Wire and cable quality testing three important indicators

Selection of qualified wire and cable products related to people's production and life safety. For ordinary consumers, in addition to master how to select qualified wire and cable products, to understand the regular monitoring of wire and cable knowledge is necessary. In the wire and cable quality testing, mainly in the following important indicators.
 
Insulation resistance test:
 
Insulation resistance reflects the insulation characteristics of wire and cable products, an important indicator, it with the product of the electrical strength, dielectric loss, and insulation materials in the working state of the gradual deterioration of the relationship are closely related. For the communication cable, the line insulation resistance is too low will increase the circuit attenuation, the crosstalk between the circuit and the conductive wire on the long-distance power supply leakage, so the insulation resistance should be higher than the specified value.
 
Determination of insulation resistance can be found in the process of defects, such as insulation drying impermeable or sheath damage damp; insulation contamination and conductive impurities mixed with a variety of reasons caused by the insulation cracking. In the operation of wires and cables, it is necessary to check the insulation resistance and leakage current as the main basis for whether it can continue to operate safely.
 
The current wire and cable insulation resistance measurement, in addition to the ohm meter (shake table), the commonly used galvanometer comparison method high impedance meter method (voltage - current method).
 
Capacitance and loss factor measurement:
 
Cable with AC voltage, there is a current flow, when the voltage amplitude and frequency of a certain, the size of the capacitor current is proportional to the cable capacitance (Cx). For EHV cables, the current of this capacitor may reach a value that can be compared to the rated current, making it an important factor limiting cable capacity and transmission distance. So the cable capacitance is also one of the main electrical performance parameters of the cable.
 
In an alternating current field, the insulator in the cable, due to leakage current and various polarities, forms a dielectric loss, expressed as a dielectric loss factor or a loss tangent (TAN), which not only wastes power, but also causes the dielectric ) Heat, to accelerate the aging of the insulation, so TAN is one of the main parameters of the cable.
 
Through the measurement of capacitance and loss factor can be found insulation damp, insulation and shielding layer off and other insulation deterioration phenomenon, so both in the cable manufacturing or cable operation are carried out capacitance and TAN measurements. The measurement of high-voltage cables, Cx and TAN is carried out under its operating conditions, that is, under high frequency power, which are usually used in high voltage Xilin bridge, and this year also began to use current than the transformer bridge.
 
Partial discharge measurement:
 
There is basically no partial power generation for the oil-filled cable; even if there is a partial discharge in the oil-paper cable, it is usually very weak as a few PCs, so these cables can be undetected in the factory test. For the extruded cable, not only the possibility of local discharge, and partial discharge of plastic, rubber damage is also more serious, with the voltage level increases, the field strength to improve, this problem is even more serious, so the high pressure Extrusion cable, in the factory test to do partial discharge measurement.
 
Partial discharge measurement methods are many, according to the discharge generated by the instantaneous charge exchange, measuring the discharge pulse (electrical measurement method); can also be generated according to the ultrasonic wave, measured its voltage (acoustic method); also according to the discharge of light , Measure the intensity of light (light measurement method). For the cable are basically using electrical measurement.