Why the armature resistance is kept very small as compared to shunt field resistance?

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.

What is field resistance and armature resistance?

Speed Control of DC Motor: Armature Resistance Control and Field Flux Control. The dc motor converts mechanical power into dc electrical power. Here equation (1) shows the speed is dependent upon the supply voltage V, the armature circuit resistance Ra and the field flux ϕ, which is produced by the field current.

What is the effect of the armature range on the shunt resistance?

The Shunt field is parallel to the armature field, so its resistance must be high for minimum value of shunt field current. If its value will be low then armature current will be lower and power delivered will be less.

How the starting resistance is connected with armature of DC motor?

During starting, full resistance is added in series with the armature winding. Then, as the lever is moved further, the resistance is gradually is cut out from the armature circuit.

What is an armature resistance?

[′är·mə‚chər ri′zis·təns] (electricity) The ohmic resistance in the main current-carrying windings of an electric generator or motor.

What is the resistance of armature winding?

Armature Winding resistance is the ohmic resistance of the copper winding wires. A brush is used to provide electrical contact between the stationary contacts and moving parts like commutator or slip rings. Brushes are mainly made of carbon material which is high resistance brushes compared to copper brushes.

Why is field resistance higher than armature resistance?

There need to be sufficient winding resistance within the field winding to restrict the current drift. However, it is necessary that the armature resistance is low because the DC generator generates excessive currents and any DC armature resistance will cause decrease in generator performance.

What is meant by armature resistance?

Why should the resistance of shunt field winding be high?

Hence as the current through series field winding is high, in order to keep voltage drop across it to a small value, its resistance is very low. On the other hand, the shunt field winding is directly connected across the rated supply voltage hence to limit current through it, resistance is very high.

What is the purpose of a starting resistance in a DC motor starter?

Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.

How to calculate the resistance of an armature circuit?

The armature circuit resistance can then be calculated by using the following basic steady state DC motor equation: E = I x R + (Ke x w), where E = applied voltage

How does the armature resistance affect the speed of a motor?

By varying the armature circuit resistance, the current and flux both are affected. The voltage drop in the variable resistance reduces the applied voltage to the armature, and as a result, the speed of the motor is reduced. The speed–current characteristic of a series motor is shown in the figure below.

What are the disadvantages of armature resistance control?

Disadvantages of Armature Resistance Control Method A large amount of power is wasted in the external resistance Re. Armature resistance control is restricted to keep the speed below the normal speed of the motor and increase in the speed above normal level is not possible by this method.

What is the resistance of the resistor in the field circuit?

The resistor in the field circuit should have zero resistance during the starting period. The armature current rises to a predetermined value, the armature begins to rotate and a rotational or back e.m.f. is generated.