Basic calculation process

The required effective and maximum power demand of the application are calculated based on the intended application speed and the resistance forces to be overcome. A suitable motor is selected after calculating these criteria. In this case, the startup behavior of the grid-powered motor power must be taken into account as a central feature. This can be considered only after the preliminary selection of the motor because of the significant influence of individual motor characteristics.

While torque development can be influenced for motors operated on an inverter, a line-powered drive always follows its acceleration characteristic curve.

During a grid-powered startup process, the motor current is far above the rated current, regardless of the load condition. Starting at values that can be greater than 8 × I_N, the motor current drops as the motor speed increases. Under nominal load, the rated current I_N flows at the rated speed n_N in the motor.

Since the motor current affects motor temperature rise quadratically, grid-powered startup operations lead to disproportionate heat generation. Due to the speed-dependent air flow, the internal cooling of the motor by the integrated fan has a reduced effect during startup. In order not to exceed a permitted temperature increase limit for a large number of starts per time, correspondingly long times with or without reduced torque requirements are necessary in intermittent duty. The permitted temperature increase limit relates to the reference time of 10 minutes described in the standard.

The result is a maximum no-load starting frequency, meaning the permitted number of starts of the motor without load. This permitted switching frequency is reduced if relevant application data, such as load torque and load moment of inertia, are included. To avoid overheating the motor under consideration, the calculated number of starts per hour may not be exceeded.

Non-controlled applications can be decelerated either through sufficient friction in the application or by a mechanical motor brake. Similar to acceleration torque, the deceleration torque of the gear unit output, deceleration times and braking distances are determined from existing inertia and load conditions as well as from the electromechanical properties of the drive. Only a change in inertia, braking torque or motor type has an influence on the braking behavior.