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Sr. Member
Posts: 95
Reply with quote  #16 
Starting fluting in coupling side bearing:

1x =20,19 Hz. VFD feeding with  40,38 Hz LF.

1xBpfo + harmonics (+/-) 1x starting

Misalignment between motor and pump.

1x + harmonics mountainous peaks to this rpm.

fluting starting.jpg    


Sr. Member
Posts: 1,478
Reply with quote  #17 
In my world, if you have significant Lf or multiples when running on like 42Hz it indicate leaking thru the VFD and that indicate a rectifier problem to me unless the VFD is made very differently than I have seen or you have a vibration from a synch neighboring machine. On the other hand, how much of the 50Hz are seen in the linear scale I am used to? You maybe always have some noise and I never normally see it. Levels are not that hi.  
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
Dave Reynolds

Posts: 39
Reply with quote  #18 
2 cents worth and then some.....

It is my understanding that all motors have shaft voltage/current to ground/circulating thru the rotor, typically the values are low enough as to not damage a bearing. There are acceptable current values per bearing size, voltage to ground, current to ground. A bearing can flute whether in a motor or on a roll in printing press or whether on a vfd or across the line start or soft start, been there seen that...

90+ % of all vfd's made use IGBT to switch the firing frequency at very high rates, the IGBT's can discharge voltages from 1200v to 1900v for an instant such as a lighting strike.

Fluting can come from:
Improper machine to earth ground
Ground wire in jct box needs to be connected at both ends
Distance from vfd to the load affects all vfd's
Large amount of harmonics/electrical noise from vfd
Eccentric rotor/airgap in motor
Segmented rotor laminations
Firing frequency of vfd is above 5khz/excessive drive harmonics
No oil film on motor bearing, this is the insulator to ground
Large thru bolts holding motor laminations together
Insulated shaft gets damaged and leaks to ground
Improper cabling from vfd to motor
Over voltage to motor
Shaft grounding mechanism fails to create a low resistance path to ground
....this list is not meant to be all inclusive

If you want to stop the voltage from getting to the motor, this could be a solution

SKF offers several styles and sizes of insulated bearing with long track record of success

Shaft grounding options

Dave Reynolds
Midlands Reliability & Consulting LLC


Posts: 11
Reply with quote  #19 
I've had good luck using the SKF TKED1 tester to detect electrical discharges. Very simple, and you don't have to touch the machine or shaft. On one new pump we were seeing 21,000 discharges in 10 seconds. The motor lasted less than two months and the elect discharges also jumped the coupling and destroyed the pump bearings.
As far as vibration, I usually look for the haystack at 120-180k cpm or in peakvue.

I'm no electrician, but most of our fluting issues are bad grounds or non-vfd rated cables, especially in new construction.

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Sr. Member
Posts: 95
Reply with quote  #20 
[QUOTE = Dave Reynolds] 2 centavos de valor y luego algo ...

Según tengo entendido, todos los motores tienen voltaje / corriente de eje a tierra / circulan a través del rotor, por lo general, los valores son lo suficientemente bajos como para no dañar un rodamiento. Hay valores de corriente aceptables por tamaño de rodamiento, voltaje a tierra, corriente a tierra. Un rodamiento puede oscilar ya sea en un motor o en un rollo en la imprenta o en un vfd o en el inicio de la línea o el arranque suave, se ha visto que ... más del

90% de todos los vfd utilizados utilizan IGBT para cambiar la frecuencia de disparo a tasas muy altas, los IGBT pueden descargar voltajes de 1200v a 1900v por un instante, como un golpe de luz.

Fluting puede venir de:
máquina inadecuada a tierra
cable de tierra en la caja jct necesita ser conectado en ambos extremos
Distancia desde el VFD a la carga afecta a todos de VFD
cantidad grande de armónicos / ruido eléctrico de VFD
excéntrico rotor / entrehierro en el motor
segmentado laminaciones del rotor
Firing frecuencia de VFD está por encima de 5 kHz / armónicos de accionamiento excesivas
No película de aceite en los cojinetes del motor, este es el aislante a tierra
grande a través de pernos que sujetan laminaciones motor junto
eje aislante se daña y fugas a tierra
cableado incorrecto de VFD a motor
sobre voltaje al motor
de puesta a tierra del eje el mecanismo no crea una ruta de baja resistencia a tierra
... esta lista no pretende ser completa

Si desea evitar que la tensión llegue al motor, esta podría ser una solución
http: //www.coolblue-mhw .com /

SKF ofrece varios estilos y tamaños de rodamientos aislados con un largo historial de éxito

Opciones de conexión a tierra del eje

Dave Reynolds
Midlands Reliability & Consulting LLC

[/ Q UOTE]

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Sr. Member
Posts: 95
Reply with quote  #21 

thanks Reynolds!
Walt Strong

Sr. Member
Posts: 709
Reply with quote  #22 
I will add another shaft current tester (no experience with it) and corrective bearing current brushes:

There is a lot of technical information on that Website.


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Sr. Member
Posts: 902
Reply with quote  #23 
I'll Throw in my two cents as well ;-)

Vendor warning.

Our Take on the shaft grounding ring.

And this has also been a good fix for some applications.

Initially, I think the installation stage and correct grounding is the best method.
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