NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
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NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Author: Noyafa–CCTV Tester
The nature and classification of cable faults 1. Cable faults can be divided into series and parallel faults from the type. Series fault refers to the disconnection of one or more conductors (including lead and aluminum sheaths) of the cable; usually, before at least one conductor of the cable is disconnected, the series fault is not easy. The nature and classification of cable faults 1111MicrosoftInternetExplorer402DocumentNotSpecified7.8 poundsNormal01. Cable faults can be divided into series and parallel faults from the type. A series fault refers to the disconnection of one or more conductors (including lead and aluminum sheaths) of a cable; a series fault is usually not easily detected until at least one conductor of the cable is disconnected.
A shunt fault is a drop in the insulation of the conductor to the outer sheath or between the conductors, which cannot withstand the normal operating voltage. There are many combinations of actual failure types. Figure 1.1 shows several possible failure modes. For example, as shown in Fig. 1.1.c, the open circuit of the conductor is often caused by the fault current of the cable being too large and blown. This kind of fault is usually accompanied by parallel grounding or the decrease of the phase-to-phase insulation.
Most of the actual faults are single-phase-to-ground insulation drop faults. a. One-phase to ground b. Two-phase-to-ground c. One-phase disconnection and grounding Figure 1.1 Several types of cable faults The cable fault point can be equivalent to the circuit shown in Figure 1.2. Rf represents the insulation resistance, G is the breakdown gap with a breakdown voltage of Vg, and Cf represents the local distributed capacitance. The above three values vary greatly with different fault conditions, and there is no necessary connection between them.
Figure 1.2 Cable fault equivalent circuit gap breakdown voltage Vg depends on the distance of the discharge channel, the resistance Rf depends on the carbonization degree of the cable medium, and the capacitance Cf depends on the degree of moisture at the fault point, the value is very small, can generally be ignored.
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