Estimate the pu regulation at full load and 0.8 pf lagging for a 300 KVA, 50Hz, 6600/400 V, 3 phase, delta/star core type transformer. The data given is

HV Winding:

Outside diameter = 0.36m

Inside diameter = 0.29m

Area of conductor =$ 5.4mm^2$

LV Winding:

Outside diameter = 0.26m

Inside diameter = 0.22m

Area of conductor =$ 170mm^2$

Length of coil = 0.5m

Voltage per turn = 8V

Resistivity = $0.21\Omega/m/mm^2$