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The nature of power cables, causes of failures, and failure classification
(1) The nature of the power cable. Between the cable insulation cores, insulation cores and jacket or shield are insulated from each other.
(2) The cause of the failure of the power cable. 1 mechanical damage, the cable is directly damaged by external forces, such as vibration, thermal expansion and shrinkage caused by lead sheath damage; 2 insulation damp, due to improper construction of the terminal head or connection box so that moisture intrusion; 3 insulation aging; 4 sheath corrosion; 5 Overvoltage, lightning strike or other overvoltage breaks down the cable; 6 Overheating, overload or poor heat dissipation, breakdown of the cable insulation; 7 Material defects.
(3) Classification of power cable faults (based on fault resistance and breakdown clearance). 1 Open circuit fault; 2 High impedance fault; 3 Low resistance fault; 4 Flashover fault.
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Power transmission is an important part of the power supply system. In recent years, due to the acceleration of infrastructure construction and the need for safe power supply, buried power cables are increasingly used in the power facilities of urban and rural areas and industrial and mining enterprises. However, because the cable is buried underground and the line is long, when the cable fails to affect the normal power supply, it will bring certain difficulties to the search for the fault point. Without test equipment, simply relying on manual troubleshooting of cable faults will not only waste manpower and material resources, but also cause incalculable power outage losses. As a result, fault testing of power cables has become one of the most important issues that have plagued power supply departments for normal power supply for many years. In recent years, the test technology of power cable faults has made great progress. The pulse current method of fault location, the pulse magnetic field method of path detection, and the acousto-magnetic synchronization method of fault fixed point using the difference between sound and magnetic fields have emerged. This article uses the bridge method to test the principle of the cable flaw detector and analyze it with examples.