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RMWG Meeting 20 Feb 2008 1
Advanced Machines and Energy Systems
(AMES) Group
ENERGY EFFICIENCY
PROJECTS AT UCT
Department of Electrical Engineering
RMWG Meeting 20 Feb 2008 2
Overview
Vision
Key Group Members
Collaboration
Research Outputs & HR Development
Laboratory Facility
Research Areas
Details of Current Research
RMWG Meeting 20 Feb 2008 3
Vision
To provide feasible technical solutions to relevant industrial problems, whilst maintaining a high scholarly research content
This is achieved by engaging highly skilled personnel and by applying a methodical approach to problem solving
To disseminate research findings through technical reports and peer-reviewed publications
To develop human resource capacity in electrical machines, drives and energy systems, which will eventually contribute towards innovation and poverty alleviation
RMWG Meeting 20 Feb 2008 4
Prof. Pragasen PillayPhD, CEng, FIEEE, FIETProfessor UCT, ClarksonElectrical Machines, Drives and Renewable Energy
Mr. Marubini Manyage MSc, MIEEEResearch Officer, UCTMachine Design, Energy Efficiency
Dr. Paul BarendsePhD, MIEEELecturer, UCT Electric Drives, Fault Diagnosis
Mr. Chris WozniakBScTechnical Officer, UCTElectrical Machines & Energy Systems
Key Group MembersDr. Ben SebitosiPhD, CEng, MIEEESnr Research Officer, UCTRural Electrification,Renewables, Energy Policy
Dr. Azeem KhanPhD, MIEEESenior Lecturer, UCTPM Machines & Drives, Wind Energy
Post Graduate Students PhD Students: (5)
• Mr F. Endrejat, Mr M. Manyage , Mr R. Naidoo, Mr D. Singh, Mr R. Okou
MSc Students: (8)• Miss P. Ijumba, Miss K. Masemola, Mr R. Solomon, Mr G. Mwaba, Mr T. Madangombe, Mr H. Mzungu,
Mr S. Sager, Mr P. Kiryowa
BSc(Eng) Final-year Thesis Students: (15)• About 15 students supervised per year for final-year thesis project
RMWG Meeting 20 Feb 2008 5
Collaboration – South Africa
Academic Institutions:• DUT - Deepak Singh, Senior Lecturer – Physics• DUT - Dr. Poobie Govender, Prof Krishnan Kanny• University of Pretoria – Mr Raj Naidoo, Senior Lecturer – EE• University of Stellenbosch – Prof W. van Niekerk, Prof M.J. Kamper, Dr D.
Johnson
Government / Parastatals:• NRF• THRIP• DST – Mr L. Simpsom, Ms T. Mailula, Dr Boni Mehlomakulu• SANERI – Mr K. Nassiep, Dr M. Bipath, Dr T. Mali
Industry:• ESKOM – Mr L. Pillay, Mr S. Bisnath, Mr J. Gosling, Dr S. Higgins, Mr R. Koch, Mr
Y. Brijmohan, Dr T.L. Mthombeni,• SASOL – Mr F. Endrejat, Mr T. Perumal, Mr D. Willemse• LHM – Mr R. Melaia
RMWG Meeting 20 Feb 2008 6
Clarkson University, Potsdam, NY, USA• SMMA - The Motor and Motion Association • EMERF Consortium - Electrical Motors Educational and Research Foundation• NYSERDA - New York State Energy Research and Development Authority
Aalborg University, Denmark (wind energy)
University of Picardie, France (condition monitoring)
Politecnico di Torino, Torino, Italy (motor lamination losses)
Graduate school of Telecom. and IT, Addis Ababa, Ethiopia (Cellphone Keyboard Customization for Rural Applications)
GTZ, German Aid Agency (environment and rural electrification)
Centre for Research in Energy and Energy Conservation of Makerere University, Uganda (white LEDs dissemination)
Collaboration – International
RMWG Meeting 20 Feb 2008 7
Research Outputs & HR Development
2007 2006 2005 2004
Human Resource Development 3xPhD1xMSc12xBSc
2xPhD0xMSc6xBSc
1xPhD1xMSc5XBSc
1xPhD0xMSc6XBSc
Journals papers(Peer-reviewed, international)
6 5 6 11
Conference papers(Refereed international mainly and some local)
16 12 14 7
Contract Research - Eskom 3 3 1 1
Contract Research - Other Industries 1 1 1 0
RMWG Meeting 20 Feb 2008 8
Laboratory Facility Flexible distribution system with the capability of various DC and AC supplies Two, 250kW DC machines and 4-quadrant drives
• Fed directly from the UCT 11kV ring mains through 11kV/500V transformers 6.6kV, 520kW Alternator (driven by afore-mentioned DC machines) 75kW induction motor with a 75kW drive Several small and medium DC, AC machines and drives including test benches and
testing equipment These unique capabilities, allows lab testing of machines that is not capable at some
international institutions
RMWG Meeting 20 Feb 2008 9
Current Research Areas Energy Efficiency - Machines
• Core loss study• Electric motors for demand side
management• MV petrochemical drives
Machine Design Projects• Small wind generator design• Low voltage High Current Traction
motor design
Condition Monitoring• Fault studies and condition
monitoring of induction motors, PM motors and wind generators
Rural Electrification and Alternate Energy Sources• Applications of white LEDs• Optimization of solar water pumping
systems• Solar water heaters• Flywheels for energy storage• Biomass
Power Systems Applications• Power quality• Dip classification using wavelets• Impacts of renewable energy
sources on power systems
RMWG Meeting 20 Feb 2008 10
Background: • Motorized applications are major electricity consumers, in SA
and USA, 64 % and 60 % of total electricity, respectively• Core losses can be 25 % ~ 30 % of the total losses, even
higher with newer designs, such as SRMs and BDCMs• Variable speed drives produce harmonics that increase core losses
Research Focus: • Develop a scientific understanding of lamination core losses • Develop core loss design equations suitable for motor designs
applications especially in software design packages
Goals: • Improving motor efficiency by reducing core losses• Aid motor designers with better models• Realize energy and dollar savings• Reducing peak demand levels and delaying the need for new stations
Environmental benefits:• Reduce C02 emissions by efficient use of electricity
Motor Lamination Core Losses
Core Losses
RMWG Meeting 20 Feb 2008 11
Core Loss Predictions Classical core loss predictions use:
Steinmetz formulae for predictingarea under BH-Loop
Several improvements suggested overthe years
However current disagreements in literature on: • Computing coefficients for formulae• Structure of coefficients• Dependence on the operational
parameters, such as frequency and flux density
Current work in this areas has led to reliable analytical expressions for predicting core losses in lamination strips
Formulae validated on Epstein test bench
Plan to integrate formulae into Finite Element Analysis software - Magsoft
h eP P P= +
1.6 2( )h p e pP k fB k fB= +
2( )a bBh p e pP k fB k fB+= +
2 1.5( ) ( )h p e p ex pP k fB k fB k fBα= + +
2 1.5( ) ( )h p e p ex pP k f B k fB k fBβ α= + +2 2 1.5( ) ( )p pa bB cB
h p e p ex pP k fB k fB k fB+ += + +
2
1 2 3( )e p
h h h
p p p
fP k fBk k kB B Bα β λ
= ++ +
Core Losses
RMWG Meeting 20 Feb 2008 12
New Commercial Test Bench System
Fully customized • Streamlined for high f tests• The only unit in the US!
Uses a 352-turn frame Up to 4.0 kHz Fully automated
• Can run tests faster Temperature monitoring
Core Losses
RMWG Meeting 20 Feb 2008 13
Traction Motor Design
Description and Use• Design a high efficiency Low Voltage High Current Permanent Magnet
Synchronous Motor for traction applications• Motor will be used in a 24V battery-operated pallet truck• Compete with DC and AC induction motors• Benefits: Long battery lifespan and extended operating cycles
Design Challenges• Low voltage inverter limit (14.5 VLL AC)• Cogging and Ripple torque• No cooling, Maximum temperature (180degC)• Stator outer diameter < 120mm
Efficiency improvement • Better core loss prediction using improved core loss formula and new test bench• Choice of laminations• Reduce winding resistance
Funding: ESKOM Senior Fellowship, US DOE and NYSERDAMr. Marbini Manyage
Pallet truck
Traction motor
Machine Design
RMWG Meeting 20 Feb 2008 14
Machine Design
Traction Motor Prototyping
RMWG Meeting 20 Feb 2008 15
SMC Axial-flux PM Generator
Background:• Axial-flux PM generator design has highest torque density• However, slotting of AFPM stator core is problematic:
Difficult to machine tape-wound stator core Magnetic properties of core affect by machining process
SMC Axial-flux PM generator with single rotor, double stator:• Uses Soft Magnetic Composite (SMC) material• Easy to manufacture - Slotted cores are pressed• Shorter flux paths, high torque density, high efficiency
Previous work showed need for composite (SMC + steel)stator core structure:• Steel in magnetic circuit increases effective
permeance of circuit, thus reducing effect of lower SMC permeability
• Steel in circuit also reduces SMC required, thus reducing effect of higher SMC core loss
Machine Design
Funding: 2004 – present NRF Thuthuka; April 2005 – December 2006 ESKOM, US DOE, NYSERDA, Warner Energy
Dr. Azeem Khan
RMWG Meeting 20 Feb 2008 16
Construction of the prototype SMC teeth:- Machining of SMC cores by end-mill:
• Cost effective, easily accessible process• Avoids high cost of pressing SMC parts for prototyping• Good dimensional tolerances
Pre-machined SMC core:• Core in pressed and heat-treated state• Good insulation between iron regions through bulk of material• Microscopic image of SMC surface shows this clearly:
Machined SMC core:• Machining action results in elongation / smear of iron regions on machined surfaces• Degradation of insulation between iron regions• Increased conductivity and hence eddy current losses on / near machined surfaces
Acid treatment process introduced to eliminate smeared iron on machined surfaces• Phosphoric acid solution used to etch smeared iron• Acid reacts with iron only and not with insulation epoxy• Etched parts ultrasonically cleaned in methanol to prevent corrosion• Lower surface conductivity
Machine Design
Pre-machined Machined Acid treated
RMWG Meeting 20 Feb 2008 17
Stator cores tested
Two identical machined SMC cores prototyped:• 1st case : machined SMC core with untreated teeth• 2nd case: machined SMC core with acid treated teeth
Untreated core Acid treated core
Machine Design
RMWG Meeting 20 Feb 2008 18
Effect of Armature Rewinding on Induction Motor Efficiency
Background• Motorized loads such as induction motors account for 60% the load in industry.• With more than 5 billion Rands spent on over 2 years on motor repair, the impact
of motor repair on efficiency in South Africa is unknown. Research Focus
• The comparison of the different procedures followed in international standards such as the IEEE 112, IEC 60034, JEC 37 and others
• The impact of the process of armature rewind on induction motor efficiency Objectives
• Construction of state of the art test rigs to produce very accurate efficiency values for the different motors
• Rigorous testing of motors before and after rewinding
Funding: 2007 – ESKOM
Mr. Heskin Mzungu
Motor Efficiency
RMWG Meeting 20 Feb 2008 19
Test Rigs Two test rigs commissioned in Electric Machines lab at UCT Range of motors to be tested and rewound: 3kW, 7.5kW, 11kW, 15kW, 22
kW, 37.5kW, 45kW, 55kW
Motor Efficiency
15kW tested motor
Torque transducer amplifier
Inline Torque
Transducer
DynanometerTested AC Motor
Inline Torque Transducer
2:3 Pulley System
250kW Dynamometer
55kW test rig to test from 22-55kW15kW test rig to test from 3-15kW
RMWG Meeting 20 Feb 2008 20
Accuracy and repeatability of tests are very important. A 15kW motor is used to validate this.
Efficiency vs Load for 15kW motor
1420.00
1430.00
1440.00
1450.00
1460.00
1470.00
1480.00
1490.00
1500.00
0 20 40 60 80 100 120 140 160
Loading (%)
Spee
d (r
pm)
Motor Efficiency
Speed vs Load
Losses vs Torque^2
80
82
84
86
88
90
92
94
0 20 40 60 80 100 120 140 160
Loading (%)
Eff
icie
ncie
s
0
100
200
300
400
500
600
700
800
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Torque Squared (N.m ^2)
Str
ay L
oad
Loss
es (W
)
Test Rigs
RMWG Meeting 20 Feb 2008 21
Comparison of Efficiency Standards
83
84
85
86
87
88
89
90
15 25 35 45 55 65 75 85 95 105
Loading (%)
Eff
icie
nc
y (
%)
IEEE IEC 61972 CSA-390 Catalogue JEC SANS IEC 34-2 Pout/Pin
Motor Efficiency
Efficiency tests performed as per SANS IEC 34-2, JEC 2137, IEEE 112 and CSA 390 standards and compared with Pout/Pin and catalogue
Discrepancy between the efficiencies are due to the treatment of stray losses, temperature (Pout/Pin) and manufacturers quoting calculated catalogue efficiencies rather than tested values
70
72
74
76
78
80
82
84
86
88
90
10 20 30 40 50 60 70 80 90 100
Loading (%)
Eff
icie
ncy
(%
)
CSA-390 IEC 61972 IEEE 112 SANS IEC 34-2 JEC
Two 3kW motors tested (standard and high efficiency motors)
Standard motor High Eff
motor
RMWG Meeting 20 Feb 2008 22
Comparison of Efficiency Standards
,( ) ( )stray elec mech Fr W Fe rotor statorP P P P P P P= − − + + +
Motor Efficiency
Standard Method of SLL
IEEE 112 Indirect Method*
SANS IEC 60034-2 Assumed Values
JEC 2137 Ignore SLL
CSA 390 Indirect Method
Stray Load losses are losses that are the most difficult to measure. This is due to there non-linearity and numerous causes.
The different standards employ different ways of calculating them. This is where the biggest difference is in the standards
*
RMWG Meeting 20 Feb 2008 23
240
290
340
390
440
490
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Torque Sqaured
Stra
y Lo
ad L
oss
(W)
Effects of Temperature Investigation on the effects of
temperature on efficiency during testing
Losses increase with an increase in temperature. Efficiency therefore is affected
Motor Efficiency
55.00
65.00
75.00
85.00
95.00
105.00
115.00
0.00 1000.00 2000.00 3000.00 4000.00 5000.00 6000.00 7000.00 8000.00
Time (sec)
Tem
pera
ture
(C)
Thermocouple 1Thermocouple 2
100%
75%
50 %
25%
SLL variation of up to 1%
RMWG Meeting 20 Feb 2008 24
85
86
87
88
89
90
91
0 20 40 60 80 100 120 140 160
Loading (%)
Effi
cien
cy (%
)
Series1Series2
Effects of Temperature
Motor Efficiency
Efficiency maximum variation of up to 0.5% This is significant when trying to investigate the effects of rewinding It has been reported in literature that motor can loss or gain up a 1%
in efficiency
RMWG Meeting 20 Feb 2008 25
Armature rewinding Impact on motor efficiency (and/or losses)
can occur at any point during the rewind process
South African Rewind and Refurbishment standards such SANS 1804 and 10242 have a standard procedure
Motor Efficiency
Motor loss Affected by
Stator core losses
• Overheating core steel during stripping•Damaging core insulation during winding removal•Excessive abrasion and grinding during core cleaning
Friction and Windage losses
•Bearings and cooling fan not replaced to original conditions•Incorrect bearing fits•Incorrect bearing preload
Stator Winding
Losses (I2R losses)
•Reducing conductor cross-sectional area•Changing number of turns•Using wrong winding configuration•Machining rotor
Rotor losses (I2R losses)
•Altering rotor bars and end rings•Changing cage design
Stray load losses
•Change in air gap symmetry and air gap unconventional behavior•Bent motor shaft or damaged end shields
Visual inspection for fault
Overhang is cut
All parts are cleaned
Mechanical Winding
Winding data and Winding Stripping
Core Testing
Oven Burn Out or
Mechanical Stripping
Visual inspection for fault
Paint and Insulate Core
Electrical tests are done on Rotor
Varnishing by impregnating and baking
Rotor is balanced
Bearings are replaced if needed
All electrical connections done and reassembly of motor
Final Testing
Stator rewound and insulated
RMWG Meeting 20 Feb 2008 26
Comparison of 3kW Std and HE Motor Two induction motors were compared:
• Standard motor: 3kW, 4-pole• High efficiency: 3kW, 4-pole
Objectives:• Efficiency differences between motors assessed
• Operating performance differences between motors, when subjected to the same load assessed
• To assess effectiveness of retrofitting standard motors with high efficiency motors
3kW HE Motor with Dynamometer
Motor Efficiency
RMWG Meeting 20 Feb 2008 27
Methodology IEC 60034-2-1 standard used to assess efficiency both motors
Equivalent circuit parameters determined for both motors:• No-load test• Locked Rotor test
Operating performance differences assessed using equivalent circuits and superimposing pump load curve
Motor Efficiency
RMWG Meeting 20 Feb 2008 28
IEC60034 Test Results
Motor Efficiency
IEC 60034-2-1 standard used to assess efficiency both motors:• 3kW Standard and High Efficiency
motors tested• Full temperature compensation for losses
as per standard
20 40 60 80 100 120 140 1600
50
100
150
200
250
300
350
400
Load [%]
Sta
tor C
u lo
sses
[W]
Stator Copper losses vs load
Std-MotorCubic-fitH-Eff-MotorCubic-fit
20 40 60 80 100 120 140 1600
100
200
300
400
500
600
700
Load [%]
Rot
or C
u lo
sses
[W]
Rotor Copper losses vs load
Std-MotorCubic-fitH-Eff-MotorCubic-fit
Efficiency vs Load comparison
20 40 60 80 100 120 140 16074
76
78
80
82
84
86
88
90
Load [%]
Effi
cien
cy [%
]
Indirect Method Efficiency vs Load
Std-MotorBest-fitH-Eff-MotorBest-fit
RMWG Meeting 20 Feb 2008 29
Equivalent Circuit Parameters Equivalent circuit parameters determined for both motors:
• No-load test• Locked Rotor test• IEEE recommended equivalent circuit used:
Equivalent circuit parameters:
• Standard motor High Efficiency motor
Motor Efficiency
IEEE recommended equivalent circuit
RMWG Meeting 20 Feb 2008 30
Operating Performance Equivalent circuits used with Matlab program to predict performance of motors
Centrifugal pump load curve superimposed on characteristics of both motors
Comparison with experimental results
Motor Efficiency
RMWG Meeting 20 Feb 2008 31
Operating Performance: Torque vs Speed Torque vs speed curves of both motors with centrifugal pump load curve superimposed Experimental results show good correlation
Standard motor:• Slip=6.1%• Speed=1408.5rpm
High Efficiency motor:• Slip=4.85%• Speed=1427.3rpm
Motor Efficiency
0 500 1000 15000
10
20
30
40
50
60
n [rpm]
Torq
ue [N
m]
IM Torque vs speed characteristic
High Eff CalcStd CalcHigh Eff ExpStd ExpCentrifugal load
RMWG Meeting 20 Feb 2008 32
Operating Performance: Current vs Speed Current vs speed curves of both motors Experimental results show good correlation
Standard motor:• Slip=6.1%• Speed=1408.5rpm• I1_load=6.28A• pf=0.78 lagging
High Efficiency motor:• Slip=4.85%• Speed=1427.3rpm• Current=6.1A• pf=0.8 lagging
Motor Efficiency
0 500 1000 15000
5
10
15
20
25
30
n [rpm]
Cur
rent
[A]
IM per-phase stator current vs speed characteristic
High Eff CalcStd CalcHigh Eff ExpStd Exp
RMWG Meeting 20 Feb 2008 33
Operating Performance: Efficiency Efficiency vs speed curves of both motors Experimental results show good correlation
Standard motor:• Slip=6.1%• Speed=1408.5rpm• Eff_load=83.1%
High Efficiency motor:• Slip=1%• Speed=1427.3rpm• Efficiency=87.8%
Motor Efficiency
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 15000
10
20
30
40
50
60
70
80
90
100
n [rpm]
Effi
cien
cy [%
]
IM Efficiency vs speed characteristic
High Eff Calc.Std. Calc.High Eff. ExpStd. Exp
RMWG Meeting 20 Feb 2008 34
Operating Performance: Energy Energy saving based on reduction in input power drawn by High Eff motor:
• Same centrifugal pump load• 3kW Std motor replaced with 3kW High Eff
Standard motor input power:• Pin = 3.39kW
High Efficiency motor input power:• Pin = 3.38kW
Reduction in input power drawn by High Eff motor:• ∆Pin = 10.64W !!!• ∆Pin = 0.3% !!!
Motor Efficiency
RMWG Meeting 20 Feb 2008 35
For further enquiries, please contact:
Name: Number: E-mail:
Dr Azeem Khan 021-650-5956 Azeem.Khan@uct.ac.zaDr Ben Sebitosi 021-650-5253 Adoniya.Sebitosi@uct.ac.zaProf Pragasen Pillay pillayp@clarkson.edu
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