A Power Point Presentation on Condition Monitoring Of Electrical Rotating Machines

1. Condition Monitoring
of Rotating Machines
ROHIT KAUSHIK
SIBABRATA PRADHAN
SAMRAT ROY
SHYAM KR. SINGH
EE 629 High Voltage and Insulation Engineering

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3. Introduction
By condition monitoring we mean continuous evaluation of the health of plant
and equipment throughout its serviceable life.
Condition monitoring and protection are closely related functions. The approach
to the implementation of each is, however, quite different.
Condition monitoring can, in many cases, be extended to provide primary
protection, but its real function must always be to attempt to recognise the
development of faults at an early stage.
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4. WHAT AND WHEN TO MONITOR
Larger electrical drives, which support generating, process or production plant if
a high margin of spare capacity exists, will benefit from monitoring, although
perhaps not continuous monitoring.
We can include induced and forced-draught boiler fan drives, boiler water feed
pump drives, and cooling water pump drives in power stations in this category.
It must be kept in mind, however, that successful monitoring can allow a big
reduction in the requirement for on-site spare capacity.
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5. WHAT AND WHEN TO MONITOR
The parameters to be monitored are essentially those that will provide the
operator and maintainer with sufficient details to make informed decisions on
operation and maintenance scheduling, but which ensure security of plant
operation.
Traditionally quantities, such as line currents and voltages, coolant temperatures,
and bearing vibration levels, have been measured and will continue to be used.
Other specialist methods, involving the accurate measurement of rotational
speed, or the sensing of leakage fluxes, are being developed in order to monitor a
variety of fault conditions.
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6. WHEN TO MONITOR
One should monitor when it is cost-effective to do so, or when there are over-
riding safety considerations to be observed. The assessment of cost-effectiveness
can be a relatively complex matter, but in general terms monitoring is worthwhile
when the net annual savings are increased by its use.
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7. FAILURE
SEQUENCE
AND EFFECT
ON
MONITORING
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8. ROOT
CAUSES AND
FAILURE
MODES
Root causes:
 Defective design or manufacture
 Defective material or component
Defective installation
Defective maintenance or operation
Ambient conditions
Overspeed
Overload
Component failure
Excessive temperature
Winding over temperature
Bearing over temperature.
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9. FAILURE
MODES
Failure modes:
oElectrical:
Core insulation failure
Stator winding insulation failure
Rotor winding insulation failure
Brush gear failure
Slip ring failure
Commutator failure
Electrical trip
◦ Mechanical:
Bearing failure
Rotor mechanical integrity failure
Stator mechanical integrity failure.
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10. Stator winding insulation
Stator winding insulation is affected by all of the stresses: thermal, electrical,
environmental and mechanical; however, the extent to which these stresses in
normal operation will cause problems in the short- or long-term will depend on
factors such as the operating mode and type of ambient cooling conditions.
Deterioration may be like delamination and voids, slot discharge etc.
The principal stresses of concern on rotor windings are thermal and mechanical.
It may be induction motor rotor faults, turbine generator rotor winding faults,
rotor winding faults in dc machine.
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12. Temperature Measurement
RTD
(Resistance Temperature Detection)
 Thermocouple
RTD used in Wheatstone bridge
Configuration:
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13. Thermocouple Types
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14. Vibration Measurement
Used for monitoring of components
of Gear boxes, Shaft couplings
Bearing etc.
Methods:
 Displacement Transducer (< 100Hz)
 Velocity Transducer (100-1000Hz)
 Acceleration Transducer (> 1000 Hz)
Displacement Transducer:
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15. Velocity Transducer
E = Blv
where,
ov is the velocity of magnet in axial
direction
oE is induced emf which is the measure
of vibration.
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16. Acceleration Transducer
When subjected to vibration mass held
against piezoelectric material exerts a
force upon it which is proportional to
the acceleration which produces
electric voltage proportionally.
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17. Electrical & Magnetic measurement
Electrical Quantities like (currents ,
voltages) are measured by CT s, PT s .
Magnetic Quantities like (flux) are
measured by Hall Sensors.
When current flows through the hall sensor
in direction perpendicular to applied
magnetic field then direction of motion of
electron is in direction mutually
perpendicular to both axes.
V=KIB/nq.
where, K/nq is hall constant of material.
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18. Chemical Monitoring
The insulating materials used in
electrical machines are complex
organic materials when degraded
by heat or electrical action,
produce a very large number of
chemical products in the gas,
liquid and solid states.
Methods Of Chemical
Monitoring:
Particulate Detection (Using Core
Monitor)
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19. Chemical Monitoring
Infrared Ananlysis
A beam of light is focused through a
film of used oil and the wavelengths
are then compared to light transmitted
through new oil of the same type. The
differences in readings provide
information with respect to the
degradation of the used oil
Image Processing
The image processing and computer
vision system reveals more information
in the form of quantitative data not
revealed by the human eye.
This technique is used to collect
quantitative information from wear
particle images
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21. Vibration monitoring
The principal sources of vibration in electrical machines are:
 The response of the stator core to the attractive force developed magnetically between
rotor and stator
 The dynamic behavior of the rotor in the bearings as the machines rotates
The response of the shaft bearings, supported by the machine structure and
foundations, to vibration transmitted from the rotor
The response of the stator end windings to the electromagnetic forces on the
conductors.
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22. Frequency responses of the machine
elements
Stator response
The forces acting on the stator core are the result of the interaction between the
air gap flux wave and the currents flowing in the windings embedded in the stator
slots.
The forces acting on the end winding are due to the interaction between the end
leakage flux and the winding currents. It is apparent, therefore, that the precise
nature of the applied force waves will be a function of the form of the current
distribution, and the geometry of the air gap and end regions.
The simplest method of calculating the flux wave form is to multiply the
magnetomotive force (MMF) distribution because of winding currents, by the
permeance of the air gap.
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23. Frequency
responses of
the machine
elements
Transverse forces are due to asymmetries in the
machine, while torsion is primarily due to the
driving torque; however, both may be affected by
electrical or mechanical faults in the machine itself
or electrical or mechanical system disturbances
outside the machine.
There will also be a coupling between torsional and
transverse effects due to the transfer function or
stiffness between these axes of the machine, so
torsional effects, like current faults in rotor and
stator windings, can cause transverse effects like
vibrations, and vice versa.
Rotor response
We now consider the motion
of a rotor in response to:
Transverse force excitation
Torsional torque excitation
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24. Frequency responses of the machine
elements
Bearing response
Rotor vibration force is transmitted to the stator via the air gap magnetic field and
the bearings in parallel. It is therefore important to consider the response of the
bearings to that vibration force so that its effect is not confused with vibrations
generated by faults within the bearings themselves.
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25. Monitoring techniques
Overall level monitoring
This simple form of monitoring is the most commonly used technique but its efficiency is
limited. The measurement taken is simply the rms value of the vibration level on the stator side
of the machine over a selected bandwidth. The usual bandwidth is 0.01–1 kHz or 0.01–10 kHz
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26. Monitoring techniques
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27. Monitoring techniques
Shock pulse monitoring
The shock pulse method is used exclusively for rolling element bearings ,which deteriorate at the
moving surfaces, developing small pits or imperfections.
The interaction between such surfaces generates mechanical stress wave or shock pulses, in the
bearing material, propagating into the structure of the machine.
These shock pulses are at ultrasonic frequencies and can be detected by piezoelectric transducers
with a resonant frequency characteristic tuned to the expected frequency of the pulses, around 32
kHz. The condition of the bearing is assessed by defining a quantity known as the shock pulse
value (SPV), defined as
SPV=R/N²*F².
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28. Monitoring techniques
Shock pulse interpretation
Overall vibration level trend Shock pulse value trend Comments
Low and rising Remains low No bearing damage
Low and rising Low but rising at the same
rate as the overall vibration
level
Bearing damage likely
Low and rising High value but constant Damaged bearing but another
problem is causing the rising
vibration
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29. Current & Flux monitoring
Faults on either rotor or stator disrupt the radial and circumferential patterns of
flux in the machine causing changes to the power being fed to the machine,
which can be detected via its terminal quantities voltage, current and power
measured outside the machine to give an indication of its condition.
A) Generator stator winding fault detection- The most significant technique in
this area is on-line discharge detection, which is dealt in further slides.
B) Generator rotor faults detection-
Turn-to-turn faults in a generator rotor winding may lead to
local overheating and eventually to rotor earth faults. In
addition, the shorting of turns causes unequal heating of the
rotor leading to bending and an unbalanced pull, which
together cause increased vibration
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30. Current & Flux monitoring
A way of detecting them on-line ,is using a
stationary search coil fitted in the air gap of the
machine. The search coil, of diameter less than
the tooth-width of the rotor, is fixed to the
stator usually in the air gap, and detects either
the radial or circumferential component of
magnetic flux.
New techniques have been developed utilising
a digital storage oscilloscope connected to the
search coil to give an initial indication of the
development of an inter-turn fault. The purpose
is to identify any asymmetry in the MMF
waveform caused by shorted turns.
Photographs of typical search
coil installation in large
generators
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31. Motor rotor faults detection
Stator current monitoring for rotor
faults
Any rotor fault in an induction
motor will cause a characteristic
swing in the supply ammeter
reading, Careful measurement of
the stator current will therefore
enable such a fault to be
monitored.
Detecting side bands in the supply current of
an induction motor
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32. Generator and motor comprehensive
methods
Shaft flux-
Shaft flux, or axial leakage flux, occurs in all electrical machines. It is
produced because no machine can be constructed with perfect symmetry.
Faults, such as winding short circuits, voltage imbalance and broken rotor
bars, represent severe disruptions to the internal symmetry of the machine. It
is logical to conclude, therefore, that the effect on the production of axial flux
will be readily observable.
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33. Generator and
motor
comprehensive
methods
Shaft voltage or current-
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Current spectrum with typical fault sidebands

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35. Temperature Monitoring
The limits to rating of electrical machines are generally set by the maximum
permissible temperature that the insulation can withstand.
There are three basic approaches to temperature monitoring.
• To measure local temperatures at points in the machine using embedded temperature detectors.
• To use a thermal image, fed with suitable variables, to monitor the temperature of what is
perceived to be the hottest spot in the machine.
• To measure the bulk temperatures of coolant fluids.
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36. Local temperature measurement
This can be done using thermocouples, resistance temperature detectors or
embedded temperature detectors.
To monitor the active part of the machine they are usually embedded in:
• The stator winding and in the stator core.
• temperature detectors embedded in the stator winding need to be located close to its hottest part, which
may be in the slot portion or end-winding portion.
• The bearings to detect hot running.
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37. Local
temperature
measurement
Location of
temperature
detectors in
electrical machines
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38. Local temperature measurement
On a winding the devices have to
be embedded in the insulation at
some distance from the copper
itself.
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39. Local temperature measurement
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As a result, the measured
temperature will not necessarily
be that of the winding itself but
an image of it.
SAMRAT ROY

40. Local temperature measurement
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The heat flow per unit area,
Q, through the insulation
system can be described by
simple conduction equations
as follows
𝑄 = ℎ 𝑇𝑠 − 𝑇𝑔 =
𝑘
𝑡2
𝑇𝑠 − 𝑇𝑡 =
𝑘
𝑡1
𝑇𝑐 − 𝑇𝑡
𝐸𝑙𝑖𝑚𝑖𝑛𝑎𝑡𝑖𝑛𝑔 𝑇𝑠
𝑇𝑡 = 𝑇𝑔 + 𝑄
𝑡2
𝑘
+
1
ℎ
SAMRAT ROY

41. Local temperature measurement
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𝑇𝑡 = 𝑇𝑔 + 𝑇𝑒 − 𝑇𝑡
𝑡2 + (𝑘/ℎ)
𝑡1
𝑇1 =
𝑇𝑔 + 𝑇𝑐
𝑡2 + (𝑘/ℎ)
𝑡1
1 +
𝑡2 + (𝑘/ℎ)
𝑡1
𝑠𝑜, 𝑇1~𝑇𝑐 𝑖𝑓 𝑇𝑔 ≪ 𝑇𝑐 &
𝑡2 +
𝑘
ℎ
𝑡1
≫ 1
SAMRAT ROY

42. Local temperature measurement
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So the measured temperature Tt will approach the temperature of the hottest
active component Tc if the thickness of insulation, t2 , applied over the ETD is
sufficient compared to the main insulation.
This problem does not occur for devices embedded in the slot portion between
two conductors, where there is a low heat flux between the active copper parts.
𝑇1~𝑇𝑐 𝑖𝑓 𝑇𝑔 ≪ 𝑇𝑐 &
𝑡2 +
𝑘
ℎ
𝑡1
≫ 1
SAMRAT ROY

43. Hot-spot measurement and thermal
images
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The thermal image technique has not received wide application on rotating elec-
trical machines.
The thermal image consists of a dial-type thermometer with its bulb immersed in
the region where the transformer oil is hottest.
A small heating coil, connected to the secondary of a current transformer, serves
to circulate around the bulb a current proportional to the load current and is such
that it increases the bulb temperature by an amount equal to the greatest winding-
to-coil temperature gradient.
SAMRAT ROY

44. Hot-spot
measurement
and thermal
images
Comparison between
measurements and the
predictions of a thermal image
of an electrical machine.
(a) Comparison for 5.5 kw
induction motor.
(b) Duty cycle for (a)
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45. Hot-spot
measurement
and thermal
images
Comparison between
measurements and the
predictions of a thermal image
of an electrical machine.
(a) Comparison for 7.5 kw
induction motor.
(b) Duty cycle for (a)
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46. Bulk measurement
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This can be found from the measurement of the internal and external coolant
temperature rises, obtained from thermocouples located.
This is done in most large machines
An increase in temperature rise would clearly show:
 when a machine is being overloaded.
 the coolant circuits are not performing as they should.
SAMRAT ROY

47. Conclusion
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Temperature measurement can yield very valuable bulk indications of the
condition of an electrical machine using
 simple sensors
 narrow bandwidth (<1 Hz)
 low-data-rate signals
Temperature rises are important rather than absolute temperature.
There are advances in the application of modern sensors, which will allow temp-
erature measurements to be made closer to the active parts of a machine.
SAMRAT ROY

48. References:
[1]. P.TAVNER, L.RAN, J.PENMAN , H.SEDDING, ‘Condition Monitoring of Rotating
Electrical Machines’ 2008 – Book
[2]. TAVNER .P.J ‘ Review of condition monitoring of rotating electrical machines’, IET
Electric Power Applications, November 2007.
[3]. A. NEGOITA ,Gh. SCUTARU, R.M. IONESCU ‘A brief Review of Monitoring of
Rotating Electrical Machines ‘. Bulletin of the Transilvania University of Brasov • Vol. 3
(52) – 2010 Series I: Engineering Sciences.
[4]. NANDI S., TOLIYAT H.A., LI X.: ‘Condition monitoring and fault diagnosis of
electrical motors – a review’, IEEE Trans. Energy Convers., 2005, 20, (4), pp. 719–729.
[5]. TAVNER P.J., GAYDON B.G., WARD D.M.: ‘Monitoring generators and large motors’,
IEE Proc. B, Electr. Power Appl., 1986, 133, (3), pp. 169–180.
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