Current limiting breaker with si
Current limiting breaker with si
(OP)
Good morning Gentlemen
Several days ago I found in Internet(Google) one poor description about Current Limiting Circuit Breakers with combination of the dual-pivot contacts and single-pivot contacts. The work principle based on the high arc impedance during tripping action.(It could be SIEMENS product) Do you have some opinions about it?
Thanks in advance Evgueni.
Several days ago I found in Internet(Google) one poor description about Current Limiting Circuit Breakers with combination of the dual-pivot contacts and single-pivot contacts. The work principle based on the high arc impedance during tripping action.(It could be SIEMENS product) Do you have some opinions about it?
Thanks in advance Evgueni.






RE: Current limiting breaker with si
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Current limiting breaker with si
There are current-limiting circuit breakers, but these are not standard breakers.
To be considered current limiting, the fault must be cleared or limited within the first 1/2 cycle, I believe.
All circuit breakers provide some impedance to fault current, but UL has specific criteria that must be met before a breaker can be called "current-limiting", at least in the US.
RE: Current limiting breaker with si
RE: Current limiting breaker with si
RE: Current limiting breaker with si
1/4 cycle theworetically gets you to the peak of the first 1/2 cycle and you may still have maximum current.
At unity power factor we need less than 1/4 cycle.
respectfully
RE: Current limiting breaker with si
RE: Current limiting breaker with si
RE: Current limiting breaker with si
A lot of times this is applied to make a 600 Amp Frame into a 800 Amp. The fuses used where Buss KAF-800 Limiter.
Don't know if that helps your discussion but we try.
RE: Current limiting breaker with si
I think you need to look at some molded case circuit breaker time current curves. At high currents, they trip much faster than that. And the contacts part even faster. In modern MCCBs, the contacts can open before the breaker trip mechanism even operates if there is enough fault current.
RE: Current limiting breaker with si
The Siemens current limiting circuit breakers do seem to work well. We've done some fault testing using them and they have shown to be capable of really limiting the fault current. We got some fault ratings that were as good with the breaker as with a class J fuse. An example breaker would be the CED6 for up to 125A sizes.
RE: Current limiting breaker with si
Yes VK is Medium Voltage. The breaker times I stated earlier are for metal clad. Most instantaious curves even in molded case, insulted case are still around 0.01 to 0.05 sec's Have to admit that I haven't seen the curves for the Siemens CED6 yet.
RE: Current limiting breaker with si
RE: Current limiting breaker with si
RE: Current limiting breaker with si
Why do you say no LV C/B will open in less than 0.0033 sec?
Because of arc-flash, manufacturers are re-testing their MCCBs and publishing new TCCs that are more accurate at the very high end.
RE: Current limiting breaker with si
RE: Current limiting breaker with si
RE: Current limiting breaker with si
RE: Current limiting breaker with si
Could you tell why those curves were published . If its not practical information why Engineers have used it?
RE: Current limiting breaker with si
When looking at a TCC for a molded-case circuit breaker instantaneous trip, the top line represents the maximum clearing time. The breaker contacts will have to open at some point before the maximum clearing time. But modern MCCBs with "blow-apart" contacts can actually open **before** the breaker trip mechanism even releases the stored energy spring in the breaker. This is due to the magnetic forces on the contact arms at high current levels.
These breakers can clear high current faults pretty quickly. They really have to, or else the breaker will tremble and disassemble. This fast clearing time is the only way that the very high interrupting ratings can be achieved in such a small, inexpensive device.