[guide] the selection of qualified wire and cable products is related to the safety of people's production and life. For ordinary consumers, besides knowing how to select qualified wire and cable products, it is also necessary to know the routine monitoring knowledge of wires and cables.

The selection of qualified wire and cable products is related to the safety of people's production and life. For ordinary consumers, besides knowing how to select qualified wire and cable products, it is also necessary to know the routine monitoring knowledge of wires and cables. There are several important indexes in the quality detection of wire and cable.

Insulation resistance test:

Insulation resistance is an important index reflecting the insulation characteristics of wire and cable products. It is closely related to the electrical strength, dielectric loss and gradual deterioration of insulation materials under the working condition. For communication cables, the insulation resistance between lines is too low, which will also increase the attenuation of loops, the crosstalk between loops, and the long-distance power leakage on the conductive core. Therefore, the insulation resistance should be higher than the specified value.

The defects in the process can be found by measuring the insulation resistance, such as insulation, dry or sheathing, dampness, insulation, contamination and conductive impurities, insulation cracks caused by various reasons. In the operation of wires and cables, insulation resistance and leakage current are often detected as the main basis for continuing safe operation.

At present, wire and cable insulation resistance measurement, in addition to using an ohmmeter (shaking table), used a galvanometer comparison high resistance meter method (voltage - current method).

Measurement of capacitance and loss factor:

When the cable is added to the AC voltage, the current flows through. When the amplitude and frequency of the voltage are fixed, the capacitance current is proportional to the capacity of the cable (Cx). For EHV cable, the current of this capacitor may reach the value that can be compared with rated current, and become an important factor limiting cable capacity and transmission distance. Therefore, the capacitance of the cable is also one of the main electrical properties of the cable.

In AC electric field, the cable insulator due to leakage current and polarization, will be formed to dielectric loss, dielectric loss factor or loss tangent (TAN) to said, it is not only a waste of energy, but also can make the medium (insulator) heating, insulation aging, so it is one of the main parameters of TAN cable.

By measuring capacitance and loss factor, we can find various insulation deterioration phenomena such as damp, insulation and shielding shedding. Therefore, capacitance and TAN measurements are made in cable manufacturing or cable operation. High voltage cables, Cx and TAN are all measured under their working conditions, namely power frequency and high voltage. They are usually used in high voltage Xilin bridge. This year, the current ratio transformer bridge has been started.

Partial discharge measurement:

For oil filled cables, there is basically no local power generation. Even if partial discharge is present, oil paper cable is usually very weak, such as several PC. Therefore, these cables can not detect partial discharge in factory test. For extruded cables, not only the possibility of the local discharge, and the failure of partial discharge on plastic, rubber is more serious, with the increase of voltage level, work intensity increases, this problem becomes more and more serious, so the high pressure extrusion cable to do, in the measurement of partial discharge test in the factory test.

Many measurement methods of partial discharge, can exchange according to the instantaneous charge discharge, discharge pulse measurement (Electrometric method); can also be based on ultrasonic discharge generated by measuring the voltage (acoustic emission); can also according to the discharge light, measure the intensity of light (optical method). The electric cable is basically used for the cable.