high vibration starting high voltage motor

dear all

i face with high vibration  when starting free run test high voltage electro motor.by starting the motor vibration rise rapidly then trip the motor. to evaluate vibration at nominal speed we have to rise setting of trip protection  temporarily . after that motor work at low vibration (1x) at nominal speed(3000).we have this problem on three same motor in site. what does comes high vibration at starting ?i think we have structural weakness and resonance ,   any opinion will be appreciated.

 

beast regard 

Original Post
John from PA posted:

Can you post any transient data, preferably a shutdown?

Also, your words "free run"...what if anything are you doing to compensate for the unbalance caused by the keyway of the motor?

dear john

the motor is new. i dont have history data. high vibration dont let us to record data, so the motor trip after 3 or 4 second.but after bypass the protection system(by rise up the trip setting)motor reach to nominal speed by 1x low vibration.

we dont have any correction maintenance on it.

aziz58 posted:
John from PA posted:

Can you post any transient data, preferably a shutdown?

Also, your words "free run"...what if anything are you doing to compensate for the unbalance caused by the keyway of the motor?

dear john

the motor is new. i dont have history data. high vibration dont let us to record data, so the motor trip after 3 or 4 second.but after bypass the protection system(by rise up the trip setting)motor reach to nominal speed by 1x low vibration.

we dont have any correction maintenance on it.

Why can't you have the vibration equipment on the machine, and when it trips you capture the shutdown?

If by "we don't have any correction maintenance on it" you mean you are doing nothing to compensate for the missing material due to the keyway, then that may be a big part of your problem.  Get some form of fitted key in place held by a dummy hub or a coupling half.

John from PA posted:
aziz58 posted:
John from PA posted:

Can you post any transient data, preferably a shutdown?

Also, your words "free run"...what if anything are you doing to compensate for the unbalance caused by the keyway of the motor?

dear john

the motor is new. i dont have history data. high vibration dont let us to record data, so the motor trip after 3 or 4 second.but after bypass the protection system(by rise up the trip setting)motor reach to nominal speed by 1x low vibration.

we dont have any correction maintenance on it.

Why can't you have the vibration equipment on the machine, and when it trips you capture the shutdown?

If by "we don't have any correction maintenance on it" you mean you are doing nothing to compensate for the missing material due to the keyway, then that may be a big part of your problem.  Get some form of fitted key in place held by a dummy hub or a coupling half.

dear john

you mean because of missing material we have high vibration? but we should doing field balanc...

abbas1970 posted:

Can you measure at which speed you get the highest peak   i understand that before reaching 3000 rpm you face the high vibration.

dear abbas

after starting ,vibration rise immediately and rapidly  .so because of high vibration protection system trip the motor . but we cant have enough time to record data. so we have to change and increase trip setting in order to reach 3000 rpm. after that we can measure vibration at 3000 rpm. we find 1x by low amplitude

aziz58 posted:
dear john

you mean because of missing material we have high vibration? but we should doing field balanc...

When motors are manufactured, the rotor is balanced with the missing material in the keyseat area replaced by a "dummy" keyway.  Often the weight of this missing material is very carefully calculated and the amount used is carefully matched.

When you test a motor in a solo condition you have to replace the missing material.  This is often done by using the final fitted key and coupling hub to hold it in place.  If you don't do this the motor is essentially out of balance but if it passes through the 1st flexural mode (a possibility with a large motor) then it may enter a region of speed where it "self" balances.  The behavior, without the dummy" key, is high vibration up to the critical, then the rotor may operate at a lower level after passing through the critical.  You need to identify where the flexural mode may be; this is the reason why I asked if you can acquire shutdown transient data, something like a polar plot or bode plot.

You should examine some past threads that have similar discussion:

http://www.maintenance.org/topic/solo-run-motor

http://www.maintenance.org/top...tical-motor-solo-run 

Another good resource is at https://www.industry.usa.sieme...r-vibration-prob.pdf.  Check the paragraph on page 7 of 16, left column, specifically the paragraph just above the words "Thermal Unbalance".

 

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