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Working underground? Do you want power down there?

Mines are complicated places with big electrical needs; it’s important for mine owners to involve electrical experts early in the process

By Julian Fisher, Senior Electrical Consultant (Tempe, Arizona)

I’ve spent a good portion of my career working on “more electrical stuff.” At least that’s what many mine owners call my work. That viewpoint is often to the deriment of their projects

I’ve worked on underground mines all over the world. And it seems I’m frequently the last one called in to help on a project. Then the electrical team is forced to “make do” with what’s already been established. That can get costly.

The bottom line: involving electrical early in the process helps the bottom line!

All  that “electrical stuff” is very important. Large underground mines depend on electrical power for production with jumbo drills, rock breakers, ventilation fans, cooling, dewatering pumps, conveyors, hoisting, electric rail, communications, and controls. Electricity is a significant portion of operating costs. To some mine planning engineers, excavating space for utilities is a necessary evil. This means that every cubic foot of excavated space for infrastructure, substations, mine load centers, pump starters, and the like must be justified.

Excavation takes time and costs money. That’s an even more important reason why electrical needs to be brought into the project right from the start.

Related item: Mine power distribution

‘Do you want power with that?’
That question—“Do you want power with that?”—is one I’ve asked for years at every weekly project managers meeting and at practically every planning meeting I attend. I ask because I want to get involved in projects early and proactively.  

When the electrical discipline is brought in early, plans can be made for substation allowances based on typical tunnel cross section, areas perpendicular to the drift or even parallel in good ground. It is not that planners forget these issues, it’s just that it is a lower priority compared to their bigger picture—the mining itself. The cost of infrastructure excavations adds up and needs to be scheduled, so considering them at the last minute is disruptive to budgets and schedules.

At the start of a project the design basis document defines and maintains information for pumps, ventilation, electric jumbos, conveyors, compressors, hoists etc. I like to be involved from the beginning and with electrical maintaining that list.  This not only means that electrical is involved and contributing early but ensures that they have the right information. 

Shafts and train systems have special requirements, often with client, geographic, and statutory preferences. This is very important for international projects that have their own unique issues, potentially including different voltage, frequency, extreme altitude, access, availability and quality, of personnel.

Underground mines are accessed by vertical shafts and tunnels, so it is important to know the largest component sizes to be hoisted and transported. Here’s a quick comparison on two projects:

  • Project 1: During a final project review it was discovered that the access ramp to the underground hoist chamber could not fit the 36-foot, 30-ton shaft. The profile had to be increased to accommodate it. This affected the project cost and schedule at the last minute.
  • Project 2: The starting point for the access tunnel design was the friction hoist’s 55-ton rotor and 60-ton stator. The final confirmed sizing was similar to the typical dimensions used, so no last-minute changes were required.

This is where mines can take a lesson from literature. Robinson Crusoe’s build-a-boat project failed because he couldn’t get it into the water. Recently, there has been a trend to provide packaged electrical systems underground, for example mine load centers and packaged electrical distribution in prefabricated electric houses or “E-Houses”. If the E-House can’t fit into the mine or it can’t handle the electric needs, it’s of no value. It is important to consider the specification, sizing, and handling upfront.

Another project example comes from far-north Canada where ice roads are frequently used to deliver equipment. One mine owner specified that the maximum component weight and dimensions should allow for air freight delivery. That’s something to know early in the design.

Related item: What’s it like to work underground?  

Challenges, solutions, and flexibility
The challenges with a new mining facility can be extensive. From an electrical perspective, here are a few:

  • Power quality and the adequacy of the power supply for the project can take time to define and resolve.
  • Mines are rarely in prime locations with strong utility power available, so the power quality can be a large consideration.
  • Diesel generation can be reliable but expensive, but for some projects that may be much better than unreliable cheap power with higher consequential costs. Nonproductive “down time” at the mine can be expensive.

One example of critical electric design is the ventilation plan, and it likely will evolve during the course of the mine planning project. Main ventilation fans on the surface are less expensive from an electrical distribution perspective than providing that capacity in the underground infrastructure. Sometime the approach changes from one to the other during the project, so flexibility is always important.

If the power supply is weak, then large motors may not be viable, so we would design for multiple small motors. Commonly, we initially design with 200 horsepower (hp) vent fans. But with a weak power supply, those 200 hp vent fans might be replaced with more 100 hp fans. This changes the specification of the mine load center and possibly the quantity of mine load centers. That can be a significant change. Large fixed ventilation fans on a dedicated ventilation districts typically require less power than the multiple development fans they replace. To work within a power restriction, bringing those permanent fans on earlier may be necessary to operate within their power means.

Most of my career has been supporting mining owners and planners deal with “more electrical stuff.” It’s proven true time and again that early electrical discipline engagement helps produce a better project.  So, I’m going to amend my earlier statement: “Do you want power with that? Do you want to save money?” Then involve electrical right from the start.

Related item: Mining

Julian Fisher, PE, is a senior associate with more than 30 years of experience in the mining industry. He will be presenting a paper at the Canadian Instite of Mining, Metallurgy and Petroleum Convention in Montreal (April 30 to May 3).

Mines are rarely in prime locations with strong utility power available, so the power quality can be a large consideration.

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