felix said:
To say that my thoughts on balanced supplies where not well researched would be an understatement! I had this vague idea that the three phase substation transformer could have isolated, centre tapped secondaries with those taps being earthed.
did you ever think that there might be a REASON we connect one end of each output together. its done because it means instead of three cores each carryiing lots of current and causing lots of volt drop you have one core that carries almost no current.
lets say your loads are all 230V and you need to supply 230KW of demand (figures chosen to make the arithmetic easy)
now lets consider how we could configure the transformer output and power system.
lets first consider a 230V 2 wire system
we need two cores each rated at 1KA
now lets consider a 230V/460V split phase system
we need two phase cores and a neutral core if the system is perfectly balanced the phase cores will need a rating of 500A and the neutral core a rating of 0A in practice imbalance will mean the ratings need to be higher than this.
now a 230V/400V 3 phase system of the type normally used in the UK
we need three phase cores and a neutral core. If the load was perfectly balanced each phase core would need a rating of 333A and the neutral core a rating of 0A in practice imbalance will mean the ratings need to be higher than this.
now lets consider your proposal
if the system was perfectly balanced you would need 6! cores with a rating of 333A if the system is perfectly balanced in practice imbalance will mean the ratings need to be higher than this.