overcurrent protection for utility poles.

[aelectricalman]

Does anyone know the required fusing formula for cutouts, to protect a pole mounted cap bank ? Does it follow IEEE or is there another code body?

Would I have to acount for Inrush current and oversize for about 50% ish or is there a law of the land?

 

[mivey]

For a grounded wye bank:

Fuse link 100% rating = 1.35 * kvar_3ph / sqrt(3) / kV_LL

For a 150% rated fuse like a NEMA T-link, divide the current value above by 1.5

add:
For an ungrounded wye bank:

Fuse link 100% rating = 1.25 * kvar_3ph / sqrt(3) / kV_LL


The 25-35% adder comes from the normal allowance of:
10% for voltage
5%-15% for capacitor tolerance
5% for harmonics on ungrounded or 10% for harmonics on grounded wye

 

[mivey]

Would I have to acount for Inrush current...?

Transients from switching and lightning is addressed somewhat by the fuse type. A type T fuse can handle higher surge current than a K and would be better at the lower amp range.