Failure of Tripping Coil in MV Breaker

If the breaker is energize-to-trip, check for loose connections or other open circuits in the trip circuit components and wiring.

Quote"(If the breaker is energize-to-trip, check for loose connections or other open circuits in the trip circuit components and wiring.)"

Thanks for the quick response;

Later on we found mechanism for 2nd opening coil(back up) the engagement lever was detached; that could be the reason for 2nd opening coil faulty because it was continuously energized without opening the breaker; while stop command given .

But for the failure of 1st coil still we can't able to identify the cause.

Make sure that you have breaker NC aux contacts in series with your trip and close coils.....in that way you should not burn your coils....must I send you a picture how its done or will you manage

Regards

Quote: "Make sure that you have breaker NC aux contacts in series with your trip and close coils.....in that way you should not burn your coils....must I send you a picture how its done or will you manage"

THANKS FOR THE ANSWER

Yes ;Already NC Aux contact is connected in series with coil to cut the supply when coil has done the job(to drive mechanism to open breaker). That's why the coil is burn because the supply was not cut off before breaker open and activating also Aux. contact.

A freewheeling diode provides a path for discharging the very high voltage induced by the collapsing DC field whenever the breaker is opened/tripped.

The freewheeling diode being faulted will allow the induced voltage to circulate within the control voltage circuit(s) and cause failure of the close and/or tripping coil(s) and possibly other components.

If the breaker mechanism was/is mechanically binding, the higher current required to overcome the mechanical load will magnify the collapsing field affect and cause the induced voltage to go even higher.

I would thoroughly clean and PM the breaker following the manufacturer's recommended procedure, replace all of the bad components, then test the breaker electrically and cycle it at least 5 times to ensure it is fully functional.

Quote "One question nobody has asked is what is the mechanical condition of the circuit breaker? When was the last time it had a complete inspection and mechanism maintenance performed? Many people operate their breakers periodically, and assume just because the breaker opened or closed this time it will do it again next time.In my experience, one of the most common causes of trip coil failure is that the breaker mechanism lubrication has thickened or been worn away to the point that the mech sticks. In that case, the trip coil solenoid is unable to cause the latch to release the springs (or other energy storage) to cause the breaker to trip. The coil then sits there trying to trip the breaker until it burns up, and the owner wonders why it happened since the breaker worked fine the previous time.

The breaker mechanism has many rotating and pivoting parts, as well as cams and bearing surfaces, that need periodic lubrication. When the grease or oil ages or is worn away, the friction can increase dramatically, and a mechanism that operated freely last week will stick and sit immovable today.

Get a qualified service organization to do a complete maintenance on your breaker. I'm willing to be that they find it to be gummed up to where it won't operate."

THANKS FOR SHARING GREAT IDEA! Your point of view is very useful for us

Hi,

I am sitting with the same problem on metal-clad switchgear. I keep on loosing a blocking diode, burning a output 1 contact and burning the trip coil. It happens on different schemes all in the same station. I also took station earthing into consideration but to no avail. I also have a linear resistor/snubber to protect against contact burning and the diodes is supposed to be able to handle the back EMF.

I have attached a couple of documents for you to see that the circuit is simple but the damage is extensive.

Any help or advise would be appreciated taking into account that I did have the mechanical part of the breakers maintained and tested.

Thank you in advance

Thanks for the advise. I did arrange for the scope before your answer but I am impressed with the "retrofitting" of the MOV. I will keep you updated on the progress.

South African Thanks