Launched into the global market in January 2016, Caterpillar’s 291 t payload Cat 794 AC (alternating current) mining truck sets a new standard for best-in-class performance, ease of service, practical use of technology, safety, and for delivering overall return on investment.
The design evolution of the Cat 794 AC is driven by decades of in-field diesel-electric power train experience to deliver a truck that is easy to maintain and operate, with excellent slow speed control for safety within the service areas; superior throttle response on acceleration to move out of the loading or dump zones; and dynamic retarding with blended four corner wet disc service brakes.
Though Caterpillar’s mechanically driven mining trucks have set the standard for maximum power train efficiency, productivity and delivering the lowest cost per unit moved, Caterpillar has also long been at the forefront of diesel-electric trucks.
As far back as 1965, Caterpillar brought innovation – like applying Cat wet oil cooled disc brakes to their own proprietary DC (direct current) drive system in the form of the Cat 779. Now the 794 AC leverages Caterpillar’s own advanced AC drive system, as well as pulling from Caterpillar’s 50 years of experience as a leader in diesel-electric power generation and years of knowledge and experience from Unit Rig and EMD.
Today, Caterpillar is the industry’s sole original equipment manufacturer (OEM) that designs and delivers the entire drive train, from the engine to the final drives, with the exception of Mitsubishi Electric high voltage state-of-the-art IGBTs (Insulated-Gate Bipolar Transistor) intelligent Phase Modules.
The fully integrated drive system on the 794 AC works seamlessly with the diesel engine, hydraulics and Cat drive controls. Having this full integration enables the 794 AC to provide top electric drive efficiencies, best in class controls, superior throttle response and smooth retarding with blended four corner wet disc braking.
The Cat 794 AC is manufactured by Caterpillar in Decatur, USA, for worldwide distribution and joins the larger 313 t payload Cat 795F AC in the OEMs current two model diesel-electric line-up. The full range of Cat earth moving products is supplied and supported locally by Caterpillar’s southern African dealer, Barloworld Equipment.
As on other Cat mining trucks, whether equipped with a mechanical or diesel-electric power train, the Cat 794 AC comes to market with a variety of proprietary technology options that include the well-entrenched MineStar telemetry suite, as well as the more recently introduced Cat fatigue monitoring system. In terms of power train, the Cat 794 AC is equipped with the Cat C175-16 diesel engine (the same unit installed on the Cat 795F AC), which produces a gross output (SAE J1995) of around 2 610 kW, coupled to a proven Cat AC power train that has logged three million reliable hours in the field.
The close coupled, dual bearing traction alternator allows for easy mounting to the C175-16 engine. A further plus is that the engine, traction alternator, motors, inverter, grid, and final drives can be removed independently.
This is a high voltage system that operates at lower current than the competition. The result is less heat generation, smaller/lighter components, and longer life.
Another key feature is the reverse shift inhibitor, which ensures reverse propulsion is not applied when the machine is moving forward. This helps prevent costly damage to the engine and drive system.
Drive propulsion via DC link
The C175-16 diesel engine drives the close connected traction alternator/generator through an isolation coupler, and the AC power is rectified to a nominal 2 600 V to form the DC link.
The DC link supplies power to the inverter where IGBTs convert the DC signal to 3-phase AC to drive the traction motors. Traction motor output drives the wheels through a double reduction ring gear output final drive. The end result is smooth, clean power transfer, with excellent fuel economy, low emissions and less environmental wastage, due to features such as continuous rear axle fi ltration and extended maintenance intervals. The 794 AC also has an exceptionally low oil and lube consumption.
Efficient and quiet, the radial grid is rated at 4.086 MW – allowing excellent control of the truck speed in long retarding applications. During retarding the traction/ wheel motors act as generators and power is fed back through the DC link. The power is fed to the contactor and chopper circuits and then exhausted through the radial grid. A maintenance free AC fan blows air across the grid to dissipate the power and control retarding speed. Cat electric trucks are very effective at maintaining applied loads at the engine’s optimum operating point; plus the use of brushless AC motors creates a constant retarding force even at low speeds.
In fact Cat AC drive systems are reputed to have the best retarding, braking, and control in the industry and operators really appreciate the power when climbing out of the pit.
The hydraulic brake actuation system is electrically modulated so that the first 80% of brake pedal travel uses dynamic braking, while the remaining 20% uses the wet disc service brakes. Whether idling or on the move, the operator can monitor critical machine health and payload information in real-time via the VIMS (Vehicle Information Management System) in-cab display monitor. Up to ten different machine parameters can be viewed at once. Data can also be downloaded easily by service technicians for troubleshooting, planning and lowering costs.
More productivity at less cost per ton: these are hallmarks of Cat haulers, making them a highly attractive option for fleet owners with a medium to longer-term investment horizon. Caterpillar can deliver the broadest options of truck size and drive systems to meet the different needs of miners around the world. Now for the African market, where AC trucks are favoured and home to some of the world’s largest open pit operations, Caterpillar off ers the new 794 AC to improve productivity and lower costs. MRA