TSI presentation for Bentley Nevada System, Vibration system of steam turbine for 150 MW unit. It demonstrates vibration in power plant. for BHEL turbine.

1. Turbine Supervisory
Instruments
BY ANKITA CHAUHAN

2. Turbine Supervisory Instruments
Why Monitor Turbine Supervisory
Parameters?
What are the Turbine Supervisory
Parameters?
How measurement is done?
What are the different measuring systems?
Why analysis is required?

3. Turbine Supervisory Instruments

4. What is vibration
To and fro motion.
In Vertical, Horizontal and / or Axial direction.
This includes the torsional to and fro motion of a shaft.
Mechanical vibration is the dynamic motion of machine components.
Vibration measurement is the measurement of this mechanical vibration relative to known
surface.
In the simplest form vibration can be considered to be the oscillation or repetitive motion of
an object around an equilibrium position. The equilibrium position is the position the object will
attain when the force acting on it is zero.

5. Characteristics of vibration
Characteristics of Vibration:
•Mechanical Vibrations are the Oscillatory Motions, either continuous or transient, of
objects and structures.
•Vibration can be periodic, random or transient.
•In periodic vibration the oscillatory motion of the body is repeated exactly after a
fixed interval of time.
•Random vibration is continuous but non-periodic and contains many frequency
components.
•A transient vibration is one which is non-continuous.

6. Common Causes of Vibration
Unbalance
Misalignment
Defective/ damaged anti friction bearing
Worn Gear
Mechanical looseness
Bent Shaft
Eccentric journals
Aerodynamic and Hydraulic Forces

7. AMPLITUDE
FREQUENCY
PHASE
GAP VOLTAGE
CHARACTERISTICS OF VIBRATION

8. (A) DISPLACEMENT
MICRONS, PEAK TO PEAK
MICRONS, 0 TO PEAK
MICRONS, RMS
(B) VELOCITY
MM/SEC, PEAK
MM/SEC, RMS
UNITS OF VIBRATION
(C)ACCELERATION
M/SEC2, PEAK
M/SEC2, RMS
G, PEAK
G, RMS

9. Average RMS 0 - Peak
Peak - Peak
UNITS OF VIBRATION
RMS = 0.707 x (0-Peak)
Average = 0.637 x (0-Peak)
Peak to Peak= 2 x (0-Peak)

10. 1 CYCLE/SEC.
TIME IN SECONDS
MEAN POSITION
UPPER LIMIT
LOWER LIMIT
FREQUENCY IN Hz
1 Hz
FREQUENCY SPECTRUM
DEMO

11. What is a phase angle
360 0
Ø

12. Turbine Supervisory Parameters
Housing Vibration
Shaft Relative Vibration
Thrust Position
Eccentricity
Differential Expansion
Casing Expansion
Phase
Other Parameters such as - Valve Position, Speed,
etc.

13. What we have
1 2 3 4 5HP-IP LP GEN
E
X
Speed
Key-phazor
Radial vibration
Housing Vibration
Differential Expansion
Eccentricity
Radial vibration
Housing Vibration
Differential Expansion
Eccentricity
Radial vibration
Housing Vibration
Radial vibration
Housing Vibration
Radial
vibration
Housing
Vibration
Casing
Expansion
Casing
Expansion

14. PROXIMITY PROBE
VELOCITY PICK UP
ACCELEROMETER
DISPLACEMENT
TYPES OF VIBRATION PICK UP

15. Housing Vibration
Housing Vibration monitoring is perhaps the primary method of machine health monitoring on
steam turbines.
This type of measurement is seismic in nature and can be a velocity transducer or accelerometer
For machines with a light Casing to Rotor Weight Ratio, vibration is readily transmitted to the bearing
housing, so these are the vibrations which can be measured on the surface of the machine.
ISO2372 recommends the use of rms value of vibration velocity in the frequency range of 10 to
1000Hz, also referred as Vibration Severity.

16. Housing vibration measurement

17. Relative Shaft Vibrations: These are the fast motions of
the rotor shaft relative to the bearing shell.
Relative shaft vibration is measured with non-displacement
pickups.
Two pick-ups are mounted at 90 Degree to each other and
perpendicular to the rotor axis.
Evaluation of relative shaft vibration as per ISO 2372
guidelines.
It is an indicator of bearing condition and useful in
correcting rotor unbalance.
Shaft Radial vibration measurement

18. Y X
Shaft Radial vibration measurement

19. Thrust Position/Axial Shift/ Relative Shaft
Displacement:
Axial shaft displacement of rotor is measured relative to
the thrust bearing. It is a measure of axial forces on the
rotor and of thrust bearing wear.
Thrust position indication includes one or two non-
contacting displacement pickups to observe the position
of the thrust collar within its bearings.

20. Eccentricity:
Turbine rotors can bend in one direction due to gravity while at rest or due to effects of
temperature. This bending of shaft is referred to as eccentricity.
During run-up, this can cause dynamic overloads of the bearings and rotor which in turn lead
to touch down or rotor fracture during passage through the resonance region. To avoid this, it
is usual to monitor eccentricity during run-up of the turbine.
A rotor which has been sitting idle during overhaul or has been inadvertently stopped
during coast down for an extended period will develop a bow or bend. This condition must
be corrected by turning gear operation and, possibly, with auxiliary heating prior to high
speed operation to prevent internal clearance rubbing.
Non-contacting displacement pickups are used to measure eccentricity.

21. Differential Expansion/ Relative Shaft Expansion:
In steam turbines, the rotor heats up more quickly than
the machine casing during the run-up phase.
The difference in the thermal expansion between rotor
and casing is monitored in order to avoid touch down of
the turbine rotor.
Non-contacting displacement pickups are used to
measure Differential Expansion/ Relative Shaft
Expansion.

22. HP-IP DIFFERENTIAL EXPANSION PICK UP
MOUNTED ON BEARING NO. 2 PEDESTAL

23. LP DIFFERENTIAL EXPANSION PICK UP
MOUNTED ON BEARING NO. 3 PEDESTAL

24. Casing/Shell Expansion:
Casing of the machines expand relative to their foundations during the
heating up phase. This is called absolute casing expansion.
Uneven heat distribution leads to deformation and internal stresses in
casing in the axial direction.
Absolute casing expansion is measured at the free end of the machine.
Linear Variable Differential Transformer (LVDT) or Inductive
displacement pickups are used for measurement.

25. Phase:
Phase, or phase angle, is a measure of the relationship of how one
vibration signal relates to another vibration signal and is commonly
used to calculate the placement of a balance weight.
This parameter is not usually displayed continuously but is monitored
periodically to determine changes in the rotor balance condition,
deviations in system stiffness such as a cracked shaft.

26. Proximity Probe Used
as a Keyphasor®
NOTCH

27. Transducer Element
Signal Conditioning
Element
Display or Recording
Element
Physical
Variable
Outputs
Vibration Measurement System

28. Measurement Technique
1. Measurement of displacement using Non-Contact pickup.

29. Proximity Transducer
System Operation

30. Motion
Metallic Surface
Output
Eddy Current Type Transducer:
Eddy current transducer is of non-contacting displacement type. Coil is excited
by high frequency carrier, inducing an oscillating magnetic field around the coil.
The field gets changed due to the metallic surface, whose vibrations are to be
measured.
Due to magnetic field, eddy currents are induced in the metallic surface, setting
upon a magnetic field of their own, interfering with the primary magnetic field
due to the AC supply resulting in beats. After suitable conditioning a voltage
proportional to the displacement of metallic surface is obtained as the output.

31. Advantages: -
 Measure displacement accurately for very slow speed
machine.
 Shaft vibration and deflection can be measured
directly.
Disadvantages: -
Cannot convert readings into velocity and acceleration.
This pickup is applicable for magnetic material body.
Difficult to get accurate readings.
Sources of error:
a) Run-out of journal, b) Movements of pickup,
c) Magnetic and electrical field,d) Calibration error.

32. Proximitor:
The Proximitor is an electronic device that
has two basic functions:
1. Generates a radio frequency (RF) signal
using an oscillator
circuit.
2. Conditions the RF signal to extract usable
data using a demodulator circuit.
To do this it needs a -17.5 to -26 Vdc supply
voltage connected between its VT and COM
terminals.

33. Proximitor Calibration Graph
CHANGEINVOLTAGE
CHANGE IN GAP
24
OUTPUTINVOLTS-DC
PROBE GAP
mils 0
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140
2
4
6
8
10
12
14
16
18
20
22

34. Once the Proximitor’s oscillator has power it will generate an RF signal at a specific
frequency. This frequency is dependent on the INDUCTANCE (L) value of the
probes coil and the CAPACITANCE (C) value of the extension and probe cables.
The RF signal frequency will be within a range from 500 Kilohertz (KHz) to 2.0
Megahertz (MHz). Having a MISMATCHED transducer system (cable length too
long or too short) will change the RF signal frequency and result in an incorrect
Proximitor.
The RF signal is transmitted from the probe coil which creates an RF field around
the probe tip. When conductive material is present in the RF field, EDDY
CURRENTS flow in the surface of that material. The penetration depth of the
eddy currents depends on the materials conductivity and permeability.

35. Once the probe is close enough to cause eddy currents to flow in a conductive material the RF
signal is affected in tow ways :
1. Amplitude is at a minimum when distance (GAP) between probe and material (TARGET) is at a
minimum. Maximum eddy current flow occurs.
2. Amplitude is at a maximum when distance (GAP) between probe and material (TARGET) is at a
Maximum. Minimum eddy current flow occurs.
If the target is moving SLOWLY within the RF field, the signal amplitude INCREASES or
DECREASES SLOWLY. If the target is moving RAPIDLY within the RE field, the signal
amplitude INCREASES or DECREASES RAPIDLY. Oscillatory movement of the target causes
the RE signal to modulate.

36. The demodulator circuit deals with a slow or fast changing signal amplitude in the same way.
If the target is oscillating slowly (gap changing slowly) or NOT oscillating (gap not changing),
the Proximitors output is a negative d.c. voltage, shown opposite by a dashed line. If the
target is oscillating fast (gap changing fast) the Proximitors output is a varying d.c. voltage
(a.c.) shown above by a sinewave. If the probe sees a vibration, the Proximitor will have a d.c.
and a.c. component output

37. GAP VOLTAGE OF SHAFT VIBRATION PROBE
IT INDICATES AIR GAP BETWEEN PROXIMITY PROBE TIP AND ROTOR SURFACE
IT IS MEASURED IN DC VOLTS
IT IS SET IN COLD CONDITION AT ZERO RPM WITHOUT OIL SUPPLY (LUBE OIL /
JACKING OIL)
IT IS NORMALLY SET IN THE MID POINT OF LINEAR RANGE
ANY CHANGE IN GAP VOLTAGE INDICATES CHANGE IN THE POSITION OF THE
SHAFT PROVIDED THERE IS NO LOOSENESS IN PROXIMITY PROBE FIXATION
IT CAN BE USED TO DETERMINE THE LIFT OF THE ROTOR
IT CAN BE INDICATIVE OF BEARING BABBIT WEAR

38. Velocity Pick up: Converts the
mechanical vibration to an electrical signal
that is proportional to the velocity of
vibration.
This device operates on the
spring-mass-damper principle,
is usually of low natural
frequency and operates above
its natural frequency. The
transducing element is either
moving coil with a stationary
magnet or a stationary coil with
a moving magnet.
A voltage is produced in a
conductor when the conductor
cuts a magnetic field and the
voltage is proportional to the
rate at which magnetic lines
are cut. Thus a voltage is
developed across the coil,
which is proportional to the
velocity.

39. Velocity Probe
Advantages:-
This pickup is robust and withstands high temperature
(1500C).
Cheaper compare to other types of pickup.
This pickup is also used to read displacement.
Disadvantages:-
It will not work in magnetic and electrical field.
Can not read low frequency vibration accurately.
This pickup is quite big and heavy.
It can not read acceleration.

40. Accelerometer:
The accelerometer uses a piezo-electric crystal
situated between the accelerometer base and an
inertial reference mass. When the
accelerometer is mounted on a machine casing or
bearing housing, machine vibration causes a
compression or tension force to act on the
crystal. The crystal, in turn, acts as a precision
spring to oppose the compression or tension
force. The crystal thus generates a displaced
electric charge. An integrated amplifier
converts the charge to a voltage signal.

41. Advantages:-
This pickup is small and light.
It can be used to measure vibration
amplitude in acceleration, velocity and
displacement.
This pickup measures vibration
accurately in magnetic and electrical
field.
Disadvantages:-
It can not measure very low
frequency vibration.
Comparison between Shaft and
Housing Vibration.
Advantages of shaft vibration:-
•Shaft vibration is the cause and
housing vibration is its effect.
•Shaft vibration will be affected by
minor disturbance of rotating
element. This may not affect the
housing vibration.
•In case of shaft vibration, shaft
orbit analysis is possible in addition to
conventional vibration analysis.

42. Parameter Indicates Physical significance
Frequency What is Vibrating? Why it is
Vibrating?
Identify the source of the
Vibration.
Amplitude How much is it Vibrating? Identify the severity of the
problem.
Phase Angle How is it Vibrating? Identify the cause of the
Vibration.
Physical significance of vibration characteristics:
Amplitude Indicates Units
Physical
Significance
Displacement Total distance travel by
the mass
Microns, Mils Stress
Indicator
Velocity Rate of change of
displacement.
Mm/sec,
Inch/sec
Fatigue
Indicator
Acceleration It is the rate of change of
velocity.
M/sec2,
inch/sec2
Force Indicator

43. SPEED MEASUREMENT
SPEED measurement is based on Differential Hall effect.
6 numbers of probe mounted over the tooth gear.
Differential Hall effect sensors provide signals that are edge sensing over a target
tooth/valley. The signal shape is roughly sinusoidal with up to two times the peak-to-peak
magnetic field. Differential Hall effect sensors detect target edges.

44. Sl.No. Make Model
01. Bentley Nevada - USA Model-3500
02. Reutlinger-Germany
03. Carl-Schenck-Germany Vibrocontrol-2000
04. Carl-Schenck-Germany Vibrocontrol-4000
05. Bentley Nevada - USA Model-3300
06. Carl-Schenck-Germany Vibrocontrol-4000 with Vibrocam

45. Thank you