I could use some help please.
I am looking at a facility with 3 parallel MV transformers. The electric utility is providing 26.4kV with a fault current of 31.5kA. The building's 480V switchgear is rated at 100kAIC. When questioned about the available short circuit rating the "utility" will only tell us it is 107kA at the line terminals of the switchgear.
The building is over 30 years old with original equipment and we are trying to determine if the "utility" calculation is accurate or just an estimate so we can determine what the most feasible course of action is to properly protect the electrical equipment.
Here is the information I have obtained on the system so far:
- Primary voltage: 26.4kV
- Primary fault current: 31.5 kA
- Secondary voltage: 480V
- Secondary fault current: 107kA (as per utility)
- Five conductors per phase output
The utility has stated that trade off for secondary side conductor type/length/raceway type/bus bar is not acceptable.