What is critical resistance of a 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 Critical Speed of a DC shunt generator also explain the condition for voltage development?

This speed n2 is hence called Critical Speed. Thus Critical Speed is that speed at which the DC Shunt Generator just fails to buil up voltage with no external resistance in the field circuit.

How do you find the critical resistance of a DC shunt generator?

Generally data for plotting the open circuit characteristics is given. Plot the characteristics on the graph paper to the scale. Draw the tangent, to the initial part of this O.C.C. then the slope of this line is the critical resistance for the speed at which the data is given.

What is DC shunt generators?

A DC shunt generator is one kind of electric generator where both the windings like field & armature are allied within parallel. So the armature provides both the field & load currents. A DC generator without a permanent magnet needs a DC field for excitation.

What is critical speed and critical resistance of dc 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.

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 do you mean by critical speed?

Critical speed (nk) is the rotational speed at which acting dynamic forces cause a machine component (e. g. shaft, rotor) to vibrate at its natural frequency (also referred to as intrinsic frequency, fi) and can even result in resonant vibrations throughout the entire machine and pump set.

Does the OCC change with speed?

The O.C.C. curve is just the magnetization curve and it is practically similar for all type of generators. curve is obtained by operating the generator at no load and keeping a constant speed. Field current is gradually increased and the corresponding terminal voltage is recorded.

How does shunt generator work?

A shunt generator is a type of direct current electric generator in which field winding and armature winding are connected in parallel, and in which the armature supplies both the load current and the field current.

What is critical speed of a shunt generator?

Critical speed is defined as the speed at which the given shunt field resistance is equal to the critical resistance. It is the speed at which the shunt generator just fails to build up its voltage without any external resistance in the field circuit. It is denoted by N c. Significance of Critical Speed :

What is critical speed of a DC generator?

Significance of Critical Speed : If the speed of the dc machine is reduced to a value such that the field resistance line does not pass through the O.C.C then the machine fails to induce i.e., it may not generate any appreciable voltage. The speed at which the generator fails to build up the voltage is known as the critical speed.

Why does voltage build up in a shunt DC generator?

There are three important reasons of voltage buildup in a shunt DC generator there must be residual magnetic flux in the generator to start the process going. The direction of rotation of generator and connection of the field circuit must be correct. The field resistance may be adjusted to a value lesser than the critical resistance value.

What is critical resistance in a shunt field circuit?

The voltage corresponding to this point is E C. This voltage is just sufficient to drive the current through field resistance so that cumulative process of building the voltage starts. This value of field resistance is called critical resistance denoted as R C, of the shunt field circuit at given speed.