The Scaling of Machines for Renewable Energy ApplicationsRamzi 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 laboratory-based system.
Different Scaling Methods
Laboratory setup
Defining the design process
Analytical design 5 kVA wound rotor
synchronous generator
Optimization
Design 5 kVA using FEA
Prototype micromachine
Convergence
Test micromachineunder steady-state
and dynamic conditions
Define scaling factors
Analytical pu design of utility-scaleIPP using scaling factors
Yes
No
Compare test results to industrial-size IPP
Convergene
Acquire dimensions and putest data of utility-scale IPP
Yes
No
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
Name Value
Number of phases 3
Real Power P 5 kW
Power Factor 1
Apparent Power Q 5 kVA
Line to line voltage 380 V
Stator current per phase
7.6 A
Synchronous speed 1500 rpm
Frequency 50 Hz
Number of poles 4
Number stator slots 36
Slots per pole per phase
3
Name Value
Number of phases 3
Real Power P 55 MW
Power Factor 1
Apparent Power Q 55 MVA
Line to line voltage 11,000 V
Stator current per phase
2919 A
Synchronous speed 1500 rpm
Frequency 50 Hz
Number of poles 4
Number stator slots 36
Slots per pole per phase
3
55 MVA 5 kVA
Sizing SpecificationSizing
Stator bore D=0.796 m
Gross length of machine
L=6.8045 m
Specific magnetic loading
Bav=0.54
Specific electric loading
Ac=45,000
Current density J=3.2
Power coefficient Co=255.27
Winding factor Kw=0.955
Pole pitch 0.0747
Minimum teeth width 0.0226 m
Permissible slot width 0.0521 m
Sizing
Stator bore D=0.12 m
Gross length of machine
L=0.1269 m
Specific magnetic loading
Bav=0.4
Specific electric loading
Ac=13000
Current density J=3.4
Power coefficient Co=54.7219
Winding factor Kw=0.9567
Pole pitch 0.0942
Minimum teeth width 0.0046 m
Permissible slot width 0.0132 m
55 MVA 5 kVA
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.
