SEPARATELY EXCITED DC GENERATORS

A DC generator in which current is supplied to the field winding from an external DC source is called a separately excited DC generator. The flux produced by the poles depends upon the field current with in the unsaturated region of magnetic material of the poles (i.e., ɸ ∝ I_f), but in the saturated region, the flux remains constant. Its conventional diagram is shown in Figure 11.16.

Fig. 11.16  Conventional diagram of a separately excited DC generator

Important relations

Here, I_a = I_L, where I_a is armature

Current and I_L is the line current

Terminal voltage, V = E_g − I_a R_a

If brush contact drop per brush (v_b) is known,

V = E_g − I_a R_a − 2 v_b

Power developed = E_g I_a

Power output = VI_L = VI_a