Operating point

The machine creates the counter-torque, e.g. by being a moved device which needs permanent energy or a wheel turning against the static friction of the track.

At the operating point, the driving torque and the counter-torque are balanced, so the speed does not change anymore.

Also in case of an unstable operating point the law of the balance of the torques is always valid.

In the lower right picture the electrical drive (AC motor) moves a conveyor belt.

At the other operating points the majority of the electrical power (proportional only to the torque) will be only converted into heat inside the drive.

In case of such machines with constant torques a coupling can be used to prevent stopping during start up, it should be rotation speed dependent.

With the coupling the counter torque will only be introduced when the load-less drive has reached a speed outside of the unstable working point.

The operating point in an amplifier is set by the intersection of the load line with the non-linear characteristics of the device.