Resistive loading

In order to extract maximum power from an electrical machine it is necessary to make the external load resistance equal to the internal resistance. Because the inductance of this machine is comparatively low, this can be achieved by attaching a load equal to the coil resistance, just over 16 Ohms, to the phase terminals.

Figure 5.36 shows a comparison of the experimental and predicted voltages of all three phases when the machine is connected to three 17 Ohm resistors in a star configuration. The general correlation between the two plots is good, with the three phase shape being accurately predicted.

Figure 5.36: Comparison predicted and experimental voltages for a 17 Ohm load
Figure 5.37: Varying voltage peaks

Figure 5.37 shows an enlarged section of the voltage waveforms and highlights the change in amplitude between the consecutive peaks of velocity. Consider the predicted waveform for the yellow phase (shown in ♦). In the first cycle, between t = 0 and t =

1.5 s, the peak is only 80 Volts, yet in the second cycle, for t above 1.5, it reaches nearly 100 Volts. The blue and red phases, however, peak at around 95 Volts in the first cycle and 85 Volts in the second. Two effects are apparent: firstly all the phases alternate between higher and lower maximum values in consecutive cycles. Secondly the blue and red phases are closely related and have a larger maximum whilst the yellow phase has a lower peak. The effect is exaggerated in the predicted results, but also present in the experimental. It is a result of the unbalanced mutual inductances between the coils.

Comparison of the results gives an error on the prediction of ± 6%.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

Get My Free Ebook

Post a comment