Flexible Mining Cables Made for extremes Mining Cables

Flexible Mining Cables Made for extremes Mining Cables – Owen Barry – Mine Safety – 16/10/2013

Trailing Cables A trailing cable is a large electrical cable which connects to a piece of mine equipment. These cables are strong and well-insulated with a heavy rubber-like covering. They carry large amounts of electricity and can be extremely dangerous. Therefore, trailing cables should be kept in good condition and care should be taken that they are not run over or crushed by machinery. Trailing cables are typically 500 feet long but may be longer depending upon size

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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 – 1 st 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: 2003 Class 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: 2003 Class 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 construction Flexibility § 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 construction Composite 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 construction Elastomer 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 Voltage Phase volts 0 volts Insulation Semi-conductive rubber earth screen Distance – phase conductor to screen

Cable construction Electrically 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

Armoured Cable § It is as type of power conducting cable that is covered in a metal sheath. § In most cases, it consists of a bundle of wires covered in metal tube, which may be covered in a plastic insulation layer.

Types of Armoured cable § The various types of armoured cable are made in similar fashion. § At the core of the cable is as wire bundle. § These copper wires are covered in their own plastic insulation, keeping them separated from the metal cover and each other. § Next comes the metal covering which protects the wire from physical impacts and wear. § The metal is generally a long metal strip that winds around the cable, this gives the metal covering a corrugated, spring like appearance.

Type : § The three basic types of cable are: 1. BX cable 2. True armoured cable 3. Metal clad(MC) cable

BX cable § This cable went into production during world war II and saw heavy use for several years. § While this cable provided the protections common in armoured cable, it has a tendency to leak, and its grounding system was poor

True armoured cable § It is essentially just a heavier from of BX. § It features a better grounding system and a heavier internal insulation. § The process used to cover the cable in its metal covering allows for a better water proofing and in overall tough design.

Metal Clad (MC) cable § It uses a different grounding system from true armour cable and may have additional water proofing. § It is found in a wide range of commercial and industrial buildings.

Basic grounding difference between the three cable types: § BX cable generally goes to ground through metal sheath, which works well if the cable is buried or covered in some way, but nod good if it is exposed. § True armoured cable also grounds to the sheath, but has the ability to ground to predetermined areas, which allows certain portions to be exposed without exposing the grounding system § MC cable has a grounding wire inside the wire bundle, allowing users to create a ground wherever they want, which makes the system safe for exposed areas.

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 standard Tests § 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

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