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.

What will happen if the field circuit resistance of a DC shunt generator exceeds its critical value?

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

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 critical resistance of DC shunt generator?

The critical field resistance (RC) of a DC shunt generator is defined as the maximum field circuit resistance with which the shunt generator would just excite. The voltage build-up in a shunt generator depends upon field circuit resistance.

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

Voltage will not build up if the field resistance is greater than critical resistance. The speed of the generator should be greater than the critical speed. This can be remedied by increasing prime mover speed above critical speed.

What is the effect of field resistance?

Explanation: As the field resistance increases the speed decreases.

What is the purpose of resistance wire used in the commutator connection in dc generator?

The function of a commutator in a dc generator is to collect the current generated in armature conductors. While in the case of a dc motor, the commutator helps in providing current to the armature conductors. A commutator consists of a set of copper segments that are insulated from each other.

What are the conditions to buildup EMF in dc shunt generator?

Conditions to build up the voltage in shunt generator: The shunt winding should have a residual magnetic field. The direction of the shunt winding and armature winding should be in such a way that flux generated by them should aid together. The shunt winding should have critical winding resistance.

What is critical speed and critical field resistance of dc shunt generator?

Answer:Critical Field Resistance: It is that value of the field resistance at which the D.C. shunt generator will fail to excite. Critical Speed: It is that speed for which the given shunt field resistance becomes the critical field resistance.

What will happen if field resistance is decreased?

What will happen if field resistance is decreased? Explanation: When field resistance is decreased, it will increase field current by Ohm’s law. Thus, field resistance line will lie below the older line of field resistance. Eventually, it’ll intersect OCC afterwards causing increase in no-load voltage.

How to increase the load current in a shunt field DC generator?

When we run the shunt field DC generator with its rated speed the terminal voltage will build up and will get fixed at its rated value. Now we connect the load and slowly increase the load current by introducing load resistance in parallel one by one.

Why is the slope angle of a shunt DC generator constant?

Because in shunt dc generator the armature terminal voltage appears across the shunt field winding. Hence, this armature voltage divided by the corresponding field current is nothing but the shunt field resistance. Now if we slowly increase the resistance of the field coil, the slope angle of the straight line increases accordingly.

What is the Critical Resistance of the shunt field?

The maximum resistance below which the generator builds the armature EMF. We call this value of resistance as the critical resistance of the shunt field. So we can conclude that, above the critical resistance a dc generator fails to build up armature EMF.

How does a shunt wound DC generator work?

In shunt wound DC generators the field windings are connected in parallel with armature conductors as shown in figure below. In these type of generators the armature current Ia divides in two parts. One part is the shunt field current Ish flows through shunt field winding and the other part is the load current IL goes through the external load.