Vesa Kajander and Teemu Ronkainen discuss how regenerative drives built for rugged mining conditions are enabling the increasing use of electric vehicles and their associated cost savings
Interest in the mining industry for the possible use of fully electric or hybrid-electric vehicles, such as trucks, front loaders, drill rigs and excavators, is clearly beginning to show an upward trend. This growing interest is being driven by several factors that have converged in the past few years to make both OEM vehicle producers and mine operators aware of the large potential benefits that electric vehicles offer. The major OEMs have recently started to introduce models having hybrid-electric or even fully electric functionality.
The bottom line, of course, is the bottom line – when used as part of a long-term strategy, electric vehicles can bring considerable cost efficiencies and savings to mining companies. In times like today, when profitability is extremely squeezed, mine operators are searching hard for any possible cost savings. But even when the market is up, electric vehicles have the potential to further improve the healthy margins.
Greater efficiencies in many areas
The reason for this is efficiencies concerning toxic emissions, waste heat generation, energy use and costs, and expenses associated with constructing and running ventilation systems. Frankly speaking, the capital investment required for electric vehicles based on batteries can be far more than the present diesel technology. But even considering this, payback times of one to two years are feasible, and immediate payback is even possible in some cases.
Diesel engines, the traditional industry standard for mining, are inherently very inefficient at converting energy input into movement output. In the best case, they can achieve approximately 45% efficiency, with the rest of the energy lost to waste heat. Electric drivetrains, on the other hand, can easily reach energy efficiencies of 90% or more.
Robust for a tough environment
Until now, diesel has been the dominant technology for good reasons. The mining environment is very tough and diesel has been able to tolerate the conditions. Mining vehicles, and the equipment inside them, must be robust enough to withstand challenging conditions including: high ambient temperatures; constant vibration; violent shocks; harsh start/stop load cycles; corrosive acidic liquids and gases; aggressive pressure washing; and other unforgiving treatment.
With these facts in mind, ABB Drives and Controls has been developing drives to control the electric motors in low/no-emission mining equipment. Working closely with mining OEMs and starting with a blank sheet of paper, the strategy has been to design a new tailor-made mine drive from the ground up. The idea is not to simply repackage a standard product, but instead design a rugged and purpose-built drive.
The regenerative function of drives is important as it allows the capture of braking energy from the motor, and even from hydraulic pumps, to be stored in a battery or supercapacitor. The drive is controlling the flow of energy and transforming any kinetic or potential energy back to electric energy.
The issue of ventilation
Ventilation and air circulation are also key drivers and big cost items in underground mines. Since electric vehicles reduce both waste heat and emissions generated, ventilation requirements are lower compared to diesel engines. On a day-to-day basis, this can drastically reduce the cost of energy needed to circulate air to meet health and safety requirements. Savings can amount to millions of euros per year. And, when a mine expansion is being considered, the reduced heat and emissions from electric vehicles means the dimensioning of the ventilation system can be much smaller and therefore much cheaper.
Maintenance costs and reliability are other important issues. Many of the OEMs have seen, as they have been working closely with electric vehicles and drives, that the maintenance cost for electric is much less due to fewer wearing parts. For example, there is no gearbox, and no oil lubrication system is necessary.
Diesel-electric is also a possibility to extend the range of vehicles. Sometimes called series-hybrid technology, the diesel runs a generator that feeds electricity to the motors to drive the vehicle. The key benefit is that, instead of using diesel for the maximum peak power, the dimensioning of the diesel engine can be smaller to cover the average power demand.
Considering all the requirements for electric mining vehicles, and based on careful listening to the market and close work with OEMs, the new purpose-built HES880 mobile drive has been developed. This is a brand new design, although it is based on the well-proven ACS880 all-compatible drive technology, which mine operators and OEMs are already familiar and comfortable with.
In addition to being robust and compact, this electric-vehicle drive is a modular product, based on a single design model and three different types of firmware. This single model is tailored to specific applications simply by installing the appropriate firmware for the different applications. These software options can control the motor and generator, the power grid connection, and power flow to and from the energy storage. So the hardware is the same whatever the application, to simplify stocking of equipment by allowing interchangeability of parts.
Due to the compact size of the drive, the layout of the components becomes much more flexible. In a typical diesel vehicle, the engine and powertrain take up most of the available space and are very fixed in the positioning in the middle of the vehicle. Electric drivelines, conversely, are more flexible and therefore can be placed to allow the driver a greater field of view in the workspace. As the electric vehicle technology develops, this greater freedom of placement and layout could well mean more user-friendly and safer equipment.
The mining industry, like many other older established sectors, is inherently conservative about adopting new technology. So although it has taken some time for electric vehicles to gain acceptance, the growing list of advantages is clearly starting to get noticed by the progressive pioneers at OEMs and mining companies.
Considering the large potential cost savings and efficiencies that electric vehicles offer, as well as the short payback times, ABB has decided to invest resources in this technology to catalyse these trends. New mining-vehicle solutions such as the HES880 drive have the potential to create both a stronger market pull from the mining operators and a greater market push from the OEMs that will be very beneficial to the mining industry. The future for electric mining vehicles has started.
Teemu Ronkainen & Vesa Kajander are with ABB Drives and Controls.