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Sichuan power cable fault causes and common detection methods

Release time:2021-05-14 Author:admin

With the acceleration of the pace of social modernization, the demand for electricity is also growing. As a power cable connecting various electrical equipment, transmitting and distributing electric energy, it has been more and more widely used, but the faults caused by power cables account for a considerable proportion of all power supply faults. Then, how to determine the location of the fault point and determine the type of fault has become one of the key technologies in the use and operation of power cable.

Types of faults

According to the nature of fault, Sichuan power cable can be divided into low resistance grounding or short circuit fault, high resistance grounding or short circuit fault, broken line fault, broken line and grounding fault and flashover fault.

Cause analysis of cable failure

Now several common main reasons are summarized as follows

1. Mechanical damage

Cable failure caused by mechanical damage accounts for a large proportion of cable accidents. Some of the mechanical damage is very slight, and it did not cause failure at that time, but it developed into failure only after a few months or even years.

Sichuan power cable

The main causes of cable mechanical damage are as follows

Damage during installation: accidentally bump the cable during installation, pull the cable due to excessive mechanical traction, or damage the cable due to excessive bending of the cable;

Direct external force damage: urban construction is carried out on the cable path or near the cable after installation, so that the cable is directly damaged by external force; The vibration or impact load of driving vehicles will cause lead (aluminum) cladding crack of underground cables;

2. Damp insulation

The insulation is affected by damp and causes failure. The main causes of cable damp are: water inflow due to unsealed structure or poor installation of joint box or terminal box; The cable is poorly manufactured, and the metal sheath has holes or cracks; The metal sheath is punctured or corroded by foreign objects;

3. Aging and deterioration of insulation

Under the action of electric field, the air gap inside the cable insulating medium is free, which makes the insulation drop. When the insulating medium is ionized, ozone, nitric acid and other chemical products are produced in the air gap to corrode the insulation; The moisture in the insulation makes the insulation fiber hydrolyze, resulting in the decline of insulation. Overheating can cause insulation deterioration. The electric dissociation in the air gap of the cable causes local overheating and carbonizes the insulation.

Diagnosis of cable fault nature

The so-called nature of cable fault diagnosis is to determine whether the fault resistance is high resistance or low resistance; Flashover or closed fault; Is it grounding, short circuit, disconnection, or a mixture of them; Single phase, two-phase or three-phase fault.

1. Bridge method

The fault phase and the non fault phase of the tested cable terminal are terminated, and the two arms of the bridge are respectively connected with the fault phase and the non fault phase. The bridge is balanced by adjusting the resistance, and the distance of the fault point is calculated by the formula.

2. Low voltage pulse reflection method

During the test, low voltage pulse is injected into the fault phase of power cable. When the pulse propagates along the cable to the impedance mismatch point, i.e. the fault point, the pulse is reflected and sent back to the test point, which is recorded by the instrument. According to the time difference between the transmitted pulse and the reflected pulse and the wave velocity of the pulse propagating in the cable, the distance between the fault point and the test point can be calculated.

3. Pulse current method

The pulse current method is to break down the cable fault point with high voltage, use the instrument to collect and record the current traveling wave signal generated by the fault click through, and calculate the fault distance by analyzing and judging the time of the current traveling wave signal to and from the measuring end and the fault point. The pulse current method uses linear current coupler to collect the current traveling wave signal in the cable.

Sichuan power cable

Common methods of cable fault location

1. Acoustic measurement point method

The acoustic measurement method is the main method of cable fault location, which is mainly used to measure high resistance and flashover faults. When measuring, high-voltage equipment is used to make the fault click through and discharge. When the mechanical vibration generated by fault gap discharge is transmitted to the ground, the sound of "Pa, Pa" can be heard, The disadvantage is that it is greatly disturbed by the outside world.

2. Acoustic magnetic method

When the impulse high-voltage signal is applied to the cable to discharge the fault point, the circulating current will be induced in the circuit formed by the cable skin and the earth. The circulating current will generate the pulse magnetic field around the cable. When the sound signal is monitored and the pulse magnetic field signal is received, it can be judged that the sound is generated by the fault point discharge, and the fault point is nearby.

3. Audio frequency induction

Audio frequency induction method is generally used to detect fault resistance less than 10 Ω When detecting the low resistance fault, a 1 kHz audio signal generator is used to supply audio current to the cable to be tested and emit electromagnetic wave; Then, on the ground, the probe is used to receive the electromagnetic field signal along the measured cable path and send it to the amplifier for amplification.

In the power cable fault detection, we should seriously and calmly analyze the type and nature of the fault, correctly apply the search methods and instruments, and accumulate more fault search experience. So the above is the summary of this issue, which is about the relevant information of Sichuan power cable. If you want to know more, please call our company!