Views:196 Author:Site Editor Publish Time: 2020-11-17 Origin:Site
The most direct cause of cable failure is breakdown due to reduced insulation. Many cable faults can be summarized as grounding, electric wire short circuit, and disconnection. Let's analyze in detail, what are the cable faults? How to solve the fault?
Correctly judging the type of cable fault is the first step to find the fault. The required instruments are a high resistance meter (shake meter) and a multimeter. The specific steps are divided into two steps: the first step: measure the relative ground insulation resistance and the phase-to-phase insulation resistance, and identify the cable fault phase; the second step: check whether the cable conductor is disconnected. (1) When measuring the phase-to-ground insulation resistance and phase-to-phase insulation resistance, first use a high resistance meter (shake meter) to measure the insulation resistance between A to ground, B to ground, C to ground, AB, BC, and CA to find out Phase with unqualified insulation resistance value. If the measured value of the high resistance meter (shake meter) is 0M ohms, use a multimeter to retest. (2) Conduct a conductor continuity test. When checking whether the cable conductor is disconnected, the first power line short circuit the three-phase conductors at the far end and suspend them, and measure the resistance of the conductor loop between the phases with a multimeter at the near end. If all are zero ohms, there is no wire. Core disconnection fault; if there is a value of zero, there is also a disconnection fault. You can also use a fault current indicator and an earth fault indicator to find out the problem quickly.
According to the first step of the cable fault location procedure to determine the nature of the cable fault, it can be divided into the cable main insulation fault and the cable outer sheath fault according to the location of the cable. On the basis of the main insulation fault of the cable, it is further divided into: low resistance short circuit to earth fault, low resistance electric wire short circuit fault, disconnection fault, high resistance ground short circuit fault, high resistance cable short circuit fault, flashover fault, leakage fault, intermittent fault, etc.
When the insulation resistance between the phases of the cable fault or the insulation resistance to the ground is between 0.00-10.00 ohms, cable professionals call it "dead ground fault", also called "zero resistance ground fault" or "permanent ground fault". Since the insulation resistance of the dead ground fault point is very low or even close to zero, even if the impulse energy and impulse voltage are used, the discharge sound of the fault point is weak or unable to discharge, and it is very difficult to accurately locate the fault point.
The method to solve the dead ground fault is to use the audio method, including the audio frequency twisting method and the minimum distortion method. That is, use the high-power audio generator FLG200 to connect with the cable to send out audio signals, and then use the audio receiver FLE10 to accurately determine the point near the fault point.
From the inside to the outside, the cable structure is: conductor core, insulation layer, copper shielding layer, inner lining, armoring layer, and outer sheath. Both the insulation layer and the outer sheath of the cable may have insulation breakdown faults. Cable professionals refer to the breakdown of the cable insulation layer (oil-paper insulation layer or cross-linked insulation layer) as the main insulation fault of the cable.
To find the type of cable fault, we need an accurate cable fault indicator, which will help us find the short circuit and overloading faults of the cables.