Flexible Mining Cables

Made for extremes

Mining Cables – Owen Barry – Mine Safety – 16/10/2013

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Cable damage

Likelihood of cable damage is elevated– Machines are big and mobile– Cables being dragged and pulled– Some are continually reeled– Other large equipment moving in close proximity

to cables Connection to mine earth dependent on integrity of

cable

Risk from cable damage

Electrocution Electric shock Ignition of gas or dust Fires Burns (proximity to arc flash)

Controls to minimise risks- from cable damage Cable management plans

– Training of personnel– Placement of cables – Cable handling equipment

IT supply systems– 1st fault is low energy earth fault

Electrical protection systems– Sensitive earth leakage

Cables constructed to set standards– AS/NZS 1802– AS/NZS 1972– AS/NZS 2802

Cable handling – O/Cut

Standards for mining cables

AS/NZS 1802:2003 Electric cables—Reeling and trailing—For underground coal mining

AS/NZS 1972:2006 Electric cables—Underground coal mines—Other than reeling and trailing

AS/NZS 2802:2000 Electric cables—Reeling and trailing—For mining and general use (other than underground coal mining)

Cable design

Earth screened– Damage to earth before another phase

Voltage rated for line to earth, not phase to earth– Function of the IT supply system

Solid construction gives impact resistance Sheath materials resistant to:

– Cuts, abrasions and tears– Water ingress– Chemicals – UV, oils and greases, acids & alkali– Heat

Extreme cable handling

Example of poor cable handling.Dragline cables being towed behind a dozer

AS/NZS 1802:2003 Scope Reeling and trailing electric cables for use in

underground coal mines. Cables used for alternating current supply must be

electrically symmetrical. Specifies construction and dimensional

requirements for specific types of cables

Cable constructions – Type 240

Cable constructions – Type 241

AS/NZS 1972:2006 Scope Specifies the construction of cables for use in

underground coal mines other than reeling and trailing cables, ie– Reticulation/feeder cables– Machine cables– Mine shaft winder cables

Generally, does not apply to cables for IS circuits, data, communication and control cables unless specifically covered.

AS/NZS 2802:2003 Scope Intended for:

– surface mining, – underground mining (other than coal mining),

and – general use,

Allows for two classes of multicore, elastomer insulated and sheathed flexible reeling and trailing cables.

No requirement for symmetrical construction

Cable construction – Type 450

AS/NZS 2802:2003Class 1 cables Insulated with a high grade ethylene propylene

rubber (XR-EP-90) Permits a reduced radial thickness for the

insulation compared with equivalent rated Class 2 cables

Cable sheath is extra-heavy duty (XHD-90-CSP, XHD-90-CPE or XHD-85-PCP)

Designed for slow reeling or trailing applications

AS/NZS 2802:2003Class 2 cables Insulated using standard R-EP-90 insulation Sheath material is HD-90-CSP, HD-90-CPE or HD-

85-PCP Greater insulation radial thickness required,

providing a more robust cable Designed for trailing and most reeling applications

Cable constructionFlexibility Issues affecting flexibility

– Insulation materials– Stranding– Length of lay

• Bunches• Cores

– Screening technique– Sheath thickness– Ability of internal parts to move during flexing and

bending

Type 245 cable

Cable constructionComposite screens Each phase individually screened

– Semiconductive layer over insulation• May be elastomer and or tape• For stress relief and potential equalisation• VR < 200 Ωm

– Copper and high tenacity yarn• Usually woven• May be helically wound

– Screening is also cable earth

Cable constructionElastomer screens Phases individually screen Complete assembly collectively screened

– Must carry fault current• VR <1 Ωm

3 interstitial earth conductors embedded in semiconductive elastomer

N.B. When crushed, the collective earth screen may separate from the phase conductor

Insulation Voltage Gradient

Distance – phase conductor to screen

Vol

tage

Phase volts

0 volts

Insulation

Semi-conductive rubber earth screen

Cable constructionElectrically symmetrical Cores arranged in geometrically symmetrical

pattern to minimise the effects of induced voltage Important in hazardous zones underground

– Minimises sparking between machines– Minimises touch voltages of machines relative to

remote earth• shuttle cars have rubber tyres

Mandatory testing for symmetry by cable repair facilities

Future developments

Cable standards presently being revised– A lot of prescriptive elements– 1802 & 2802 will possibly be combined into

single standard – Present tests do not adequately assess cable

performance• No tests for bending and flexing• No tests for semiconductive individual screen

Future developments Performance based standard Cable performance outcomes to be defined

– Bending and flexing– Tension loads– Aging under elevated operating temperatures

Allow for future requirements– Fibre optics– New insulation materials– New manufacturing techniques– Higher operating voltages

Performance based standard

Performance requirements for each application of cable to be defined:– Draglines– Shovels– Feeder cables – fixed equipment– Continuous miners– Shuttle cars– Monorail systems– Shearer

Performance based standardTests Type tests to be developed

– Verify design achieves required outcomes– Pass/fail criteria to be identified

Routine tests to be developed– Routine tests demonstrate that the production

run of cable is the same as the type tested unit– Frequency of sampling– What elements need to be checked– Allowable tolerances from type tested unit

Repair of cables

Presently addressed under AS/NZS 1747– Will be revised after 1802 & 2802

Manufacturers will need to identify how repairs will be performed when developing new cable designs– Repair materials– Repair techniques

Issue: Mines will need to define element such as stranding and length of lay for compatibility with existing cable fleet

Thank you

Questions