Applying the Altivar ATV61 AC Drive in Constant Torque Applications
The AC drive industry has traditionally identified applications as either variable torque or constant torque. Schneider Electric has produced a guide to applying their Altivar ATV61 variable torque drive in constant torque applications to give significant price savings.
Normally selected to deliver robust energy saving performance for centrifugal pump and fan applications the variable torque capability Altivar ATV61 is also suitable for some in normal duty, constant torque applications.
In variable torque applications, motor load changes with the square of the speed and horsepower changes with the cube of the speed. Variable torque applications include centrifugal pumps and fans and typically require drives able to provide up to 120% of normal current for variable torque applications for up to one minute.
Most other AC drive applications have conventionally been defined as constant torque. In this application, motor load is not a function of speed; as speed changes, load torque remains constant and power changes linearly. Constant torque applications include: augers, some compressors, conveyers, hoists, mixers, and positive displacement pumps. Constant torque drives are generally able to provide up to 150% of normal current for constant torque applications.
For an increasing number of constant torque applications however, an AC drive rated at 150% is not required for starting and operating the load connected to the motor. In some instances, excessive torque may damage connected equipment.
Importance of Torque Requirements
Understanding the starting-torque requirements, over-torque requirements, and the operational speed of the application are all important factors in selecting and providing the most cost-effective solution for the end user. There are a significant number of applications where the ATV 61 drive is a more cost-effective solution than the ATV 71 drive or a competitive AC drive.
Lower power ATV 61 and ATV 71 drives are built with a common power platform and are dimensionally equal for any given power rating. In the higher power range, the ATV 61 hardware design, power components, and frame sizes are optimized for normal duty and variable torque applications.
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