Dont trust vacuum circuit breakers

[australiantroubleman]

Had a bad experience with a 11kv vacuum circuit breaker last week , I denergised a 33kv/11kv transformer and noticed some strange voltages existing with both 33kv and 11kv breakers open on the trf voltage transformer . I walked outside and the transformer was humming loudly and erractically in a pulsating sort of way .

I assumed a faulty circuit breaker and was correct it was the 11kv breaker one phase had lost its vacuum and current was flowing though the faulty pole ,back energising the transformer on one phase through the wye connection to ground. The current was jumping a 12 mm gap internally .

The breaker checked ok with a 2.5 kv meggar but broke down when tested with a 5kv meggar.

Dont believe what the manufacturers say about the seals used on vacuum interrupters be wary and dont trust them.

[Special ED]

Isolate, Open, Test, and Ground is best policy. I don't trust any breakers.

[Pootnaigle]

Ummmm its best if ya never ever trust an opening that you cannot see. i always made a phyisical opening ( opened both sides of the breaker) or if that was not possible I checked it every way from Sunday n then grounded it. Never ever trust a breaker indicator. If theres no possible way for voltage to get in or out its safe to work on , otherwise lottsa testin needs to be done before gettin onnit.

[Special ED]

Exactly.. Hell on the Dominion system last time I was up there an open cut out didn't even qualify as a visible opening. But that was due to the large amounts of cut out failures that would track over when open.

[Chris]

Exactly.. Hell on the Dominion system last time I was up there an open cut out didn't even qualify as a visible opening. But that was due to the large amounts of cut out failures that would track over when open.

Indeed. We often will pull the jumper after opening the cutout switch.

[australiantroubleman]

We dont generally trust non visual breaks or use breakers as a isolation point, but we leave spare zone substation transformers open on high voltage and low voltage c/bs with automatic standby switching availible.

It was this situation where the breakers are left open and one pole was faulty that caused the problem.

The manufacturers told our company managers that this was the only failure ever recorded, i dont believe that for one minute.

And on the topic of non visual breaks ....

In our and other companies here there is a large scale rollout of SF6 pole mounted switches replacing Air break switches. Us older troublemen do not trust them but company management say its the future and we must accept non visual break equipment that depends on SF6 gas pressure.

Many years of experience makes us skeptical of any mechanical device to be 100% reliable and I will reserve my judgement on how reliable the gas pressure seals will be and how many suffer internal failures after lightning strikes and switching surges once the SF6 gas leaks out.

[west coast hand]

Indeed. We often will pull the jumper after opening the cutout switch.

I always lift the high side of a cutout if I open it for a visual open and I never trust a breaker always test

[thrasher]

Basically if you can't see an open it doesn't exist. Also don't forget to test before opening a lead to give you a visual opening. As I related once before we opened a oil switch to a cap bank then pulled open a series non-loadbreak cutout to give us a visual. However back then (1987) we didn't require a test first. The oil switch had welded closed contacts and while the handle dropped it was not open. The resultant load arc went into the steel and knocked out the substation.

[slimdalineman]

I always lift the high side of a cutout if I open it for a visual open and I never trust a breaker always test

Why? do you feel the cutout is failing and voltage is leaking? Do you then test before lifting the high side in case the cutout is leaking? I have always been taught to work it hot unless it is grounded. Just curious for the reasoning of lifting the high side.

[Special ED]

Why? do you feel the cutout is failing and voltage is leaking? Do you then test before lifting the high side in case the cutout is leaking? I have always been taught to work it hot unless it is grounded. Just curious for the reasoning of lifting the high side.

Everywhere you go its pretty much the same procedure. Open, test, ground, flag, and tag. The open must be visible meaning leads going to a kyle, recloser, ect must be disconnected since your trusting a piece of equipment that you cant visually see inside of to see if its open or not.

The cutouts high side being removed isn't really a new thing. But more and more places are requiring it to be done when grounding and working a line dead. Yes the cutout is open and you obviously can see that it is but with manufacturing being shipped out of the USA quality control has dropped and alot of cutouts though open still bleed over. Therefore to establish your visible opening prior to grounding at a cutout you must remove the highside jumper to eliminate any possibilities..

It only takes ya couple seconds more to take it off so why not?



Anything built by man has the posibility of failure so why not put it in gods hands?