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Although it may seem like there are many reasons for cable failure, there are actually only four basic reasons why a cable fails
in the field (open or underground) when a cable is dragged.
They are: mechanical damage; The bending radius exceeds the recommended value; current overload; Excessive tension.
Single or combined causes of the above can lead to serious downtime failures
.
Recognizing the symptoms of the problem can help cable users identify the problem and begin to resolve it
.
When one of the four basic triggers arises, it either causes the cable to become immediately unusable, or a series of problems occur one after another, indicating that the cable has failed
.
1.
Mechanical damage
Direct manifestation: The outer sheath of the cable is often torn or cracked, and the surface of the sheath without cracking has burrs or friction marks
.
(Figure 1)
Figure 1
Indirect performance: There are no traces of damage on the outside of the sheath, but the wire insulation inside the cable is partially or completely broken
.
If it is not completely failed, it will lead to leakage, tripping and shutdown
.
As shown in Figure 2
.
Analysis of possible causes: sharp rocks, mine collapses, sharp and overloaded
edge of the winch cable drum.
Corrective action: Cable operators, helpers, and other operators need to understand the properties
of the soft copper stranded wire and rubber material inside the cable.
There is still a long way to go to identify product performance and limitations and reduce mechanical damage
.
Figure 2
2.
The bending radius exceeds the recommended value
When the cable is bent and its bending radius is much smaller than the bend radius recommended by the manufacturer, the internal components of the cable are prone to mechanical damage
.
When dragging the cable, problems such as
screwing, knotting, knotting rings should be avoided.
Otherwise, the cable knot loops will get tighter and tighter, and eventually the bend radius will be only twice the diameter of the cable instead of the normal 12 to 16 times (Figure 3).
Figure 3
If the bending radius is less than the recommended value for the cable, damage to the conductors and insulation can occur
quickly.
Small-diameter cables cut their sheath and/or squeeze the cable core until the insulation is damaged
.
Possible cause: Wrong dragging method/routing technique
Corrective action: Train operators on the correct bending radius
.
The use of larger diameter steel cables and slings reduces operational damage
.
3.
How to avoid twisting:
Screwing is initially caused by knotted rings, most often when "pulling" the cable from a fixed reel and is not easily undone
.
Twisting can lead to permanent "weaknesses"
.
Do not pull the loop, unfold
it slowly.
Keeping the cable straight and opening from the winding loop, "rolling" the reel or coil
.
Figure 4
Incorrect pay-off method (Figure 4, top panel)
Correct pay-off method (Figure 4, top panel)
Incorrect pay-off method (Figure 4, bottom figure) Correct take-up method (Figure 4, figure below)
4.
Current overload
Performance: The cable insulation can withstand a rated temperature of 90°C, but the sheath has no temperature
rating.
Sheaths are synthesized to form the highest mechanical strength, which is their basic function
.
If the conductor operates in free air at 90 °C and the current does not exceed the rated current, the service life of the cable can meet expectations
.
(Figure 5)
Figure 5
Although it may seem like there are many reasons for cable failure, there are actually only four basic reasons why a cable fails
in the field (open or underground) when a cable is dragged.
They are: mechanical damage; The bending radius exceeds the recommended value; current overload; Excessive tension.
Single or combined causes of the above can lead to serious downtime failures
.
Recognizing the symptoms of the problem can help cable users identify the problem and begin to resolve it
.
When one of the four basic triggers arises, it either causes the cable to become immediately unusable, or a series of problems occur one after another, indicating that the cable has failed
.
1.
Mechanical damage
Direct manifestation: The outer sheath of the cable is often torn or cracked, and the surface of the sheath without cracking has burrs or friction marks
.
(Figure 1)
Figure 1
Indirect performance: There are no traces of damage on the outside of the sheath, but the wire insulation inside the cable is partially or completely broken
.
If it is not completely failed, it will lead to leakage, tripping and shutdown
.
As shown in Figure 2
.
Analysis of possible causes: sharp rocks, mine collapses, sharp and overloaded
edge of the winch cable drum.
Corrective action: Cable operators, helpers, and other operators need to understand the properties
of the soft copper stranded wire and rubber material inside the cable.
There is still a long way to go to identify product performance and limitations and reduce mechanical damage
.
Figure 2
2.
The bending radius exceeds the recommended value
When the cable is bent and its bending radius is much smaller than the bend radius recommended by the manufacturer, the internal components of the cable are prone to mechanical damage
.
When dragging the cable, problems such as
screwing, knotting, knotting rings should be avoided.
Otherwise, the cable knot loops will get tighter and tighter, and eventually the bend radius will be only twice the diameter of the cable instead of the normal 12 to 16 times (Figure 3).
Figure 3
If the bending radius is less than the recommended value for the cable, damage to the conductors and insulation can occur
quickly.
Small-diameter cables cut their sheath and/or squeeze the cable core until the insulation is damaged
.
Possible cause: Wrong dragging method/routing technique
Corrective action: Train operators on the correct bending radius
.
The use of larger diameter steel cables and slings reduces operational damage
.
3.
How to avoid twisting:
Screwing is initially caused by knotted rings, most often when "pulling" the cable from a fixed reel and is not easily undone
.
Twisting can lead to permanent "weaknesses"
.
Do not pull the loop, unfold
it slowly.
Keeping the cable straight and opening from the winding loop, "rolling" the reel or coil
.
Figure 4
Incorrect pay-off method (Figure 4, top panel)
Correct pay-off method (Figure 4, top panel)
Incorrect pay-off method (Figure 4, bottom figure) Correct take-up method (Figure 4, figure below)
4.
Current overload
Performance: The cable insulation can withstand a rated temperature of 90°C, but the sheath has no temperature
rating.
Sheaths are synthesized to form the highest mechanical strength, which is their basic function
.
If the conductor operates in free air at 90 °C and the current does not exceed the rated current, the service life of the cable can meet expectations
.
(Figure 5)
Figure 5