5715ch3 - 3 Wound Rotor Induction Generators(WRIGs Design...

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3 -1 3 Wound Rotor Induction Generators (WRIGs): Design and Testing 3.1 Introduction . ...................................................................... 3 -1 3.2 Design Specifications — An Example . ............................. 3 -2 3.3 Stator Design . ..................................................................... 3 -3 3.4 Rotor Design. ...................................................................... 3 -8 3.5 Magnetization Current . ................................................... 3 -12 3.6 Reactances and Resistances. ............................................. 3 -16 3.7 Electrical Losses and Efficiency. ...................................... 3 -19 3.8 Testing of WRIGs. ............................................................ 3 -21 3.9 Summary. .......................................................................... 3 -22 References. ................................................................................. 3 -23 3.1 Introduction WRIGs have been built for powers per unit up to 400 megawatt (MW) in pump-storage power plants and down to 4.0 MW per unit in windpower plants. Diesel engine or gas–turbine-driven WRIGs for standby or autonomous operation up to 20 to 40 MW may also be practical to reduce fuel consumption and pollution for variable load. Below 1.5 to 2 MW/unit, WRIGs are not easy to justify in terms of cost per performance against full power rating converter synchronous or cage-rotor induction generator systems. The stator rated voltage increases with power up to 18 to 20 kV (line voltage, root mean squared [RMS]) at 400 mega voltampere (MVA). Due to limitations in voltage, for acceptable cost power con- verters, the rotor rated (maximum) voltage occurring at maximum slip is today about 3.5 to 4.2 kV (line voltage, RMS) with direct current (DC) voltage link alternating current (AC)–AC pulse-width modulated (PWM) converters with integrated gate controlled thyristors (IGCTs). Higher voltage levels are approached and will be available soon for industrial use, based on multiple-level DC voltage link AC–AC converters made of insulated power cells in series and other high-voltage technologies. So far, for the 400 MW WRIGs, the rated rotor current may be in the order of 6500 A, and thus, for S max = ± 0.1, approximately, it would mean 3.6 kV line voltage (RMS) in the rotor. A transformer is necessary to match the 3.6 kV static power converter to the rotor with the 18 kV power source for the stator. The rotor voltage V r is as follows: (3.1) VKS V rr s s =⋅ || max © 2006 by Taylor & Francis Group, LLC
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3 -2 Variable Speed Generators For , V (per phase), V (phase): K rs = 2/1. So, the equivalent turn ratio is decisive in the design. In this case, however, a transformer is required to connect the DC voltage link AC–AC converter to the 18 kV local power grid. For powers in the 1.5 to 4 MW range, low stator voltages are feasible (690 V line voltage, RMS). The same voltage may be chosen as the maximum rotor voltage V r , at maximum slip. For S max = ± 0.25, V, V r = V s , . In this case, the rotor currents are significantly lower than the stator currents. No transformer to match the rotor voltage to the stator voltage is required. Finally, for WRIGs in the 3 to 10 MW range, to be driven by diesel engines, 3000 (3600) rpm, or gas turbines, stator and rotor voltages in the 3.5 to 4.2 kV are feasible. The transformer is again avoided. Once the stator and rotor rated voltages are settled, the design may proceed smoothly. Electromagnetic and thermomechanical designs are needed. In what follows, we will touch on mainly the electromagnetic design.
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5715ch3 - 3 Wound Rotor Induction Generators(WRIGs Design...

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