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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.