These motors are made for the application requirements of variable acceleration drive systems. You can expect both the following types of motors:
• Constant Torque: Motors specifically designed to handle continuous torque loads, such as for example Variable Drive Motor conveyors, positive displacement pumps, cranes, etc.
• Variable Torque: Motors specifically designed to handle variable torque loads such as pumps and fans.
Due to speedy switching and reflections in the cables, motors are subject to more voltage tension in the windings when fed by frequency converters than with sinusoidal supply voltage. The result of these voltages can be an increase of up to 2.5 times the motor’s nominal voltage. This stresses the electric motor winding insulation and can cause it to break down, resulting in feasible sparking. ABB recommends:
Between 500 V or more to 600 V, the motor will need reinforced winding insulation, or the drive must have a du/dt filter.
Above 600 V, the motor will need reinforced winding insulation and the 
drive must have got a du/dt filter.
If the cable length between the drive and electric motor is greater than 150 meters and the voltage is between 600 and 690 V, the electric motor will need to have reinforced winding insulation.
A variable-frequency drive is a system for controlling the rotational quickness of an alternating electric current electric motor. It handles the frequency of the electrical energy supplied to the motor. A variable frequency drive is certainly a specific type of adjustable-quickness drive. Variable-frequency drives are also called adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, or inverter drives.
Automatic frequency control consist of an primary electrical circuit converting the alternating electric current into a direct current, after that converting it back to an alternating electric current with the required frequency. Internal energy reduction in the automated frequency control is rated ~3.5%
Variable-frequency drives are trusted on pumps and machine device drives, compressors and in ventilations systems for large buildings. Variable-frequency motors on followers save energy by allowing the volume of air moved to complement the system demand.
Reasons for employing automated frequency control can both be linked to the functionality of the application form and for saving energy. For example, automatic frequency control can be used in pump applications where the flow is definitely matched either to volume or pressure. The pump adjusts its revolutions to confirmed setpoint with a regulating loop. Adjusting the flow or pressure to the real demand reduces power intake.
An AC motor speed control-also referred to as a variable frequency drive, adjustable frequency drive, variable acceleration drive, adjustable acceleration drive and AC inverter-is an electro-mechanical object that can be utilized to improve the output speed of an AC engine by adjusting the input frequency in to the motor.