ABB regenerative drives give big payback on downhill conveyors.


ACS800-11 - regenerative wall-mounted single drives


ABB regenerative drives give big payback on downhill conveyors.


Using ABB regenerative AC drives fed 520,000 kW of power back into the mains and significantly reduced maintenance costs by improved control on two limestone conveyors used in cement making.


Continuous raw material flow is important in cement making and when processing minerals. Raw materials are mostly transferred using various conveyors. Downhill conveyors are used to transport ore, limestone and other materials, from deposits high in the hills.


Continuous braking of the downhill conveyor is needed to prevent excessive movement of the belt and its raw material. The level of braking needed varies depending on the amount of raw material transported. This braking control avoids unnecessary conveyor wear. Downhill conveyors also require smooth and controlled starting and stopping.


An AC drive provides the most efficient and effective way to meet the challenges presented by downhill conveyors.


Regenerative braking saves energy

AC drives provide accurate speed and dynamic torque control of the conveyor’s belt motors. Precise speed and torque control is required for the continuous braking need demanded by downhill conveyors. With an AC drive, the braking energy can be fed back into the plant’s electrical network, thereby reducing energy consumption. AC drives offer smooth and controlled starting and stopping of the motors, minimizing belt stretching and breaking while eliminating belt slipping. This results in prolonged belt lifetime and high uptime.


Option 1            Regenerative single AC drives

Regenerative single AC drives (one drive per one motor) can be used to control the two downhill conveyor motors running the belt (see A). Both motors are mechanically connected to the belt and therefore need to rotate at identical speed and torque. Since the conveyor belt speed is limited continuously, the motors act as generators. Braking energy of both motors is fed to the AC drives, which in turn, feed the energy into the plant’s electrical network for use elsewhere in the plant.


Option 2            AC drives with braking choppers and resistors

If the amount of energy consumption is not important, the operation of a downhill conveyor can be controlled using a diode supply unit(s) instead of the above mentioned regenerative supply unit(s). Braking energy is dissipated with the help of braking choppers and braking resistors.


With a downhill conveyor, the single AC drives are connected to each other in a master-follower arrangement. The master drive is given the speed reference by the automation system. The master drive then sends a speed reference and a torque reference to the follower drive. This arrangement ensures that the speeds of both motors are identical and that the load is equally divided between the motors.


Huge energy savings

At Vigier Cement, Switzerland, variable speed control of two limestone conveyors, by means of ABB AC drives, generated back into the mains over 520,000 kWh of electrical energy in less than two years.


Maintenance costs were reduced by the smooth starting and stopping of the conveyers, and from less wear and tear through equal distribution of load between the motors and elimination of undesirable dynamic effects


See full ABB article here


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