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OLi

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I have a few customers including a service company that say they see more VFD related bearing problems lately. I thought that was on the decline but it seems to be popping up again, have the VFD guys invented some new electronics?

Other thing is a couple of larger plants where you find 300Hz in motor vibrations, new record seem to be 22mm/s and, no DC drives at all, only huge amounts of VFD's, and no VFD on the actual motor that drives a pump in one case and a couple of fans in other cases and no, not the same plant, not the same transformer supply...... and no, no soft start either on the victims.
Direct grid connected motors both direct and belt connected things and yes we have 50Hz grid and vibration is 300.00 Hz.
So some filtering of 3 phase full wave rectifiers are failing, how to find them? Current clamp and getting higher level as you get closer? A bit time consuming they say, any other suggestion? No shutting down one at a time is no possible option.


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MarkL

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Reply with quote  #2 
Funnily enough Olov I have noticed a lot more VFD related issues again the last few months, and as you mention electrical type issues on machines that aren't VFD controlled which is really Baffling. I had a few ones lately I was just about to type 'Looks to be Vfd related' til I remembered ...there DOL /Star Delta.

I'm Feeling like we are back in 2006 again.
OLi

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Reply with quote  #3 
Yes, happy days are here again in that way but I wonder what "improvement" they made or if it is age.
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electricpete

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Reply with quote  #4 

6*LF as you know is generated by the ac to dc stage (3 phase full wave rectifier) on the input to a vfd or other electronics.

It might occasionally show on the output of the vfd if there is not good filtering, but it is more likely to affect the input (spikes of current with high 6x harmonic create voltage drop accross supply impedances like transformers, resulting in high 6*LF on the  voltage supply bus).

In a plant with a lot of electronics where 6*LF is showing up on a non-vfd motor, it seems clear the supply voltage is being distorted with a 6*LF component.

Vibe-Rater

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Reply with quote  #5 
Stupid alert here.  6.06x, 4.04, 2.02 x is what electrical line frequency appears at for 6 pole, 4 pole and 2 pole.... isn't it?  The diff being slip?? regardless of where you are.  Australian blenders run faster here in Hawaii. Oli will be able to add history why 50 hertz and US 60 Hz.  I worked on a yacht once and Northern Lights diesel generators made 60 Hz - 1800 rpm for both 115 or 240 volts. mm. This margaritas were faster on the yacht!! And yes I edited. For those that got in very quickly.
OLi

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Reply with quote  #6 
Well there are no reason (and it is 6xLF fore 3-phases no decimals in a diode on the grid, motor speed is another thing)...... just no standard.......    https://en.wikipedia.org/wiki/Utility_frequency
On train system here at 16 2/3 Hz you can't run anything but trains I think and they do the VFD thing anyway these days but they used to be driven by hydropower now it is mostly rotating converters part from 1 static electronic that works sometimes. wiki says 40Hz would be a nice compromise, it would likely give some work,,,,

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