My electronics /PCB software can't do a ground plane 
Rob,
Are you sure?
I managed to do a copper pour to fill. What i couldn't do was neatly connect a pad to the plane. I've uninstalled it now so can't tell you exactly how to do it.

Phil.
Hi Phil
I think I am driving it correctly , I added the copper fill but I cant connect to it
, I thought just add the copper fill ,then remove/delete all the traces that are at 0 volts , but it just isolates the pads .
how did you get a connection ?
Cheers Rob 
Rob,
You have to draw a track from the pad to the filled area. (I found somewhere in the help that told me that was the only way.)
I found this in one of their tutorials which shows the filled area but no connections to any pads.

I don't know if you can get sufficient clearance for the pads for your transformer or whether you're stuck with a standard clearance. There will be a way round it I'm sure.
Other software allows you to specify on the pad properties if it's isolated or not.
In my PCB I used one plane for 0v to connect to my Pi and one plane for the 0v from my proximity sensor inputs. I wanted to keep both sides completely separate to keep the 24v away from the Pi which is limited to 3.3v on the inputs.

Phil.