A. Constant Torque and Variable Speed Loads Characteristic
The torque required by this type of load is constant regardless of the speed. In contrast, the power is linearly proportional to the speed. Equipment, such as screw compressors, conveyors and feeders, has this type of chacteristic. Fig. 2 shows constant torque and variable speed loads characteristic of induction motor.
B. Variable Torque and Variable Speed Loads Characteristic
This is most commonly found in the industry and sometimes is known as a quadratic torque load. The torque is the square of the speed, while the power is the cube of the speed. This is the typical torque-speed characteristic of a fan or a pump. Fig. 3 shows variable torque and variable speed loads characteristic of induction motor.
C. Constant Power Loads Characteristic
This type of load is rare but is sometimes found in the industry. The power remains constant while the torque varies. The torque is inversely proportional to the speed, which theoretically means infinite torque at zero speed and zero torque at infinite speed. In practice, there is always a finite value to the breakaway torque required.