**External Characteristics of DC Shunt Generator:**

The External Characteristics of DC Shunt Generator can be predetermined from a knowledge of the OCC and armature and field resistances (which can be determined by simple dc test), without actually performing the load test which in fact is not feasible for a large generator. Assume for the time being that the armature reaction voltage drop is negligible.

Because of the nonlinearity (saturation in the OCC), the solution of Eqs (7.44)-(7.46) to determine the terminal voltage for given R_{f} and l_{a}R_{a} can be carried out graphically as shown in Fig. 7.33. For given l_{a}R_{a}, Eq. (7.44) is represented by a straight line parallel to the R_{f }line and above it by vertical intercept of I_{a}R_{a}. The intersection of this line with the OCC gives two solution points R and S for the induced emf.

For these solution points the two terminal voltage values V_{1} and V_{2} can be read from the R_{f }line corresponding to points R’ and S’. Maximum possible armature current corresponds to point Q at which a line parallel to the R_{f }line is tangent to the OCC. Corresponding to each solution point, values of V and I_{f} can be read and I_{L} = I_{a} + I_{f},

can be calculated and subsequently the External Characteristics of DC Shunt Generator plotted as shown in Fig. 7.33. The short-circuit point on the external characteristic corresponds to I_{a}R_{a} = V_{r}, the residual voltage.

The voltage drop of armature reaction origin can be accounted for by modifying the OCC empirically.