Sorry about the delay in my response. I have attached another set of plots for your consideration. These plots come from Bently Nevada’s Adapt.Wind software. The measurement parameters are not configurable by the end user. I have two sets of plots that include the Envelope Spectrum, Asynchronous Time Waveform (320 ms), Spectrum of the 320 ms time waveform, and a Synchronous Time Waveform (3 revolutions). The vibration data is sorted by “Mode” which corresponds to output of the generator. In this document, the first plots (Figures 1 – 4) are from Mode 3 operation (55 – 70% maximum power). The second set of plots (Figures 5 – 8) are from Mode 4 operation (70 – 85% maximum power). You can see the Mode designation in the upper right-hand corner of the plots.
Nothing really new here, although I am seeing the same behavior on the Upwind Main Bearing as well. I’m not sure if this indicates that the issue is “real” or if it has to do with the Enveloping spectrum. One item that was brought up to me was that wind turbines use a DFIG (Double Fed Induction Generator).
The engineer that told me about this suggested that the “chopping frequency” associated with the DFIG convertor may be affecting the envelope measurements. However, I’m not sure that the converter on the generator would affect the Main Bearings (at the other end of the machine) and not the generator or gearbox measurements.
Eletricpete – “…Could in theory be that your TWF envelope varies at 1x even though the contents of that envelope is broadband. Let's say you had a rub for approx 1 sec every time a piece (may one particular blade) passed a certain particular location. You have a one second burst of random TWF every 4 seconds (for 15 rpm). The envelope would be full of 15rpm harmonics.”
I thought you were onto something here as the timewaveform in Figure 2 shows the behavior you describe (a burst of energy for part of the time record). However, the timewaveform in Figure 6 does not have this same behavior, but the Envelope Spectrums (Figure 1 and Figure 5) are similar.
Beatnik – “…I'd also love to see your peakvue and normal TWF.
Often on very slow machines it's hard to see 1x impact in the traditional waveform, but if you see 1x impact in peakvue and it's spectrum, there might be a problem that we associate with 1x impact. Looseness in the bearing, cracked shaft, loose tapper, bad coupling etc.”
The “normal” waveforms are shown in Figures 2, 4, 6 and 8. No Peakvue though.
Vibe-Rater – You are right, wind turbines are complicated beasts. Most of the ones I look at have a single planetary stage and two parallel stages. However, I have seen some double planetary stage machines. We are working in Orders, but it can be difficult sometimes to figure out what shaft the software is assigning “X” to in any given plot. Thank you for the recognition of my Cat IV!