What Are The Methods And Reasons For Judging Power Cable Faults?

The power cable in work may produce various faults. The faults occurring at the joints at both ends of the cable are easy to find. If the cable fault is underground or in the cable trench, it is difficult to find the fault point. Therefore, the judgment and analysis of the cable fault is the focus of troubleshooting. Before testing the cable fault, the fault type shall be judged to determine which test method to use. With the help of multimeter or megger or other tools and field experience, the fault type can be predicted. If the fault type is open circuit, short circuit, poor contact, or low impedance grounding, the low-voltage pulse method shall be used for measurement. In case of high resistance fault, high voltage impact method shall be adopted. If the fault type cannot be determined, the waveform comparison method can be used. What are the methods and reasons for judging power cable faults?

Methods of judging power cable faults

Generally speaking, power cables mainly have broken line fault, grounding or short circuit fault, broken line and grounding fault, flashover fault, etc. We can determine the fault type of power cable according to the following methods. Here we need to use an insulation resistance meter. We put the insulation resistance meter at one end of the line to measure the insulation resistance of each phase.

(1) When one or more cores of the telemetering cable are discontinuous and grounded through resistance, it can be judged as broken wire and grounding fault.

(2) When the insulation resistance of one or more cores of the cable to the ground is telemetered, or the insulation resistance between cores is much lower than the normal value, but higher than 100 kiloohms, it is a high resistance grounding fault.

(3) When the insulation resistance of one or more cores of the telemetered cable to the ground is high or normal, the conductor continuity test shall be carried out to check whether there is broken wire. If there is, it is a broken wire fault.

(4) When the insulation resistance of one or more cores of the cable to the ground is telemetered, or the insulation resistance between cores is less than 100 kiloohms, it is a low resistance grounding or short circuit fault.

(5) Flashover faults often occur in preventive voltage withstand tests, mostly at cable terminals and intermediate joints. Flashover may occur several times in succession, with intervals of several seconds to several minutes.

At present, the popular test method is the flash method, which includes impulse flash and direct flash, and the impulse flash method is commonly used. The flash test has high accuracy, simple operation, safety and reliability. The equipment is mainly composed of two parts, namely high voltage generator and current pulse meter. High voltage generator is used to generate DC high voltage or impulse high voltage, which is applied to the fault cable to force the fault point to discharge and generate reflected signals. The current pulse meter is used to pick up the reflected signal to measure the fault distance or directly measure the open circuit, short circuit or low resistance fault with low-voltage pulse.

Causes of power cable line failure

Power cables are used to transmit and distribute electric energy. They are often used in urban underground power grids, outgoing lines of power stations, internal power supply of industrial and mining enterprises, and underwater transmission lines crossing rivers. In power lines, the proportion of cables is gradually increasing. Power cables are cable products used to transmit and distribute high-power electric energy in the trunk lines of the power system, including 1-500KV and above voltage levels, and various insulated power cables.

1. External force damage: external force damage may be suffered during the storage, transportation, laying and operation of cables, especially the direct buried cables that have been in operation are vulnerable to damage during ground construction of other projects. Such accidents often account for cable accidents. In order to avoid such accidents, in addition to strengthening the work quality of cable storage, transportation, laying and other links, it is more important to strictly implement the earth moving system.

2. Corrosion of protective layer: the electrochemical corrosion of underground stray current or the chemical corrosion of non neutral soil makes the protective layer invalid and lose the protective effect on insulation. The solution is to install current drainage equipment in the area with dense stray current; When the local soil on the cable route contains chemical substances that damage the lead wrap of the cable, this section of cable shall be installed in the pipe, and neutral soil shall be used as the cable pad and cover, and asphalt shall be coated on the cable.

3. Outdoor terminal is immersed in water: due to poor construction, the insulation glue is not fully filled, which causes the terminal to be immersed in water and eventually explode. Therefore, it is necessary to strictly implement the construction process specification and carefully accept; Strengthen inspection and timely maintenance. The sealing structure is damaged due to oil leakage at the terminal, which causes the loss and drying of impregnant at the cable end, increases the thermal resistance, accelerates the aging of insulation, and easily absorbs moisture, causing thermal breakdown. In case of oil leakage at the terminal, patrol inspection shall be strengthened, and in case of serious leakage, power failure shall be carried out again.