Transformer Losses:


Copper Loss


Whenever current flows in a conductor, power is dissipated in the resistance of the conductor in the form of heat. The amount of power dissipated by the conductor

is directly proportional to the resistance of the wire, and to the square of the current through it. The greater the value of either resistance or current, the greater is the

power dissipated. The primary and secondary windings of a transformer are usually made of low-resistance copper wire.


The resistance of a given winding is a function of the diameter of the wire and its length. Copper loss can be minimized by using the proper diameter wire. Large

diameter wire is required for high-current windings, whereas small diameter wire can be used for low-current windings.


Eddy-Current Loss


The core of a transformer is usually constructed of some type of ferromagnetic material because it is a good conductor of magnetic lines of flux.


Whenever the primary of an iron-core transformer is energized by an alternating-current source, a fluctuating magnetic field is produced. This magnetic field cuts the

conducting core material and induces a voltage into it. The induced voltage causes random currents to flow through the core which dissipates power in the form of

heat. These undesirable currents are called eddy currents. The eddy current produced due

to the resistive nature of the core and hence The eddy current loss is proportional to the

square of the current in the winding.


To minimize the loss resulting from eddy currents, transformer cores are LAMINATED. Since the thin, insulated laminations do not provide an easy path for current,

eddy-current losses are greatly reduced.


Hysteresis Loss


When a magnetic field is passed through a core, the core material becomes magnetized. To become magnetized, the domains within the core must align themselves

with the external field. If the direction of the field is reversed, the domains must turn so that their poles are aligned with the new direction of the external field.


Power transformers normally operate from either 60 Hz, or 400 Hz alternating current. Each tiny domain must realign itself twice during each cycle, or a total of 120

times a second when 60 Hz alternating current is used. The energy used to turn each domain is dissipated as heat within the iron core. This loss, called

HYSTERESIS LOSS, can be thought of as resulting from molecular friction. Hysteresis loss can be held to a small value by proper choice of core materials.