Electrical Engineering ⇒ Topic : Losses in DC Generator

The various losses occurring in a generator are given below:

(i) Copper loss 

(a). Armature copper loss = I²_aR_a where Ra is resistance of the armature and Ia is the armature current.

(b). For shunt generator, field copper loss is equal to I²_sh R_sh where R_sh is the resistance of the shunt field winding and I_sh is the current through shunt field winding. The loss for shunt generator is practically constant. For series generator, it is equal to I²_seR_se where R_se  is the resistance of the series field winding and I_se  is the current through it. This loss is about 20% to 30% of full losses.

(c). The loss due to brush contact is generally included in armature copper loss.

(ii) Magnetic losses or iron losses or core losses

(a). Hysteresis loss ∝ Bⁿ_max f (n is generally 1.6)

(b). Eddy current loss ∝ B_maxf²

Iron losses are constant for shunt and compound generators as their field currents are approximately constant. This loss is about 20% to 30% of full-load loss.

(iii) Mechanical losses

(a). Air friction or windage loss of rotating armature.

(b). Friction loss at bearings and commutator.

These are about 10% to 20% of full-load losses. Mechanical losses together are known as stray losses.

LOSSES IN A D.C. GENERATOR

Losses in D.C. generators are below :-

Copper Loss:-

1. Armature  Copper Loss
2. Field  Copper Loss

Magnetic losses:-

     (a) Hysteresis loss

     (b) Eddy current loss

Mechanical losses :-

   (a) Friction loss

   (b) Air friction loss