The power lost in the form of heat in the armature winding of a generator is known as COPPER
LOSS. Heat is generated any time current flows in a conductor. Copper loss is an I2R loss, which
increases as current increases. The amount of heat generated is also proportional to the resistance of the
conductor. The resistance of the conductor varies directly with its length and inversely with its cross-
sectional area. Copper loss is minimized in armature windings by using large diameter wire.
Q14. What causes copper losses?
Eddy Current Losses
The core of a generator armature is made from soft iron, which is a conducting material with
desirable magnetic characteristics. Any conductor will have currents induced in it when it is rotated in a
magnetic field. These currents that are induced in the generator armature core are called EDDY
CURRENTS. The power dissipated in the form of heat, as a result of the eddy currents, is considered a
Eddy currents, just like any other electrical currents, are affected by the resistance of the material in
which the currents flow. The resistance of any material is inversely proportional to its cross-sectional
area. Figure 1-11, view A, shows the eddy currents induced in an armature core that is a solid piece of
soft iron. Figure 1-11, view B, shows a soft iron core of the same size, but made up of several small
pieces insulated from each other. This process is called lamination. The currents in each piece of the
laminated core are considerably less than in the solid core because the resistance of the pieces is much
higher. (Resistance is inversely proportional to cross-sectional area.) The currents in the individual pieces
of the laminated core are so small that the sum of the individual currents is much less than the total of
eddy currents in the solid iron core.
Figure 1-11.Eddy currents in dc generator armature cores.