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Noknroll

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Reply with quote  #1 
Hi
I had a motor show a spike in trend with 50Hz peak in spectrum, I dont know the exact bearings fitted but assumed a 6209 (got from a chart on another motor manufacturers same size motor) which is also very close to bpfi on a 6 pole motor. As a precaution asked for electricians to run a multi meter over it for any issues and they sent back the figures below. Now, I'm not electrically trained, so to those who are do the numbers look ok?

Voltage phase to neutral
          C/B Line     C/B Load      Contactor Line    Contactor Load
R/N      230 V         230 V              230 V                230 V
W/N     231 V         231 V              231 V                231 V
B/N      231 V         231 V              231 V                231 V
Voltage phase to phase
R/W     401 V        401 V               401 V                401 V
R/B      401 V        401 V               401 V                401 V
W/B     400 V        400 V               400 V                400 V
Current per phase
R 20.1 A
W 19.2 A
B 18.6 A

All terminals are tight.

OLi

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Reply with quote  #2 
B phase current is low bad connect or breaker contacts burned, but voltage is nominal, not consistent maybe, not so hi diff but anyway, what do you say some strange but not dramatic w/o being sparky...
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electricpete

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Reply with quote  #3 
At no-load, induction motor current unbalance can be 5 to 10 or even 20 times as high as the voltage unbalance.
As load increases, the current unbalance tends to decrease. 
I would not worry about those readings, especially if they are uncoupled / unloaded.  

I've never seen 1*LF show up on a motor, although it occasionally gets mentioned in the literature.  As you know, 2*LF is the frequency of the magnetic force created by 1*LF current. 
I'm inclined to suspect another explanation. As you said maybe bearing defect. Or maybe you have a synchronous 2-pole machine nearby.


Danny Harvey

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Reply with quote  #4 
I would say that I have only seen 1 x lf in dc motors. Never in an AC induction motor that I can recall.
OLi

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Reply with quote  #5 
I like to have data at nominal load..... it's like gbx' under 70% load it is not that useful IMHO.
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