The function of oil in a transformer is

Keeping in view the requirement of parallel operation, which of the $$3$$-phase connections given below are possible?

Supply to one terminal of a $$\triangle$$ - Y connected three-phase core type transformer which is on no-load, fails. Assuming magnetic circuit symmetry, voltages on the secondary side will be:

The percentage impedance of a 100 kVA, 11 kV/400V, delta/wye, 50 Hz transformer is 4.5%. For the circulation of half the full load current during short circuit test, with low voltage terminals shorted, the applied voltage on the high voltage side will be __________.