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motor overloads tripping on several motor in New School

motor overloads tripping on several motor in New School

motor overloads tripping on several motor in New School

(OP)
We've been having some problems with several motor overloads tripping out at a new elementary school. We are monitoring on of the motors the overload is a square D motor logic solid stat overload relay (SSOLR) that's adjustable. It also has the ability to trip on a current imbalance or phase lose. The current imbalance has to be + or – 25% of the average within 3 seconds and it will work on lightly loaded motors down to 75% of the minimum trip adjustment.

I believe the problem is a current imbalance from the utility

Using a Hioki 3196 we are not getting any events captured when the unit shuts down. But I don't have the current imbalance set up to trigger. (I changed that today) because at no load it sees a huge fake imbalance.

We looked outside the buildings and found voltage regulators less then a mile away hooked on two of the three phases. The amperage is higher on A and C phase and lower on B. Typical 10.6, 9, 11. We also experience a voltage imbalance at or above 3 % occasionally I understand a general rule of thumb is current imbalance can be 6 times the voltage imbalance. The real math is dependent on a lot of factors including slip.

I'd really like to know how the voltage regulators can affect current and voltage imbalance and if this is a utility problem.

Any information needed please let me know I have the meter setup file and readings.
 
The meter setup file that tells what the triggers are set at is attached

RE: motor overloads tripping on several motor in New School

The utility cannot cause current imbalance at your location. That can only come from the load itself.

However, the utility can be responsible for voltage imbalance (which is an indirect cause of current imbalance on their system).

The solution is to measure the 3 phase voltages at your load. It's not likely to be something that varies too much unless they're doing switching on the distribution system.

RE: motor overloads tripping on several motor in New School

It's quite possible that the voltage imbalance is being cause by the local system and not the utility.  These facilities typically have a lot of single-phase loads.  If the contractor did not properly balance the loads in the panelboards and switchboards, the phase imbalance can create voltage imbalance due to voltage drop across the service transformer.  

It could be the utility, but it might not be.  

RE: motor overloads tripping on several motor in New School

I would start with the basics. Check that all relays are set properly and they are tested.

10.6, 9 and 11 amps and 3% voltage variation does not appear out of ordinary nor can it be a cause for the trips.

It is possible that you indeed have single phasing events (since several motors are involved). You have not posted any useful information. I would suggest you get some experienced electrical engineer on the site.

The posted PQ monitoring data seems pretty useless at this point. I would keep an open mind and gather facts and analyze rather than trying to prove a hunch.

Rafiq Bulsara
http://www.srengineersct.com

RE: motor overloads tripping on several motor in New School

Just FYI, this has been a frequent problem plaguing the Sq. D Motor Logic SSOL, because the Imbalance trip feature cannot be disabled. They solved the problem a few years ago by offering a "special" version of it which does not have the Current Imbalance trip. But it is disabled at the factory, you cannot do it in the field. We discussed this here once before a few years ago.


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RE: motor overloads tripping on several motor in New School

Previous discussion, we got into the Motor Logic SSOL towards the end.
thread237-196453: Fuses blowing in the wind...

Now that I re-read it, it may be the same issue you are experiencing. That unit does not need to see an overload condition to trip on unbalance, because it is assuming the added heating effect of an unbalanced current and biasing the thermal model to trip earlier / lower than you would otherwise expect. A laudable feature, but not if it causes nuisance trips, which a LOT of people have complained about in the field. So much so, that Sq. D started using the "no imbalance" versions in their own Pumping Plant Panels now, as explained in this bulletin

 


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RE: motor overloads tripping on several motor in New School

You also said that you saw voltage regulators on 2 phases of the supply system.  This is not the norm.  Some utilities will put regulators on a 3 phase rack, all at the same location.  Others will put a single phase regulator on different poles along the line, so make sure you did not miss one.

Otherwise I agree that the utility does not supply a current imbalance.....utilities supply voltage that might be unbalanced to the point of causing problems, but most likely not.  Customers create/draw the current.

Alan

RE: motor overloads tripping on several motor in New School

I'm on board with jraef.  Those things are too prone to false tripping.  It's a horrible problem when you're saddled with it.  You show up and everything is fine. Two days later you get called again. You return, reset and can not do anything but note that the voltages are imbalanced more than you'd like. But it works fine, you leave.. two days later. Step-an-repeat.

They missed the point that a lot of times facilities just do not have balanced voltages and there's nothing you're going to be able to reasonably do about it.

If you want to risk designing one of these in you need to go to the site and make sure the phase voltages are fairly close to each other.  If they're not, don't bother with a SeriouslySuckyOverLoad Relay.

Keith Cress
kcress - http://www.flaminsystems.com

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