Wire and cable fault and pre-control

The construction of power cables into the ground is the direction of
urban modernization development.
With the increasing number of cable routes and the increase of operating life, cable faults have gradually increased, and the faults of cable bodies, cable accessories, cable accessories and other equipment in cable operation have also increased
significantly.
In the following, I will tell you about the causes of cable failures and the measures taken to
prevent them.

Analysis of insulation failure causes

Insulation failures generally occur for the following reasons: insulation failures, accessory problems, outer sheath problems, etc
.

Insulation failure

The insulation aging of cables mainly occurs in the later stage of operation, generally occurring in cable routes that have been in operation for 15 years and more, resulting in a significant increase
in cable failure rates.
Insulation aging is mainly divided into dendritic aging, electrothermal aging and insulation material aging
.
Overheating will accelerate the deterioration of the insulation
.
The electric ionization generated by the air gap inside the cable insulation will cause local overheating, carbonize the insulation material, and cause a decrease
in dielectric strength.
Cable overload is an important factor
in cable overheating.
Cables installed in poorly ventilated places such as cable dense areas, cable trenches and cable tunnels, cable paths parallel or intersecting thermal pipelines without effective thermal insulation measures, etc.
, will overheat the cable and accelerate the damage
of the insulation layer.
Cable insulation operates under the action of electricity and heat for a long time, and its physical properties will change, resulting in a decrease in its dielectric strength or increased dielectric loss, and eventually causing insulation collapse, aging and failure
.

Attachment issues

The cable intermediate joints and terminations are usually completed by the installer at the laying site, and it is easy to make mistakes
if you do not pay attention.
Cable accessory faults account for the main part of cable line faults, and their macro is mainly manifested as composite interface discharge and accessory material aging
.
The failure of cable accessories is often due to the poor production process, personnel thinking paralyzed, in the production process, bubbles, moisture, impurities and other defects appear inside the accessories, resulting in partial discharge and insulation breakdown
.

Outer cladding problems

In the medium and high voltage power grid, cables are more and more widely used, the outer sheath of the power cable is the first line of defense to protect the cable, its integrity is directly related to the internal structure safety and cable service life
.
There are three main causes of cable outer sheath failure: First, hard object damage or external force damage around the cable
.
Direct buried cable above and below hard objects sharp corners directly contact the outer sheath, especially in the section where vehicles pass, long-term road surface vibration, hard object sharp corners may pierce the outer sheath, resulting in damage to the internal structure, coupled with cable load changes, the cable itself thermal expansion and contraction and the damaged part of the electric field is not evenly distributed, eventually resulting in damage to the insulation layer; When the pipe is laid, the steps or the inner wall of the pipe connection may cause damage to the outer sheath; Mechanical construction or pipe jacking around the cable path causes damage
to the outer sheath.
Second, defects and hidden dangers
left during construction.
The strained and cracked parts of the outer sheath during the cable laying process are in the pipe row, and the personnel cannot find them in time; After the bending part of the cable of 110kV and above is operated for a period of time, cracking occurs, the insulation of the outer sheath is reduced, the metal sheath is grounded at multiple points, and the circulation current increases, which finally leads to the thermal aging breakdown of the insulation
.
Third, termite erosion
.
Once a termite erosion site is found, often there should be multiple erosion parts on this cable route, and we should pay enough attention to
it.
Termite erosion hazards, the northern power grid is relatively rare
.

Take steps to prevent cable failure

Cable line engineering is a systematic project, only from the design, construction, operation and maintenance aspects of its whole process management, in order to ensure its safe operation
to the greatest extent.
Below, we look at what measures are used to prevent cable failure
from six aspects.

First, from the beginning of the design, have a full understanding of the grounding system used by the cable, select the cable that meets its voltage level, and avoid the cable working
under long-term overvoltage conditions.
The selection of the outer sheath should meet the requirements of the use environment and service life, and the selection of the cable sheath protector should meet the principle
that when the relative ground is grounded, the protector can reliably pass the grounding current without damage.
Second, the cable path selection should avoid the cable from being affected by external environmental influences such as heat, corrosion, and external damage, and also avoid the cable laying being too concentrated, causing the heat to not spread in time, and causing overheating of internal factors
.
In addition, the cable path of dual-loop power supply is not recommended to be laid in the pipeline of the same path to prevent simultaneous damage and cause large-scale power outages
.
Third, strengthen the selection of cables and cable accessories, manufacturer supervision, arrival acceptance, etc.
, to ensure the quality level of
cables and cable accessories.
During the on-site inspection, there should be multiple parties such as the manufacturer, the construction party, the supervision party and the project competent department, and check one by one according to the packing list, record the problems found in time and put forward rectification suggestions, which are signed and approved
by multiple parties.
For parts that are susceptible to moisture, after the inspection is completed, they should be sealed in time to prevent moisture from affecting normal use
.
4
.
Strengthen personnel training, conduct necessary business qualifications and technical assessments for cable head production personnel, and hold certificates.
If two consecutive failures occur due to production reasons during the warranty period, the cable head production qualification shall be canceled, and only after passing the retraining assessment can they be re-employed
.
5.
Strengthen the acceptance of hidden engineering and intermediate links in all links of cable engineering, strictly control the quality acceptance, thoroughly rectify defects and hidden dangers found in the acceptance of civil, electrical and other projects, and make various records, and leave photos, film and television and other materials
when necessary.
6.
Use advanced online monitoring technologies such as outer sheath circulation online monitoring technology, online optical fiber temperature measurement technology, and online partial discharge detection technology to strengthen the real-time online operation monitoring of cables, discover hidden defects in advance, and avoid power outage
accidents.

Whether the cable line can operate safely is directly related to the safe operation and system stability
of the entire power grid.
Only by strengthening quality control and acceptance control from various aspects such as cable production, transportation, laying, installation, testing, inspection, etc.
, can cable failures be minimized and long-term safe operation
of cable lines can be ensured.