Dd0 protection

[pavement]

Im considering protection of the above transformer in a unearthed LV system,and ive considered the percentage differential, balanced earth fault, wont be any Buccholz since its dry type, thermal relays and overcurrent for back-up functionality. But im wondering if ive managed to neglect something, im fairly new to the protection side of power systems so any expert help would be grand!

Also can anybody explain the 'make and break' philosophy of switchgear, as my colleague is a buffoon and makes it sound like a gameshow question!

Many Thanks

 

[busbar]

Protection is a judgment call, based on operating experience, transformer cost and its criticality to a larger operation. For simplicity, ANSI/NEC allows 3-wire &#8710;-&#8710;, primary overcurrent protection to also protect the secondary and, to a certain extent, a single load. Practically, you may want to limit application to <600V and maybe 500kVA. See 99NEC240-3(f).

What is the kVA rating and voltage of the proposed unit? Can the transformer be applied 3-wire primary, 3-wire secondary?