Switchboard Vibration

[nildo]

hi guys,

I built a switchboard a while back and it has just been installed and under load it vibrates. I havnt seen this happening but I have been told that it vibrates quite violently. Im not sure about the load that it is suppling but i think it may be a couple of very large variable speed drives. I am having a look at it in 2 days and some help/reasons why this may be happening would be much appreciated.

other info:
3 phase
400 volt
2000amp
suppling 2 switches that are 1000amp and 800amp

 

[rumrunner]

hi guys,

I built a switchboard a while back and it has just been installed and under load it vibrates. I havnt seen this happening but I have been told that it vibrates quite violently. Im not sure about the load that it is suppling but i think it may be a couple of very large variable speed drives. I am having a look at it in 2 days and some help/reasons why this may be happening would be much appreciated.

other info:
3 phase
400 volt
2000amp
suppling 2 switches that are 1000amp and 800amp

hi,
The only time ive seen it is where an Electrician working in a factory thought he had done a super neat job when fitting a new switch under an existing bus bar ,he drilled 4 holes and ran the cables down to the switch ,i was told as an apprentice not to do this and never to have any metal between phases or phase and neutral,due to currents being induced ,after we put it right the vibration stopped ,i dont suppose this is the case in your situation as the fact that your building 2000a switchboards should mean you know about this,and im sure youve done the job correctly,maybee someone else knows another reason for vibration
but ive only come accross it that one time
good luck

 

[tony.towa]

I assume you've used an acb as an incomer, what have you used as outgoers. Is there a main busbar system (vertical or horizontal, and possibly the important one is it a fully rated neutral and earth.

 

[wayne]

i'd say loose connection or youve got "magnetic" problems such as that previously mentioned
keep us informed

 

[wattsup]

I've seen gland plates bent because no slots between big single's. But vibration is a new one on me, perhaps the larry hagman syndrome -

Some common sources of harmonics are
Adjustable Speed Drives
Overcurrent in the neutral, may be the problem.
Possible Remedy: Oversize the neutral conductor, harmonic filters
Harmonics make my head hurt

If it is harmonic probs, you need to sort quickly. Transformers can fail, breakers will burn out (even if you measure load, it will seem ok) The neutral conductor can exceed phase current, and this can mean all frequency goes ape****.

You may get 180hz or even 360hz

 

[tony.towa]

Hi Wattsup,

Harmonics were what I Had in mind, hence the question about the rating of the busbar. Quite often a half rated neutral busbar and high harmonics will create a sustancial vibration under extreme circumstances.

If this is the cause of the problem I agree with you 100% it HAS to be sorted out fast as it if obvious that the harmonic effect is creating a "load" greater than the rated capability of the busbar.

 

[wattsup]

Hi Tony, I'm no expert at all but I've heard it discussed a few times with the powers that be. I was off that day at college when they did harmonics -

 

[wayne]

ive just started understanding it( harmonics)from the 17th
also could be a faulty switch ..but thats an easy spot

 

[tony.towa]

From his entry Nildo was supposed to have been seeing the switchboard two days ago. From the fact he has not come back with more information it may well be that there was a simple explanation and the problem is now resolved.

 

[wattsup]

Perhaps the busbar was humming cos it didn't know the words...
God I'm bored, and Wednesday got beat 6-0, where's the rope?

 

[wayne]

From his entry Nildo was supposed to have been seeing the switchboard two days ago. From the fact he has not come back with more information it may well be that there was a simple explanation and the problem is now resolved.

yeah and the insurance is now involved!!

 

[WarrenG]

I would have gone for loose connections, slightest margin could make a big difference with those loads.

How well balanced are these loads? Large loads starting up equipment on one phase might not go down to well with big in rush?

 

[tony.towa]

Hopefully it was a simple problem but normally loose conections produce a severe buzzing rather than a vibration. Whether this description from the customer was accurate we still have to learn however variable speed drives are renowned for creating harmonics and often if they have internal filters they only go as far as the thirteenth.

This looks like one of those questions we will never know the answer to, unless we read it in the paper!!!!