In order to mine coal effectively in thick seam areas (seams with a height of around 1.8m) it has for many years become common practice to use a longwall shearer. Due to the efficiency of this method, new machine designs are also finding use in areas of thinner seams of around 0.6m. These machines can cut coal from the seam, quickly and effectively, with the aid of their cutting drums, which have an asynchronous motor running directly off the electrical network. The coal is then transported away from the longwall by means of a conveyor belt. To move the machine, up to four electrically powered main motors are used, each operated by a gear unit and a gear wheel engaging with a lantern wheel, a type of chain. The harsh underground conditions require all machine components to be extremely robust. Repairs on-site are extremely complicated due to limited space, the position of the machine in an explosion-proof area and the high exposure to dust. A longwall cutter can mine coal with a value of up to €1 Million per month. All the more important therefore for it to have a high degree of operational availability (>= 98.5%).
Due to the machine’s operational availability being very high and the difficult surrounding conditions, the ideal scenario for propelling the machine is to use maintenance friendly 3-phase AC motors with frequency converter control. The REFU components are directly integrated into the machine, so that they automatically benefit from explosion protection. While the one inverter is connected to the motor that powers the machine, the other ensures that the energy produced from, for instance, moving downhill is feed back into the electricity network. Energy recovery here is not simply a way of increasing efficiency, but also to prevent the generation of heat.
In addition to this, a master-slave mode ensures that the load distribution of the drives is optimally aligned so that an increase in vibration is prevented and that control and regulating efforts are reduced. The REFU solution also provides input and output voltages of up to 1140V, which means that additional transformers or cross-sectionally strong (copper) cable are not needed.
Power electronics from REFU
2 REFUdrive inverters designed especially for mining with strengthened resistance to shocks and vibrations. Incl. power recovery (block type) and cross communication for load distribution
Supplemented by customer with
- Motors (asynchronous motor, sensor-equipped or sensor-less operation (torque at zero speed, reverse rolling lock))
- Control system (PLC or PC with bus system)
For large machines, two of the described systems are required and synchronized using REFUlink.