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New Cat variable frequency drive for longwall systems

World Coal,

The new Cat® Variable Frequency Drive for longwall systems increases face conveyor speed and torque control to boost productivity in mining applications.

The Cat VFD-A800/W800 Variable Frequency Drive is designed to work in conjunction with Cat UEL and Cat CST gearboxes to deliver variable speed of the armored face conveyor, accurate load sharing between gearboxes, and better efficiency when operating in weak power networks.

Longwall productivity

The advanced technology medium-voltage drive controls torque and speed to optimise longwall productivity, reduces wear and breakage of armored face conveyor (AFC) components and makes efficient use of electrical power.

The VFD delivers optimum start-ups, 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 reducing stress on drives and chains. The system also optimises power usage and even returns energy into the system when motors are used to brake drives.

Face conveyor systems

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.

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 almost 100% effectiveness to reduce stress on AFC chains and on plow chains.

Improved control

The VFD adds an improved level of control to the Cat AFC drive technology series. The Cat Controlled Start Transmission (CST), a planetary drive system with an integrated infinitely variable multi-disc clutch, provides automatic and instant overload protection, soft starts and synchronised heavy-load startup. Caterpillar also offers a cost effective alternative that employs Cat UEL gearboxes rather than CST gearboxes.

Adjusting speed and torque by varying the frequencies of the alternating current enables precise and stepless control. The Cat VFD allows maximum torque at start-up and evenly distributes the load between the drives at both ends of the longwall. The system instantly reacts to a blockage or chain break with a controlled shutdown. In regular operation the speed of the AFC can be adjusted to load requirements when the plow or shearer are cutting the same direction or opposite direction of the AFC. In addition, the complete longwall can easily adjust to the capacities of the subsequent coal clearance components such as the crusher, stage loader and belt conveyor.

Instant analysis

Since data on power input, effective power, speed and torque is instantly available through an external encoder interface, they can be analysed instantly. This allows optimised production with reduced variability. Major advantages of the Cat VFD include:

  • Operating in the ‘green zone’ most of the time
  • Dynamically adjusting to changing production needs
  • Avoiding standstills
  • Facilitating fast start-ups

Plug and play

The Cat VFD will plug into 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 km from motors. Compared to other systems that integrate VFD control into motors, they do not require additional space at the face ends. In addition, unlike other systems, the Cat VFD does not cause EMC effects such as over-voltages, reflection waves or other unwanted ground currents or network disturbances.

Adapted from press release by Katie Woodward

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