Conveyor users and conveyor manufacturers have accepted the drum motor as the most efficient way to drive belt conveyors. With no external motor and gearbox, the drum motor saves space, eliminates the need for scheduled maintenance and enhances operator safety.
However, the challenge has been the ease and ability to adjust belt speed as plant processing requirements change. This is achieved via a frequency inverter (VFD), which often is located in a control room some distance away from the conveyor drive electric motor.
The long cable connecting the VFD to the electric motor can impede motor performance and substantially reduce its life and reliability. Voltage attenuation, due to the long cable length, contributes to inconsistent power being delivered to the motor. Resulting high-voltage electrical spikes amplification in the motor windings can cause complete motor failure.
The general approach to overcome these issues is to substantially increase the dielectric strength value of the magnet wire used in the electric motor windings. Sinusoidal filters also are installed to condition the power going to the motor and filter high-voltage spikes caused by the pulse-simulated sine wave of the VFD.
Recently, Van der Graaf (VDG) began developing an advanced drum motor design with the VFD integrated into the motor junction box. The follow-up design to the built-in VFD is the development of an electric motor with even higher efficiency and additional capabilities.
On a standard electric motor, the rotor has to be magnetically induced by the stator. Using part of the magnetization produced by the stator windings to magnetically induce the rotor results in significant magnetic energy losses and reduces mechanical output. As a result, motor efficiency decreases.
With the VDG Intelligent Drum Motor (IntelliDrive) design, the rotor is magnetically self-induced by the use of permanent magnets installed on the rotor body. Lab test results show electrical savings of up to 72 percent vs. a conventional motor/gearbox conveyor drive.
The IntelliDrive requires a sensorless vector control to operate, and due to this requirement, must be used with the integrated VFD. The integrated VFD is EtherNet/IP and MODBUS compatible and enables communication with other plant equipment. It also can provide conveyor drive data feedback and control belt speed either remotely or directly at the drum motor. The combination of the rotor with permanent magnets and the integrated VFD, distinguishes the IntelliDrive from a standard drum motor.
The IntelliDrive simplifies the selection of belt speed without loss of torque or belt-pull, substantially increasing the efficiency and the life of the electric motor, further minimizing downtime and decreasing overall operating costs. The innovation is best for portable plants, according to VDG.
Van der Graaf (VDG), www.vandergraaf.com