Load families

Constant torque, fan and constant power loads: torque and power against speed.

Try it: the three load families

Speed50 %

Constant torque
Variable torque
Constant power

Torque needed at this speed: 25 %
Power needed at this speed: 13 %

Centrifugal pumps and fans. Torque grows as speed squared and power as speed cubed: at half speed the fan needs only 25 % torque and 12.5 % power. This is why a VFD saves so much energy on fans.