What would happen if the critical resistance of a generator is more than the field resistance of generator?

Critical Field Resistance of DC Shunt Generator If the field circuit resistance is increased to R2, then the generator will build-up a voltage V0 slightly less than V0. Now, if the field circuit resistance is increased beyond this point (as line OD), then the generator will fail to excite.

What is the effect if the field resistance is above critical resistance value in DC generator?

The field circuit resistance is increased to R2 (line OB), the generator will build up a voltage OL, slightly less than OM. Now the field circuit resistance is increased beyond this point (say line OD), the generator will fail to excite.

Why the armature resistance of a DC generator is very low?

The armature produces a back EMF depending on its speed, which bucks the supply voltage. The armature current then will depend on the difference between the supply voltage and the EMF. So the armature resistance must be low enough to allow sufficient current to flow even with this reduced voltage.

Why the external characteristics of a DC shunt generator is more drooping than that of a separately excited generator?

The DC shunt generator has drooping characteristics because the terminal voltage decreases as the load current increases.

How can the critical resistance of a dc generator be increased?

The speed for which the given field resistance acts as critical resistance is called the critical speed, denoted as NC. The range of Critical resistance of a DC generator can be increased by increasing its speed.

What is the significance of critical resistance?

The critical field resistance is defined as the maximum field circuit resistance (for a given speed) with which the shunt generator would just excite. The shunt generator will build up voltage only if field circuit resistance is less than critical field resistance.

What will happen to the DC generator if the field winding attends the critical resistance?

If the field resistance of a d.c. generator is more than particular value ( critical resistance), The generator will fail to build up the voltage.

What will happen if the field resistance is above the critical resistance?

Note : If field circuit resistance is more than RC at start then induced e.m.f. fail to drive current through field circuit and generator fails to excite at given speed. The critical resistance is the slope of the critical resistance line.

Is the field of dc shunt generator of comparatively low resistance or high resistance?

The shunt field, therefore, must have a comparatively high resistance that it does not take too great a proportion of the generator current. The compound generator is similar to the shunt, but has an additional field winding connected in series with the armature or load.

Why the external characteristics droop?

(b) There is voltage drop across armature resistance (= ILRa = IaRa). Due to these reasons, the external characteristic is a drooping curve [curve 3 in Fig. Note that in the absence of armature reaction and armature drop, the generated e.m.f. would have been E0 (curve 1).

What are the characteristics of a DC shunt and series generator?

Characteristics of DC Shunt Generator To build up voltage of a shunt generator, the generator is driven at the rated speed by a prime mover. Initial voltage is induced due to residual magnetism in the field poles. The generator builds up its voltage as explained by the O.C.C. curve.