Hello everyone. I am currently performing an arc flash study and I am some confused with modeling for the switchgear installed on the facility that I am working at.
I have attached some photos of the equipment that I need to analyze both switchgear and main breaker. Upwards of the swithgear there is the transformer and it is protected by primary fuses.
So I think there is a very important point regarding the switchgear, although the main breaker seems to be enclosed, when it was opened, I realized that the main breaker was not insulated from the line side and distribution bus.
Attachment:
File comment: ALSO HERE IS SHOWN BACKSIDE OF THE MAIN BREAKER. AS YOU CAN SEE THERE IS NO DIVISION BETWEEN THE MAIN BREAKER AND THE LINE SIDE BUS OR THE LOAD SIDE BUS. SO SHALL I CONSIDERED THE ARCING TIME ONLY FOR A ARC ON THE BUS THAT WILL BE SEEN BY PRYMARY BUSES?
MAIN BREAKER.png [ 1.25 MiB | Viewed 6246 times ]
First, do I need to consider the switchgear as open bus? or I need to take only dimensions of the front side of the main breaker (because technically the main breaker it is not inside a box, unless the switchgear as a whole is considered as a big box)?
Second, according to Annex C of the 1584 standard, I need to calculate the incident energy for the bus as if the main breaker failed if it had a stud connection problem with the VCBB electrodes type, and type VCB if the breaker presented an internal failure so, it could not open.
My point of view is the following.
I understand that in both cases the arcing time will be calculated based on the total melting time from the primary fuses of the transformer for both cases aforementioned (because the main breaker of the switchgear already failed).
Then if I am analyzing the case when the main breaker can trip the arcing current (arcing occurring in the distribution bus) the model applied for the analysis will be VCCB according to the same ANNEX C.
So do I need to analyze the switchgear with 2 incident energy results? One for the main section and the second for the distribution section?
Attachment:
File comment: AS YOU CAN SEE, SWITCHGEAR HAS 1 MAIN BREAKER AND THEN THE DISTRIBUTION BUS WITH THE FEEDERS BREAKERS
SWITCHGEAR.png [ 1.22 MiB | Viewed 6246 times ]
What do you think?
Thank you,