Transcript The Motor Challenge

Energy Efficient Motors and
Transformers Workshop
MOTORS
LIEN 7 May 2003
Dr Hugh Falkner MIEE CEng
Future Energy Solutions
© FES 2003
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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
 Don’t 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?
Don’t 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% don’t 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 efficiency
labeling scheme
4 pole
% Efficiency
2 pole
kW
1.1
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90
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The Effect of voltage variation on
motor characteristics
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Characteristic
Voltage
6% High
Voltage
6% Low
Full load speed
Starting Torque
Starting Current
Full load current
Temp rise
Efficiency ½ load
Efficiency ¾ load
Efficiency Full load
Power Factor ½ load
Power Factor ¾ load
Power Factor Full load
Up to 0.5%
Up 12.0%
Up to 6.0%
Down 4.0%
Down 4.0%
Down 1.5%
Down 1.5%
No Change
Down 4.0%
Down 3.0%
Down 2.0%
Down 0.75%
Down 11.0%
Down 5.0%
Up 5.0%
Up 6.0%
Up 5.0%
Up 2.0%
Down 1.0%
Up to 4.0%
Up to 2.0%
Up to 1.0%
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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 OF
REPLACEMENT 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
Repair
Replace - HEM
Cost
$1,233
$1,595
2 yr running cost
$38,663
$37,622
Total cost
$39,895
$39,217
Original - 90.5%
Repair - 90.0%
HEM - 92.5%
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HEM saving - $679
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Policy on Motor Failure
 Decide using Replace:Repair chart
 If less than _kW - REPLACE anyway
 If very damaged - REPLACE anyway
 If an HEM - REPAIR
 For over-riding operational reasons
these 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 don’t 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)
Input Power (%)
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
90
100
Speed (%)
 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
• Restarts
spinning load
• Controls speed
swings
• Enhances
product quality
• Conserves
energy
• Repeats results
• Supports soft starts
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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 don’t have to apply any derating 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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Prescreening Motor Systems getting at the VITAL FEW
To categorize by motor size and run time, don't we
need to do a plant-wide inventory?
 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
 Don’t 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 don’t 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 torque:slip 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 =
Nrated
(nno load - n meas) x kW (rated)
(nno load - nrated)
Nmeas
nno load = No load (synchronous) speed
n meas = Measured speed
n rated = Nameplate rated speed
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Speed
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no load
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.
You’ll 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 you’re 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.
Don’t 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
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hi alarm
hi alarm
lo alarm
lo alarm
vibration
level
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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
Frequency
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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
73.5°C
LI01
SP02
SP01
70
60
50
40
30
27.8°C
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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
79.6°C
SP01
60
LI01
40
AR01
21.1°C
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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 Analysis
Fault Diagnosis
primary rotor
fault sidebands
good motor
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bad motor
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Motor Current Analysis
winding insulation
degradation
air gap
eccentricity
cracked
end rings
oscillating
load
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broken
rotor bars
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
 Don’t 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?
© FES 2003
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