Arc Flash in SKM

[Kanu_01]

I am getting a maximum trip time of 2 seconds. The protective device arcing fault current is 4kA.
As I have put only relay in the upstream and no breaker is there. Can I safely assume that the upstream device will trip prior to 2 sec as the protective device arcing fault current is around 4kA? I have my instantaneous setting of relay at 5.8kA.

 

[mparenteau]

Assuming you have a MV or HV circuit breaker w/ no "brains", the relay is the brains. So, there will be a slight delay between relay sensing, and the relay issuing a trip command. So it would actually be longer than 2 sec, unless you included the opening time of the breaker.

Mike

 

[Kanu_01]

Assuming you have a MV or HV circuit breaker w/ no "brains", the relay is the brains. So, there will be a slight delay between relay sensing, and the relay issuing a trip command. So it would actually be longer than 2 sec, unless you included the opening time of the breaker.

Mike

SKM is making analysis based on the maximum arcing duration i.e. 2 secs as I haven’t included any breaker. But it makes sense to not assume it to trip seeing just the protective device arcing fault.

 

[dpc]

Why not just add a breaker to the model? I'm not sure what you are trying to accomplish. Two seconds is generally used as a maximum arc time in the IEEE 1584 calculations, so there's no way of knowing if your relay is operating or at what time.

 

[Kanu_01]

Why not just add a breaker to the model? I'm not sure what you are trying to accomplish. Two seconds is generally used as a maximum arc time in the IEEE 1584 calculations, so there's no way of knowing if your relay is operating or at what time.

SKM consider the relay as well; there is no need of breakers generally. As you all here are well versed with all these things, so I asked. I am sorry if it sounded so basic.