1. Classification of power cable structure
Power cables can be divided into three types according to their structure:
Single-core or multi-core power cables with metal shielding layer;
Two-core or more power cables with steel armor metal sheath but without metal shielding layer;
Two-core or more power cables without metal shielding layer and steel armor sheath.
2. Fault test methods for cables with different structures
Single-core or multi-core power cables with metal shielding layer:
All faults occurring in the main insulation and core conductor can be effectively tested using the traveling wave method test principle without the need to use other methods.
Power cables with steel armor metal sheath but without metal shielding layer:
For short-distance cable faults within hundreds of meters, the metal sheath can be used as the test site for traveling wave method test.
For long-distance cable faults over hundreds of meters, due to the high resistivity of the metal sheath, the equivalent impedance is large and the echo amplitude is small when using the "traveling wave method" test, making it difficult to determine the location of the fault point. The test line or method needs to be changed, and it is usually treated as a cable structure without metal shielding layer and steel armor sheath.
Power cables without metal shielding and armored sheath:
Single-phase to ground fault: If the cable is three-phase or multi-phase, or the same type of auxiliary power cable, the "bridge method" can usually be used to roughly measure the cable fault. The "traveling wave method" cannot be used at this time.
Two-phase or multi-phase fault, or phase-to-ground fault: If there is an auxiliary cable of the same type, the "bridge method" can be used to roughly measure the cable fault, or one of the faulty phases can be safely grounded to make it a working ground, and the "traveling wave method" can be used to apply the corresponding test method for rough measurement.
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