Three-Phase versus Single Phase Alternators

[Hans Sinkovec]

Good morning,

I have checked into sound curves, some certified by licensed laboratories, and found little difference in noise levels between single-phase and three-phase alternators employing virtually identical test methodologies.

On this forum I have read that the Hummer turbines (size not given, too bad) are terribly
noisy because they are single-phase and not three-phase.

If anyone has an accurate and technically sound explanation for the difference in noise
production between the two technologies, please explain.

Real world experiences are anecdotal and therefore subjective, to say the least. Unless identical conditions are created in a laboratory setting, caution is advised. No two turbine installations out in the field are ever the same and meaningful test data for a fair noise comparison are virtually impossible to obtain.

Different methods may be employed to obtain the same or similar effect. What matters in the end are measurable, reproducible results employing the scientific method. When noise data obtained in this way show no significant difference between single-phase and three-phase alternators, lambasting one methodology over another is not helpful.

Hans

[Cor van Houtum]

just listen to the end of this film
here it is just a little noisy
this is because it is producing almost nothing
but when you program the inverter to get real power from the generator
it will sound like a sick wolf

http://youtu.be/fjaxgBjDf-g

[Rob Beckers]

Hans, there is a technical explanation why 3-phase can be quieter vs. single-phase: A 3-phase alternator puts the same load on the rotor all the time, while a single-phase alternator has a variable load (more-less-more-less etc.).

That's not the whole story though. There are many causes for sound from a wind turbine. A major one are the blade tips. High TSR (tip-speed-ratio) turbines haul those tips around at many hundreds of km/h, and any deviation of laminar flow will cause 'disturbed' air, and that's sound.

Another big source of noise with almost all small turbines is in the way the current from the alternator is rectified: A regular (passive) diode bridge rectifier with capacitors on the DC side will only pass current when the AC Voltage exceeds the DC Voltage, and that happens in very short, very high current 'spikes' as the rotor turns around. During these current spikes the alternator in effect "puts the brakes on", there's a high mechanical load on it, while between the spikes it free-wheels. So, these current spikes translate to mechanical spikes in the alternator, which translates in load spikes on the rotor, and that generates noise. It's the typical "whining" noise you hear many small turbines make, usually very obvious.

The Scirocco turbine used a mechanical low-pass filter inside the alternator to mechanically dampen those load spikes, so they would not feed back to the rotor. That worked very well, but had it own set of issues.

So, it may well be that a single-phase wind turbine is quieter than a 3-phase one. It depends on many more factors than the alternator.

-RoB-