1. The Scaling of Machines for Renewable Energy Applications Ramzi Solomon Energy Postgraduate Conference 2013

2. 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?

3. 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.

4. 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.

5. Different Scaling Methods

6. Laboratory setup

7. Defining the design process Analytical design 5 kVA wound rotor synchronous generator Optimization Design 5 kVA using FEA Prototype micromachine Convergence Test micromachine under steady-state and dynamic conditions Define scaling factors Analytical pu design of utility-scale IPP using scaling factors Yes No Compare test results to industrial-size IPP Convergene Acquire dimensions and pu test data of utility-scale IPP Yes No

8. 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.

9. Comparison in machine specification for two machines NameValue Number of phases3 Real Power P5 kW Power Factor1 Apparent Power Q5 kVA Line to line voltage380 V Stator current per phase7.6 A Synchronous speed1500 rpm Frequency50 Hz Number of poles4 Number stator slots36 Slots per pole per phase3 NameValue Number of phases3 Real Power P55 MW Power Factor1 Apparent Power Q55 MVA Line to line voltage11,000 V Stator current per phase2919 A Synchronous speed1500 rpm Frequency50 Hz Number of poles4 Number stator slots36 Slots per pole per phase3 55 MVA5 kVA

10. Sizing Specification Sizing Stator boreD=0.796 m Gross length of machineL=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 width0.0226 m Permissible slot width0.0521 m Sizing Stator boreD=0.12 m Gross length of machineL=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 width0.0046 m Permissible slot width0.0132 m 55 MVA5 kVA

11. 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.