Soft Start- Noise

[littleriver]

I have a Motortronics 500hp soft start.The unit has been in service for 5 years.When starting the unit it has always made a humming noise for about the first 5 seconds.Recently this noise has gotten much louder.The unit appears to still be working.Ramp time is 10 seconds,60%intial voltage,200% intial current,400%max current.Output current and voltage are balanced when up to speed and also when under load.The unit does not make noise during operation only starting.
Iam looking for ideas on where to look for cause.

 

[sreid]

Acoustic noise always has some mechanical source. Loose transformer lamination? Steel cable raceway?

 

[blutfort]

Does the soft start have a bypass? If so does the noise stop after the bypass engages.
Is the duration of the noise related to temperature? is something loose when at room temperature, but as bypass heats up from current flowing through it it "tightens" up?
Is it a buzzing noise-two things rattling together?
Or is it an electrical hum? 60/50 hz type sound?

None of these will specifically solve your problem, but they might help you see the forest for the trees. Or however that old saying goes..

 

[littleriver]

Thank you for response. The drive does not have a bypass.Temperature does not appear to make a difference.
It is not a rattling noise,more like a loud humming.The noise only occurs in the first 5 seconds of start when the current is the highest.The application is on a hog grinder.
while grinding when the current goes up and down,sometimes as high as a 1000 amps the noise does not happen.

 

[dpc]

You might look at the SCR and heat sink assemblies and make sure things are snug. Noise is occurring a lot of chopping is going on. I'd also check the main connections into and out of the starter for tightness. All the usual suspects. There are a lot of high frequency components during starting that can cause vibrations that would not be present during normal running.

 

[blutfort]

I'm going to guess that this related to the current ripple that occurs when switching at line frequency.
I'm really just guessing at this point but other things to look at:
If you haven't changed the programming of the soft start recently, do you have any sort of PM records on motor current vs. time at startup.
If the startup is limiting the current at startup to no more than 400% is the soft start needing to stay in one of the harmonic switching frequencies longer than it used to?
Have you verified the program hasn't been changed? Curious fingers or loss of memory in the eeproms.

Good Luck!

 

[itsmoked]

I would turn off all power, uncover the unit, and tighten every nut and screw. If it is a semiconductor hold down that is getting loose imminent failure is on the way if not found soon.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[DickDV]

If none of the mechanical suggestions produce results, you might want to check to see that all the SCR's are firing properly during the noisy phase.

There is a small chance that the problem is electrical rather than mechanical.

 

[jraef]

I used to work for them, I know the product well. You must have an XLD correct?

Is it a "static" like sound, or a mechanical rattle?

 

[littleriver]

Sorry for my late reply.I was called away on another problem.The unit is a BXLD-718-N. The noise is not a mechanical rattle. The best description is a loud hum something like an overloaded breaker. The unit will make the noise for a second on a bog down during grinding,but for the most part the sound happens during starting.

 

[DickDV]

I don't think its a problem. The unit is responding to high current but a little noise doesn't necessarily mean anything is wrong.

 

[jraef]

DickDV is right. It will hum quite a bit when pumping out that much current. Understand that even at the lowest setting of 200% current limit, that's over 1400A! Lots of magnetic field strength there my friend. Even cables will make noise.

 

[itsmoked]

DickDV, jraef; Then why would it recently get MUCH LOUDER without something changing?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Whoops sorry, missed the part about it recently getting louder. Still, with a unit that size there are a lot of magnetic forces.

Motortronics mounts the SCR stacks off of the back panel using glastic isolators, referred to as "apples", which can get loose over time. It's quite a job to get at them to tighten them though, it involves both removing the stack and removing the back panel.

It would be prudent to just go around and double check tightness of all of the bolts you can see. Be careful of the ones holding the stacks together on the SCRs though, they are critical and if overtightened you can damage the SCRs themselves. They have specific tightening requirements that must be followed to the letter. Before enbarking on that, check the resistance across each stack (power off of course). They will all be high, but if one is extremely different (lower) from the others, it may be getting loose. But before tightening them, get instructions from Motortronics based on your serial number because over the years they have changed the clamp design on that stack and some of them are done by numbers of turns, others have a gauge built in.

Also check the compression lugs on your line and load leads as well while you're at it, they tend to loosen over time.