| A liquid cooled variable frequency drive (VFD) monitors and shares the load between gearboxes. |
The new Cat VFD-A800/W800 Variable Frequency Drive (VFD) for longwall systems is designed to work in conjunction with UEL and CST gearboxes to deliver variable speed of the armored face conveyor (AFC), very accurate load sharing between gearboxes, and better efficiency when operating in weak power networks. The advanced technology medium-voltage drive controls torque and speed to optimize longwall productivity, reduces wear and breakage of AFC components and makes the most efficient use of electrical power.
The VFD delivers optimum startups, helps avoid overload stopping and fine tunes AFC speed to match the rate of production. At the same time, the system increases equipment life by minimizing stress on drives and chains. Also, the system optimizes power usage and even returns energy into the system when motors are used to brake drives. It can be easily retrofitted to existing AFCs. Since the VFD operates on standard asynchronous motors, it does not require a change of the electrical network. In fact, it will generate more effective power, even from weaker sources.
Substantial changes to the load on the AFC as well as blockages always present the danger of chain breakage, and such events certainly cause chain stretching. The Cat VFD system monitors and shares the load between gearboxes with nearly 100% effectiveness to reduce stress on AFC chains and on plow chains. Extending chain life also reduces the need for chain tensioning, and adjusting speed and torque by varying the frequencies of the alternating current enables precise and stepless control. The Cat VFD allows maximum torque at startup and evenly distributes the load between the drives at both ends of the longwall. The system immediately reacts to a blockage or chain break with a controlled shutdown. In regular operation, the speed of the AFC can be adjusted steplessly to load requirements when the plow or shearer are cutting the same direction or opposite direction of the AFC. Also, the complete longwall can easily adjust to the capacities of the subsequent coal clearance components such as the crusher, stage loader and belt conveyor.
The Cat VFD will plug in to existing systems. Cat VFD drive systems are housed in separate explosion-proof cabinets, and, due to current source inverter technology (CSI), they can be installed as far as 4 kilometers (2.5 miles) from motors. Compared to other systems that integrate VFD control into motors, they do not require additional space at the face ends. Also, unlike some other systems, the Cat VFD does not cause EMC effects such as over-voltages, reflection waves, or other unwanted ground currents or network disturbances.
