The exact cause of XLPE insulated cable accident

The cable fault generated
A joint design and manufacturing process
B insulation aging metamorphism
C insulation
D cable overheat
E mechanical injury
F corrosion protection layer
G overvoltage
H material defects
According to the report, the following reasons XLPE cable accident:
A water tree deterioration
B copper shield fault zone
C copper shield grounding fault
D cable sheath fault
E core shielding layer of uneven thickness
1 water tree degradation
It is the main reason of XLPE insulated cable accident, about 71% of the accidents, mostly occurs in the natural deterioration.
2 copper shield fault zone
In the copper shielding cable with one end grounded, when the copper shield with fracture, non grounded at one end of the copper shield with a non ground state, the copper shield with the induction high voltage, the high voltage if the rupture site discharge, often cause the destruction of insulation. Is shown schematically in Figure fracture site discharge.
The characteristics of fault zone is the copper shield:
(1) Single core cable  than the three core cable accident.
(2) from the production to the ravages of time, from a few weeks to a few years.
(3) the conductor resistance fracture site increases to the thousands of Europe, not the protection of non ground side cable a flashover to ground.
(4) fracture site discharge fire, smoke, fire may have caused serious.
3 copper shield grounding fault
XLPE copper cable shield grounding fault has been the scene of the attention. For example, a region of the XLPE cable are often adopted in buried, the terminal head of copper shielding wire and steel armor wires are led, grounding wire section were no less than 25mm2 and 10mm2, from thermal glove leads should be insulated from each other, through the above two improvements, there are conditions in the terminal head of regular measurement of steel armor insulation resistance and steel armor on the copper shield, can indirectly reflect the cable outer sheath, no damage, which can determine the cable damping.
Detection of copper cable shielding and grounding, a change point in the terminal side of the insulating resistance of 0.01M. Cable laying is shown schematically in figure.
Further detection, fault point location away from the substation 1973m 4 cable connection. The 4 joint digs, the joint, the outer sheath are respectively opened inspection, found the cause of the copper shield grounding is the inner, outer sheath of joint sealing lax, steel armor and copper shield has the moisture. Aiming at the fault reason, the joints were sufficient moisture use a blowtorch, the copper shield in the interface is disconnected, respectively, both sides of the joint copper shield on telemetry insulation resistance, test result is: substation side is 4.5M Ω, the terminal side of 5M. Due to timely treatment, to avoid accidents
4 cable sheath fault
XLPE single core cable can run safely and reliably, and the protective layer can be closely related to the safe and reliable operation. By the end of the cable sheath grounding, shield of the cable insulation requirements must be good. When the cable shield grounding, operation of cable sheath will be subjected to an alternating magnetic field, will be in the corrugated aluminum sheath voltage induced, directly to the ground terminal and the cable sheath insulation bad produced “circulation”. “Circulation” to make corrugated aluminum layer heating, and the transmission capacity is reduced to 30% to 40%; and the metal protecting layer serious burn, burn after the protective layer will enable the cable main insulation is exposed outside, and the underground (or air) of water or moisture contact, so that the insulating layer is destroyed, eventually lead to the breakdown of insulation.
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