Underground super highway

Rugged fibre optic cables are opening an entire new world underground.

Clear communication is key.

And quality communications and information equipment is now, more than ever before, integral in mine development as the industry moves towards greater remote control and automation of machinery and mining processes.

In an underground mine, access to communications and information equipment has often been limited due to thermal extremes, physical hazards and dangerous chemicals.

On top of this, copper conductors that are often used for communication equipment do not operate as efficiently because of the excessive noise generated by mining equipment, and may also pose a safety hazard.

However, the design of extremely rugged fibre optic cables is now enabling ten gigabit transmission links in places that were never before thought possible in mining.

One place though, has still proved a challenge for the expansion of fibre optic networks, and that is in an underground coal mine.

Until now.

Optical Cable Corporation (OCC) has developed the rugged tight buffered breakout fibre optic cables for transmission links in harsh mining environments.

Working at depths of over 300 metres below ground, and having seen roof falls actually bury the cable between rocks and still, the cables are able to operate in a myriad of conditions.

OCC vice president of international sales, Michael Newman, told Australian Mining that these cables will assist in revolutionising underground communications as “the cables provide a communication link that is completely immune to electro magnetic interference and can provide higher data rates at longer distances than was possible with copper.”

He went on to say that while there are already underground communications systems in place, these tight buffered fibre optic cables can perform the same task copper cables or leaky feeder systems but consist of smaller cables over longer distances which can also carry all of the voice and data on a single, tough cable.

These cables have been designed to be more heavy duty than existing loose tube fibre optic cables.

Rugged, tight buffered fibre optic cables, as opposed to loose tube designs which have only one thin coating surrounding each optical fibre, have two.

In the loose cable design, the fibre coating is only 62 microns thick, which provides very little mechanical and environmental protection to the glass fibre.

For the tight buffered cables, in addition to a primary coating, they have a secondary buffer which reaches a weight of 387 microns, six times thicker than the primary coating alone. 

In the design of the breakout cable, it has another layer of protection, where each fibre is surrounded by aramid yarns and a tight bound elastomeric jacket.

This means that even at this sub-cable level, the sub units are highly crush resistant and able to withstand the environmental extremes often encountered in coal mines.

OCC then ensure the sub cables are helically stranded and surrounded by a special pressure extruded outer jacket.

This outer jacket assists in locking all the sub elements of the cable in place, and makes the structure of the cable act like a single unit, similar to a rope.

This aids in enhancing crush resistance, jacket tear resistance and overall survivability.

According to the Newman, the cables have a flex resistance of thousands of cycles, come with a crush resistance of 2200N/cm, and have the ability to withstand 1000 impacts while operating in temperature extremes of between minus 55 right through to 124 degrees Celsius.

Importantly, these cables do not propagate a flame or give off toxic fumes.

The cables are also designed to work within an underground environment.

With a typical mine being extremely dusty and dirty, a loose-tube gel-filled cable is very hard to work with, when you set it down to do the termination it typically picks up a lot of dust.

However, the breakout cables are dry, meaning no degraded connection at assembly time.

The cables are suitable for use across the whole scope of underground mining, as “all kinds of mining have similar requirements for communications and information equipment, and the use of these fibre cables within the mine is beneficial for increased safety and production,” Newman said.

The cables allow for internet and information transfer speeds of up to 100 gig per second, although they are typically used at 1 gig or less, he added.

OCC manufactures the cables for high bandwidth transmission of data and video and audio communications.

The cables are available in Australia.

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