Reed frequency

[HamidEle]

We are currently working on 2000HP vertical motor (8 pole) and in the process of selecting VFD. We haven't decided which VFD to choose.

If we choose Rockewell VFD, typical CSI(Current source VFD), we would have to face potential reed frequency resonances excited by VFD output capacitors.

Is there any issue if we choose Voltage Source VFD?

 

[Skogsgurra]

Do not quite understand. "Reed" frequency?

Gunnar Englund

http://www.gke.org

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[flexoprinting]

Hi skogsgurra

I'll be darned I found it here!

http://www.eng-tips.com/viewthread.cfm?qid=171701&page=1

And also here.

http://www.globalspec.com/Industrial-Directory/vibrating_reed_frequency_meter

 

[jraef]

I've never heard of that, but then again, vibration is not my thing. There is a long known issue regarding what is called "cogging" in CSI drives used for low frequency operations. Because of how they alter the frequency, the original CSI drives ended up causing torque pulsations that, at slow speeds, are sometimes even visible. That then could end up becoming a critical frequency problem from a mechanical standpoint, which may be what you are referring to as "reed frequency".

I'm not sure however if that is still true. I'm not in the CSI drive business, but I know there have been advancements in the power system topology that may (or may not) have solved that problem. Mainly, I think they are able to do higher speed switching now because of the advent of IGCTs, instead of the much slower GTO thyristors that were use in the past.


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[Skogsgurra]

There is quite a "mental distance" between the vibrating reed as in a reed frequency meter or the vibrating reed of a saxophone and the "reed frequency" caused by capacitors in a CSI inverter.

The latter is (guessing) an electrical vibration/oscillation while the former are mechanical. That is why I needed to ask.

I have had rather nasty ringing in a system feeding an 800 kW, 690 V fan pump for a paper machine. The ringing was on the 11 kV side and caused by the step current waveform of the CSI triggering resonances between transformer leakage capacitance and cable capacitance.

Three 1200 kVA 11/.69 kV dry resin transformers lived less than two years with this ringing. Ozone production in voids in primary insulation believed to be the failure.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...