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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
From
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To
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And
Picture courtesy of NSW T&I Image Library
From
Picture courtesy of NSW T&I Image Library
To
Picture courtesy of NSW T&I Image Library
And
Picture courtesy of NSW T&I Image Library
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
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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 2802:2003
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 HD85-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
Thank you