Q. DC Motor Characteristics?

We gain an understanding of the speed-torque characteristics of a dc motor from Equations. In shunt motors, the field current can be simply controlled by the use of a variable resistance in series with the field winding; the load current influences the flux only through armature reaction, and its effect is therefore relatively small. In series motors, the flux is largely determined by the armature current, which is also the field current;

it is somewhat difficult to control the armature and field currents independently. In the compound motor, the effect of the armature current on the flux depends on the degree of compounding. Most motors are designed to develop a given horsepower at a specified speed, and it follows from Equation that the angular velocity ω_m can be expressed as

Thus, the speed of a dcmotor depends on the values of the applied voltage V_t, the armature current I_a, the resistance R_a, and the field flux per pole φ.