VOLTAGE EQUATION OF MOTORS
Let in a d.c. motor
V = applied voltage
Eb = back e.m.f.
Ra = armature resistance
Ia = armature current
Since back e.m.f. Eb acts in opposition to the applied voltage V, the net voltage across the armature circuit is V-Eb.
The armature current Ia is given by
APPLICATIONS OF DC MOTORS:
1. D.C Shunt Motors:
It is a constant speed motor.Where the speed is required to remain almost constant from noload to full load.Where the load has to be driven at a number of speeds and any one of which is nearly constant.
Spinning and Weaving machines.
2. D.CSeries motor:
It is a variable speed motor.The speed is low at high torque.At light or no load ,the motor speed attains dangerously high speed.The motor has a high starting torque.(elevators,electric traction)
3. D.C Compound motor:
Differential compound motors are rarely used because of its poor torque characteristics. Industrial uses:
CLASSIFICATION OF DC MOTOR
DC motors are more common than we may think. A car may have as many as 20 DC motors to drive fans, seats, and windows. They come in three different types, classified according to the electrical circuit used. In the shunt motor, the armature and field windings are connected in parallel, and so the currents through each are relatively independent. The current through the field winding can be controlled with a field rheostat (variable resistor), thus allowing a wide variation in the motor speed over a large range of load conditions. This type of motor is used for driving machine tools or fans, which require a wide range of speeds.