Common cable failures:
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 should be found, the fault should 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 eliminated. 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 temperature of the cable and cause aging of the insulation, which will breakdown the insulation and reduce the construction quality.
b. Electrical aspects include: The cable head construction technology fails to meet the requirements, and the cable head is poorly sealed. Moisture intrudes into the cable and the cable insulation performance deteriorates. When the cable is laid, no protective measures are taken and the protective layer is damaged and the insulation is reduced.
c. Civil engineering: Drainage of the well pipe trench is poor, the cable is immersed in water for a long time, and the dielectric strength is damaged; the working hole is too small, the cable bending radius is not enough, and it is destroyed by the external force for a long time. It is mainly the construction of mechanical construction in the municipal construction that is used to cut and cut cables.
d. Corrosion protection 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 cable head is poorly sealed, the insulation glue is dissolved, and the cracking occurs. The resonance phenomenon at the station causes the line disconnection fault to make the phase capacitance of the line and the capacitance between the ground and the excitation inductance of the distribution transformer resonate. Circuit, thus exciting the harm of resonance caused by the disconnection of the ferromagnetic resonance Breaking line resonance In severe cases, 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 lead to the system Point displacement, overvoltage in windings and conductors, severe flashover of insulation, explosion of arrester, damage of electrical equipment. In some cases, the phase sequence of the load transformer may be reversed, and overvoltage may also be transmitted to the transformer's low voltage. Side, causing harm.
The main measures to prevent overvoltage and disconnection overvoltage are:
(1) Do not use fuses to avoid non-full-phase operation.
(2) Strengthen the inspection and maintenance of the line to prevent the occurrence of disconnection.
(3) Do not hang the transformer on the line for a long time.
(4) Use ring network or dual power supply.
(5) The phase-to-phase capacitance is added on the transformer side. The principle is that the capacitor is used as the energy-absorbing element to absorb the energy in the transient process, thereby reducing the impact disturbance strength to suppress the occurrence of resonance. s 1 (o+3C,,) 1C. Adding the phase-to-phase capacitance ΔC to the transformer side, which increases the value of 8-[Co+3(CU+A0)/Ca], thereby increasing the equivalent capacitance C and the equivalent electromotive force. The required capacitance of Eo can be calculated according to the method in [6].
(6) Transformers with good excitation characteristics can help reduce the occurrence of breakage and overvoltage.
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 should be found, the fault should 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 eliminated. 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 temperature of the cable and cause aging of the insulation, which will breakdown the insulation and reduce the construction quality.
b. Electrical aspects include: The cable head construction technology fails to meet the requirements, and the cable head is poorly sealed. Moisture intrudes into the cable and the cable insulation performance deteriorates. When the cable is laid, no protective measures are taken and the protective layer is damaged and the insulation is reduced.
c. Civil engineering: Drainage of the well pipe trench is poor, the cable is immersed in water for a long time, and the dielectric strength is damaged; the working hole is too small, the cable bending radius is not enough, and it is destroyed by the external force for a long time. It is mainly the construction of mechanical construction in the municipal construction that is used to cut and cut cables.
d. Corrosion protection 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 cable head is poorly sealed, the insulation glue is dissolved, and the cracking occurs. The resonance phenomenon at the station causes the line disconnection fault to make the phase capacitance of the line and the capacitance between the ground and the excitation inductance of the distribution transformer resonate. Circuit, thus exciting the harm of resonance caused by the disconnection of the ferromagnetic resonance Breaking line resonance In severe cases, 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 lead to the system Point displacement, overvoltage in windings and conductors, severe flashover of insulation, explosion of arrester, damage of electrical equipment. In some cases, the phase sequence of the load transformer may be reversed, and overvoltage may also be transmitted to the transformer's low voltage. Side, causing harm.
The main measures to prevent overvoltage and disconnection overvoltage are:
(1) Do not use fuses to avoid non-full-phase operation.
(2) Strengthen the inspection and maintenance of the line to prevent the occurrence of disconnection.
(3) Do not hang the transformer on the line for a long time.
(4) Use ring network or dual power supply.
(5) The phase-to-phase capacitance is added on the transformer side. The principle is that the capacitor is used as the energy-absorbing element to absorb the energy in the transient process, thereby reducing the impact disturbance strength to suppress the occurrence of resonance. s 1 (o+3C,,) 1C. Adding the phase-to-phase capacitance ΔC to the transformer side, which increases the value of 8-[Co+3(CU+A0)/Ca], thereby increasing the equivalent capacitance C and the equivalent electromotive force. The required capacitance of Eo can be calculated according to the method in [6].
(6) Transformers with good excitation characteristics can help reduce the occurrence of breakage and overvoltage.
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