WIND ENERGY SYSTEMS - Cd3wd
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WIND ENERGY SYSTEMS - Cd3wd

WIND ENERGY SYSTEMS - Cd3wd WIND ENERGY SYSTEMS - Cd3wd

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Chapter 6—Asynchronous Generators 6–25 tization curve. Approximate curves for L m,pu for the two machines are presented in Fig. 13. We see that the inductance is constant for voltages less than about one-half of rated. The inductance then decreases as saturation increases. Figure 13: Per unit magnetizing inductance as a function of load voltage. We see that any detailed analysis is made difficult because of the variability of the machine parameters. Not only must a nonlinear solution technique be used, the solution must be obtained for the allowable range of machine parameters. This requires a great deal of computation, with the results being somewhat uncertain because of possible inadequacy of the machine model and because of inadequate knowledge of the parameter values. We shall leave such detailed analyses to others and turn now to an example of experimental results. Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001

Chapter 6—Asynchronous Generators 6–26 Figure 14 shows the variation of terminal voltage with input mechanical power for the 40-hp machine mentioned earlier. The rated voltage is 230 V line to line or 132.8 V line to neutral. Actual line to neutral voltages vary from 90 to 150 V for the data presented here. Figure 14: Variation of output voltage with input shaft power for various resistive and capacitive loads for a 40-hp self-excited induction generator. All resistance was disconnected from the machine in order to establish oscillation. Once a voltage close to rated value was present the load was reconnected and data collected. Voltage buildup would not occur for speed and capacitance combinations which produce a final voltage of less than 0.8 or 0.9 of rated. For example, with 285 µF of capacitance line to line, the voltage would not build up for speeds below 1600 r/min. At 1600 r/min the voltage would slowly build up over a period of several seconds to a value near rated. The machine could then be operated at speeds down to 1465 r/min, and voltages down to 0.7 of rated before oscillation would cease. Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001

Chapter 6—Asynchronous Generators 6–25<br />

tization curve. Approximate curves for L m,pu for the two machines are presented in Fig. 13.<br />

We see that the inductance is constant for voltages less than about one-half of rated. The<br />

inductance then decreases as saturation increases.<br />

Figure 13: Per unit magnetizing inductance as a function of load voltage.<br />

We see that any detailed analysis is made difficult because of the variability of the machine<br />

parameters. Not only must a nonlinear solution technique be used, the solution must<br />

be obtained for the allowable range of machine parameters. This requires a great deal of<br />

computation, with the results being somewhat uncertain because of possible inadequacy of<br />

the machine model and because of inadequate knowledge of the parameter values. We shall<br />

leave such detailed analyses to others and turn now to an example of experimental results.<br />

Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001

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