50 kva pole mount transformers are made using a core

50 kva pole mount transformers are made using a core made from laminations of sheet steel stacked and either glued together with resin or banded together with steel straps. Where large numbers of transformers are made to standard designs, a wound C-shaped core is economic to manufacture. A steel strip is wrapped around a former, pressed into shape and then cut into two C-shaped halves, which are re-assembled on the copper windings.
Formerly, distribution transformer

for indoor use would be filled with a polychlorinated biphenyl (PCB) liquid. Because these liquids persist in the environment and have adverse effects on animals, they have been banned. Other fire-resistant liquids such as silicones are used where a liquid-filled transformer must be used indoors. Certain vegetable oils have been applied as transformer oil; these have the advantage of a high fire point and are completely biodegradable in the environment.