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06-27-2013 09:15 AM

High current in small motors

we had received a complaint of HIGH CURRENT in small motors, which are used for agitator application. And motors were getting tripped.

When i visited the site in the first instance i had look into the purity of the supply and confirmed it is ok, and then i measured the current drawing, pf and voltage and concluded there is no issue with motor as a individual component.

The main concern of the customer is motor is running at full load when we took trials on the water, but real substance which is going to come in agitator is 1.14 denser than the water. So motors will definitely run over loaded as the density is more load will be more, and all motors are going get tripped for sure as the SIMCODE relay set exactly for rated current.

Then what i concluded to the agitator manufacturer and customer that there is no issue with the motor, but agitator designer has opted for lower capacity motor, so motor rating needs to be increased.

Now you guys tell me,

1) What could be the reason?
2) Can we work out anything so that without replacing motor, it should take load of 1.15 dense material.
3) How to calculate the which rating motor is suitable for the agitator.
06-27-2013 09:37 PM
Top #2
06-27-2013 09:37 PM
Is that sure motor is designed for 1.0 S.F only. why because most of manufactures offer 1.15 S.F In such cases, setting relay for 1.15 S.F currect can rectify the problem.
06-27-2013 09:56 PM
Top #3
06-27-2013 09:56 PM
Motors were designed for 1.15 only. Let's consider your case only,
if motors were designed for 1 SF, are you sure, replacing this with 1.15
would resolve the issue of tripping, but main issue is motors were running
at full load when trials taken with water (density of water 1). But when
actual product of 1.15 density is put, it would not be suffient (ie: 15
percent increase )......can anyone tell what would be the difference in
motor rating req when material changes from water to denser
06-27-2013 10:50 PM
Top #4
06-27-2013 10:50 PM
Please check with motor manufacturer about suitability motor for 1.25 or 1.20 S.F
Usually designers take more caution to avoid field issues.
06-27-2013 11:21 PM
Top #5
06-27-2013 11:21 PM
Motors were designed for 1.15, and continuous run of motor 24*7 at
1.20 or 1.25 would definitely hamper the life of motor, and more ever
customer would ask for 1 year more than usual warranty period. So I will
not suggest.

Probably what we can do is cutting of the rod which is below the propeler
fan (which is of no function) may reduce the weight of the load intern some
load on motor can be reduced I feel.

But that is also left to the agitator manufacturer design scope.
06-28-2013 08:22 AM
Top #6
06-28-2013 08:22 AM
If a motor is in good electrical and mechanical condition high current is always load related. It is not good practice to run a motor continually in it's service factor. For every 10 degrees you run a motor above its rated temperature you cut the life of the motor in half. I would say that the motors are not large enough to handle the load.

If the motors presently are manufactures with a class "F" insulation system you might consider rewinding them using a class "H" or better still, a class"N" insulation system. It won't make the current levels go down but a higher insulation class will elongate the life of the motor at higher temperatures. If a decision is made to re-manufacture the motors using a class "N" insulation system it is important that the final bonding resin be Class "N" also
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