O/Ls randomly tripping

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milemaker13

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Suburbs of Chicago
I have an oven with 3 starters running various blower motors. For a while now any one (or more) of these o/ls will randomly trip. We have checked amp draws & O/L settings and all seems ok there. The O/Ls have been turned up a little bit but the problem remains the same. Reset and go. Sometimes its every day (primarily early, several minutes after startup), sometimes it doesn't happen for months. We've been chasing this gremlin for over a year now.

Just looking for possible suggestions, similar observations....

These motors all run 480v, small amp draws (1.1, 4 something & 8 or so- sorry I don't have my notebook with me).
 
milemaker13 said:
I have an oven with 3 starters running various blower motors. For a while now any one (or more) of these o/ls will randomly trip. We have checked amp draws & O/L settings and all seems ok there. The O/Ls have been turned up a little bit but the problem remains the same. Reset and go. Sometimes its every day (primarily early, several minutes after startup), sometimes it doesn't happen for months. We've been chasing this gremlin for over a year now.

Just looking for possible suggestions, similar observations....

These motors all run 480v, small amp draws (1.1, 4 something & 8 or so- sorry I don't have my notebook with me).
Click to expand...

You have been suffering with this for over a year. Is the oven older and this problem began a little over a year ago? Or have you experienced the problems with the oven all the time and it was installed a little over a year ago?

The blowers are supply, exhaust, combustion ? Gas fired oven?

Is there a seasonal aspect to the problem? Worse in winter, pulling in fresh air that is cold, denser.

All three blowers have been a problem?


Swanee


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Checking amp draw only tells you what it is drawing at the time you checked.

You about need some sort of recording monitor to know for certain if it is responding to actual overload, or even phase unbalance.

If you swapped overload devices and it still has same problems it likely isn't defect in the overload.

If it is overloaded, even if only occasionally, don't assume the motor has a problem - mechanical problems could very well be what you are looking for.

You mention these are blower motors - are there adjustable dampers in the air stream? The more air the blower is moving the more load it puts on the motor - maybe there is times when damper is wide open and putting additional load on the motor?
 
Presuming motors are 3 phase....if the site has sporadic voltage imbalance, the motors will experience current imbalance with high current on at least one of the legs. Different overload types react to this differently.

A rather small voltage imbalance will result in a larger current imbalance.

Voltage dip can be a problem also.

I concur with the suggestion of a current monitor.
 
The two things that immediately come to mind are voltage imbalances, and old motors with worn bearings that occasionally hit a harmonic or resonance causing the bearings to chatter and the motor to draw more current and overload. Wags of course, but that's what I got...
 
retirede said:
I concur with the suggestion of a current monitor.
Click to expand...
I also agree with the suggestion of a monitoring system.

I work at a 24/7/365 operation and we have had many "phantom" problems that I was able to diagnose with a rather unconventional monitoring system. I used a residential style home camera security system with a DVR to record the events. This allows you to record non electrical events as well as electrical events with a time stamp and you can playback the events.

The cameras have their own lighting system (infrared) so you can mount them inside an enclosure to monitor analog meters connected to CT's to monitor current. I use the split core type so I can insert the CT without disrupting the process. The analog meters do not need a power supply other than the CT's and this makes setting up the system much easier.

The ability to record non electrical events makes it possible to record temperature (bulb style thermometer), humans, process, vibration (via camera focus on a Styrofoam cup filled with water, monitoring waves), along with electrical events. I use cheap analog meters (don't require batteries or power to display).
 
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