This document provides guidance on proper cable care and maintenance to reduce downtime in surface mining operations. It discusses how cables commonly fail due to excessive tension, mechanical damage, current overload, and improper splicing. Following procedures like choosing appropriately rated cables, avoiding excess tension and damage, using proper splicing techniques, and educating personnel can reduce cable-related downtime by over 50%. Maintaining failure records and educating staff on cable limitations and proper practices are key aspects of an effective cable maintenance program.
A Presentation based on Underground Cables Used In the Transmission And Distribution System.It is a topic covered in the syllabus of B.E. in Electrical Engineering in 5th semester Subject named "Electrical Power System" For more detail you can check the book "Electrical Power System" by Author V.K.Mehta and S.Chand Publication.
250um loose tube vs. 900um tight buffered fiberAngelina Li
Choosing the right fiber-optic cable has become more challenging than ever. Factors like the advent
of new cable designs, suppliers, changes in fiber specifications, and the many claims of cable
performance can confuse even the most seasoned network designers.
this ppt is base on construction of under ground cable. in this ppt i gave information the all type of insulation and its specification. and is advantages.
A Presentation based on Underground Cables Used In the Transmission And Distribution System.It is a topic covered in the syllabus of B.E. in Electrical Engineering in 5th semester Subject named "Electrical Power System" For more detail you can check the book "Electrical Power System" by Author V.K.Mehta and S.Chand Publication.
250um loose tube vs. 900um tight buffered fiberAngelina Li
Choosing the right fiber-optic cable has become more challenging than ever. Factors like the advent
of new cable designs, suppliers, changes in fiber specifications, and the many claims of cable
performance can confuse even the most seasoned network designers.
this ppt is base on construction of under ground cable. in this ppt i gave information the all type of insulation and its specification. and is advantages.
Underground cables are used for power applications where it is impractical, difficult, or dangerous to use the overhead lines. They are widely used in densely populated urban areas, in factories, and even to supply power from the overhead posts to the consumer premises.
The underground cables have several advantages over the overhead lines; they have smaller voltage drops, low chances of developing faults and have low maintenance costs. However, they are more expensive to manufacture, and their cost may vary depending on the construction as well as the voltage rating.
The underground cables are classified in two ways; by the voltage capacity, or by the construction.
By Voltage
LT cables: Low-tension cables with a maximum capacity of 1000 V
HT Cables: High-tension cables with a maximum of 11KV
ST cables: Super-tension cables with a rating of between 22 KV and 33 KV
EHT cables: Extra high-tension cables with a rating of between 33 KV and 66 KV
Extra super voltage cables: with maximum voltage ratings beyond 132 KV
By Construction
Belted cables: Maximum voltage of 11KVA
Screened cables: Maximum voltage of 66 KVA
Pressure cables: the Maximum voltage of more than 66KVA
Modern underground power cables are sophisticated assemblies of insulators, conductors and protective materials. Within these components are sensors, which enable cable operators to monitor conditions along the cable in real time.
The condition of the cable insulation is usually monitored through the following two main methods:
Loss tangent measurements
Partial discharge (PD) measurements
1- Low Tension Power Cable
2- Contents
Introduction
Construction
Types & sizes
Features
Application
More Details
3- Introduction
Power Cables - An assembly of two or more electrical conductors usually held together with an overall sheath. The assembly is used for transmission of electrical power.
4- Construction
5-
Conductor – Stranded / Solid / Circular shaped-Aluminum / Copper
Insulation – PVC /XLPE/HR PVC / Zero Halogen
Inner Sheath – PVC/HR PVC /FR/FRLS PVC
Armouring – G. S.Round Wire/ Flat Strip or Aluminum Wire /Flat Strip
Outer Sheath – PVC /HR PVC/FR/FRLS PVC /Zero Halogen
6- Types & Sizes
Types
1.1 kV PVC /XLPE as per IS : 1554 – (Part-I) / IS : 7098(Part- I)/BS /IEC.
Sizes
Single Core 1.5 to 1000 sq. mm
Multi core 1.5 to 630 sq. mm
7- Features
These cables can carry high current with high short circuit rating 250°C as against 160°C for PVC.
Dielectric losses are very less in these cables.
LT power cable is flexible, lightweight, fire-resistant in nature.
8- Application
LT power cable may be installed as permanent wiring within buildings, run overhead, buried in the ground or exposed.
And Flexible power cables are used in mobile tools, portable devices, and machinery.
9- More Details At
Rallison Electricals Pvt. Ltd.
G I / 118, Mayapuri, Phase – I, New Delhi – 110064
Phone: 91-11-28112644
Mobile: 9311104000
URL: http://www.rallison.com/lt-power-cable/
Since the loads having the trends towards growing density. This requires the better appearance, rugged construction, greater service reliability and increased safety. An underground cable essentially consists of one or more conductors covered with suitable insulation and surrounded by a protecting cover. The interference from external disturbances like storms, lightening, ice, trees etc. should be reduced to achieve trouble free service. The cables may be buried directly in the ground, or may be installed in ducts buried in the ground.
Underground cables are used for power applications where it is impractical, difficult, or dangerous to use the overhead lines. They are widely used in densely populated urban areas, in factories, and even to supply power from the overhead posts to the consumer premises.
The underground cables have several advantages over the overhead lines; they have smaller voltage drops, low chances of developing faults and have low maintenance costs. However, they are more expensive to manufacture, and their cost may vary depending on the construction as well as the voltage rating.
The underground cables are classified in two ways; by the voltage capacity, or by the construction.
By Voltage
LT cables: Low-tension cables with a maximum capacity of 1000 V
HT Cables: High-tension cables with a maximum of 11KV
ST cables: Super-tension cables with a rating of between 22 KV and 33 KV
EHT cables: Extra high-tension cables with a rating of between 33 KV and 66 KV
Extra super voltage cables: with maximum voltage ratings beyond 132 KV
By Construction
Belted cables: Maximum voltage of 11KVA
Screened cables: Maximum voltage of 66 KVA
Pressure cables: the Maximum voltage of more than 66KVA
Modern underground power cables are sophisticated assemblies of insulators, conductors and protective materials. Within these components are sensors, which enable cable operators to monitor conditions along the cable in real time.
The condition of the cable insulation is usually monitored through the following two main methods:
Loss tangent measurements
Partial discharge (PD) measurements
1- Low Tension Power Cable
2- Contents
Introduction
Construction
Types & sizes
Features
Application
More Details
3- Introduction
Power Cables - An assembly of two or more electrical conductors usually held together with an overall sheath. The assembly is used for transmission of electrical power.
4- Construction
5-
Conductor – Stranded / Solid / Circular shaped-Aluminum / Copper
Insulation – PVC /XLPE/HR PVC / Zero Halogen
Inner Sheath – PVC/HR PVC /FR/FRLS PVC
Armouring – G. S.Round Wire/ Flat Strip or Aluminum Wire /Flat Strip
Outer Sheath – PVC /HR PVC/FR/FRLS PVC /Zero Halogen
6- Types & Sizes
Types
1.1 kV PVC /XLPE as per IS : 1554 – (Part-I) / IS : 7098(Part- I)/BS /IEC.
Sizes
Single Core 1.5 to 1000 sq. mm
Multi core 1.5 to 630 sq. mm
7- Features
These cables can carry high current with high short circuit rating 250°C as against 160°C for PVC.
Dielectric losses are very less in these cables.
LT power cable is flexible, lightweight, fire-resistant in nature.
8- Application
LT power cable may be installed as permanent wiring within buildings, run overhead, buried in the ground or exposed.
And Flexible power cables are used in mobile tools, portable devices, and machinery.
9- More Details At
Rallison Electricals Pvt. Ltd.
G I / 118, Mayapuri, Phase – I, New Delhi – 110064
Phone: 91-11-28112644
Mobile: 9311104000
URL: http://www.rallison.com/lt-power-cable/
Since the loads having the trends towards growing density. This requires the better appearance, rugged construction, greater service reliability and increased safety. An underground cable essentially consists of one or more conductors covered with suitable insulation and surrounded by a protecting cover. The interference from external disturbances like storms, lightening, ice, trees etc. should be reduced to achieve trouble free service. The cables may be buried directly in the ground, or may be installed in ducts buried in the ground.
Performance of 400 kV line insulators under pollution | PDF | DOC | PPTSeminar Links
Visit https://seminarlinks.blogspot.com to download.
Outdoor insulators are subjected to nature Polluted environmental contaminants, which may include sea salt, cement dust, fly ash, birds droppings, industrial emissions etc. deposit on their surface With the increasing industrialization not only the degree of pollution but also the type of pollution has an effect on the performance of the insulators.
DC testing has been accepted for many years as the standard field method for performing high-voltage tests on cable insulation systems. Whenever DC testing is performed, full consideration should be given to the fact that steady-state direct voltage creates within the insulation systems an electrical field determined by the geometry and conductance of the insulation, whereas under service conditions, alternating voltage creates an electric field determined chiefly by the geometry and dielectric constant (or capacitance) of the insulation.
Under ideal, homogeneously uniform insulation conditions, the mathematical formulas governing the steady-state stress distribution within the cable insulation are of the same form for DC and for AC, resulting incomparable relative values; however, should the cable insulation contain defects in which either the conductivity or the dielectric constant assume values significantly different from those in the bulk of the insulation,the electric stress distribution obtained with direct voltage will no longer correspond to that obtained with alternating voltage.
Hybrid battery +solar pv grid tie power project presentation by jmv lpsMahesh Chandra Manav
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Isolation Procedures for Safe Working on Electrical Systems and Equipment by the JIB | solation Procedures for Safe Working on Electrical Systems and Equipment
This chart shows the safe isolation procedure that you should use when working on electrical systems and equipment.
You'll receive a printed copy of this from your Training Provider, but it's also here as a handy reference to keep electronically.
THE RULES OF SAFE ISOLATION ARE:
Obtain permission to start work (a Permit may be required in some situations)
Identify the source(s) of supply using an approved voltage indicator or test lamp
Prove that the approved voltage indicator or test lamp is functioning correctly
Isolate the supply(s)
Secure the isolation
Prove the system/equipment is DEAD using an approved voltage indicator or test lamp
Prove that the approved voltage indicator or test lamp is functioning correctly
Put up warning signs to tell other people that the electrical installation has been isolated
Once the system/equipment is proved DEAD, work can begin
Uploaded by THORNE & DERRICK LV HV Jointing, Earthing, Substation & Electrical Eqpt | Explosive Atmosphere Experts & ATEX IECEx.
THORNE & DERRICK based in the UK are international distributors of LV, MV & HV Cable Installation, Jointing, Substation & Electrical Equipment.
Since 1985, T&D have established an international reputation based on SERVICE | INTEGRITY | TRUST.
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The UiPath Test Manager overview with SAP heatmap webinar offers a concise yet comprehensive exploration of the role of a Test Manager within SAP environments, coupled with the utilization of heatmaps for effective testing strategies.
Participants will gain insights into the responsibilities, challenges, and best practices associated with test management in SAP projects. Additionally, the webinar delves into the significance of heatmaps as a visual aid for identifying testing priorities, areas of risk, and resource allocation within SAP landscapes. Through this session, attendees can expect to enhance their understanding of test management principles while learning practical approaches to optimize testing processes in SAP environments using heatmap visualization techniques
What will you get from this session?
1. Insights into SAP testing best practices
2. Heatmap utilization for testing
3. Optimization of testing processes
4. Demo
Topics covered:
Execution from the test manager
Orchestrator execution result
Defect reporting
SAP heatmap example with demo
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
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The IoT and OT threat landscape report has been prepared by the Threat Research Team at Sectrio using data from Sectrio, cyber threat intelligence farming facilities spread across over 85 cities around the world. In addition, Sectrio also runs AI-based advanced threat and payload engagement facilities that serve as sinks to attract and engage sophisticated threat actors, and newer malware including new variants and latent threats that are at an earlier stage of development.
The latest edition of the OT/ICS and IoT security Threat Landscape Report 2024 also covers:
State of global ICS asset and network exposure
Sectoral targets and attacks as well as the cost of ransom
Global APT activity, AI usage, actor and tactic profiles, and implications
Rise in volumes of AI-powered cyberattacks
Major cyber events in 2024
Malware and malicious payload trends
Cyberattack types and targets
Vulnerability exploit attempts on CVEs
Attacks on counties – USA
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In-depth analysis of the cyber threat landscape across North America, South America, Europe, APAC, and the Middle East
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Cyber risk predictions
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Systemic attacks in the Middle East
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How To Cut Downtime & Extend Cable Life - Surface Mining Cable Care & Maintenance Guide
1. How To Cut Downtime
And Extend Cable Life
Surface mining cable care
and maintenance
2. “Colossal” is the best word to characterize modern surface mining
operations—both in terms of scope and size of equipment. A fact
which has placed growing importance on ensuring a continuous flow of
current to these massive mining machines. This has become even more
important given today’s highly competitive economic environment.
Anaconda®
Brand mining cables have been designed to reduce cable-
related downtime, as this factor represents a serious impact to mine
profitability. In operations of these magnitudes, every minute of
downtime is very expensive, and once lost, can never be recovered.
This has led us to assemble considerable information and know-how
over the years on how such downtime can be minimized.
This booklet represents a timely updated body of knowledge for surface
mining. It reduces our recommendations to simple procedures that can
readily be passed on to all your operating personnel.
A companion piece is available on underground mining cable care
and maintenance.
How To
Cut Downtime
And Extend
Cable Life
Surface mining
cable care and
maintenance
contents
The huge cost of cable
downtime today
Design of surface
mining cables
How surface mining
cables fail
Proper care and maintenance
greatly reduces downtime
Summary of ways to cut
cable downtime
How General Cable helps
you cut downtime
3
3
6
8
12
14
The information contained herein is
intended for evaluation by technically
skilled persons. Any person relying on this
document does so at their own independent
discretion and sole risk, assumes all risks
and liability whatsoever in connection with
such use, and General Cable will have no
liability with respect thereto, whether the
claim is based in contract, tort or other legal
theory. General Cable makes no representa-
tions or warranties, expressed or implied,
with respect to the accuracy, completeness
or reliability of this document.
3. The Huge Cost of Cable Downtime Today
Reliable performance of modern trailing cables is essential to low-cost coal mining. The
unscheduled interruption of production, resulting from cable failures, costs much more
than is generally realized. Lost tonnage, interest, depreciation, overhead and labor costs
associated with this kind of downtime can surpass the initial investment in cable.
Obviously, it has become vitally important in today’s mining operations to minimize
downtime through proper handling and maintenance of cables. In order to do this most
effectively though, an understanding of the design of trailing cables and an awareness of
their optimum performance limitations can be of great value.
Design of Surface Mining Cables
Surface mining with large electric shovels began in the early 1920s. At that time, shovel
cables were relatively small in size, insulated with natural rubber and protected only
with coverings of asphalt-impregnated cotton braid or a spiral wire armor.
Over the years, conductor sizes increased greatly along with growing shovel capacities.
But at the same time, many sophisticated advances took place in polymeric insulating
and jacketing materials, as well as in stranding and shielding techniques.
General Cable played a leading role in
pioneering these advances, which have lead
to cables such as the highly engineered,
tough, flexible design shown in Figure 1.
Here is a brief description of each of the
components:
Jacket
Chlorinated Polyethylene (CPE) is now the standard for a tough, flexible jacket.
In addition to superior tensile strength and abrasion resistance, it has a wide thermal
range from 90°C down to -50°C.
CPE possesses natural resistance to ozone, making it especially suitable for high-
voltage applications.
Even so, a common problem with jackets occurs when excessively long lengths of
the cable are put on a hitch and dragged with a caterpillar. The jacket will normally
tear under the load. Ways of avoiding this are described under the “Proper Care and
Maintenance Greatly Reduces Downtime” section.
Shielding
Remember that an ungrounded shield is dangerous and should be treated as an energized
conductor. The shield must be grounded at least at one end and preferably at two or
more locations. It is recommended that shields be grounded at all cable terminations and
splices. Stress cones should be installed at all high-voltage shield terminations.
The well-known functions of the shield include:
1. To obtain symmetrical radial stress distribution within the insulation and to
eliminate, for practical purposes, longitudinal stresses on the surface of the
insulation or jacket
2. To provide a definite capacitance to ground for the insulated conductor,
thereby presenting a uniform surge impedance and minimizing the reflection
of voltage waves within the cable run
3. To reduce the hazard of shock and danger to both life and property
Reliable
performance
of modern
trailing cables
is essential to
low-cost coal
mining.
Figure 1
Ground-Check Conductor
Jacket Shielding Insulation
Grounding Conductor
Phase Conductor
4. Shielding (con’t)
Shielding wires have also been found to perform another function, especially important
where ground continuity is essential. In constructions where grounding conductors are
laid in the cable, in contact with the shield throughout the length of the cable, ground
continuity is assured through the infinite number of parallel paths provided.
There are two types of flexible shielding
which have become associated
with surface mining:
1. Full copper braid
2. Copper/textile braid
Tests have shown that the copper/textile
braid shield is mechanically superior to a
full copper braid. This is largely because the
individual wires cross over threads instead of other wires. (Figure 2)
The problems that develop with shielding systems are generally related to kinks in
the semi-conducting tape which cause stress points, leading to dielectric breakdown
over a period of time. The best protection is to observe the minimum bending radii
recommended by Insulated Cable Engineers Association (ICEA).
Grounding System
Grounding conductors and shielding wires cannot be separated from each other
when considering effective ground impedance because together they form the total
grounding system.
As a result, little change occurs in the grounding system impedance after individual
components have suffered extreme flex fatigue. In fact, it has been shown that the
grounding system will continue to function long after phase conductor failure renders
the cable inoperative.
The function of the grounding system, theoretically, is to carry fault current and
simultaneously limit the resulting voltage drop in the grounding circuit external to the
grounding resistor to not more than 100 volts. This means that the fault current flowing
in the grounding conductors and shield wires, all connected in parallel, multiplied
by the resultant impedance cannot exceed 100. Where the maximum fault current is
limited by a grounding resistor, it seems that the parameters for sizing the grounding
conductors are thereby defined.
Even though the grounding system might be considered fail-safe, continuous ground
monitoring is required by Federal law to ascertain continuity through connections and
to assure solid terminations.
Ground-check conductors are included in trailing cables to facilitate this ground
monitoring. Premature flex fatigue of these ground-check conductors has been virtually
eliminated by the application of a heavy wall of polypropylene insulation that prevents
kinking. In cases where the ground-check conductor is much smaller than the phase
conductor, its flex life is best improved by increasing the insulation wall thickness. The
objective is to derive maximum resistance to kinking.
Insulation
Ethylene Propylene Rubber (EPR) insulation is now standard in mining cables, and
has helped reduce insulation thickness by one third, while nearly doubling typical
breakdown voltage.
Ethylene Propylene Rubber has excellent mechanical properties over a temperature range
of -60°C to +90°C. Within this range, EPR has high tensile strength, resistance to tear,
abrasion, and compression cut. In addition, it is flexible and easy to repair, making it well
suited for rugged mining environments.
Figure 2
1
2
Tests have
shown that the
copper/textile
braid shield is
mechanically
superior to a full
copper braid.
5. Conductor Stranding
Mining cable conductors are stranded to provide both flexibility and flex life. The flex
life of a particular construction is the number of times it can be bent back and forth
before the strands fatigue. Flex life or resistance to flex fatigue is a function of stress.
The relationship is nonlinear, especially in the low-stress portion of the curve. (Figure
3) Theoretically, at some point on the curve below you could increase the flex life by a
factor of 10 simply by reducing the stress by
one half, however operating at very low-
stress levels can be impractical.
Flex fatigue in any portable cable is a
certainty and just a question of time. To
prolong the time before it happens, the
important thing is to balance the tensile
load among the individual conductors as
uniformly as possible.
Manufacturers’ recommended minimum bending radii and maximum tensile loads are
calculated with this in mind. Exceed them, and you will greatly accelerate failure rates.
In which case, the percent reduction in flex life exceeds the percent increase in operating
limitations by a large margin.
The recommended Insulated Cable Engineers Association (ICEA) minimum bending
radii is as follows:
• Braid-shielded portable cable—8 times the cable diameter
• Nonshielded portable cables—6 times the cable diameter
• Flat nonshielded cables—6 times the minor dimension
The control sample was flexed
continuously for a specified number of
cycles over a given bending radius, under
specific tension, until only a few strands
remained unbroken.
The second sample was flexed the same
number of cycles over the same bending
radius, but the tension weight was
reduced by one half. As can be seen,
reduction of tension greatly reduced
strand breakage.
The third sample was again flexed the
same number of cycles using the same
tension as with the control sample.
However, a bending radius two and one-
half times larger was used. Increasing
the bending radius practically eliminates
strand damage.
Figure 3
Conductor stress—lbs. per in2
Cyclestoflexfatigue
Increasing the
bending radius
practically
eliminates
strand damage.
6. How Surface Mining Cables Fail
Cable breakdowns are neither mysterious nor unaccountable, and almost without
exception can be traced to one or more of the following causes:
1. Excessive tension
2. Mechanical damage
3. Current overload
4. Improper splicing and termination techniques
Excessive Tension
Many cable failures are the direct result of excessive tension. A cable that has been
“stretched” no longer has the balanced construction that is so vital to long life. Tension
on the conductors subjects the individual wires in the strand to compression and shear.
These thin wires are then damaged and will break more easily when bent or flexed.
Tension also elongates the conductor insulation. The elongated insulation is then
vulnerable to compression cutting. It will rupture more easily when it is crushed against
the stranded conductor during runovers. The insulation will also have a tendency to
creep over the conductor at a splice.
Jackets under tension lose a considerable part of their resistance to mechanical damage.
A jacket under tension is much more likely to be cut or torn. Stretching also causes
the copper conductors to take a permanent set. Of course the insulation and jacket
are stretched as well, but they will return to their original length when the tension is
removed. This difference in the properties of rubber and copper when subjected to
tension will cause the conductors to be wavy and fail prematurely.
Mechanical Damage
This is one of the most prevalent sources of trailing cable failures. Factors initiating
mechanical damage include cutting, compression (crushing), punctures and abrasion.
In extreme cases of mechanical damage, the failure is instant and the cause can be
assigned on the spot. Many times, however, the cable components are merely “injured”
and become latent failures. At that point, it may be more difficult to pinpoint the exact
cause and to take remedial action.
Current Overload
The temperature of the conductors, insulation and jacket are, of course, elevated when
cables are subjected to an electrical load. The resistance of the copper is increased,
voltage drop in the cable is increased and therefore, a reduced voltage is supplied to
the machine. As a result, the machine calls for even more current which adds further to
cable heating.
Cable
breakdowns
are neither
mysterious nor
unaccountable,
and almost
without
exception the
cause can
be traced.
7. Current Overload (con’t)
A trailing cable’s insulation and jacket
materials exhibit maximum resistance
to physical abuse at the rated conductor
temperature of 90°C or less.
The ability of these components to
withstand damage decreases as the
temperature increases. Conditions
which normally cause few cable failures
suddenly become a problem. At elevated
temperatures, the jacket has lost much of
its resistance to cutting, crushing, tearing
and abrasion.
The section of the cable that remains on the reel is most likely to be damaged by
electrical overload. Layering on the reel hinders ventilation and heat dissipation. (Figure
4) Continued exposure to elevated temperatures will age the jacket, making it hard and
brittle, and causing crazing or cracking upon subsequent reeling.
Improper Splicing and Terminating Techniques
Over the years, much work has been done to improve both splicing materials and
techniques. The following items have been found to be primarily responsible for
unsatisfactory splice service:
1. Ending up with a grounding or ground-check conductor which is shorter
than the power conductors
2. Semi-conducting residue on the insulation surface that was not removed
3. Gaps, voids or soft spots in the insulation tape build-up
4. Improper termination of shielding system, leaving inward-pointing projections
5. Damage to factory insulation by improper removal of shielding systems
6. Excessive slack in one or more individual conductors
7. Splice has low tensile strength and is easily pulled in two
8. Individual wires are damaged during application of connector
9. Splice is too bulky—will not pass through cable guides or over sheaves
10. Improper application of the outer covering allowing water to enter the cable interior
By choosing a cable with an adequate current rating, avoiding excessive tension and
mechanical damage, and using proper splicing techniques, it is not unreasonable to
reduce cable-related downtime by more than 50 percent. This will, of course, translate
into increased production and profits.
Figure 4
No. of Multiply
Layers Ampacities By
1 0.85
2 0.65
3 0.45
4 0.35
When cables are used with one or more
layers wound on a reel, the ampacities
should be derated as follows:
A trailing cable’s
insulation
and jacket
materials exhibit
maximum
resistance to
physical abuse
at the rated
conductor
temperature of
90°C or less.
8. Proper Care and Maintenance Greatly
Reduces Downtime
The cable failure mechanisms described in the previous section are usually brought into
play by one or more of these common surface mining situations:
1. Rock falls and slides
2. Runovers by pit equipment
3. Dragging
4. Improper splicing
The best means of minimizing the occurrence of these harmful situations is a workable
cable maintenance program. This program should not be limited to a few “Dos and
Don’ts,” but must consist of a series of good cable practices that become a habit and fit
naturally into the daily mining routine.
An Effective Program
There is no magic formula for cable maintenance that fits all conditions. The following
basic outline suggests an approach that can be applied at any operation:
1. Choose a cable design that is consistent with voltage, safety and
expected performance
2. Maintain a record of causes of cable failures
3. Educate operating personnel to recognize the limitations of a portable cable
4. Take remedial action based on records and education. Records will point to
what made the cable fail. Education will help explain why the cable failed.
Effective maintenance begins with choosing the most suitable cable construction
obtainable for the application. Economic considerations alone are a poor substitute
for sound engineering. Cable manufacturers like General Cable supply an abundance
of data to serve as a guide, but the following should be emphasized in choosing a cable
type and size:
1. Safety
2. Current-carrying capacity
3. Voltage drop
4. Ambient temperature—for example, extreme summer heat
5. Mechanical strength
6. Unusual conditions that might require a special cable construction
The second step in a good maintenance program is analysis of performance.
An accurate record must be maintained and should include:
1. The date of installation
2. Record of removal for repairs
3. The cause of each failure
Information on number 3 is the most important of all.
The best
means of
minimizing the
occurrence
of harmful
situations is a
workable cable
maintenance
program.
9. An Effective Program (con’t)
An accurate record of causes of failure will point out those areas where maintenance is
most urgently needed. This record will also indicate the effectiveness of any remedial
action that might be taken. Experience is a good teacher and can be most useful in
setting up a program; but experience can be greatly enhanced by an accurate record.
There is too great a tendency to classify practically every failure under “improper
handling by operating personnel.”
There should be mutual understanding between the cable manufacturer and mining
operator concerning the physical and electrical limitations of a cable. Such an
understanding will prove to be one of the most rewarding steps in the entire program.
Cable manufacturers like General Cable can offer valuable assistance in training
programs designed to instruct operating personnel in good cable practice.
Rock Falls and Runovers
Falling rock and runovers are responsible for approximately 50 percent of all cable
failures, calling for a concentrated maintenance effort. Cables subjected to rock falls
and runovers by heavy equipment are damaged by impact and crushing.
Trailing cables have, on occasion, exhibited outstanding resistance to mechanical
damage, but to a large degree their ability to withstand impact and crushing is limited
by the following:
1. The concentration of impact on a small area of cable—a rock striking the
jacket surface, sharp-edge-first, can do more harm than a larger rock landing
flat-side-down.
2. The position of the conductors at the point of impingement—the most vulnerable
is when one conductor rests directly over another. The metal conductors serve
as blunt cutting edges, and under severe impact, will initiate breaks or ruptures in
the insulation.
3. The physical characteristics of the jacket and insulation—relatively speaking,
jackets have the properties found in tire treads. High-voltage insulations are
approximately one-half to two-thirds as tough as the jackets.
4. Flexible shield and grounding conductors are, of necessity, constructed with
small-diameter wires—when subjected to impact or crushing, they are readily
deformed and easily broken. For example, an individual shielding wire has a
breaking strength of approximately 4 lbs.
Damage to cable components by rock falls and runovers are all potential blowout
points. Cuts in jackets provide entrances for water to penetrate the cable. Deformed or
injured copper wires accelerate fatigue breaks. Insulation with compression breaks will
rupture electrically.
Maintenance suggestions that require repetition are:
1. Move cables into the clear during blasting.
2. Position cables in the pit where the possibility of them getting hit
by rock slides from the spoil bank or highwall is minimized.
3. Provide vehicles and areas of heavy traffic with adequate lighting during
nighttime operation. Cables should be kept visible at all times.
4. Either bury cables or provide arched runways at vehicle crossings.
There should
be mutual
understanding
between
the cable
manufacturer
and mining
operator
concerning
the physical
and electrical
limitations of a
cable.
10. 10
Dragging
It is quite possible to avoid jacket tearing and other cable injuries caused by dragging—
instead of putting a single loop on a caterpillar hitch, you should pull the cable into
more loops, thereby shortening the length of each pull.
Proper Splices
While it is true that no splice is as good as a new cable, the use of quality materials and
proven techniques can dramatically improve the service life of a spliced cable. A good
splicing has the following characteristics:
1. High tensile strength—the splice cannot be easily pulled in two
2. Balanced conductors—equal tension on each conductor
3. Small outside diameter—the splice can be passed easily through
existing cable guides
4. Low electrical resistance
5. Adequate insulation
6. High resistance to fatigue
7. A covering that is capable of keeping moisture from entering the cable interior
Preparation of Cable for Splicing
In preparing cable ends for splicing and terminating, there are certain steps that require
special attention and technique to insure against premature failure. These are listed
below:
1. Cable ends should always be cut carefully and squarely.
2. The outer jacket should be removed without damaging shield tapes
or braid by the following procedures:
a) Ring jacket circumferentially through approximately
80 percent of the jacket thickness.
b) Holding knife at an angle, cut the jacket longitudinally in such a manner
so that repeated traverses of these cuts will only have penetrated
approximately 80 percent of the jacket thickness.
c) Using pliers, grip the edge of the jacket and pull in the direction of the
slant cut. If the jacket does not readily tear at the cut, a knife may be
used with tension applied to the jacket, still avoiding damage to the
underlying shield tapes or braid.
3. Thoroughly clean jacket on both ends of the splice to obtain good adhesion
between the factory jacket and the completed splice jacket.
While it is true
that no splice
is as good as a
new cable, the
use of quality
materials
and proven
techniques can
dramatically
improve the
service life of a
spliced cable.
11. 11
Making the Splice
1. Stagger the conductors so that
the finished splice will have the
smallest possible diameter, and so
that all reconnected conductors will
be of equal length. (Figure 5)
2. Cut the shield wires at the point of
termination carefully. A smooth
shield edge is essential in preventing
premature splice failure.
3. Remove the semi-conducting insulation shield, if present, to within approximately
1/4 of the end of the metallic shield. Improper termination of shield
components is one of the major causes of splice failure.
4. Pencilling of the insulation requires a 360° perpendicular cut through all but the
last 1/16 of insulation, and at a predetermined distance from the conductor
end. This distance is directly
dependent on the type of connector
and type of cable insulation. Pencil
and smooth the taper before removing
the short section of insulation from
the conductor. This buffer technique,
illustrated in Figure 6, protects the
conductor surface against undue
abrasion and scoring.
5. Any traces of semi-conducting residue remaining on the conductor or surface
of the insulation must be removed. Normally a lintless cloth slightly dampened
with cleaning solvent will suffice. (Note: Semi-conducting insulation shield
materials are generally not used on mining cables rated less than 8000 volts)
6. Reconnect the conductors, being
careful not to damage the individual
wires. (Figure 7)
Re-Insulating the Joint
At this stage, the ultimate electrical integrity of the cable joint will be in direct
relationship to the skill of the splicer. If the individual fails to properly address
any phase of the operation, failure could result. Areas requiring strict attention
to details are:
1. Application of a semi-conducting
tape over the conductor connector
must result in a smooth contour.
(Figure 8) Insulation putty can
assist in this, as well as seal
against moisture.
Figure 6
length determined by connector
and insulation types
Figure 5
Figure 7
Figure 8
At this stage,
the ultimate
electrical
integrity of the
cable joint will
be in direct
relationship to
the skill of the
splicer.
12. 12
Re-Insulating the Joint (con’t)
2. The high-voltage insulating tape
should be applied half-lapped,
introducing uniform stretch as
specified by the tape manufacturer.
(Figure 9)
3. Frequent rolling of the work with a concave tool, screwdriver shank or
other round object helps to eliminate any entrapped air which could
otherwise ionize if sufficient voltage gradient is impressed across it.
4. Wrap insulating tape to approximately 1/4 from cable semi-conducting
component. The space allows for proper transition between materials in
reshielding. For proper metallic shielding, a tinned, all-copper braided tape
is recommended for proper conductance.
Re-Jacketing the Completed Splice
Attempting to rebuild the cable as close to
its original condition as possible includes
consideration of the jacketing material.
Uncured thermosetting rubber tapes have
been used for this purpose with considerable
success. (Figure 10) It should be vulcanized
in a molding press for best results.
The Finished Job
A well-made, permanent-type splice with a vulcanized covering approaches all the above
characteristics, with good resistance to fatigue being the most difficult to achieve. As
voltage ratings increase, the margin of safety will be on the decrease. Therefore, it is
essential that every aspect of the installation be precisely engineered and supervised by
capable individuals. The same applies to pre-fabricated splicing devices.
Summary of Ways to Cut Cable Downtime
Following is a summary of the steps which have proven effective in prolonging cable life:
1. Prevent twisting or kinking of cable during installation—a kinked conductor
is a damaged conductor.
2. Avoid excessive tension.
3. Use the largest-size cable possible for the application. Take advantage of the
extra tensile strength and current-carrying capacity of the next larger size.
It is more economical in the long run.
4. Keep runovers to a minimum. Any form of crushing is a potential source
of rupture in the insulation and jacket.
5. Remove damaged sheaves, guides and rollers. Make certain cable guides
are large enough for splices to pass through freely.
6. Repair cut or crushed cable even if a blowout has not occurred.
7. Provide a spare cable. Remove cable with temporary repairs and make
permanent repairs. This will pay off, especially in wet pits.
8. Keep water out of the cable interior.
9. Keep a record of what caused failures. It will point out where steps must
be taken for more effective maintenance.
By adopting
these
practices,
cutting
cable-related
downtime by
more than
50% isn’t at all
unreasonable!
Figure 10
Figure 9
13. 13
By adopting all the pre-mentioned practices, cutting cable-related
downtime by 50 percent isn’t at all unreasonable!
Here’s the information in tabular form:
Causes of Damage Evidence of Damage How to Avoid Damage
Excessive Tension 1) Cable necked down resembling an
hourglass in shape
2) Jacket creeping back from
temporary splice
3) Grounding conductor pulled in two
4) Cable kinked or jacket torn where
pulling hitch is attached
Keep proper tension on trailing cable reel. (1, 2, 3)
Pull the cable into several loops (rather than a
single long length) when moving. (4)
Mechanical Damage 1) Short sections of cable crushed or
flattened to a larger diameter
2) Excessive abrasion, cable grooved
or shows uneven wear
3) Gouges, cuts and punctures
Move cables into the clear during blasting. (1)
Position cables in the pit where there is the least
possibility of their getting hit by rock slides from
the spoil bank or high wall. (1)
Provide vehicles and areas of heavy traffic with
adequate lighting during nighttime operation. (1)
Either bury cables or provide arched runways at
cable crossings. (1)
Replace broken sheaves or broken guides. (2, 3)
Current Overload 1) Blistered jacket
2) Tinned copper conductor wires
turn to a blue-black color
Choose a cable with an adequate current rating.
Consult cable manufacturer or mining machine
manufacturer for recommendations. (1, 2)
Avoid unnecessary earth covering of long lengths
of cable. (1, 2)
Temporary Splices
and Terminations
1) Bare conductors exposed in a
temporary splice
2) Open grounding or ground-check
conductor
3) Kinked cable
Carry insulating tapes back over the original
conductor insulation, and replace temporary
splices with permanent splices as soon as
possible. (1)
Connect these smaller conductors approximately
1/4 longer than the power conductors in all
splices and terminations. (2)
Balance the conductors in all splices and
terminations so that there will be an even stress
on all conductors. (3)
Guide To Trailing-Cable Maintenance
14. 14
How General Cable Helps You Cut Downtime
General Cable would be glad to work closely with you to reduce cable-related downtime in
your own mining operation. To do this, we have three separate areas of competence we can
lend to your situation:
1) Anaconda®
Cables
We’ve long been the leading supplier of portable cables designed for reliable operation
in the toughest of mining environments. And we’re still pioneering advances!
2) Field Assistance
We’ve learned a lot from years of providing engineering assistance right at the
mine site. Experience which we’re happy to share with you at your own locations.
We can even train your personnel in proper cable care!
3) Mining Cable Test Lab
We believe no other supplier can offer you the services of a facility like this. Located
at Marion, Indiana USA, we have all the test equipment necessary to simulate
actual conditions in a mine. But with one important difference—our Portable
Cable Lab can test a cable to
destruction in a fraction of the time
it would take under normal field
conditions. Yet we can accurately
extrapolate the results, in terms of
the type of end-use the cable is
expected to receive.
Thus, the laboratory can give you fast,
reliable advice on your problems with
trailing cable life. It can help you
with correct recommendations on which cables to select. And of course, it has helped
General Cable immeasurably in the past in designing cables that are in-tune with the
realities of the mine site. The following chart describes common types of failure, and the
lab tests we can perform to induce such damage.
Cable Tests for Simulating
Cable Damage Source Service Damage
Excessive tension and wire fatigue: • Tension reeler
• Flexing machines
• Torsion bending machine
Mechanical damage: • Compression cut machine
• Abrader
• Free-fall impact (crusher)
• Pile driver (repeating impacter)
Electrical stability: • Current overload test
• Cyclic aging
• EMA
• ac life endurance test
• dc proof test
Flame and heat resistance: • Flame test
• Air oven
• Electrical overloads
Splices and terminations: • Mechanical and electrical tests
Environment: • Chemical- and oil-resistance
• Oven aging
• Weather sunlight
General Cable
would be
glad to work
closely with
you to reduce
cable-related
downtime
in your
own mining
operation.
15. You already know
it’s the best.
Now you
know where
to find it.
If you’ve been looking for the best-built
mining cable on the market, your search just
ended. General Cable offers a full line of
premium Anaconda®
Brand cables engineered for
superior performance in the most challenging
applications. And they’re manufactured at the same
facility, to the same exacting specifications, that have
made the Anaconda®
Brand name famous worldwide.
As always, specially designed conductors, insulation
and jackets that exceed industry standards have made
Anaconda®
Brand cables the most reliable choice for
mining equipment. For over 50 years, they’ve been the
right cable. And now, they’re right here.