[woodchips]

Thanks for the comments.

Both primary and secondary are three wire Wye connected, so each primary is 230V, each secondary is about 14V.

I have four essentially identical transformers. Each just has rectifiers with some smoothing which I am not using.

The transformer is the normal three leg three phase type, each limb with its own primary and secondary. There is no connection to the star points. Each limb has a full wave rectifier, so six rectifiers in total. Rating plate says 400V +/-5% to 24V 40A.

I thought I sort of understood 3ph transformers and motors, taken a bit of a dent! No books I have, 200 or so, think anyone would be silly enough to do what I am trying to do. Just energizing one limb and I get voltages on the other two, about 2/3 on one, 1/3 on the other, which is understandable. Connecting any two limbs in flux series aiding works happily. Run from a variac to stop any unexpected blue smoke and the result takes about 0.2A magnetizing etc current at 230V. But it is the total lack of any voltage induced in the third limb that took me by surprise. Read books on magnetism and they talk about leakage across the air gaps, I assumed that having a lump of core would increase this leakage many times, nope.

I am making a static single to three phase converter rated at 8kW, the transformer I am using isn't really up to it so bought these to boost the power. Need the 150V to add to the generator 230V to get 380V for the motor. Because the 230V in actually provides all the three phase current it is not obvious what the various currents circulating are. Got lots of spare time to think about it at the moment though.