Step Up transformer Installation

[Bugman1400]

I doubt a reflected wave from the transformer could generate enough current to blow the breaker
even if we assume at the 150 kva transformer:
-incident 20 x 150000/(1.732 x 480) = 3600 A
-0% transmitted/refracted
-100% (opposite sign) reflected ~ 3600 + whatever the feed was putting out (even if very short lines and still supplying 3600 inrush)
but it would be opposite sign and sum to ~0

it was a cb rated at aic 65 ka

my wag, by grounding both h0/x0 he some how completed a ground loop thru earth and possibly in parallel with the egc's
ground fault from feeder phase to ground thru the 150 kva xfmr winding

But, how would there be enough ground current to exceed the breaker ratings and cause failure? I thought perhaps the resonance caused a much higher voltage than rated for a 480VAC MCCB and that an arc flash occurred between phases through the casing. As Phil suggests, perhaps we need more info from the OP.

 

[Ingenieur]

But, how would there be enough ground current to exceed the breaker ratings and cause failure? I thought perhaps the resonance caused a much higher voltage than rated for a 480VAC MCCB and that an arc flash occurred between phases through the casing. As Phil suggests, perhaps we need more info from the OP.

need data on the feeder xfmr
mva and pu Z
Phil is right, we definitely need more info

if we had info on the cables we could est a surge Z
and from that a v wave profile
perfect problem for a Bewley lattice diagram
the fact that h0/x0 were connected and grounded complicates it a bit