Caterpillar has developed a new VFD for longwall systems to increase conveyor speed and torque control.
The VFD-A800/W800 VFD for longwall systems is designed to work in conjunction with CAT UEL and CST gearboxes to provide variable speeds for the armoured face conveyor, with increased load sharing between gearboxes and better efficiency in weak power networks.
According to the company "the medium voltage drive controls torque and speed to optimise longwall productivity, reduces wear and breakage of AFC components, and makes efficient use of electrical power".
It is built to avoid overload stopping and fine tunes AFC speed to match the operator's rate of production.
The VFD also increases equipment life by minimising stress on drives and chains, while optimising power usage and returning energy to the system when motors are used to brake drives.
"The Cat VFD can be easily retrofitted to existing Cat face conveyor systems. 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," Caterpillar added.The system has also been developed to overcome some of the danger of chain breakage as it monitors and shares the load between gearboxes to reduce stress on the AFC chains and on plow chains.
Extending chain life also reduces the need for chain tensioning.
It integrates Cat's Controlled Start Transmission, which is a planetary drive system with an integrated, infinitely variable multi-disc clutch.
This provides an automatic overload protection, soft starts, and a synchronised heavy-load startup.
The Cat VFD allows for maximum torque at startup and evenly distributes the load between the drives at both ends of the longwall shearer.
"The system immediately reacts to a blockage or chain break with a controlled shutdown," Cat stated.
"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."
Importantly, they are designed for use in underground mines, and are housed in separate explosion-proof cabinets, and due to current source inverter technology can be installed as far away as four kilometres from the motors, cutting the need for additional space at the face ends.
It has a rated power of 800kW, has a nominal speed of 1500 rpm with a max operational torque of 210%.