That’s why a number of mine operators are actively considering upgrading the low-voltage infrastructure for underground mines from 480 volts (480V) to 995 volts (995V) as a strategy to achieve savings on energy infrastructure costs.
Studying Alternatives
We recently analyzed the cost and operational differences between the 480V and 995V systems for a major mining company specializing in exploration and production of metals needed for the ongoing upsurge of electrification technologies.
The analysis focused on comparing the costs and operational needs of the two electrical infrastructure systems from the decline down through to production areas. Power needed throughout all these zones feeds drills, roadheaders, ventilation fans, pumps and the material handling systems needed to transport ore from production areas to the surface.
Under both conventional 480V and proposed 995V setups, networks of small-scale substations — called mine load centers (MLCs) — are needed to step down the high-voltage power from a surface substation. Distribution feeders are connected from the MLC to a series of breakers that in turn supply power to various pieces of equipment, the material handling system and lighting, pumps and fans.
The 995V alternative is considered optimal because the current for specific equipment on this system is about half the current of a 480V system. Because of this lower current, cable diameters can be reduced and distances increased by approximately two times, thus allowing equipment to be spaced at longer distances, which in turn requires fewer MLCs. The 995V — like the 480V level — also avoids a requirement under the National Electrical Code (NEC) that mandates the use of electricians certified specifically to work on systems carrying 1,000 volts or greater. The NEC is published by the National Fire Protection Association and sets rules for safe installation of electrical systems within the U.S.
The MLC — a package of preassembled transformers, switchgear, breakers and other components needed to step down power from 13.8 kV or higher to either 480V or 995V — often exceeds $500,000 per unit, making it a high-cost component of the mine’s underground electrical infrastructure. Although MLCs would be priced roughly the same for both 480V or 995V systems, the 995V configuration results yielded significant savings of 30% or greater because fewer MLCs would be needed, by increasing the transformer size to feed more equipment off the single MLC. Other economies are attributable to smaller diameter power cable and less costly miscellaneous components needed for the mine electrical system.
On top of the savings in equipment costs, a significant savings in labor and productivity costs could be expected due to fewer hours allocated for mine electricians and other personnel tasked with moving cables and installing equipment needed as production moves to new horizons in the mine. One of the largest areas of savings would be due to the need for fewer MLCs under the 995V configuration, resulting in less excavation needed.
When an MLC is added, it incurs both development time and cost for excavating rock for a bay enclosure to house the MLC unit. Within a mine setting, it is typical for excavation to cost many thousands of dollars per foot because of the need to drill, blast and then haul away material. In addition, ground support must be installed to stabilize the walls and back of the bay. These development costs must be planned for along with the cost of lost production due to crews being reassigned from mining operations to excavation of the new bays.
Pros and Cons of 995V
Much of the equipment that consumes a great deal of power can run equally efficiently on either 480V or 995V configurations. For example, the stope drill, or the drill that is used for production, can run efficiently with 995V power and reach much further to the extents of the ore body without requiring an MLC move.
However, this is not the case with all systems.
Variable frequency drives (VFDs) and Soft Starters are currently manufactured almost exclusively to run on 480V only. These drives are needed to adjust speeds of motors for a variety of applications, for example some haulage systems require VFD driven motors to be evenly spaced every 50 to 60 meters along the track so that they engage sequentially as the train cars pass over them on track inclines that may be as steep as 45 degrees. Because VFD manufacturing standards are currently specified for 480V systems, the 995V system would be required to step down to 480V.
This limitation could be overcome by installing a series of transformers at each motor station, although the costs of installing hundreds of transformers would obviously offset some of the savings that could otherwise be achieved with a 995V haulage system configuration. Despite this factor, there are indications that this situation could be addressed in the future as more mine operators begin demanding VFDs and other equipment be manufactured to function at higher voltages.
Solution Gaining Momentum
The concept of converting mine electrical infrastructure to higher voltages is gaining increasing attention from a number of operators, particularly at mines that currently are using or considering battery electric mine equipment. These fleets use electricity instead of diesel as the fuel to get the job done.
In addition, some larger equipment needed for deep mine operations require 4,160 volts, making the argument for conversion to 995V systems even more logical, as the economics of stepping down voltage to a 995V system become even more attractive. Soon this system's voltage can spread beyond the underground, out into the processing plant where you have a higher concentration of electrical loads.
It’s clear that these electrical infrastructure upgrades require careful analysis. However, we’re seeing the benefits outweighing the drawbacks in many cases. It’s a solution whose time may have come.
