Mining, Oil, & Gas: Leaky Feeder

A Case Study for the Kidd Creek Leaky Feeder Network for Mine “D”

Building a two-way radio network is challenging, but building one to operate underground to support mining operations is extremely difficult due to the harsh and ever-changing propagation environment. Signals reflect inside a mine and cause multipath interference. In addition, these same signals will not penetrate the mine walls.

Having worked on several types of mines – in situ, open pit, and shaft – the deep Kidd Creek mine north of Timmons, Ontario offered a particularly difficult technical challenge for a “Leaky Feeder” design.

TechTarget (2015) defines a leaky feeder as a coaxial cable that has small sections of its copper shielding stripped away to allow radio frequency (RF) signals to escape. Leaky feeders, which act as extended antennas, are also called radiating cables.

Leaky feeders are used in places where the actual structure makes RF communication difficult. Leaky feeders are often used in structures with metal frameworks such as skyscrapers, tunnels, ships and planes to extend mobile coverage. They are also useful in situations where low power levels are required to prevent interference with other communication technologies that share the same frequency spectrum.

Leaky feeders were originally used in underground mines. Normally it would be impossible for someone in a mine to communicate with the surface with a hand-held radio. Sufficient cabling working in conjunction with signal amplifiers, however, can be strong enough to cover an entire mine. Base stations on the surface can then route and combine multiple audio channels so the miner’s communications to can remain separate or be combined as needs require. The Kidd Creek Leaky Feeder network included an underground LMR (Land Mobile Radio) design amongst other signal types that were all integrated into a shared harmonized network.

In 1964, geologists discovered the ore body and at its peak, this mine employed nearly 3,000 staff and contractors.

It started as an open pit mine until it reached its maximum allowable depth and then shaft mining was begun. The vertical shafts run down beside the ore body and horizontal levels extend into the ore body for ore extraction and back-filling.

In 2000, the vision was to automate the mine with cameras to permit remote mining operation from the surface. The worker commute time from the surface to the greatest depth was over two hours. Therefore, in order to be productive and recover the ore for a profit, automation was required. Automation requires communications on the machines, between pieces of equipment, and man-machine interfaces.  It was deemed worthwhile to remotely operate the mine operations from the surface near the mine headframe.  Parts of the mining process where considered that followed the workflow and the ores journey from in the rock face to the Met Site.

The original project request began with the desire to bring video cameras from the 9,600 feet deep mine into the control centre on the surface. More than 100 cameras have been installed in the Mine D shaft. With four main shafts and many layers into the main ore body, Kidd Creek is a significant mine. In fact, it is the world’s deepest copper / zinc mine. The operations are extensive with a series of multi-stage, variable speed conveyor belts on all production levels and high-speed skiffs running up towards the 4,300 foot level and ultimately to the surface. At the 4300’ level, a rock crushing plant was built to pre-crush rocks before the final lift to the surface. Kidd Creek operates its own railroad that carries the ore from the mine surface to the Metallurgical Site located 27 kilometres away where the ore is processed and the minerals extracted and separated from the tailings.

A hybrid communication network solution was defined that used high capacity single mode optical fibre on the vertical runs and a leaky feeder solution on the horizontal levels. It was critical to control the RF signals within the levels to avoid multipath and interference problems. Careful planning was needed for the calculations to determine the power levels for the leaky feeder links. Custom spreadsheet tools provided by Andrew Corporation were used to estimate the energy and to manage the harmonics. Ultimately, the radio links were optimized in the mine itself with field test equipment and a standard model was developed to configure the network. A real-time monitor and control system was added to manage the power levels from the surface in order to optimize the leaky feeder links as the levels were played out and closed and new levels opened up for mining operations.

Eight different communication signals are carried over the network. These include:

1. Two-way radio
2. Cellular
3. Data communications
4. Video Cameras
5. Automation command and control
6. Air handling and ventilation
7. CAD / CAM
8. Monitor and control systems

As stated, a leaky feeder is effectively a form of coaxial cable that acts like a waveguide with precisely cut slots to control the radiation of the signals ingress and egress to the cable. Normally, VHF and UHF bands are used and all signals are deemed to be line of sight. Inline amplifiers are used to boost the low-level signals along the cable pathways.  Typically leaky feeder systems are narrow band systems.  But, this network was designed as a broadband solution.

The original analog two-way radio network was needed for safety as well as to coordinate logistics, processes, people and resources. Mine operations used the Motorola 800 MHz trunk radio network to manage operations, coordinate activities, call for pumps, generators and equipment, manage blasting operations and generally to communicate and share information. The two-way radio network is essential to a safe mine operation. By controlling the transmit power and managing zones within the mine, connections can be made to all underground locations as well as to the engineering and business offices on the surface, to the train rolling stock along the rail line and to the “met site” many kilometres to the southeast of the mine. In an emergency, the two-way radio could be the lifeline to save miners from harm.

Technology now exists to bring broadband communications to hostile mining locations and provide services to the workforce similar to what they can access on the surface, including internet, intranet, email, and more.

About the Author:

Michael Martin has more than 35 years of experience in broadband networks, optical fibre, wireless and digital communications technologies. He is a Senior Executive Consultant with IBM Canada's GTS Network Services Group. Over the past 11 years with IBM, he has served in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He was previously a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN:TSX). He holds three Masters level degrees, in business (MBA), communication (MA), and education (MEd). As well, he has diplomas and certifications in business, computer programming, internetworking, project management, media, photography, and communication technology.

Reference:

Kable Intelligence Systems. 2015. RFS Leaky Feeder RadiaFlex Coaxial Cables. Retrieved on October 25, 2015 from https://www.railway-technology.com/contractors/cables/radiofrequency/radiofrequency3.html

TechTarget. 2015. Networking and Communications Glossary. Retrieved on October 25, 2015 from https://whatis.techtarget.com/definition/leaky-feeder