What are the common faults of cable lines?

Common faults in cable lines include mechanical damage, insulation damage, moisture insult, insulation degradation, overvoltage, and cable overheating. When the above fault occurs on the line, the power of the faulty cable should be cut off, the fault point must be found, the fault must be checked and analyzed, and then the repair and test should be carried out. The cut should be removed and the power supply can be restored after the fault is removed.

The most direct cause of a cable fault is the breakdown of insulation and breakdown.

There are:

a, overload operation. Long-term overload operation will increase the cable temperature, insulation aging, resulting in breakdown insulation, reduce construction quality.

b, electrical aspects are: cable head construction process is not up to the requirements, poor cable sealing, moisture intrusion into the cable, the cable insulation performance decreased; failed to take protective measures when laying the cable, the protective layer is damaged, the insulation is reduced.

c. Civil engineering aspects include: poor drainage of work wells, long-term water immersion of cables, damage to insulation strength, too small working hole, insufficient bending radius of cables, and long-term destruction by external forces of extrusion. Excavate and cut the cable.

d. Corrosion. The protective layer is subject to chemical corrosion or cable corrosion for a long time, resulting in failure of the protective layer and reduced insulation.

e. The quality of the cable itself or the cable head attachment is poor, the sealing of the cable head is poor, the insulation glue is dissolved, and the cracking occurs. The resonance phenomenon of the station causes the line disconnection fault to make the phase capacitance of the line and the capacitance of the ground resonate with the excitation inductance of the distribution transformer. Loops, thereby exciting ferromagnetic resonance.

Harm caused by breakage fault Harmonic resonance Under severe conditions, the high frequency is superimposed on the resonance of the fundamental frequency, which can cause the overvoltage amplitude to reach 2.5 times the phase voltage [P], which may cause the system neutral displacement, windings and wires. Overvoltage occurs. In severe cases, insulation flashover, lightning arrester explosion, and electrical equipment damage may occur. In some cases, the phase sequence of the load transformer may be reversed, and overvoltage may be transmitted to the low voltage side of the transformer, causing damage.

Measures to prevent over-voltage and over-resonance of broken wires The main measures to prevent over-voltage and resonance over-voltage are:

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

(2) Strengthen the line inspection and maintenance to prevent the occurrence of broken lines.

(3) Do not hang the transformer on the line for a long time.

(4) Use ring or dual power supply.

(5) Adding interphase capacitance on the transformer side,

The principle is: the use of capacitors as energy-absorbing elements to absorb the energy of the transient process, thereby reducing the impact of disturbance intensity to suppress the occurrence of resonance .s a (o + 3 C,,) 1 C., with additional phase capacitance in the transformer side â–³ C, to make 8 a [Co +3 (CU + A0) / Ca increase, thereby increasing the capacitance value of the equivalent capacitance C and the equivalent electromotive force Eo can be calculated according to the method in [6]. (6) Transformer with better excitation characteristics helps to reduce the occurrence of broken wire overvoltage.

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