Energy Efficient Motors and Transformers Workshop MOTORS LIEN 7 May 2003

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Energy Efficient Motors and Transformers
WorkshopMOTORSLIEN 7 May 2003

• Dr Hugh Falkner MIEE CEng
• Future Energy Solutions

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Contents

• The System Perspective
• Higher Efficiency Motors
• Motor Management Policy
• VSDs
• Identifying energy saving opportunities
• Maintenance and Energy Saving
• Condition Monitoring

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Motors

• Understand the system - its about much more than
  the motor
• Focus you efforts where the best opportunities
  are
• Dont make an issue of it, make energy saving
  projects a matter of policy
• Assess the non-energy saving benefits, the
  paybacks are better and you get more support
• Look to integrate energy saving in to higher
  management concerns
• Is it set up right - are you sure?

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Before you look at the equipment.Ask some
simple questions first

• What is it trying to do?
• Is it useful?
• Is is still needed, or has the process changed?
• Dont waste time making a useless system more
  efficient!

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Which Systems Merit the Most Attention?
Some likely candidates

• Problem systems
• Production-critical systems
• Large systems
• Systems with high operating hours

Keep in mind the 80/20 rule of thumb

• About 80 of the potential savings will come from
  about 20 of the systems

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Key Points

• Higher Efficiency Motors do cost a bit more, but
  they can give a payback in as little as 1 year
• HEMs have other benefits which make them even
  more attractive
• It is rarely cost effective to replace existing
  motors with new HEMs.
• Over-sizing can waste some energy, but think
  carefully before fitting a smaller motor

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The HEM saving

• Average savings of 3 dont sound very impressive
  compared to VSDs.
• But, if all your motors were HEMs, the savings
  would be huge
• Remember
• You can use HEMs everywhere
• You do not have to make complicated calculations
• They cost much less than a VSD
• They do not affect the performance of the
  equipment

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Other benefits of HEMS

• Better power factor
• Better part load efficiency
• Less noise
• Less heat
• Increase available site electricity for other
  equipment

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The European efficiencylabeling scheme
4 pole
2 pole
Efficiency
kW
1.1
90
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The Effect of voltage variation on motor
characteristics

• Characteristic Voltage
  Voltage 6 High 6 Low
  

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Motor Management Policy

• The savings from using single Higher Efficiency
  Motors are small - but the savings from all the
  motors on a site quickly become something very
  significant.
• Understand the costs of repairing failed motors
• Have a Motor Repair/replace policy

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ECONOMICS OFREPLACEMENT VS. REPAIR

• Depends on many factors...
• Running hours
• Load
• Cost of electricity
• Cost of new motor
• Cost of motor repair

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MOTOR REPAIR - THE PROBLEMS
Typical faults from a sub-standard repair

• Increase in core losses
• Wrong winding specification
• Badly fitted bearings
• Incorrect fan
• Poor rotor alignment

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THE REAL COST OF REWINDING A MOTOR
Original - 90.5 Repair - 90.0 HEM - 92.5
HEM saving - 679
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Policy on Motor Failure

• Decide using ReplaceRepair chart

• If less than _kW - REPLACE anyway

• If very damaged - REPLACE anyway

• If an HEM - REPAIR

• For over-riding operational reasonsthese
  instructions can be ignored, but explanatory form
  must be completed

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Getting everybody involved is essential -
everyone has different motivations
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Motor Management Policy at North West Water

• Get Senior Management on your side - and get
  everybody to buy in
• Be prepared to overcome the obstacles in your way
  - and to see through changes in the way things
  are done
• Consider shifting responsibility by Contracting
  out.
• Pace yourself for a long slog - and try not to
  lose heart half way
• The energy saving benefits alone make it very
  worthwhile

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Is speed control right for you?

• Before deciding to alter the speed, make sure
  that you understand the system. Otherwise you
  could make things worse!
• If the machine can always turn at a lower speed,
  then you could alter the speed in many ways, you
  dont have to use a VSD.
• However, as the price of VSDs gets lower, they
  are being used in more and more applications

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Why do we want to control speed?

• Being able to alter the speed of a fan, pump,
  conveyor, machine tool, gives us tremendous
  opportunities to better control the process.
• In some applications, it can also save lots of
  energy.
• There are lots of ways to control the speed of a
  machine, not just the VSD!

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Altering the flow by using sequencers

• In some circumstances it makes more sense to
  switch machines on/off to match the flow to the
  demand.
• Common examples are pumps or air compressors

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Fan Affinity Laws (Applies to all centrifugal
loads)

• Flow proportional to the speed
• Pressure proportional to the speed squared
• Power proportional to the speed cubed

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Inherent VFD Benefits

• Controls speed variations
• Provides mechanical control
• Eliminates startup impacts causing system
  vibration
• Provides fault tolerance
• Supports soft starts

• Restarts spinning load
• Controls speed swings
• Enhances product quality
• Conserves energy
• Repeats results

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Getting the Economics right

• Look for applications where you can reduce the
  speed by at least 20
• Look for applications operating at least 4,000
  hours pa
• Watch out for applications with high static head

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Important Considerations for Variable Speed Drives

• Engineering analysis required for each unique
  application
• Load profile of the driven equipment must be
  evaluated over the full range of operating
  conditions
• Effect of reduced speed on torque
• Affinity laws apply for frictional pump systems,
  but not for static head-dominated systems

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Methods of control

• AVSD is only as good as the way it is
  commissioned.
• There are two methods of control
• Open Loop. The speed is simply controlled by a
  potentiometer. The speed is set either by a
  person, or perhaps by simple controls allowing
  perhaps 2-4 speeds, depending on the situation.
• Closed Loop. This is much more powerful, with
  the user setting the flow, temperature, pressure,
  or whatever else it is that they want to control.
  Using a sensor, the VSD adjusts the speed
  automatically to maintain this parameter. This
  will always give optimum results, as long as it
  is set up properly!

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How good are your controls?

• Was it properly commissioned?
• How were the settings decided on?
• How much safety margin have you got?
• How quick does your system respond?
• How good are your sensors?
• Has anyone altered the settings?
• Has it been switched to manual?

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De-rating of Motors

• Because the generated waveform is not a smooth
  sinusoid, there is additional heating within the
  motor.
• In the past this has meant de-rating the motor by
  up to 10
• With more modern PWM VSDs working at higher
  switching frequencies, the waveforms are much
  cleaner, and so the de-rating is much less.
• Some manufacturers claim that you dont have to
  apply any de-rating at all - but always check
  first
• In practice, with centrifugal loads, the power
  goes down so fast with speed, that just a small
  reduction in speed will compensate for the
  additional heating due to a poor waveform

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To categorize by motor size and run time, don't
we need to do a plant-wide inventory?
Prescreening Motor Systems - getting at the
VITAL FEW

• Not only do we not need it, it would be the WRONG
  thing to do
• The first level of screening - by size and run
  time - should be a one day effort for many plants
• Plant operations involvement is essential

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Where to look

• At many sites the main production equipment is
  well maintained, and so there is not much
  opportunity for making changes. Also the costs
  of downtime might be too high!
• Look instead at the backroom services. These are
  often neglected, running long hours and badly
  matched for current demand patterns. They also
  have big motors, and lots of opportunity for
  better controls such as VSDs or sequencers

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SYMPTOMS Looking Listening
Some symptoms of interest for pumping systems

• Systems with throttled flow control or bypass
  flow control

• The presence of significant cavitation noise,
  either at the pump or elsewhere in the system

• Frequent pump starting and stopping

• Multiple operating parallel pumps (where the
  number of operating pumps seldom changes)

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Secondary prescreening

• Required data include
• flow rate
• head
• electrical input power
• Test gauges preferred over permanently installed
  gauges
• Flow rate can estimated using pump curves

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Secondary screening - the costs increase

• This will take time and money, so think carefully
  what you need to know
• Dont collect more data than you need
• Never collect data because it may be useful one
  day
• The objective of data collection is to refine
  your estimate of the cost effectiveness of an
  energy saving measure so that you are confident
  that you should, or should not, do it.
• And dont forget to take measurements once the
  energy saving measure has been fitted. This way
  you can tell everybody how clever you are!

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Estimating power without taking any electrical
measurements

• Measuring the speed of the motor with a
  stroboscope can give a useful indication of motor
  power - ideal for initial screening
• Accuracy of perhaps /- 20
• Very Quick!

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The slip method of estimating motor power

• This is based on the fact that the torqueslip
  characteristics in the normal operating region of
  an induction motor are very straight. So, at
  full rated load the motor will be at its maximum
  slip (and hence minimum speed.) By comparing the
  actual measured speed with the nameplate rated
  slip, the power can be estimated.
• Mechanical Power
• (nno load - n meas) x kW (rated)
• (nno load - nrated)

Nrated
Nmeas
Torque
nno load No load (synchronous) speed n meas
Measured speed n rated Nameplate rated speed
Speed
Nno load
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Worked Example of estimating motor power from the
speed

• From the nameplate, 1,470rpm at 55kW (rated) load
• Using the stroboscope it is measured at 1,480
  rpm.
• What is the load?

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Solution

• Load 1,500 - 1,480 20 67 of rated
  power
• 1,500 - 1,470 30
• Mechanical (output) power is 67 x 55kW 37kW
• This is only approximate, but it does give a very
  quick indication of power consumption

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Joint benefits of system improvements

• Fitting a VSD not only saves energy, but also
• Reduced speed means less frictional wear, longer
  bearing and seal life.
• It reduces water hammer and resulting damage.
• Improved pressure control reduces leakage
• Impeller coating reduces pump wear,
• saving energy and maintenance costs.

Youll struggle to save energy and not reduce
maintenance costs, and vice versa.
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Perspectives on a Site Energy Audit

• The Energy Manager - Sees equipment as consumers
  of energy

• The Salesperson - Keen to show the latest
  technology

• The Production Manager - Reliability and
  performance of the plant

• The Maintenance Engineer - The costs of
  maintaining plant and related on-going problems

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Understand the system

• Whether youre trying to sort out a maintenance
  problem or are looking for energy savings, you
  need to understand how the equipment works.
• Just by listening to the accounts of everyone
  with an interest in the equipment, you can soon
  get very good clues as to what is going on.

Dont jump in and just try to fix the reported
problem, find out about the whole related system.
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Surplus energy is the root cause of many
Maintenance problems

• Energy Used 100kW x 24 hours 2400kWh per day
• Useful Work done (assuming 60 efficiency)
• 1140kWh. Where does the 960kWh go!?

It is this surplus energy, ie energy that is
doing nothing useful, that causes maintenance
problems. Principally Direct heat, friction and
their resultant effects. Equipment that is 100
efficient has no surplus energy for causing
maintenance problems.
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Getting it together - the benefits of integrating
Maintenance and Energy savings

• Integrate maintenance and energy management
  systems
• Install energy saving measures during routine
  maintenance breakdowns
• Capture all maintenance and energy savings when
  making proposals
• Identify the energy costs of poor maintenance
  practices and unscheduled breakdowns

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The Associated Benefits

• Increases manufacturing system availability.
• Reduces the risk of consequential damage.
• Improves the manufactured product quality
  waste.
• Improves safety characteristics
• Improves plant performance
• Contributes to more effective equipment design.
• Minimises capital expenditure by achieving the
  cost effective procurement of equipment.

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CM Programme Considerations

• Site Audit Criticality Assessment
• Selection of Appropriate Techniques
• Database Configuration
• Periodic Data Collection
• Analysis Reporting
• Continuous Improvements
• Programme Justification

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Monitoring Asset Condition

• Visual Inspection
• Vibration Monitoring
• Thermal Imaging
• Oil Sampling and Analysis
• Ultrasonic Leak Detection
• Motor Current Analysis

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Level I - Vibration Magnitude
Simple Vibration Meter
vibration level
hi alarm
hi alarm
lo alarm
lo alarm
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Level II - Vibration Analysis
Data Collector/ Analyser
vibration frequency
time waveform
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Level II - Vibration Analysis
Amplitude
Balance
Alignment
Bearing
Gears
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Vibration Monitoring

• Imbalance
• Alignment
• Bearing / Gearbox Defects
• Lubrication Quality Deficiency
• Machine and Structural Resonance

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Oil Analysis
Fluid Properties The condition of chemical And
fluid properties
Contaminants Presence of fluid and surface
destructive contaminants
Wear Debris Analysis Presence of machine wear
materials
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Thermal Imaging
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What is Thermography

• All equipment and processes have thermal
  patterns.
• Areas of hot and cold radiate invisible thermal
  or infrared energy (IR).
• Thermal imaging systems see the radiation
• Focus the IR radiation onto a detector and
  convert this into electrical signal for display
  as a thermogram.

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A typical Thermal Image
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Electrical Applications

• Electrical
• Main Transformers
• Motor Control Centers
• Circuit Breakers
• Distribution Panels
• Connections
• Cable Trays
• Control Systems

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Mechanical Applications

• Mechanical
• Rotating Equipment Bearings
• Electric Motor Pump Casings
• Couplings
• Steam Traps
• Valves
• Roofs
• Process Applications - HVAC, etc.
• Ovens, Boilers, Furnaces, Dryers
• Insulation

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Motor Issues
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Alignment Issues
Accurately Aligned
30,000 out Parallel 10,000/inch out Angular
1,000/inch out Angular
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Motor Current Analysis

• Diagnoses range of ac motor faults
• Can be integrated with vibration
• Measures deterioration by trending

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Motor Current Analysis
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Motor Current AnalysisFault Diagnosis
primary rotor fault sidebands
bad motor
good motor
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Motor Current Analysis
winding insulation degradation
air gap eccentricity
cracked end rings
broken rotor bars
oscillating load
poor brazing
bent shaft
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Some Conclusions

• Understand the system - its about much more than
  the motor
• Focus you efforts where the best opportunities
  are
• Dont make an issue of it, make energy saving
  projects a matter of policy
• Assess the non-energy saving benefits, the
  paybacks are better and you get more support
• Look to integrate energy saving in to higher
  management concerns
• Is it set up right - are you sure?