or magnetically permeable rotor
blade passes through magnetic field
Eddy currents build on blade
surface and interact with the
magnetic field and change the
magnetic flux
Eddy currents also build in sensor itself
and the sensor shield, which could be
sensor face plate or engine case. They
resist fast changes in magnetic field and
create pulse attenuation at fast tip speeds
which are converted to proportional
electrical parameters leading to blade
vibration measurement .
Magnetic flux lines

6. BVMS -- Acquisition Analysis Monitoring Data

7. BVMS Campbell Diagram for Trombay, Dotted lines show Design data

8. Turbo Supervisory Display of BVMS data @Trombay – Marked in RED Color

9.  A shut down of about TEN days after opening and placement of LP turbine top
outer and inner casings and lower diffuser casings on the turbine and generator side.
 Location for the placement of BVMS console (1M * 1M * 1M size and 100 kgs) in
the control room
 A dedicated 15 amps uninterrupted AC power supply in the control room
 Parallel output of 1/Rev signal from Bently control panels
 A dedicated and robust internet connection with static IP address exclusively for
BVMS console for online remote monitoring
 Team Viewer SW loaded in system.
 One turbine O&M engineer and instrumentation engineer from CUSTOMER for
coordination.
Following are pre requisites for BVMS from the CUSTOMER

10. Casing Vibration Monitoring System - CVMS
at SINGRENI TPS, Unit # 1 & 2, 600 MW

11. What is Casing Vibration Monitoring (CVMS)?
Blade Passing Frequency : The high and low pressure forces on rotor and stator
blades caused by Steam flow interact as pressure distributions causing fluctuating
casing pressures. These Casing Pressures vary harmonically with the rate at which
Blades pass that point called as Blade Passing Frequency BPF
Turbine Speed -- 3000 rpm i.e. 50 Hz
No. of Blades in Last stage -- 48, BPF -- 48 X 50 Hz = 2400 Hz
No. of Blades in Last but one stage – 62, BPF -- 62 X 50 Hz = 3100 Hz
Normal Side Bands (SB) -- ± 50 Hz or ± 100 Hz of BPFs
Odd Side Band (not a multiple of shaft speed) -- 62 X 52 Hz = 3224 Hz
Schematic layout of STPP TG set with accelerometer mounting location

12. CVMS at LPT 1 of Unit 1 of Singareni TPS
With crack
Odd Side Band indicating the
abnormality
BPF @2400Hz
Waterfall Diagrams

13. CVMS at LPT 1 of Unit 1 of Singareni TPS
Without crack
Odd Side Band disappears after the replacement of cracked blades BPF @2400Hz
Waterfall Diagrams

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