Three Key Indicators for Quality Inspection of Wires and Cables
Selecting qualified wire and cable products is crucial for ensuring the safety of people’s production and daily life. For ordinary consumers, in addition to learning how to choose qualified wire and cable products, it’s also essential to understand the basic monitoring knowledge related to wires and cables. In terms of wire and cable quality inspection, the following key aspects are particularly important: To indicate.
Insulation resistance testing:
Insulation resistance is an important indicator reflecting the insulation characteristics of wire and cable products. It is closely related to the product’s dielectric strength, dielectric loss, and the gradual degradation of insulation materials under operating conditions. For communication cables, excessively low interwire insulation resistance can lead to circuit attenuation, crosstalk between circuits, and leakage during long-distance power supply via the conductive wire cores. Therefore, the insulation resistance must exceed the specified minimum value.
Measuring insulation resistance can reveal defects in the manufacturing process, such as insufficiently dried or permeable insulation, damage to the jacket leading to moisture ingress, contamination of the insulation, and the presence of conductive impurities. Additionally, it can detect cracks in the insulation layer caused by various factors. During the operation of wires and cables, it is common practice to regularly measure insulation resistance and leakage current, using these measurements as primary indicators of whether the equipment can continue to operate safely.
Currently, in addition to using an ohmmeter (megger) for measuring the insulation resistance of wires and cables, commonly employed methods include the galvanometer comparison method and the high-resistance meter method (voltage-current method).
Measurement of Capacitance and Dissipation Factor:
When an AC voltage is applied to a cable, a current flows through it. Under constant voltage amplitude and frequency, the magnitude of the capacitive current is directly proportional to the cable’s capacitance (Cx). In high-voltage cables, this capacitive current can reach levels comparable to the rated current, becoming a significant factor that limits the cable’s capacity and transmission distance. Therefore, the cable’s capacitance is one of its key electrical performance parameters.
In an alternating electric field, the insulating material in cables experiences dielectric losses due to leakage currents and various polarization effects. These losses are typically expressed as the dielectric loss factor or the tangent of the loss angle (TAN). Not only do these losses waste electrical energy, but they also cause the dielectric (insulating material) to heat up, accelerating its aging process. Therefore, TAN is one of the key parameters characterizing cables.
By measuring capacitance and the dissipation factor, it is possible to detect various insulation degradation phenomena, such as moisture-induced insulation deterioration and detachment of insulation or shielding layers. Therefore, capacitance and tan δ measurements are performed both during cable manufacturing and during cable operation. For high-voltage cables, Cx and tan δ measurements are conducted under their actual operating conditions—namely, at power-frequency high voltage. Traditionally, high-voltage Schering bridges have been widely used for these measurements; however, in recent years, current-ratio transformer bridges have also begun to be employed.
Partial Discharge Measurement:
For oil-filled cables, there is essentially no partial discharge. Even if oil-paper cables do experience partial discharge, it is usually very weak—on the order of just a few picocoulombs—and thus these cables can be exempted from partial-discharge testing during factory acceptance tests. In contrast, extruded-cable designs not only have a higher likelihood of generating partial discharge but also suffer more severe damage to the plastic and rubber insulation from such partial discharges. As voltage levels increase and the operating electric field strength rises, this issue becomes even more pronounced. Therefore, for high-voltage extruded cables, partial-discharge measurements are mandatory as part of the factory acceptance tests.
There are many methods for measuring partial discharge. One approach is to measure the discharge pulses by detecting the instantaneous charge exchange caused by the discharge (electrical measurement method). Another approach is to measure the voltage generated by the ultrasonic waves produced during the discharge (acoustic measurement method). Yet another method involves measuring the intensity of light emitted during the discharge (optical measurement method). For cables, the electrical measurement method is generally used.
(This article is reproduced for the purpose of conveying additional information and does not necessarily imply endorsement of its views or confirmation of the accuracy of its content. If you have any questions, please contact us promptly. Contact phone: 010-57015801; Email: edit@dianlan.cn)
Keywords:
Previous
Other Information
Kazakhstan invests 3.25 billion yuan to build a high-voltage transmission line.
Kazakhstan Power Grid Company plans to invest 470.9 million U.S. dollars (approximately 3.25 billion RMB) in a 500-kV high-voltage transmission project that will connect the northern, eastern, and southern power grids. The project aims to establish a modern grid infrastructure capable of providing uninterrupted power supply to multiple regions across Kazakhstan.
According to reports, this high-voltage transmission project...
Get the latest messages
If you have any suggestions or requirements
