I have a 3 θ 240v 7kva generator and would like to know how to wire in a 3 θ to 1θ transformer ,I have found 3 θ to 1 θ transformers but are very $ ,I found this schmatic of one,and I can find used transformers reasonable,If anyone has done this please reply.http://http://www.wipo.int/pctdb/en/wo.jsp?wo=1983001341&IA=JP1982000311&DISPLAY=DOCS

 

The methodology sounds iffy:

Transformer for an electrical device. Conventionally, in order to convert 3-phase power into single-phase power, a motor generator is used or the 3-phase AC voltages are first converted into DC voltages which are then converted into a single-phase AC voltage. However, this transformer receives 3-phase AC voltages, produces 3 single-phase AC voltages at the secondary side and produces a single-phase AC voltage by combining the phases.

The quoted material is from the abstract.

The combination of three phases 120 deg apart into one phase sounds extremely difficult.

 

What voltage are you trying to end up with? If all you want is 240 single phase just leave out one phase. If the generator is wired for a wye output that means you should have a neutral and that will give you 120v.
If you're looking to get some other voltage, let us know and we can help.
Your link didn't work for me, in case your answer was in there.

 

if i understand what you mean,

you have to take each phase "L" with the neutral "N" to have 1 phase power.
try to connect your load as much symmetric you can on each phase.
L1-N , L2-N , L3-N. with this way you have 1 phase power from 3 phase transformer.

if you have any 3 phase loads or equipment, such as motors or big ovens, then you have to use the 3 phases and the neutral.

 

What voltage are you trying to end up with? If all you want is 240 single phase just leave out one phase.

Not correct. The voltage across two phases is 1.732 (root 3) times the voltage of each phase.

So if I have a generator that gives 3 phases each 230V from Phase to Neutral (the star point), the voltage between two phases will be 400V (398.37 to be exact).

Using two phases is probably the best way to get a single phase supply. But will only be able to use 2/3 of the generators capacity.

 

I have a 3 θ 240v 7kva generator

Since the OP hasn't returned all we have to go by is his first post which says his generator is 240v. We don't know if it's star or delta, we don't know what voltage he wants to end up with.