FPE type CJK , cannot find TCC 1

[tem1234]

Hi,

I need Time Current Curve for a low voltage breaker, FPE type CJK 600 A(s/n: CJK636F000 9007) with an inst. adjustment working on 600 V but i can't find it. Is there anybody who can help me?

thanks

 

[dpc]

EasyPower has CJL and CK, no CJK.

 

[tem1234]

I have already looked in easypower. It's for an arc flash study, so i can't take any curve that seems similar. It's really written CJK on the breaker. It is the same curve than CJL? or CK? difficult to say

I have an other one, FPE CFJ 225 A which i can't find the curve too.

thanks for your help

 

[dpc]

Actually, if it's a molded case breaker, IEEE 1584 says you can use generic breaker data as described in the standard.

Checking with the manufacturer is always as last resort option.

 

[tem1234]

Thank dpc,

i think i see what you talk about, it's the equation that are in section 5.7 of IEEE 1584. But these equation are valable if the fault current is greater than the inst. trip of the breaker. Since this breaker is the main of a substation, i don't really want it to trip instantanously because it will cause a bad coordination. I can adjust the inst. setting, but i'm not sure it's a good thing.

i'll try with the manufacturer too.

 

[dpc]

If this is a molded case circuit breaker used as a main breaker, it is unlikely that you will be able to set the instantaneous high enough to reliably avoid operation.

Maximum setting for a 600 A frame MCCB may be only 6000 A.

 

[tem1234]

You're right dpc! i didn't see that

My bolted fault current is 9,7 kA, and my arcing current is 7,6kA(100%) or 6,5kA(85%).

The inst. setting is 10, so 6kA as you said.

So, in theory, for an arcing fault just downstream of the breaker, it should trip instantanously. But this is just theory, i'm asking myself if it'll really work like that, since 6.5kA is quite close to 6kA and there's a lot of uncertainty in SC study, like junction resistance. So can i assume that the breaker will trip in the inst range? close call!

thanks

 

[dpc]

Yes, that's a reasonable assumption. The 85% calculation results in an arcing current value that is quite low compared with the bolted fault current.

You can always reduce the instantaneous pickup slightly to increase your confidence level. This will have little impact on coordination, since it was probably going to trip on instantaneous at the max setting anyway.