motor overload functional testing ABB 1

[emadshaaban]

Dear electrical experts..
i need ur help for how to functional test ABB motor overload single phase current generator.is it correct to loop the singlephase over the
three overload poles but the results i got is with larg diffrent with the over load cure.plz help

 

[DTR2011]

You need to supply more information on the ABB overloads. If they are modern units, there is generally some kind of thermal memory. If you test it 1st time, likely you get good results. Subsequent tests likely trip took soon. This is thermal memory in action. Check manual for how to reset thermal memory between tests. Also you may have other function such as current imbalance tripping, rather than overload.

Provide more information about the ABB overload and we can help you in more detail.

 

[emadshaaban]

dear sir
than u for your time
the overload that im testing are normal therminal motor overload.ABB (du 200),(TA16).

 

[emadshaaban]

waiting replies>>>>>>>>>>>>>>>>>>>>

 

[jraef]

Well, we don't know what you did, so it's difficult to comment. Your description is lacking in details.

The TA16 is just their standard bimetal overload relay. It does have phase loss sensitivity, which means it will trip MORE QUICKLY under single phase conditions. So yes, you must loop the current through all 3 phases to test it accurately.

But you said "loop the singlephase over the three overload poles". I don't know what you mean by "loop over". You must loop THROUGH, as in you connect to L1, come out of T1 and back up to L2, out of T2 and back up to L3, then out of L3 to your load simulator. If you just connected the 3 phases in parallel, you split the current flow and you would get high current before it would trip.

The instructions for the overload relay would show this to you by the way.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[emadshaaban]

thank you for your relpy
i already made the connection as u said above.
the problme is all the overload devices that we tested gived un-identical time response compared with the same overload curves.
i heard from someone that i need to multiplay current injectrd by 1.73,cause the curves of overload gives for three phases injection ,where we inject with single phase....is that correct?????

 

[jraef]

No that is not correct. Current is current is current. You are not measuring power. The heater element is a very simplistic thermal device, a bimetal stip that heats up and moves based on the heat created by current flow through it. It does not calculate anything, in fact it doesn't even "care" if it is AC or DC current or what voltage it is (within it's limits of course).

I²t trip curves in electro-mechanical devices like this are a range, not an absolute value, and they are thermally sensitive, meaning the range will not be the same every time because the temperature will not be the same every time. If you want pin point repeatable accuracy, you should change to a solid state OL relay.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[emadshaaban]

thank you sir
you relpy was very helpfull and you analyists was correct.
by the way i found while googling that marge of time results by thearmal bimetel strip is -+20% of curves .was that right?
any way you analysits will help me in my failure report.
please if you have any steps for these test link it for me

 

[DTR2011]

Before you report failures on these devices, check your procedure.

Have you applied ambient temperature correction factors? Have you checked how long it takes after a first test for the overload to regain it's original trip times after testing? These items can significantly affect the outcome of your test results.

I had an experience years ago with similar application. Field techs were reporting huge number of failures of bi-metalic overloads with bad trip times. Something like 80%. Only to find later that proper testing procedure was not carried out. Consider how your test equipment sets the current for example. If it is variac based, all of the searching (ramping) you do to preset the current is causing heat on the overload, prior to any test starting.

 

[emadshaaban]

Thank you very much
Regarding to your reply (smallgreek), some more question produced:
Q1-if there was no different whether I inject with 3ph or 2ph for bi-metallic strip overload, why there are two time curves of 3ph and 2phase (check my attached pic).
Q2- what is the max time region that keep me in warm stat for testing?
Is there a stranded ambient temperature correction factors for Bi-metric strip relies?
Q2-

Have you checked how long it takes after a first test for the overload to regain its original trip times after testing? These items can significantly affect the outcome of your test results.

do you mean cool down time? How can I get it?

 

[jraef]

There is no attached picture.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[emadshaaban]

im sorry here it is>>>>

 

[jraef]

OK, what that is showing you is what is called the "biasing" of the trip curve for a single phase condition.

IEC overloads are, for the most part, required to provide a certain level of protection against the added heating effects of a severe phase imbalance on a 3 phase motor, as most often is manifested as a phase loss. What happens in a phase current imbalance is that it creates what is called "negative sequence current" in the rotor that is flowing in the opposite direction of the main current flow, and thus creating negative torque. So the motor essentially fights itself and uses more of it's curent producing heat than it normally does. So a motor that is not technically over loaded (mechanically) can over heat without exceeding the FLC in any one phase. To prevent that, the IEC bimetal OL rlays have a device called a "differential trip" mechanism. This is essentially a balancing spring so that when the mechanical forces of the bending bimetal stips are equal to the balancing spring, everything is fine. But if one of them is pushing less hard (because there is less current flowing in it), the counter spring in the differential bar allows movement toward the trip point. So if the remaining 2 phases overload even a little, as represented by that dotted line in your chart, it trips. It may appear to be tripping "early", but in reality is it compensating for the added heating effect of a lost phase.


"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[emadshaaban]

Thank you ,this is the first time i know that bi-metalic overload provided with unbalance protection. And the unbalance may not cause overcurrent.
i sill locking for some more question answer if you have some time for me>>
1-is there diffenrt between un-balance and negative sequence?
2-for the mentioned ABB (DU200),if i inject 2 times of Is what is the time range that will indicate that the OL weather good or not?

 

[emadshaaban]

>