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Motor Problem
2

Motor Problem

Motor Problem

(OP)
I have Siemens make 150hp (164FLA), 460V motor (IEEE-841, premium efficiency) is causing main HMCP to trip on start-up. PdMA results shows all OK (PI-10; DDA-1.9; Average Phase resistance & inductance 0.0635ohm, 2.008mH)
Inst. Breaker set at 13*FLA. No problem with cable or starter.
Is motor resistance too low (0.0635ohm) or look for other parameter?  
 

RE: Motor Problem

Motor resistance has very little to do with the current drawn.

Premium efficiency, hmmm.  You can go higher than 1300% for that one.

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RE: Motor Problem

... provided you have done the coordination calcs etc.

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RE: Motor Problem

NEC allows you to go up to 1300% FLA if you have trips on standard motor and up to 1700% FLA if you have trips on an energy efficient motor.  Again providing you have evaluated coordination and protection.

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RE: Motor Problem

(OP)
As per manufacturer, LRA-1085.
Instantaneous trip at breaker is already set to maximum, cannot go above what code allows.
 

RE: Motor Problem

It is a rare motor problem that will trip a properly set instantaneous.  You would likely see a hard ground fault or a big imbalance on your resistance and inductance.   Given your low setting imo, setting is the absolute first thing to look at unless you have something in your test data a little more significant than "low resistance".

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RE: Motor Problem

Quote:

Instantaneous trip at breaker is already set to maximum, cannot go above what code allows.
Are we talking NEC code here?  If so, again max setting is 1700% FLA for your high efficient motor.

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RE: Motor Problem

(OP)
From PdMA test, the %age imbalance in resistance & inductance are 0.78% & 3.65%.......Looks like OK to me.

Also please help me under stand why high efficiency motors will have high inrush as compared to normal motor. My thoughts were other way around.
 

RE: Motor Problem

See also NEC 430.52(c)3 - Exception 1  

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RE: Motor Problem

pete - nice danfoss article. In a way, OP is right in asking the low winding resistance is the causing the trip.

JatTiw - What is the load ? I'm wondering if a starting resistor in series with the stator for the first few cycles of the start woll solve this problem.

Muthu
www.edison.co.in

RE: Motor Problem

(OP)
Application is for centrifuge pump in refinery.

Electricpete & Edison123 thanks your support & shedding light on the issue.

Best Regards
 

RE: Motor Problem

Quote:

OP is right in asking the low winding resistance is the causing the trip.
X/R ratio has a role.  R includes contributions from stator and rotor but we cannot measure the rotor resistance using pdma. The response of breaker instantaneous to that setting is a little bit obscure (does it respond to true peak, rms of the first half cycle.. how does the time delay damper affect it).  In the end selecting a high enough  instantaneous settings to avoid trip ends up being very empirical (experienced based) rather than a precise calc  (that's why NEC gives us more than one number and tells us to bump it up only if we get trips, rather than giving a recipe to calculate the setting required to prevent trips that everyone would love to have).   So the bottom line, I don't think we can realistically look at pdma data and make any prediction about instantaneous trip behavior.

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RE: Motor Problem

what's it driving? did it not always do this? New installation?

RE: Motor Problem

Driven load cannot really have anything to do with an instantaneous trip.   It is a function of the motor and the protection, not the load.

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