MCCB Failure Info 4

[OmgVlt]

I am new to the maintenance side of power systems and I'm trying to learn some quick steps for troubleshooting MCCB failures, i.e. square d 2000 RK1 failure. I'm trying to determine what could be the causes of this breaker failure. Any help is appreciated!

 

[desertfox]

Do you think a picture of the failed breaker and some information about breaker prior to failure might help?

 

[OmgVlt]

Attached is the only photo of the breaker that I have. The event happened back in August '14 and I've just been tasked with finding the possible root cause for the failure. All I know is that it tripped and would not reset. I'm not sure what condition it tripped under. I was not sure if anyone else has had a problem with this type of breaker.

Thanks,
OmgVlt

 

[flexoprinting]

Hi omgvlt

Why are you calling it a Breaker Failure if it Tripped? It looks like it is locked out, can you inspect it for damage and describe what you find. Do you have the manual or can you download one from the OME? What kind of loads are downstream?

Chuck

 

[waross]

If the breaker is in service it may be too late to determine why it tripped in August. What conditions will cause a trip?
eg:
Ground faul tcurrent?
Overcurrent?
Overload?
Under voltage shunt trip?
External tripping circuits?
Was the proper reseting procedure followed?
I have seen an operator unable to reset a breaker because he did not apply enough force to the handle to reset the breaker.

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

 

[VTer]

These breakers most likely have a trip-free mechanism. If it tripped and the fault is not cleared, the CB will not close/reset.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla

 

[OmgVlt]

VTer, that is exactly what happened, as I am slowly receiving more info because this is a remote site. The breaker tripped and the site called it a failed (@flexoprinting) breaker because it would not close when trying to reset. They replaced the breaker with a spare and the spare closed without incident. Where can I get some more information on this "trip free mechanism"? Would this be related to the type of auxiliary/relays?

Based on your explanation, would it be accurate to suggest that the fault occurred on the line side of the device because the breaker would not reset when the load was removed? However, the original breaker closed without incident prior to being tested.

Thanks,
OmgVlt

 

[FreddyNurk]

I feel somewhat compelled to point out that with those sorts of breakers, the reset operation is to push the toggle back to open before attempting to close. If your operators weren't aware of this and just attempted to close from the trip position, then they would not have had much success.

I get the impression you're aware of this constraint, but your operators may not have been.

 

[waross]

A failed undervoltage release coil would give this symptom. eg: Breaker won't reset but the replacement works fine.

What conditions will cause a trip?
eg:
Ground faul tcurrent?
Overcurrent?
Overload?
Under voltage shunt trip?
External tripping circuits?

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

 

[OmgVlt]

FreddyNurk, thanks for the information and I was not aware of this as I have been in the project management side of the field and have not had too much experience in the maintenance troubleshooting end of the business. I will follow up with the onsite guys, as well as the contractor to determine if this step was followed, or not. In either case, I can now make sure a procedure is in place to do so moving forward. Thx!

 

[FreddyNurk]

Upon reflection, waross' suggestion is more likely than mine.

 

[IBRCAN]

I take it you don't have the breaker in your hands. I suggest you send it out for testing/inspection.

I work with these Schneider breakers on a regular basis. Often after they trip, they will not reset due to the trip coil not latching, especially those breakers used in dusty conditions. I have removed and cleaned the trip coils before and got them to reset.

If you look at the top of the trip unit, right below where it says "Micrologic 6.0", there is a row of lights. After a trip, one of the lights will be illuminated indicating the cause (assuming the internal battery is good). This should be noted by the operator in the event of a trip.