Previous in Forum: Why and When We Need NGR / NER?   Next in Forum: Electrical Question -ELCB
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
11 comments
Rate Comments: Nested
Ritz11
Active Contributor

Join Date: Jul 2013
Posts: 11

Motor Lug Burnt, but Drive Didn't Trip

07/25/2013 8:01 AM

Dear friends, it has been observed that one motor was getting heated since few days. Druing shutdown we have opened motor terminal box and found that out of 6-leads coming from motor one lead is totally burnt. This motor is running with VVVF drive. Now the question is that why drive didn't tripped. Motor rating is 3 ph200 KW, 415V AC and drive used for that is ACS-800.

Also suggest that which parameters i have to check so that in future same thing will be protected.
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
4
PWSlack
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#1

Re: Motor lug burnt but Drive didn't tripped

07/25/2013 8:10 AM

One possibility for the damage is that the lug wasn't attached to the cable correctly.

Another is that the lug terminal wasn't tightened-up correctly.

As to why it didn't trip, well, that can only be because the current being drawn was lower than the trip setting in the motor overload facility.

__________________
 "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 4)
Go to Next Good Answer
2
NotUrOrdinaryJoe
Guru
Popular Science - Cosmology - New Member Technical Fields - Technical Writing - New Member Engineering Fields - Energy Engineering - New Member Engineering Fields - Electrical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Electromechanical Engineering - Old Member, New Association

Join Date: Apr 2008
Location: Lexington, KY
Posts: 1639
Good Answers: 73
#2

Re: Motor lug burnt but Drive didn't tripped

07/25/2013 8:24 AM

PW is right again. The majority of variable frequency drives have internal fault diagnostics that will indicate a problem before damage occurs. But if the settings for the motor size are not set, then it may operate under the assumption that you are using the largest motor it can drive.

Something else you will want to investigate is this: Has someone been resetting the drive without informing you that a problem was repeating? It happens quite frequently, especially when pressure is applied by management to produce results. Ultimately, if information is not being passed upstream, you may have to protect your investment in these costly motors by investing in an infrared camera to find these hot spots before your wiring is damaged.

I like to tell people that there is no such thing as an electrical failure. All failures are some kind of mechanical deterioration, usually found at connections or inside something with moving parts (like a switch). After all, the electrons are willing, but we usually keep the voltage low enough that they can't jump gaps. Thank goodness for that!

__________________
 A great troubleshooting tip...."When you eliminate the impossible, whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle
Register to Reply Good Answer (Score 2)
Go to Next Good Answer
2
JRaef
Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 4665
Good Answers: 804
#3

Re: Motor Lug Burnt But Drive Didn't Trip

07/25/2013 10:49 AM

Even if the parameters are correct, a high resistance in the connection combined with a light load on the motor may have left the total current through that connection lower than the threshold to trip. But given the size of the motor, you could have had up to and even slightly more than 400A passing through that bad connection, and the drive would have deemed that acceptable. So if the motor is only drawing 200A for the load, but that bad connection is making that phase draw 400A, the additional 200A of purely resistive heating energy can do a lot of damage, yet is still less than the motor overload trip pickup point, usually 125% of FLA.

Many VFDs do not provide output phase imbalance protection, because the drive CONTROLS the output voltage and current, so the only possibility of there being a phase current imbalance outside of the motor winding going to ground (which becomes detectable as a ground fault), is this one scenario, which they would consider an installation error.

Others, and I believe ABB may be one of them, give a fault that says something vague like "Connection Error", because it cannot discern the CAUSE, only the effect. But when operators see that error, they say to themselves something like "Well, I didn't make any changes to the connections, so the drive must be goofy!". They then reset it, as mentioned previously, and get on with production. You will be able to see those faults in the fault record inside the VFD though.

__________________
 ** All I every really wanted to be, was... A LUMBERJACK!.**
Register to Reply Good Answer (Score 2)
No more Good Answers. Go to first "Almost" Good Answer
4wsilver
Power-User

Join Date: May 2013
Posts: 351
Good Answers: 22
#5
In reply to #3

Re: Motor Lug Burnt But Drive Didn't Trip

07/26/2013 9:35 AM

A bad connection, that can cause heating of the connection point, may not cause a drive fault until the joint is nearly to the failure point. This is due to resistance at that point being enough to cause localized heating, may not affect the phase balance enough to offset the current enough to be recognized. The total reactance of the phases will determine the current the motor draws, and while the resistance of a bad connection can cause damage, it is difficult to determine because the resistance is still a small portion of the overall reactance. The settings need to be reviewed and can probably be improved, but this type of failure is not uncommon with normal settings. The biggest thing to look at is the settings for phase inbalance. The setting should be just slightly above what the motor normally runs. The other things that have to be accounted for are the imbalance in the incoming line voltages. While it should have been possible to detect the connection problem, the settings for this are tricky.
Register to Reply
Munawar Hussain
Participant

Join Date: Jun 2013
Posts: 2
#4

Re: Motor Lug Burnt But Drive Didn't Trip

07/26/2013 8:27 AM

The motor overload is big instead of your motor load.Therefore use a proper overload for motor protection.
Register to Reply Score 1 for Good Answer
No more "Almost" Good Answers.
1capybara
Power-User
Engineering Fields - Electrical Engineering - New Member Engineering Fields - Power Engineering - New Member

Join Date: Mar 2012
Location: the sandbox
Posts: 341
Good Answers: 6
#11
In reply to #4

Re: Motor Lug Burnt But Drive Didn't Trip

08/11/2013 7:20 AM

Correct! Motor overloads wrong sized. Also, you can retrofit phase imblance relays, fabricating them if necessary using comparators.

__________________
 BSEE but always learning
Register to Reply
dhayanandhan
Guru
Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2008
Location: CHENNAI, TAMIL NADU, INDIA.
Posts: 1851
Good Answers: 65
#6

Re: Motor Lug Burnt, but Drive Didn't Trip

07/27/2013 12:15 PM

Dear Mr. Ritz11,

It is possible that motor is running on 2 Phase only. Hence it will not trip as long as the relay set value is NOT EXCEEDED.

DHAYANANDHAN.S
Register to Reply
Aghvel Niazi
Power-User

Join Date: Mar 2010
Location: Islamic Republic of Pakistan
Posts: 124
Good Answers: 14
#7

Re: Motor Lug Burnt, but Drive Didn't Trip

07/27/2013 1:28 PM

For Bearing change we decoupled 0.37 kW, 400 V, 50 Hz Induction motor driven by VFD (SEW) in Weigh Feeder application.

When we connect the motor after bearing change, Drive trips on Fault " Drive not Ready"

When the fault is being reset, on start command, Drive run for not more than 2 to 3 second and then trip with the above mentioned fault.

When we check the connection inside the Terminal box, One lug was broken.

VFD there used was SEW.

Any one having experience related to such type of situation (missing / faulty Phase) with ACS-800 or any other VFD ?????
Register to Reply
debata07
Power-User

Join Date: Nov 2011
Posts: 131
Good Answers: 5
#8

Re: Motor Lug Burnt, but Drive Didn't Trip

07/29/2013 1:09 AM

If there is a failure of lug while the motor is in running condition, the motor will be subjected to 'single phasing' condition i.e one phase gets disconnected and two phases are connected to the motor. Under such situation the motor will continue to run if it is lightly loaded and will not trip on overload protection. However, due to single phasing there will be high negative sequence current which will cause rotor heating. The motor may eventually burn due to rotor failure if it continues to run in this condition for longer time.
Register to Reply
Ritz11
Active Contributor

Join Date: Jul 2013
Posts: 11
#9

Re: Motor Lug Burnt, but Drive Didn't Trip

07/29/2013 1:11 AM

We have checked the reasons for Lug burning. It is found that tightness is not the issue. Also burning happened just after the Lug crimping portion in Cu lead. This may be due to that portion of lead is bent from that portion and due to high stress this might happened.

Drive setting also verified and not fault log history was available before fault occured and no one had resetted the feeder if tripped previously.

Also in the drive we didn't found any setting related to unbalance fault.

Is it possible that such parameters are hidden parameters and only manufacturer can access them? Because other fault parameters like Earth fault etc can only be enabled or disabled from the drive but their tripping setting can't be accessed.
Register to Reply
NotUrOrdinaryJoe
Guru
Popular Science - Cosmology - New Member Technical Fields - Technical Writing - New Member Engineering Fields - Energy Engineering - New Member Engineering Fields - Electrical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Electromechanical Engineering - Old Member, New Association

Join Date: Apr 2008
Location: Lexington, KY
Posts: 1639
Good Answers: 73
#10
In reply to #9

Re: Motor Lug Burnt, but Drive Didn't Trip

07/30/2013 12:26 PM

That would be a question for the manufacturer.

__________________
 A great troubleshooting tip...."When you eliminate the impossible, whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle
Register to Reply
Register to Reply
Have a Different Question?
11 comments

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

1capybara (1); 4wsilver (1); Aghvel Niazi (1); debata07 (1); dhayanandhan (1); JRaef (1); Munawar Hussain (1); NotUrOrdinaryJoe (2); PWSlack (1); Ritz11 (1)

Previous in Forum: Why and When We Need NGR / NER?   Next in Forum: Electrical Question -ELCB

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (82 right now)
Show Members
Advertisement