The current load determines the wire gauge. Voltage, type of core material, and wave form will determine the number of wire turns. Insulation Properly insulated transformers can withstand severe environmental conditions and remain in service for many years. Bobbins that hold the wire are manufactured with either thermoset or thermoplastic. These transformers operate between 47Hz to 400Hz.
Power losses resulting in heat generated by transformers are a major design consideration.
Efficiency, defined as the ratio of Power Out vs. Power In, is influenced by frequency of operation, choice of core material, wire gauge, and current. With resistive loads, voltage and current are out of phase resulting in higher losses, since the current in the transformer is in phase with only the voltage across the resistive portion of the transformer windings. These phase angle power losses limit transformer ratings. Linear power supplies using capacitor input filters increase the transformer secondary current up to two times the DC current. An inductive input filter results in a unity ratio between DC and transformer current.