Bulk Material Handling Conveyors: About VFDs
December 8, 2016
Undue stresses on bulk material handling conveyors such as bucket elevators, aeromechanical, and flexible screw conveyors can be reduced or eliminated through the use of Variable Frequency Drives (VFD) installed on the equipment. VFD’s offer a proven and cost-effective way to reduce equipment breakdowns and malfunctions, and greatly facilitate the root cause analysis of the underlying reasons for throughput losses. VFD’s also allow the flexibility of making quick speed changes for adapting to upstream or downstream processes.
Sometimes known as adjustable speed drives, a VFD is a type of electronic regulator used on conveyor and other drive systems to control AC motor speed and torque by varying the motor input frequency and voltage. Because they allow the user to specify conveyor motor speed and torque, VFD’s protect throughout by detecting situations of abnormal motor behaviour, shutting down equipment before damage can occur. Due to their proven effectiveness in protecting throughput and equipment from harm, UniTrak often recommends the factory installation of VFD’s on new bulk material handling conveyors we supply.
When installed on bulk material handling conveyors, VFD’s provide the following benefits:
Equipment start-up control. When started “across the line”, an AC motor can draw a significant amount of current, often as much as eight times the normal full load current normally drawn by the motor. Installing a VFD can substantially reduce this start-up current draw, reducing wear and tear on the motor and extending its life.
Similarly, a high current draw at start-up can affect a facility’s power distribution system in several ways. Firstly, voltage fluctuations caused by high current draw can trip breakers and possibly damage other sensitive equipment installed on the same supply line. Secondly, at start-up, a conveyor tends to draw higher load from the distribution system. Installing a VFD can help address both of these conditions by eliminating voltage fluctuations and the amount of power required at start-up.
Torque, acceleration and speed control. Starting a conveyor AC motor without a VFD installed can create large and sudden amounts of torque, possibly inflicting significant mechanical shock and stress on the motor itself as well as on any load present in the equipment. With a VFD, the amount of torque applied can be accurately controlled, permitting equipment start-up at zero velocity with a smooth acceleration up to normal operating speed. In addition, with a VFD, a motor torque limitation threshold can be set which prevents equipment damage in the event of a jam or other catastrophic event.
Installing a VFD allows operators to easily introduce variations in operating speed to equipment without shocking the load. A VFD can also enable reversed operation without the need for a reversing starter, and the device allows a controlled equipment stop if desired. Adjustments to the VFD can even be introduced remotely to the VFD programmable controller, eliminating the need for speed adjustments to be done right at the equipment.
Equipment Efficiency. Since a VFD operates on the principle of programmable variable speeds, maintenance interventions to adjust equipment operating speeds can be eliminated. Finally, conveyors outfitted with a VFD have less energy consumption, reducing the plant energy bill as a consequence.
Equipment failure root cause analysis. Because an installed VFD can shut down equipment immediately once an abnormal motor condition is detected, operators can be immediately alerted and the causes of the failure rapidly investigated.
Modern VFD’s are often equipped with Ethernet connections, allowing remote monitoring and feedback from the motor. Ethernet will also allow connectivity to IIOT (Industrial Internet of Things).
Taken together, the installation of a VFD on bulk material handling conveyors can provide significant benefits. To find out more about how UniTrak can help protect your throughput with our lineup of quality bulk material handling conveyors, please contact our sales department.
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