Rated opening time breaker

[Guilhermebr]

Hello.

I did some opening time tests on old allis chalmers oil breakers at 138kv. Opening times are longer than 700ms.

Does anyone have experience with testing on these circuit breakers? and some opening-time reference for me to use?

GS

 

[davidbeach]

Dumb question, but are you sure that’s the opening time and not the closing time? I’ve seen really slow closing times, but an interrupting time that long is a failed mechanism. Best to leave it as just a failed mech and not let it turn into a fault in the tank when the interrupter arcs long enough to ignite the oil.

 

[jraef]

Hopefully member Zogzog sees this, that's right up his alley. He's in North Carolina so he's a tad bit busy at the moment though...


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

 

[Guilhermebr]

I'm sure, 700ms, It is tired, It was born 1962.

GS

 

[Overvoltage]

Very tired. I'm seeing trip numbers for similar AC breakers around 2-10 cycles depending on if the first or following trip. That's compared to what...40 cycles for 700ms (roughly)?

 

[Guilhermebr]

Yes, 40 cycles.
Most circuit breakers have a high opening time. They have rated current of 2000A with voltages of 138kv and 13.8kv.

Are you using which standard?

GS

 

[davidbeach]

Uhm, no, a slow breaker is 8 cycles. We still have some 5 cycles breakers and most of what we have are 3 cycle breakers. With a breaker failure time of 10 cycles, a 40 cycle breaker will never interrupt anything because the bus will be cleared instead.

 

[dpc]

700 ms indicates serious issues with the breaker and it would not be safe to interrupt fault current with the breaker.

 

[marks1080]

We use 400ms for 62c.

 

[HamburgerHelper]

Is this 52 contacts or actual interruption of current? Or both? If the 52 contacts changed quickly but current interruption was slow, I would think that would be very worrisome.

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If you can't explain it to a six year old, you don't understand it yourself.

 

[DTR2011]

I worked around a few Allis Chalmers / Siemens Allis BZO-145 breakers this spring. IIRC, the nameplate opening time is 3 cycles. The ones were were working with had hydraulic operating mechanisms, with a pressure of ~2200 PSI being normal. I think alarm was 1800 PSI and cut off maybe 1500 PSI. These are quite common breakers in my region with many still being in service after 40+ years. I believe Siemens was still making them until the mid 1980's. Aside from the charging system, they are fairly straightforward. We had a low pressure alarm come in during an outage and some work on the accumulator system was performed by others. I spent some time with a seasoned Utility "Doble Tester" and aside from a few manufacturer recommended charging system updates, he did not recall any serious problems with this type of breaker. I checked my Doble timing database, and oddly there is no Doble timing data listed for BZO type breakers.

I believe the OP can contact Siemens, USA (Mississippi) for factory support on the BZO line of breakers.

 

[Dan6779]

Wow, I did not know that Allis Chalmers made breakers! I thought they just made tractors.

I am coming at this conversation from an electrical inspector's point of view. I do what I can to enforce the NEC, but some codes just do not make very good sense to me. Before the 2008 NEC 250.32(B) would allow the grounded conductor to carry fault current. For example, if you had a building supplied by a set of feeders coming from another building's electrical supply, you were not required to use an equipment grounding conductor, as long a two conditions were met. The conditions were, no continuous metallic paths, and no ground-fault protection on the supply side.

Since the size of the grounded conductor is generally larger than the size of the equipment grounding conductor, it would provide faster breaking times for breakers.

If you are an electrical conductor manufacturer though, it makes more sense.

 

[davidbeach]

138kV is generally outside the realm of the NEC...

 

[Mbrooke]

@Dan6779: Yes, but what if the neutral breaks? What if metallic paths are added latter? In the end it makes sense to do it that way as did 1997 NEC when ranges and stoves went from 3 wire to 4 wire. I don't think its clever marketing. If you wanted the NEC to fix the issue of clearing times your best bet is to mandate the foot note on voltage drop and add a requirement about pickup/trip curves regarding LV circuit breakers. Or a section on earth fault loop impedance like the IEC.

 

[oldfieldguy]

Allis-Chalmers =>Siemens-Allis=>Siemens.

Siemens was still making the BZO OCB in the early 90's in Jackson, Mississippi. I installed a few new ones, went to a training session at the factory.

Did you use a good motion analyzer to run the tests, or is that simply a contact parting time?

It's been a decade and a half since I messed with an OCB, so I forgot what I'd expect for opening time, but 700 ms. seems way long.

Motion analysis will help you determine the cause of the tardiness.

old field guy

 

[cranky108]

In most substations we follow the NESC.

Allis-Chalmers made much more than tractors and Circuit breakers.

Years ago I did ask a breaker manufactures rep if he is stating his breaker is a 3 cycle breaker why can't I set my breaker failure at 4 cycles. I got nothing more than I don't recommend it.
There seems to be a gap of what the sales people say and no information on what is out of spec. (at least from the protection point of view).