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
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
RE: motor overloads tripping on several motor in New School
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 could be the utility, but it might not be.
RE: motor overloads tripping on several motor in New School
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
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: motor overloads tripping on several motor in New School
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
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: motor overloads tripping on several motor in New School
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
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