Wire and cable refer to materials used for power, communication, and related transmission purposes. After using wires and cables for a period of time, they may experience aging and other various faults. Let's follow Lingbo Haoyu to understand the causes of wire and cable aging. And how to protect and extend the service life.

Aging reasons

1. External force damage. Based on operational analysis in recent years, especially in the rapidly developing economy of Shanghai Pudong, a considerable number of cable failures are caused by mechanical damage.

2. Insulation is damp. This situation is also very common, usually occurring at the cable joints in direct burial or piping. For example, unqualified cable joints and joints made in humid weather conditions can cause water or steam to enter the joints, forming water branches under the action of the electric field for a long time, gradually damaging the insulation strength of the cable and causing faults.

3. Chemical corrosion. Directly burying cables in areas with acid-base interactions often leads to corrosion of the cable's armor, lead skin, or outer protective layer. The protective layer may fail due to long-term chemical or electrolytic corrosion, resulting in reduced insulation and cable failure.

4. Long term overload operation. Overload operation, due to the thermal effect of the current, when the load current passes through the cable, it will inevitably cause the conductor to heat up. At the same time, the skin effect of the charge, eddy current loss of the steel armor, and insulation medium loss will also generate additional heat, resulting in an increase in cable temperature.

5. Cable joint failure. Cable joints are the weakest link in cable circuits, and cable joint failures often occur due to direct human error (poor construction). During the process of making cable joints, if there are reasons such as loose crimping and insufficient heating, the insulation of the cable head can be reduced, leading to accidents.



6. Environment and temperature. The external environment and heat source in which the cable is located can also cause excessive temperature, insulation breakdown, and even explosion and fire.

What are the common faults of cable and wire aging?

Common faults

Common faults in cable lines include mechanical damage, insulation damage, insulation moisture, insulation aging and deterioration, overvoltage, and cable overheating faults. When the above-mentioned faults occur in the circuit, the power supply of the faulty cable should be cut off, the fault point should be found, the fault should be inspected and analyzed, and then repaired and tested. The power supply can only be restored after the fault is eliminated.

The most direct cause of cable failure is insulation degradation and breakdown

Mainly including:

a. Overload operation. Long term overload operation will cause cable temperature to rise, insulation aging, leading to insulation breakdown and reduced construction quality

b. In terms of electrical aspects, the construction process of the cable head does not meet the requirements, the sealing of the cable head is poor, moisture enters the interior of the cable, and the insulation performance of the cable decreases; Failure to take protective measures during cable laying resulted in damage to the protective layer and reduced insulation

c. In terms of civil engineering, there are: poor drainage of construction wells and trenches, long-term soaking of cables in water, which damages the insulation strength; The construction well is too small, and the bending radius of the cable is not enough. It has been damaged by external pressure for a long time. This is mainly due to rough mechanical construction in municipal construction, which damages and breaks the cable.

d. Corrosion. The protective layer is subjected to long-term chemical corrosion or cable corrosion, resulting in the failure of the protective layer and a decrease in insulation.

e. The poor quality of the cable itself or cable head accessories, poor sealing of the cable head, dissolution and cracking of insulation glue, leading to resonance phenomena in the station, is caused by line breakage fault, which forms a resonance circuit between the phase capacitance and ground capacitance of the line and the excitation inductance of the distribution transformer, thereby stimulating ferromagnetic resonance.

The harm of resonance caused by wire breakage fault

In severe cases, the combination of high-frequency and fundamental resonance can cause the overvoltage amplitude to reach 2.5 times the phase voltage [P], which may lead to system neutral point displacement, winding and wire overvoltage. In severe cases, it can cause insulation flashover, lightning arrester explosion, and electrical equipment damage. In some cases, the phase sequence of the load transformer may reverse, and the overvoltage may be transmitted to the low-voltage side of the transformer, causing harm.

The main measures to prevent resonance overvoltage caused by wire breakage include:

(1) Do not use fuses to avoid non full phase operation

(2) Strengthen line inspection and maintenance to prevent wire breakage

(3) Do not hang the no-load transformer on the line for a long time

(4) Using ring network or dual power supply

(5) Add phase to phase capacitance on the distribution transformer side