The performance of a d.c. motor under various conditions can be judged by the following characteristics
i) Torque – Armature current characteristics (T Vs Ia ) :
The graph showing the relationship between the torque and the armature current is called a torque-armature current characteristic. These are also called electrical characteristics.
ii) Speed – Armature current characteristics(N Vs Ia ) :
The graph showing the relationship between the speed and armature current characteristic.
iii) Speed – Torque characteristics(N Vs T) :
The graph showing the relationship between the speed and the torque of the motor is called speed-torque characteristics of the motor. These are also called mechanical characteristic.
The nature of these characteristics can easily be obtained by using speed and torque equations derived in previous post. These characteristics play a very important role in selecting a type of motor for a particular application.