Transformer specifications to get 18V AC output from 230V AC in Proteus simulation
Proteus looks like it is trying to design you a fly-back transformer in a switch mode power supply. Not helpful in my opinion if dealing with regular AC power frequencies.

230 volts in and 18 volts out means a turns ratio of exactly that; 230/18 - 12.78. 

Primary (magnetizing) inductance should be high (this is not the leakage inductance I mentioned in another answer). The higher the better but beyond a certain point you run into trouble with core saturation. So, ask your self how much off-load primary current are you able to tolerate in your design.

10 henries at 50Hz across 230V gives a primary magnetization current of 73mA. Is this too high? If so then more winding inductance is needed.

How many turns on the primary? This is dependent on the material in the core. Most manufacturers supply this data - they'll tell you the inductance of one turn and, because inductance is proportional to turns squared, 10uH for one turn becomes 10 henries with 1,000 turns.

Next, make sure your core doesn't saturate - one thousand turns with a mag current of 73mA is a M.M.F. (magneto motive force) of 73 ampere-turns. You need to convert this to H (magnetic field strength) by dividing through by the average length of the magnetic core.

Note - at this point some readers may be thinking that using 73mA when checking for core saturation is wrong. It's a common misconception - under load the primary may be taking "amps" from the AC supply and, it seems "right" to use this current to determine core saturation. Well, it's not right! Use the off-load primary current for working out saturation - any extra current due to the load does not contribute to magnetizing the core.

Then look at the BH curve of the core material and see if there is too much saturating of the core. B is flux density and H is M.M.F. divided by core length. Bigger cores have longer core lengths and this means less H and less B. It's peak flux density that is the killer so multiply the H number above by \$\sqrt2\$.

If there is then you'll need a bigger core or you should revise the amount of primary inductance to a lower value.