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Transcript
The Scaling of Machines for
Renewable Energy Applications
Ramzi Solomon
Energy Postgraduate Conference 2013
Introduction
• Future generation from renewable sources will employ
rotating electrical machines as generators.
• Constant & variable speed generators connected to the
grid at the sub-transmission and distribution level.
• Generator performance and power system stability
studies are of interest.
• Two questions:
1. Can a utility-scale IPP-type synchronous
generator be scaled such that a laboratory-based
equivalent system can be designed?
2. What is the impact of the connection of machines
at the sub-transmission and distribution level on
the national grid?
Project Aims
• This project will scale, design, analyse and
then prototype a micromachine of a wound
cylindrical rotor synchronous generator
typical of many constant speed generator
IPPs.
• A laboratory-based test bench will be
created to quantify the impact of the
integration of IPPs and in particular
renewables on the South African grid.
Project Aims
• Dimensional analysis is the mathematical
method that allows machines and systems
to be down-scaled by establishing laws of
similitude between the original and its
scaled model.
• Conduct detailed testing of several PQ and
grid integration issues on the laboratorybased system.
Different Scaling Methods
Laboratory setup
Defining the design process
Analytical design
5 kVA wound rotor
synchronous generator
Define scaling factors
Optimization
Design 5 kVA using FEA
Analytical pu design of utility-scale
IPP using scaling factors
No
No
Convergence
Convergene
Yes
Yes
Prototype micromachine
Test micromachine
under steady-state
and dynamic conditions
Compare test results to
industrial-size IPP
Acquire dimensions and pu
test data of utility-scale IPP
Machine Design Challenge
• Design a medium-voltage synchronous
machine of the order of 55MW that
replicates the performance of Sasol’s
compressor-driving synchronous motor.
• The rotor is cylindrical.
• The machine is a fully enclosed self-cooled
machine with air-to-water heat
exchangers.
Comparison in machine specification for two
machines
55 MVA
5 kVA
Name
Value
Name
Value
Number of phases
3
Number of phases
3
Real Power P
55 MW
Real Power P
5 kW
Power Factor
1
Power Factor
1
Apparent Power Q
55 MVA
Apparent Power Q
5 kVA
Line to line voltage
11,000 V
Line to line voltage
380 V
Stator current per phase
2919 A
Stator current per phase
7.6 A
Synchronous speed
1500 rpm
Synchronous speed
1500 rpm
Frequency
50 Hz
Frequency
50 Hz
Number of poles
4
Number of poles
4
Number stator slots
36
Number stator slots
36
Slots per pole per phase
3
Slots per pole per phase
3
Sizing Specification
55 MVA
5 kVA
Sizing
Sizing
Stator bore
D=0.796 m
Stator bore
Gross length of machine
L=6.8045 m
Gross length of machine
L=0.1269 m
Specific magnetic
loading
Specific electric loading
Bav=0.54
Specific magnetic loading
Bav=0.4
Ac=45,000
Specific electric loading
Current density
J=3.2
Current density
D=0.12 m
Ac=13000
J=3.4
Power coefficient
Co=255.27
Power coefficient
Co=54.7219
Winding factor
Kw=0.955
Winding factor
Kw=0.9567
Pole pitch
0.0747
Pole pitch
0.0942
Minimum teeth width
0.0226 m
Minimum teeth width
0.0046 m
Permissible slot width
0.0521 m
Permissible slot width
0.0132 m
Conclusion
• Analytically designed two machines, laboratory
machine (5 kVA) and reference design (5 MVA).
• Verifying designs using FEA package, FLUX.
• Establish equivalence between lab and field
machines
• Prototype 5 kVA scaled design
• Test 5 kVA in laboratory under various PQ and
transient conditions
• Use software to predict behaviour under
extrapolated scenario and compare with
prototype.