3 Phase Motor Failure

[hooverdale]

Good Day!

we have an electric motor coupled to a blower for almost 2 months and then the fault happened: burnt terminal wire.

Supply Voltage Measured:230/237/234
Unfortunately we can't measure current.


We tried to jog it but the situation get worst, Line side Line 1 of the main breaker, burnt!


We checked the motor connection and found out that Line 1 and Line3 of the 6 Wire YD connection was interchanged.(diagram attached)

Motor Details:

HP: 10
Phase: 3
Voltage: 220/380/440V (220V YD Connected)
Ampere: 26
RPM: 1800
Hz: 60
Controller: Wye Delta 40A 220V

Why did the motor controller: Breaker, contactor, OL relay and any of the control wire didn't get any damage. Instead the line side of the Main Breaker supplying the controller got burnt.

What do you guys think?

 

[waross]

Either a faulty breaker or poor workmanship. Probably workmanship.
Loose connections generally cause heating and burn damage to the wires and hardware.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Agree with Bill. Bad connections can generate a lot of heat. And on an entirely seprate subject, think about doing some remedial works on the motor terminal box - the conduit appears to be secured to the motor by the power wiring.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[jraef]

I don't mean to be rude, but from the nature of your questions you do not appear to be an Electrical Engineer, nor do you appear to be qualified to be doing this work yourself. The "We tried to jog it but the situation get worst, Line side Line 1 of the main breaker, burnt!" is the dead giveaway, no qualified EE or even a decent electrician would think to jog a motor that was already damaged!

Your situation is already bordering on a serious fire hazard, you need to hire a qualified professional to analyze the situation and come up with a cause and remedy before you kill someone.

Sorry.

"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

 

[LionelHutz]

If you mean phase 1 is wired where the diagram shows to use phase 3 then that is just to reverse the motor. Not really relevent to the motor failing.

I don't see the failure in the picture but you should never re-apply power to a damaged electric circuit without doing proper repairs first.

Line 1 on the breaker would burn if there was a crappy connection there. It could also be a crappy breaker or a breaker not rated for the application.

 

[Motorwinder]

Classic loose connection. And you don't have to be an engineer to see that.

It was engineers that designed that POS. I'd rewind it and just bring the leads out, and eliminate the terminal block.

 

[rhatcher]

I agree with waross. The type of fault that you show at the motor terminal block and that you describe at the breaker terminal looks and sounds like loose connections. Theoretically you could clean everything up, replace anything that is damaged beyond cleaning, make sure verything is properly tightened, and then continue like nothing happened.

However, the picture of the motor junction box that you provided appears to show six leads coming from your controller to the six motor terminals. This seems to indicate that you have a reduced voltage, wye-delta starter. Your nameplate supports this idea because it shows a wye-delta connection for a single voltage. I am thinking that you have starter leads coming to your motor terminals that are T1, T2, T3, T4, T5, and T6 going to a reduced voltage wye-delta starter.

In this case, the phase rotation of the T1-T3 leads must correspond to the phase rotation of the T4-T6 leads. If T1 and T3 are swapped without T4 and T6 also swapping then you will have problems.

This may account for the overheated terminals but normally the motor overloads will interrupt the process first and someone will notice the problem before two months has passed.

 

[hooverdale]

No. Its okay jraef. All of you guys are correct. Loose connection on main breaker load side (L1) one and on one of the motor terminal.

Info that i provided the other day was based on the report given to me.Upon thorough inspection, loose connection was found at main breaker load side.

@lionel, you're right sir.
@ ratcher, yes apparently they did swapped T4 and T6.


Here's what happened.

Client reported to us that the motor terminal connection got burnt.

Upon visual inspection, one of the terminal connection was damaged.
Controller did not trip.
Neither the main breaker.

Actions Taken.
Insulation Test: >550Mohms Line-Ground on all phases.
Voltage Measured: 222/224/227V
Controller rechecked by the supplier
Reconnected the motor terminals.

Main reason why, they tried to jogged it.

The motor did run at first, then the main feeder line supplying the controller to the motor, got burnt.

And guess what, loose terminal connection. How should we know? We only supplied them the motor and controller. Main Breaker and feederline was far from our reach and was assumed stable. And yes, our technician is facing the charges. Cheers!

 

[jraef]

Hard to say which one is the chicken and which one is the egg. If the main breaker terminal was loose from the get go you would have had low voltage at the motor terminal which may have caused it to over heat and become loose, especially if it was marginal to begin with. On the other hand if the motor connection was loose to begin with, the same may have happened to the main breaker terminal. Or it could have been both. I don't know if it's possible to determine that now. Did you inspect the motor starter contacts for evidence of over heating there as well?

By the way, it's not surprising that the breaker didn't trip, if the motor connection never went to ground, the current may never have exceeded the breaker rating even though the heat in the connection caused it to burn.

An IR scan after installation may have picked up the problem before damage was done. A solid state overload relay that could pick up phase imbalance would have likely prevented collateral damage as well.

"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

 

[electricpete]

My vote is they were both loose to begin with. I have a hard time imagining that unbalance or heat from one caused the other to get loose/degraded. The unbalanced current was not that severe as to cause a big cable overload (otherwise should have tripped a thermal overload) and a good connection doesn’t have higher resistance per length than the attached cable.

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(2B)+(2B)' ?

 

[1000V]

I have seen this several times by either: Recessed paxeline connections rounding off or breaking during installation therefore causing looseness. Sometimes the recesses are counter bored and therfore cannot be properly tightened properly as the bolt will turn.

Secondly: Somebody didn't tighten it up properly!