Why is armature current constant?

Basically in a field controlled dc motor, the armature current is kept constant (via some constant voltage source) while the field current is varied which will vary the field flux and interacts with the armature of motor and produce rotation.

How is armature current controlled?

Armature Control for DC Motors One way is by implementing armature resistance, which involves connecting a variable resistance in series to the circuit of the armature. Once resistance has been increased, the current flow through the circuit is reduced and the armature voltage drop is less than the line voltage.

What is armature constant?

Armature constant Ka, armature speed n in rpm & flux generated by the magnetic field φ in weber are the key elements in this calculation.

What is armature voltage control method?

In the armature control method, the speed of the DC motor is directly proportional to the back emf (Eb) and Eb = V- IaRa. When supply voltage (V) and armature resistance Ra are kept constant, the Speed is directly proportional to armature current (Ia). The motor back EMF (Eb) and Speed of the motor can be changed.

What is the unit of armature speed?

Speed of a DC Motor A = number of parallel paths. Z = total no. conductors in armature. Hence, speed of a DC motor is directly proportional to emf of rotation (E) and inversely proportional to flux per pole (φ).

How do you calculate armature power?

The power to the armature terminal is:

PT=VTIT.
PRA=I2ARA.
PRA=I2A(RA+RS)

How do you calculate armature speed?

Refer to the armature design specifications. Calculate the induced armature voltage using the formula Eo = (Z N M)/ 60 where Eo is the induced armature voltage. For example, if Z is 360 conductors, N is 1200 rpm and M is 0.04 Wb, then [(360)(1200)(0.04)]/60 equals 288 volts.

What is the major drawback of armature voltage control method?

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.

How do you calculate armature voltage?

Calculate the induced armature voltage using the formula Eo = (Z N M)/ 60 where Eo is the induced armature voltage. For example, if Z is 360 conductors, N is 1200 rpm and M is 0.04 Wb, then [(360)(1200)(0.04)]/60 equals 288 volts.