Silica gel

Sodium chloride

Ammonium chloride

Charcoal and salt mixture

More losses

Heavier in weight

Poor voltage regulation

Cannot isolate the secondary winding

Air natural

Oil natural air blast

Oil forced air forced

Oil natural air natural

Steel 97% and silicon 3%

Steel 95% and silicon 5%

Steel 93% and silicon 7%

Steel 90% and silicon 10%

Maintain primary voltage constant

Change voltage ratio in distribution

Maintain secondary voltage constant

Load the transformer for maximum efficiency