MPCB (Motor Protection Circuit Breaker) Burnt 1

[Histor]

Hi,
Today one of the Schneider make MPCB (GV2L04) rated for 0.63A burnt inside our panel. This circuit breaker was feeding to a 150W single phase (230V) motor.

We have used Tesys T LTMR for DOL starter.

When the incident happened, it was raining heavily. We suspect that the water leaked into the motor which cause current surge in Breaker and burnt. But why was it not tripped? All I understand is that the current surge is more than what the above mentioned circuit breaker can handle. So overcurrent leads to heating the components and burnt. But Please advise if there is any other causes which might have caused the issue apart from faulty/defective MPCB.
We need to develop a root cause analysis. So need to give realistic technical reason. Thanks.

 

[waross]

Possible causes;
Loose connection. Hard to verify after the breaker has been removed.
Moisture causing tracking inside the breaker so that the track bypasses the points and causes a persistent arc until the arc burns clear.
Where is the heat concentrated?
A loose connection will show most evidence of damage at or near one of the terminals.
Dirty contacts will often be badly burnt.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jraef]

Bills theory is the most plausible. Yes, the breaker should have tripped if the current surged, that the job. But a loose connection created heat at relatively normal currents, so the breaker trips do not activate until the damage is so severe enough to cause a short circuit.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[che12345]

Histor (Electrical)(OP)22 Aug 23 19:04
"....Today one of the Schneider make MPCB (GV2L04) rated for 0.63A burnt inside our panel. This circuit breaker was feeding to a 150W single phase (230V) motor".
1. The MPCB is rated 0.63A. The running current is likely to be lower than 0.63A. Let us assume the running current is 0.6A and the loose connection is 25 Ohm. Based in I[sup]2[/sup] R = 0.36 x 25 = 9W. If the loose connection is say 50 Ohm, the wattage increase to 18W. If based on 9W, it is unlikely to cause burn out. This also applies in case of bad contact, the heat generated is still very low because the current is very low.
2. However, any condensation or droplets of water that causes current to creep to ground is 230V/R which is possible to be >> 0.63A. Therefore, the heat generated is possible to cause burn out.
3. Suggested action:
a) check for loose connection,
b) improve the IP of the panel,
c) add panel heater to prevent condensation....
Che Kuan Yau (Singapore)

 

[TugboatEng]

Has this breaker tripped previously? It carries an AC-3 rating which means it's good for 100k cycles at the motor rated current (0.63amp) but the mag trip is 8 amps which means the cycle durability can be much lower at the breakers 8 amp instantaneous trip rating. The breaker may have been damaged in by previous trips.

Have you witnessed the contacts? Can you share pictures?

 

[Histor]

Please find the below picture and a video.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/video/upload/v1692931593/tips/video_20230823_144912_ur98u7.mp4[/url]

 

[TugboatEng]

No discoloration at the lugs, this wasn't caused by loose connection. The failure was certainly at the contacts in the breaker.

With that said, it appears components were blown off the breaker so there was some energy behind this. What is your potential fault current? Is it greater than 100kA? Should you consider current limiting fuses or an isolation transformer? Is there a DC component to your power?

 

[waross]

Is there a DC component to your power?

????

That looks like an internal flash-over.
You didn't say if the motor was damaged.
Two possibilities.

1.The motor shorted out and the breaker could not clear the fault current.
Do you know the ASCC at you plant? (Available Short Circuit Current.)
If you can post the KVA and the %Imp from the transformer nameplate we can calculate the ASCC.
If the ASCC is too high, the breaker may not be able to interrupt the fault current.
That is for a short downstream of the breaker.​

If water or moisture, possibly combined with dirt or dust buildup inside the breaker, there may have been an internal flashover ahead of the breaker contacts.

Either way, the arc may persist until enough material has been burned away to clear the arc.
You said that the breaker did not trip.
How can you tell.
There doesn't seem to be enough left to tell if the breaker tripped.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

Generator driven faults can produce a DC component.

https://ewh.ieee.org/r3/atlanta/ias/IEEE-Areva-Oct-09.pdf

Clearing DC faults can be difficult.

 

[Histor]

The load connected in this circuit is a Silo Vibrator (Datasheet attached).

The load is installed outdoor and the Power Panel where the DOL circuit is installed in indoor substation building.

The actual load current shown in the datasheet is 2.3Amps. But the circuit breaker selected is 0.63A. I know this is This is a mistake.

I suspect there was a overcurrent. But please explain how this could cause a such a burning MPCB?

 

[TugboatEng]

You said lots of rain. Did you have a lightning strike?

 

[Histor]

Sorry, there was no lightning

 

[waross]

Generator driven faults can produce a DC component.

Clearing DC faults can be difficult.

Not enough space here to educate you on the testing methods that ensure that ASCC ratings are able to safely interrupt DC components of fault currents.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

What eventually cleared the fault?
Did the MCC main breaker trip or did the arc burn clear?
Was the motor shorted?

The actual load current shown in the data-sheet is 2.3Amps.

2.3 Amps for a 150 Watt motor at 230 Volts is an efficiency of less than 30%.
Some small motors have terrible efficiency, or this may be an error on the data-sheet. (Motor installed is not the motor originally spec'ed.)
A motor fault, combined with the impedance of the cable to the motor may have produced a fault current high enough to arc across the internal contacts but not high enough to trip the instantaneous trip.
How old is the breaker?
Sometimes old equipment just fails.
If a 2.3 Amp motor was actually running on a 0.63 Amp starter, the starter was probably damaged already.
Check the name-plate current of the motor.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Histor]

Actually the load is not a typical motor. It's an electrical magnetic Vibrator Vibrator video Link

The Breaker and the load equipment are brand new.

 

[waross]

Was the vibrator damaged?
Is the Zener, XZ damaged?
If the breaker tripped, an inductive kick from transformer B could light up an arc across the breaker contacts if Zener XZ failed to clip the kick transients.
A high voltage transient on the supply may have overcome the Zener and initiated the internal arc in the breaker.
At this point we are guessing, but it may be well to check the Zener XZ.
A load rated at 2.6 Amps on a breaker rated at .63 Amps.
A response I used a lot of times in the third world when asked what will happen or what happened;
"I have a lot of experience doing it right. I don't have much experience doing it wrong, so I don't know."
By the way, does your utility voltage tend to run high?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!