Generator losses are referred to as the loss of energy caused due to the heating of the generator parts leading to rise of the temperature. This causes reduction of efficiency of the generator.

Generator losses:

The losses in a dc generator can be divided into three main classes-

1. Iron or core loss
2. Copper loss and
3. Mechanical loss

1.Iron loss

Due to the rotation of the iron core of the armature in the magnetic flux of the field poles, some losses take place in the core and are known as Iron Losses or Core Losses.

Iron losses consist of 

1. Hysteresis loss and 
2. Eddy Current loss

• Hysteresis loss: Every portion of the rotating core passes under N and S pole alternately, so the domains of the core oscillate to and fro between opposite poles and take up some energy in doing so. This is known as hysteresis loss.
• Eddy Current Loss : When the armature core rotates, it also cuts the magnetic flux. Hence, an e.m.f. is induced in the body of the core according to the laws of electromagnetic induction. This e.m.f. though small, sets up large current in the body of the core due to its small resistance (remember that area is inversely proportional to resistance). This current is known as eddy current. The power loss due to the flow of this current is known as eddy current loss.

Prevention of loss: In order to reduce this loss and the consequent heating of the core to a small value, the core is built up of thin laminations, which are stacked side by side. This causes the resistance to increase decreasing the area, thus eddy current gets reduced.

2. Copper loss

Losses occur due to heating of different wires, the power wasted due to heating of copper wires is called copper loss.

Armature copper loss = Ia2Ra

Field copper loss: series copper loss= Ise2Rse

shunt copper loss= Ish2Rsh

3. Mechanical Losses

Mechanical losses occur due to friction in bearings and commutator. Air friction loss(also called windage) of rotating armature also contributes to these. Windage loss is the loss caused due to friction when there is a relative movement between air and the object, in this case the friction occurs between rotating armature and air.

So mechanical losses consist of :

1.  friction loss at bearings and commutator.
2. air-friction or windage loss of rotating armature.