The use of inverter in the conveyor belt ensures reliable operation, reduced maintenance costs and energy savings. The following article from PEKKA PULKKI, ABB OY, Finland will detail the benefits of using the inverter.

Conveyors are used extensively in many stages of the mining process, often used in demanding conditions, with common problems that the conveyor belt can stretch, slip or break. Continuous conveyor belts will wear out, become unreliable and may cause malfunction. For industries with high requirements for continuity of production, the problem on conveyors will cause a lot of damage.

Inverters help protect conveyor and mechanical equipment by accurately controlling the speed and torque of the motor, extending the conveyor belt life and minimizing operator and maintenance costs. At the same time, if a joint of the conveyor needs to be repaired, the inverter will drive the conveyor belt to the correct position for easy repair.

Controller to operate the conveyor more stable

The conveyor belt drive has a very high starting torque. Large start-up torque leads to mechanical damage and overloading of the power supply. Especially on long conveyors, the higher the reload load, because there are more materials on the conveyor belt. Then the start-up process requires higher starting torque and higher start-up currents. Soft starters can be used to reduce the start-up current, but also reduce the starting torque. If the starting torque is not large enough to overcome the inertia of the conveyor belt, the conveyor will not start.

Inverter can generate high starting torque but still ensure the starting current within the allowable limits of the grid, the start-up current is not raised too high and the grid voltage does not drop during the start-up. In addition, the inverter can adjust the power factor is always a stable value, thus contributing to the stabilization of the grid. With a more stable grid, all electrical equipment in the plant operates more reliably, improving productivity and reducing malfunction. A smooth-running conveyor with a well-controlled torque also reduces the tension and slippage of the conveyor.

In addition to minimizing operational problems of the conveyor belt, the inverter offers efficient operation by smooth and precise control of the conveyor belt speed, allowing the conveyor belt to be adjusted in accordance with regulatory requirements. Inverters can also be connected to the plant's automated system, to monitor the load, the velocity from which the total load is calculated.

If the mechanical conditions permit, the inverter can help to increase the motor speed as required. For other applications requiring motor drive inverter under rated speed, there will be a problem with engine cooling if using a self-cooled engine. For such applications, the use of forced-cooling motors is better.

Energy saving

Energy is saved when the engine is running at low speed as required by the load and saved by removing the reactive power compensation device.

Furthermore, in the case of conveyor belts with multiple sloping sections, the conveyor's function can be transformed into electric power to return the grid to regenerative braking. Using the inverter, the conveyor is able to run smoothly throughout the loading line, not affected by the shape, curvature of the road. The mechanical energy as the conveyor runs on the sloping sections can be returned to the grid with the regenerative variable. In addition, this mechanical energy can also be utilized with the dual inverter multi-drives system, whereby an inverter controls multiple motors at the same time. Multi-drives inverters use the same DC bus. Then the mechanical power emitted by the engine in the generator mode (running down the conveyor belt) will be used to run another engine running in the engine mode.

The use of ABB industrial inverters with DTC controllers offers another benefit that allows the engine to divide the load. Load-sharing engines will not have to work with heavy loads, so the engine is less heat-sensitive, damaged, and the loading process is less interrupted.

The DTC also detects when the load on the conveyor belt rises abruptly, demand suddenly increases. As a result of these quick changes, the inverter can respond immediately. An inverter with other control systems may stop in these situations.

Inverters for long conveyors

The Midland Quarry Pruducts in Leicester, England, has one of the longest quarry conveyors with variable operating speeds at Old Cliffe Hill. The conveyor is 1.5 km long and transports granite from the quarry, through the 713m underground tunnel, before transporting it to the secondary processing plant.

Before being shipped, the stone was crushed by a 450kW, 3.3kV rotary mill. The conveyor system consists of six individual conveyor belts, each with a width of 1600 mm and a different length. The primary processing of granite mining (grinding + conveying) operates with a capacity of 2500 tons per hour and is the main part of the whole process. The speed of the conveyor belt is controlled by the industrial ABB. The first conveyor using 200kW inverter; 3 conveyor with 1 inverter 200kW; and the last conveyor using 132kW inverter.

Two inverters are used in the first conveyor using the master-follower software, ensuring that one inverter controls the other and the other inverter operates accordingly. This limits motors to operate asynchronously, leading to broken conveyors.

Conveyor stops with the marble on conveyor, then know the frequency of the engine start softly, bringing the conveyor gradually back to the operating speed. Without the inverter, the motor can be overloaded and burned out.

Using the inverter helps to control the speed and position of the conveyor belt to transport the stones to the right rock warehouse.

Simplified design

Inverters simplify the design of the conveyor system, reducing investment and maintenance costs. With adjustable motor speeds, it is possible to use a simpler transmission in the conveyor system. In some cases, the transmission can be completely removed, increasing the conveyor system efficiency. Asynchronous motors are used with durable structural features, low maintenance costs.

Transmission is smoothly controlled, reducing overloads in transmission couplers and transmission, increasing the life of these components.

Inverter can also help the conveyor belt maintenance process easier because of the reverse rotation of the engine. The inverter reverses and stops the conveyor at the required position for repair. If the conveyor is jammed, the inverter can detect and stop the conveyor belt.

By improving stability, lower maintenance costs, more precise control, and more energy efficiency, inverters have clearly benefited conveyors in particular and mining equipment.

ABB Vietnam (general)