A
PRESENTATION
ON
MOTOR
(Operation &Maintenance)
BY
PREPAIRED BY- KAPIL SINGH
(ENGINEER-THERMAX LTD. C&H SSBU
O&M)
INDEX
 Classification
 Laws of electromagnetism
 Rotating Magnetic Field
 AC Motor
 Induction Motor
 Synchronous Motor
 Maintenance Practices
Motor
ELECTRICAL ENERGY
Mechanical Energy
Common Motor Applications include
 Pumps
 Fans
 Conveyors
 Extruders
 Agitators
 Crushers
 Mills
 Grinders
 Elevators
 Many, many more……………….
Types of Electric Motors
AC Induction Motors
DC Motors and Generators
Synchronous
Wound Rotor
Single Phase
Permanent Magnet AC - New
AC Motor Nameplate
Phase
Frequency
Horse Power
Frame
RPM
Voltage
Temperature
Amps
6
Laws of Electromagnetism
Faraday’s Law
Lenz’s Law
Fleming’s Right Hand rule
Fleming’s Left Hand rule
Interaction of two magnetic
fields
Faraday’s Law of Electromagnetic
Induction
 When the magnetic flux
through a circuit is
changing an induced EMF
is setup in that circuit
and its magnitude is
proportional to the rate
of change of flux”
Simulation
Lenz’s Law
“ The direction of an
induced EMF is such
that its effect tends to
oppose the change
producing it”
Simulation
Fleming’s Right Hand rule
Used to measure the
direction of induced
current in a conductor
when cut by a magnetic
field.
Fleming’s Left Hand rule
Used to measure the
direction of motion of a
current carrying
conductor when placed
in magnetic field.
Interaction of two magnetic fields
+ When Current positive and going into
· When Current negative and coming from
Speed of RMF
The magnetic field established rotates at a speed given by
N = 60* f / P
where f = frequency of stator current
P = Number of pair of poles
Introduction
Induction Motor
Construction
Principle of Induction Motor
Slip
Starting Current
Torque
Torque Speed characteristics
Two Phase Induction Motor
Single phase Induction Motor
Summary
Uses in Aircraft
Induction Motor-Intro.
The induction motor is the most commonly used
type of ac motor. It is simple, low cost and rugged in
construction.
The induction motor derives its name from the fact
that ac voltages are induced in the rotor circuit by
the rotating magnetic field of the stator.
Induction Motor
Main Parts
Stator
Wound Rotor
Start Resistance
AC Machine Stator
Squirrel Cage Rotor
Principle of Induction Motor
Slip in Induction Motor
slip speed = synchronous speed - rotor speed
measured in RPM
Slip = (synchronous speed - rotor speed ) /synchronous speed
expressed as a percentage
The greater the slip speed, the greater is the force on
each conductor and the torque exerted by the whole.
Starting Current
The starting current is very high which may damage
the stator winding.
To reduce this heavy starting current, star-delta
starting switch is used.
For starting, the stator winding are connected up in
star via the switch to the supply so that the phase
voltage is 1/√3 of the normal voltage. This reduced
voltage limits the starting current.
Phase voltage is 1/√3 of the
normal voltage
phase voltage is equal to the line
voltage.
Torque- Starting
The resistance of the squirrel cage rotor
is small and inductance high.
Thus on starting rotor current and the rotor
emf are nearly 90 degrees out of phase.
The lagging rotor current interacts little with
stator current and therefore the starting
torque Torqueis poor. Running
As the rotor current come into phase with the rotor
emf with increased rotor speed (decreased slip and
inductive reactance) the rotor and the stator flux
comes more into phase and the torque increases.
Methods Of Improving Starting
Torque
In creasing the resistance of the rotor conductors
Using a combination of high and low resistance
conductors
Using a wire wound rotor connected to variable resistor
Wire Wound Rotor
Connected To Resistor
Torque –Speed Characteristic
Single Phase Pulsating Field
29
Single Phase Induction
Motor
The single phase induction motor produces a
pulsating field.
However, if the rotor is rotated forward at a bit less
than the synchronous speed, It will develop some
torque.
If the rotor is started in the reverse direction, it will
develop a same torque in other direction
Split Phase Induction Motor
Two phases are produced by
splitting a single phase.
A capacitor is inserted in one of
the windings and is called a
permanent-split capacitor motor.
The direction of the motor is
easily reversed by switching the
capacitor in series with the other
winding.
Summary
The three phase induction motor
Is very robust in construction
No need for slip rings and therefore less maintenance.
Has a high starting current reduced by star-delta switch.
Has a poor starting torque.
Runs at a speed less than synchronous speed.
 Direction of rotation can be reversed by interchanging any
two stator phases.
 Is of two types depending on motor construction: Squirrel
Cage or Slip Ring
Uses of Various Type Motors
1. Constant speed with varying loads and require
smoother torque e.g. fuel booster pumps, hydraulic
system’s Electric Motor Driven pumps.
2. Systems which need high torque and reversing e.g.
Flap Power units (for alternate flap drives),
Stabilizer Trim Actuator.
3. Two phase induction motors also used in aircraft
such as aileron trim actuators and in reversible
valve actuators in Fuel, hydraulic, oil, and
pneumatic systems etc.
Synchronous Motor
 Synchronous Motor-Intro
 Synchronous Motor-principle
 Changing the Load
 Starting Torque
 Improvement of starting torque
 Synchronous Machine Construction
 V curves
 Torque versus Speed
 Summary
Synchronous Motor- Intro
• The synchronous motor rotates at the
synchronous speed i.e. the speed of the RMF.
• Stator is similar in construction to that of an
induction motor, so same principle is applied to
the synchronous motor rotor.
• Field excitation is provided on the rotor by either
permanent or electromagnets with number of
poles equal to the poles of the RMF caused by
stator
Synchronous Motor-Principle
The rotor acting as a bar magnet will turn to line up
with the rotating magnet field. The rotor gets locked to the
RMF and rotates unlike induction motor at synchronous speed
under all load condition
Starting Torque
It cannot be started from a standstill by applying ac to
the stator. When ac is applied to the stator a high
speed RMF appears around the stator. This RMF
rushes past the rotor poles so quickly that the rotor is
unable to get started. It is attracted first in one
direction and then in the other and hence no starting
Improvement of starting torque
torque.
It is started by using a squirrel cage within a rotor
construction and therefore starts as an induction
motor.
At synchronous speed the squirrel cage has no part to
play.
Synchronous Machine
Construction
38
V curves
39
Torque versus Speed
Summary
The synchronous motor:
1.
requires to be started by an external prime mover.
2.
Runs only at synchronous speed, this is an advantage
where continuous speed is required but a disadvantage
where a variable speed is required.
3.
Can be used to adjust the power factor of a system at
the same time it is driving a mechanical load.
Electric Motor Specifications
 Inpro/seal on Drive end Only 25 HP & Above.
 Oversized J-Box per specifications.
 Blue Chip Quality. 100% cast iron construction for rigidity and reduced vibration.
 Internal and external epoxy paint.
 MAX GUARD insulation system
 1.15 Service Factor.
 Extended grease tubes, regreasable in service.
 Brass drain and breather
 Meets IEEE45 USCG Marine Duty IP54 Construction.
 Actual test and vibration data supplied with each motor
 CSA Certified
 Division 2 CSA certification nameplate, for hazardous locations, Class I Groups A, B, C, and
D.
 Temperature code T2B
 Three Year warranty.
Electric Motor Acceptance Test
 All motors for a plant should go through an acceptance test prior to be
put into service or storage
 The purpose would be to insure:
1. Not damaged during shipping and handling
2. No obvious manufacturing defects
3. Motor has been repaired properly
 Incoming visual inspection
 Electrical – Megger – PDMA
 Mechanical – Vibration Test
Electric Motor Storage Guidelines
Pick a location:
Clean and dry area indoors if possible
Avoid heat, humidity, and vibration
Store in position for the intended use- horizontal –
horizontal and vertical - vertical
Outdoor storage of large motors:
Cover – allow for breathing at the bottom
Energize space heaters if they exist – 10–20 degrees F >
ambient
Prevent rodents, snakes, birds, and small animals from
nesting inside
Electric Motor Storage Guidelines
Apply rust preventative coating to shaft and other exposed
machine surfaces
Bearing damage is possible in storage – avoid humidity and
vibration
False brinelling of ball and race
Fretting from corrosion
Recommend to rotate shafts at regular
intervals – Monthly
Redistributes lubrication to prevent corrosion
Minimize brinelling by relocating the balls within the
races
Electric Motor Storage Guidelines
Tip
 Leave all keyways the same, and in a different position each time
 This provides an easy visual indication
Periodic shaft rotation is more critical on:
Larger 2 pole (3600 rpm) machines
Machines with long shafts and heavy rotors
 Critical to avoid shaft distortion due to rotor sag
Electric Motor Storage Guidelines
Oil Lubed Bearings
 These motors are always shipped without oil
Fill to capacity as soon as set into storage
 Do not move motor with oil in the reservoirs
Drain it – Move it – Refill it
Tiered Maintenance
Define motor population
Apply appropriate maintenance and predictive tools
according to criticality, safety significance , and
economic significance of each motor
Categorize level of Maintenance
Minimum Maintenance
Moderate Maintenance
Trend able Maintenance
Extensive Maintenance
Minimum Maintenance
Category
Non-critical motors less than 50 HP
Motors having low safety and economic significance
Motors not of special design and normally readily
available
Unexpected failures are tolerable
Typically not repaired, but replaced with new
Moderate Maintenance
Category
Motors that may run to electrical failure, but not
mechanical failure
Maintenance may focus on the mechanical health of
the motor
Trend able Maintenance
Category
Mid sized low and medium voltage
motors
50 -200 Hp – 460 volt
200 – 1000 Hp – 2300/4160 volt
Larger DC motors - > 50 hp
Extensive Maintenance
Category
Mission Critical Motors
Require comprehensive electrical and mechanical
monitoring
Usually the larger and medium voltage motors
Motors that have highest safety and economic
significance
Testing Motor Windings
Motor Winding Failures
 Grounded winding
 Turn to turn short
 Single phased condition
 Roasted winding due to overload
 Locked rotor condition
 Shorted connection
 Winding damaged by voltage surge
Tests for Winding Condition
Insulation Resistance – megger test
Spot Check and Trend able
Indicates condition between the conductors and ground
Low readings indicate moisture, dirt, or damaged insulation
Minimum 1 meg ohm/1000 volts
Tests for Winding Condition
Polarization Index
Further indicates condition between the conductors and
ground
It’s the ratio of 10 min/1 min reading
A PI > 2 or 1 min reading > 5 giga ohms indicates motor is
suitable for service
PI > 7 could indicate brittle or aged insulation
PI can also help determine if a winding is wet or
contaminated
Tests for Winding Condition
DC Hipot
DC test voltage is applied to entire winding to verify the
insulation to ground
[ (2 x nameplate volts + 1000) x 1.7 x .60
Common on motors rated 4000 volts and higher
Done on low voltage motors to verify that its safe to perform a
surge comparison test
23
Tests for Winding Condition
Surge Comparison Test
Normally not performed in the field
 Indicates presence of phase to phase and
turn to turn shorts within a winding
Tests for Winding Condition
Rotor Current Analysis
Indicates the presence of cracked and
broken rotor bars or voids in cast rotors
These could be the cause for vibration especially under load
Electric Motor Lubrication
According to EASA the motor component with the
highest failure rate is the bearing.
51% of all motor failures are due a bearing failure.
Bearing lubrication is one of the many aspects of
motor care and one of major importance to the life of
a motor.
Preventive/Predictive Maintenance
The establishment of an effective predictive
maintenance system will significantly affect the life of a
motor.
Lubricating bearings at arbitrary intervals can result in
bearings that are under lubricated or over lubricated.
Either of these conditions can reduce the expected life of
Bearing
a bearing.Protection
Shaft slinger
Inpro/Seal Bearing Isolator
Bearing Types
Motor bearings are manufactured in various types of
configurations.
Shielded (2Z), shielded bearings have a metallic shield on
both sides of the bearing that is open on the ID or inner
race side.
Single Shield (1Z), same as above except one side of the
is open.
bearing
Sealed (2RS)
sealed bearings have a seal arrangement on
both sides of the bearing that will not allow any
contaminants to enter the bearing. These bearings are
lubricated at the factory and do not require any additional
grease.
Single Seal (RS) same as above, but sealed on one side
only.
Determining Frequency of
Lubrication
Determining what frequency at which a particular
bearing needs to be lubricated requires consideration
of many criteria.
1. Type of grease
2. Type of bearing
3. Motor operating temperature
4. Motor speed
5. Environmental conditions
6. Duty Cycle
Lubricant Compatibility
If two lubricants that are incompatible are
mixed they will lose their lubrication ability.
If in doubt check with your motor
manufacturer or lubrication supplier.
The majority of motor manufacturers use a
polyurea based grease that meets EP-2
standards such as Mobil Polyrex-EM
Motor Operating Temperature
Motors that operate in elevated ambient temperatures need
to be lubricated more frequently.
Motors operating in a temperature controlled environment
can be lubricated less frequently.
Motor Speed
Motors operating at 3600 RPM need to be lubricated more
frequently.
Motors operating at 900 RPM need to be lubricated less
frequently.
Roller bearings require more frequent lubrication than ball
bearings.
Environmental
Conditions
Motors operating in a cement plant need to be
lubricated more frequently.
Motors operating in a clean room need to be lubricated
less frequently.
Duty Cycle
Motors operating 24/7 need to be lubricated more
frequently.
Motors operating 8 hours/day 5 days/week need to be
lubricated less frequently.
Bearing Size
The size of a particular bearing will determine the
amount of lubricant the bearing needs.
Most motor manufacturers provide instruction
manuals detailing the correct procedures and the
amount of lubricant required to re-lubricate a bearing.
Maintenance Practices-A.C. Motors

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Clean, but don’t forget to inspect before and after cleaning
Check electrical connections for security, the insulation to be in
satisfactory condition.
Examine for signs of over heating
Check that the motor is secure
Do an audible check
Ensure that the motor is not over heating when operating, a
rule of thumb is that if it is too hot for the hand, it is too high.
When replacing a motor always ensure that the load, valve has
not seized.
Also ensure that the motor operates in the correct direction
Motor Repair Guidelines
Why do Motors Fail?
Repair vs. Replacement
Maintaining Reliability & Efficiency
Why do Motors Fail?
Failed in service
Motor stored in preparation for service
Regularly scheduled maintenance
Predictive maintenance testing reveals potential
concern regarding reliability
Motor requires upgrading
Modifications or addition of accessories
for new process
Failed or damaged accessories, i.e. brakes, tachs,
encoders, thermal devices
Why do Motors Fail?
Motors don't fail just because of age or operating hours.
Typical failures are caused by:
Heat
Power
Supply Anomalies
Humidity
Contamination
Improper Lubrication
Unusual Mechanical Loads
Motors have survived for several hundred
thousand operating hours when these stresses
have been minimized.
Common Causes For Motor Failures
Failure distribution statistics, like these
from IEEE Petro-Chemical Paper PCIC94-01, are helpful, but still necessary to
conduct a thorough root cause analysis
when determining modes of failure.
Why do motors fail?
Heat
Temperatures over the design rating take their toll in various ways. Electrical
insulation deteriorates at a rate that may double for every
10 ºC. Excessive temperature also causes separation of greases and
breakdowns of oils causing bearing failure.
Primary causes of overheating are:
 Overloading
 Too frequent starts (NEMA recommends two cold starts or
one hot start per hour)
 High ambient temperatures (NEMA typical design is 40 ºC)
 Low or unbalanced voltages
 High altitude operation
 Inadequate ventilation i.e. damaged cooling fan,
contaminated motor
Why do Motors Fail?
Power Supply Anomalies
Ideal power is a perfect sine wave on each phase at the motor's rated voltage
& frequency-rarely achieved. The following problems appear.

Harmonics: Cause overheating and decreased efficiency.

Overvoltage: At moderate levels is usually not damaging, but can reduce
efficiency and power factor. (NEMA limit 110%)

Under-voltage: Increases current and causes overheating and reduced
efficiency in fully loaded motors. It is relatively harmless in under-loaded
motors. (NEMA limit 90% of rated).

Voltage unbalance: Causes overheating and reduced efficiency.
Unbalance greater than 1% requires motor de-rating and motors should
never be powered by a system with more than
5% unbalance.
Why do Motors Fail?
Power Supply Anomalies
 Voltage spikes: Commonly caused by capacitor switching, lightning,
or cable stranding waves from a variable frequency drive (VFD).
These tend to cause turn-to-turn failures.
 Frequencies under 60 HZ from VFDs: The application should be
reviewed to insure motor is suitable for the application without
installation of supplemental cooling.
 Bearing damage from shaft currents: This usually originates from
VFDs. Consult the drive provider, motor manufacturer, or L&S
Electric for information on strategies such as an insulated bearing
sleeve, electro-conductive grease, or a shaft grounding system.
Why do Motors Fail?
Humidity
Humidity becomes a problem when the motor is
de-energized long enough to drop near the dew point
temperature.
 Moisture weakens the dielectric strength of electrical varnish
and other insulating materials
 Contributes to corrosion of bearings and other mechanical
components
 Moisture from the air can mix with certain
particulate contaminants to create highly
electro-conductive solutions.
 Insulation moisture can be significantly
reduced if the motor is kept warm.
Why do Motors Fail?
Humidity Control Strategies:
 By heating or dehumidification, keep the environment of
unpowered motors below 80% relative humidity.
 Specify new or rewound motors with heating elements for
the windings and use these when the motor is unpowered.
 Periodically rotate the shaft of stored motors to keep
lubricant on the bearing surfaces.
Why do Motors Fail?
Contamination
Contamination cannot be completely excluded by total enclosure or even
an explosion proof enclosure. Contamination destroys motors in three
ways:
 Abrasion
 Corrosion
 Overheating
Some airborne particulates are very abrasive. Motor coils flex
when in use and contamination with abrasive particles eat away
the wire enamel. Some substances, such as salt or coal dust are
electrically conductive. Heavy accumulation of contaminants
typically obstructs cooling passages.
Why do Motors Fail?
Improper Lubrication
Unfortunately, there are more ways to get it wrong than right. One
can over-lubricate as well as under-lubricate.
 Grease itself introduces contaminants into bearings if careful
control is not practiced. Mixing greases with different bases
may cause grease constituents to separate and run out.
 Different motors pose different requirements for the
introduction of lubricant and removal of old lubricant.
 Each individual application dictates the amount, type, and
frequency of lubrication required.
This is a complete subject in itself. L&S Electric
provides additional information for discussion.
Why do Motors Fail?
Unusual Mechanical Loads
A variety of mechanical conditions can either overstress bearings,
leading to early failure, or distort the motor frame causing asymmetric
air gap, which in turn can cause vibration and bearing failure or winding
overheating. Conditions to avoid are:
 Misaligned couplings
 Over-tightened belt; or mis-alignment sheaves
 Overly-compliant base or poor shimming of motor mounting feet
 "Soft Foot," (i.e. motor feet) not in the same plane
 Dynamic imbalance of load or internal imbalance of motor rotor
 Failure to bypass resonant speed point in
VFD powered motors
 Misapplication of bearings
Repair vs. Replacement
Simple answer in principle. Rewind or otherwise repair a motor when
cheaper than buying a new motor. Implementing this is a little more
difficult because you need to consider the total cost of ownership.
Ideally you have to consider:
 Difference in cost of repair vs. new purchase
 Difference in efficiency of existing and proposed new motor
 Availability of a new motor
 Lifetime discounted cost of electric energy for each scenario
 Possible mounting modifications
 Cost in downtime and repairs from a possible
early failure in either scenario
Maintaining Reliability
& Efficiency
To help assure a quality repair, you should:
 Evaluate prospective motor
repair service providers
 Don't pressure the provider
for unrealistic turnaround time
 Clearly communicate your
requirements to the provider
Evaluate Repair Providers
Make an point to spend time evaluating each potential
provider's service center.
 Look for indicators of a quality control program, such as evidence of
participation in an ISO 9000 program, membership in EASA, &
participation in EASA–Q program.
 Inquire about staff morale, training, turnover, etc.
 Determine whether the service center has sufficient facilities &
materials to handle the size & type of motors you send them.
Evaluate Repair Providers
 Note what test equipment the service center owns and routinely
uses to verify successful repair. Examples:
Core loss tester
Surge comparison tester
Voltage regulated power supply for
running at rated voltage
Vibration testing equipment
 Ask to see record-keeping system that the service center maintains
for repaired motors
 Inquire about method of insulation removal, burnoff, mechanical
pulling, etc.
For burn off, ask about methods for preventing flames or hotspots & ensuring
uniform temperature when roasting multiple motors
 Take note of the overall cleanliness of the service center
Motor Protection
Short-circuit / Instantaneous over current
Thermal overload
Phase current imbalance
Phase current loss
Over-current(instantaneous and temporized)
Ground fault / Instantaneous earth fault
Long start (stall) / Incomplete sequence
Jam (locked rotor)
Under-current
Phase current reversal
Motor temperature (by sensors)
Rapid cycle lock-out / Locking out
Load shedding
Notching or jogging / Number of starts
Phase voltage imbalance
Phase voltage loss
Phase voltage reversal
Under-voltage
Over-voltage
Difference between standard motor
and energy efficient motor
 More copper in the windings.
 Reduced fan loses.
 Energy efficient motors operate with efficiencies that are
typically 2-6% higher than standard motors.
Need:
When there is a new installation or
modification to your plant.
Old motors are damaged and need rewinding.
Existing motors are underloaded or
overloaded.
Protecting other devices.
Efficiency
Losses :
Losses are primarily of two types i.e. core and copper
losses.
Copper loss
Core loss
Friction and windage
Loss
Stray load loss
Cost of energy efficient motors:
Usually it is of normal cost and slightly more
than the normal motors. It is about 15% to 30%
more than the normal motors.
In Future, the initial cost may be available at the
same cost as a standard motor when the
population of EE Motors increases
Advantages
Operate more satisfactorily under abnormal
voltage.
Electric power saving.
Operating temperature is less.
Noise level is lower.
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C&H SSBU O&M REGION-NORTH