What is the effect of the speed of a DC motor if the resistance in series with it is increased?

Armature control method That means, when supply voltage V and the armature resistance Ra are kept constant, then the speed is directly proportional to armature current Ia. Thus, if we add resistance in series with the armature, Ia decreases and, hence, the speed also decreases.

What would happen if a series resistance is inserted in the field circuit of a DC shunt motor at a constant supply voltage?

For a constant supply voltage, what are the effects of inserting a series resistance in the field circuit of a dc shunt motor, on its speed and torque? (a) Speed will decrease and the torque will decrease.

What is the effect of inserting a resistor in series with the armature coil of a long shunt DC motor?

The starter can be used for starting a d.c. series motor if it is fitted with a separately-excited no-volt coil. A 110-V d.c. shunt motor has an armature resistance of 0·3 Ω. Determine the armature current (a) when the back e.m.f. is 104 V, (b) at the instant when the armature is connected to a 110-V d.c. supply.

What happens if the additional resistance is added in series with armature?

In DC series motor, with increase in resistance of armature circuit increases the voltage drop in armature circuit and series field increases and therefore back emf decreases.

What is the effect of the speed control of the DC motor to the resistance control?

An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed. This method of speed control is independent of load on the motor. Power wasted in controlling resistance is very less as field current is a small value.

When the speed of DC motor increases the armature current?

From the equation. (3) we can say, speed is inversely proportional to armature current. Thus, when the speed of the dc motor is increased, the armature current will decrease.

What would happen if a series resistance is inserted in the field?

If a resistance is added in series with field winding of d.c. shunt motor, then its speed increases, torque decreases.

What would happen if a series resistance is inserted in the field circuit of a DC shunt motor?

Field Rheostat Controlled DC Shunt Motor In this method, speed variation is accomplished by means of a variable resistance inserted in series with the shunt field. An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed.

What is the relation between armature torque and armature current in dc series motor?

The torque in case of a dc series motor is proportional to the square of the armature current. This relation is parabolic in nature as shown in the figure. As load increases, armature current increases and torque produced increases proportional to the square of the armature current up to a particular limitation.

What is the resistance of armature?

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.

How the armature resistance are determined?

A practical way to measure the winding resistance is to use the Ohm’s law: Resistance = Voltage / Current. If you apply a power source to the windings and measure the voltage and current flowing through them, a simple division will yield an accurate value for the resistance.

Does the variable resistance affect the flux in a DC motor?

The variation in the variable resistance does not affect the flux as the field is directly connected to the supply mains. The speed current characteristic of the shunt motor is shown below. Now, let us consider a connection diagram of speed control of the DC Series motor by the armature resistance control method.

How does the speed of a DC series motor depend on voltage?

The speed of the DC series motor depends upon voltage drop across variable resistance. Higher the voltage drop across the armature, lower the speed. However there is considerable power loss in the variable resistance. This method is economical for constant torque drives. A variable resistor is connected across the armature in this method.

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.

How do you control the speed of a variable resistance motor?

For a given value of variable resistance, the speed reduction is not constant but varies with the motor load. This speed control method is used only for small motors. Flux is produced by the field current. Thus, the speed control by this method is achieved by control of the field current.