Grid Short Circuit Data for Arc Flash Analysis!!!!!!

[D!NNy]

can someone suggest me the most conservative value to be used on the Grid Short Circuit Data for the Arc Flash Analysis??? Is there any thumb rule to go by.

I know its good to have the appropriate data from the utility to do the exact study!!!! most of the project that worked up to now SC data ranges in between 60MVAsc to 100MVAsc...!

Thanks

 

[jim dungar]

can someone suggest me the most conservative value to be used on the Grid Short Circuit Data for the Arc Flash Analysis??? Is there any thumb rule to go by.

I know its good to have the appropriate data from the utility to do the exact study!!!! most of the project that worked up to now SC data ranges in between 60MVAsc to 100MVAsc...!

Thanks

Rarely is the issue high utility values, especially once you get past 40cal/cm?. Many more problems are caused by fault currents that are lower than the 'instantaneous trip' points for protective devices. For example, it is not unusual for a 1600A class L fuse to require about 40kA @480V before it becomes current limiting, what happens if the fault current is only 30kA? (it rises from <4cal/cm? to >20cal/cm?).
If the utility provides, what I perceive to be a 'high' value, I run an alternative with a 'low' value and vice-verse. My company has developed internal standards for making the high-low decision.

My point is there is no single 'conservative value'.

 

[D!NNy]

How about the transformer configuration???

Rarely is the issue high utility values, especially once you get past 40cal/cm?. Many more problems are caused by fault currents that are lower than the 'instantaneous trip' points for protective devices. For example, it is not unusual for a 1600A class L fuse to require about 40kA @480V before it becomes current limiting, what happens if the fault current is only 30kA? (it rises from <4cal/cm? to >20cal/cm?).
If the utility provides, what I perceive to be a 'high' value, I run an alternative with a 'low' value and vice-verse. My company has developed internal standards for making the high-low decision.

My point is there is no single 'conservative value'.

 

[jim dungar]

How about the transformer configuration???

What about it?

 

[D!NNy]

What about it?

what is the effect on arc flash study with the change in the transformer configuration? is there a preferred configuration to go by? Like curve shift in the transformer damage curve and fault current amplitude decrease with change in the transformer configuration ..

 

[jim dungar]

what is the effect on arc flash study with the change in the transformer configuration? is there a preferred configuration to go by? Like curve shift in the transformer damage curve and fault current amplitude decrease with change in the transformer configuration ..

Arc flash calculations do not directly care about transformer configuration nor any phase shift, and damage curves definitely do not come into play. For example, IEEE1584 and Lee's equation care only about the 3-phase (L-L-L) bolted fault current while equations like those from the NESC use only the L-G currents.

 

[D!NNy]

Arc flash calculations do not directly care about transformer configuration nor any phase shift, and damage curves definitely do not come into play. For example, IEEE1584 and Lee's equation care only about the 3-phase (L-L-L) bolted fault current while equations like those from the NESC use only the L-G currents.

Sounds great.....Thanks for the input