Several Important Indexes of Wire and Cable Quality

1, wire DC resistance measurement:

For wire and cable, the conductor part is its most important component. The conductive core of the wire and cable is mainly used to transmit electric energy or electric signal.

Wire resistance is the main indicator of its electrical performance, and now the standard provides: Detection of core wire DC resistance or resistivity is greater than the value specified in the standard.

The main purpose of this test is to find some defects in the production process: such as wire breakage or part of the single-wire fracture; wire cross-section does not meet standards; product length is not correct and so on.

In addition, the power cable, this test can not only detect the status of the conductor, but also to detect the conductor on the wire and cable products to allow the operation of the current capacity is affected.

2, the insulation resistance of the test:

Insulation resistance reflects the insulation properties of wire and cable products, an important indicator, it and the product of the electric strength, dielectric loss, and insulation materials in the working state of the gradual deterioration of a close relationship.

Determination of insulation resistance can be found in the process of defects: such as insulating dry or impermeable damage to the jacket; insulation and contaminated with conductive impurities mixed; all kinds of causes of insulation cracking.

For the communication cable, the line between the insulation resistance is too low will increase the loop attenuation, crosstalk between the circuit and the conductive core on the remote power supply leakage, so the insulation resistance should be higher than the specified value. In the operation of wires and cables, insulation resistance and leakage current are often detected as the main basis for the continued safe operation.

3, capacitance and loss factor measurement:

Cable plus AC voltage, there is current flow, when the voltage amplitude and frequency of a certain time, the size of the capacitor current is proportional to the cable capacitance (Cx). For EHV cables, the capacitance of this capacitor can reach a value comparable to the rated current, which is an important factor limiting cable capacity and transmission distance. Therefore, the cable capacitance is the main electrical properties of the cable one of the parameters.

In the AC electric field, the insulator in the cable because of the leakage current and the existence of a variety of polarization, will form a dielectric loss, dielectric loss factor or loss tangent (TANδ) to represent, it not only waste of energy, and will dielectric (insulator ) Heat, accelerated aging insulation, so the cable TANδ is one of the main parameters.

Through the capacitance and loss factor measurement can be found in insulation damp, insulation and shielding layer loss and other insulation deterioration, so both in the cable manufacturing or cable operation are capacitance and loss tangent value measurement. For high-voltage cables, capacitors and dissipation factor measurements are in its working conditions, that is, under high frequency power.

4, dielectric strength test:

Insulation strength of wire and cable refers to the insulation structure and the insulation material to withstand electric field without breakdown breakdown capacity, in order to check the quality of wire and cable products to ensure safe operation of the product, all types of insulated wire and cable insulation strength tests are generally carried out .

Insulation strength test can be divided into pressure test and breakdown test. Withstanding voltage test is under certain conditions to impose a certain voltage on the test product, after a certain period of time, to determine whether the breakdown occurs as a test product standards. The time of the voltage is generally higher than the rated voltage of the test sample, the specific voltage and pressure time, product standards are provided.

Through the pressure test can test the reliability of the product at the operating voltage and insulation found in the serious flaws, can also be found in the production process of some shortcomings, such as: insulation has serious external damage, the conductor has a sharp distortion of the electric field of serious defects ; Insulation in the production of penetrating defects or large conductive impurities.

Breakdown test is in a certain test conditions, increase the voltage until the test product breakdown occurs, measure the breakdown field strength or breakdown voltage. Through the breakdown test can assess the ability of the cable to bear the voltage and the safety margin between the operating voltage. One of the important parameters in cable design when field strength is. Cables in operation generally bear the AC voltage, but in the DC transmission system and some special occasions also have to withstand the DC voltage, for high voltage cables may also be subject to atmospheric voltage (lightning) and operating over-voltage attacks. Therefore, according to the experimental voltage waveform can be divided into 1. AC (frequency) voltage, 2. DC voltage, 3 impulse voltage of three dielectric strength test.

5, partial discharge measurement:

This is mainly for extruded cables. Because the oil-filled cable is basically no local power generation; oil-paper cable even partial discharge, usually very weak, such as a few PC, so these cables in the factory test can not detect partial discharge. While the extruded cable is the opposite, not only have the possibility of partial discharge, and partial discharge of plastic, rubber damage is more serious, with the voltage level increases, the work of the field strength increases, the problem becomes even more serious, therefore For high-pressure extruded cable, in the factory test to do partial discharge measurement.

6, aging and stability test:

Aging test is in the stress (mechanical, electrical, thermal) under the effect of the ability to maintain stability and stability of the test. A simple thermal aging test is to test the aging of the product under the action of the characteristics of heat: the test items above the rated working temperature of the temperature of a certain value of the environment, after a specified time, the measurement of some sensitive properties before and after aging Change to assess the aging characteristics. It is also possible to accelerate the aging of the test sample by increasing the temperature, and to add an aging cycle consisting of heat, mechanical, and electrical stresses such as moisture, vibration, and electric fields. After each aging cycle, certain selected sensitive performance parameters are measured. Until the performance is reduced to the value of recognized life. This results in a shorter lifetime (time for sample heating) at higher temperatures.

Thermal stability test: thermal stability test is the wire and cable through the current heating at the same time also bear a certain voltage, after a certain period of heating, the determination of some sensitive performance parameters to assess the stability of insulation. Insulation stability test is divided into long-term stability test or short-term accelerated aging test two.