Power cable is one of the essential materials for the transmission of power energy, and is widely used in economic production. Once the cable fails, it will not only threaten the safe and stable operation of the power grid, but also cause economic losses to the enterprise, and it will cause a chain reaction of damage. Today, Xiaobian will take you to understand about safe and qualified cables, what tests need to be done before leaving the factory?

1, conductor DC resistance measurement:

The conductive core of a wire and cable mainly transmits electrical energy or electrical signals. The resistance of the conductor is the main indicator of its electrical performance. The core resistance under the action of AC voltage is larger than that under the action of DC voltage due to skin effect and adjacent effect surface, but the difference between the two is very small when the electric eye frequency is 50Hz. Now the standard stipulates that it can only be required to test whether the DC resistance or resistivity of the core exceeds the specified value in the standard. Some defects in the production process can be found through this inspection: such as wire breakage or part of the single wire breakage; The cross section of the wire does not meet the standard; The length of the product is incorrect. For power cables, you can also check whether it will affect the allowable load capacity of wire and cable products in operation. There are single-arm DC resistance method and double-arm DC bridge method to measure the conductor DC resistance, the latter is more accurate than the former. The testing procedure is also more complex than the former.

2, insulation resistance test:

The insulation resistance type reflects the important index of the insulation characteristics of wire and cable products, which is closely related to the electrical strength of the product, the loss of the medium, and the gradual deterioration of the insulation material in the working state. For communication cables, too low insulation resistance between wires will also increase loop attenuation, cross-talk between loops and long-distance power supply leakage on the conductive wire core, so the insulation resistance should be higher than the specified value. Measuring insulation resistance can find defects in the process, such as dry insulation or sheath damage and moisture; Insulation is contaminated and conductive impurities are mixed; Insulation layer cracking caused by various reasons. In the operation of wires and cables, insulation resistance and leakage current are often detected as the main basis for whether they can continue to operate safely. At present, in addition to the measurement of the insulation resistance of wire and cable, in addition to the ohmmeter (swing meter), the commonly used galvanometer comparison method and high resistance meter method (voltage-current method).

3. Measurement of capacitance and loss factor:

The cable plus AC voltage, there is a current flow, when the voltage amplitude and frequency is certain, the size of the capacitor current is proportional to the cable capacitance (Cx). For ultra-high voltage cables, the current of this capacitor may reach a value that can be compared with the rated current, which becomes an important factor limiting the cable capacity and transmission distance. Therefore, the cable capacitance is also one of the main electrical performance parameters of the cable. In the AC electric field, the insulator in the cable will form a dielectric loss due to the existence of leakage current and various polarization, expressed by the dielectric loss factor or loss Angle tangent value (TANδ), which not only wastes electrical energy, but also causes the dielectric (insulator) to heat up and accelerate insulation aging, so TANδ is also one of the main parameters of the cable. Through the measurement of capacitance and loss factor, various insulation deterioration phenomena such as insulation moisture, insulation layer and shield layer shedding can be found, so capacitance and TANδ are measured in both cable manufacturing and cable operation. The measurement of high voltage cables, Cx and TANδ are carried out under their operating conditions, that is, power frequency high voltage, usually using high voltage Schilling Bridges, and this year has also begun to use current ratio transformer Bridges.

4, insulation strength test:

The insulation strength of wire and cable refers to the ability of insulating structure and insulating material to withstand the electric field without breakdown and damage, in order to check the quality of wire and cable products and ensure the safe operation of products, all types of insulation wire and cable are generally required to carry out insulation strength tests. Insulation strength test can be divided into voltage test and breakdown test. The test of voltage resistance is to apply a certain voltage to the test under certain conditions, and after a certain period of time, whether the breakdown occurs as a standard to judge whether the test is qualified. The voltage of the time is generally higher than the rated working voltage of the test product, the specific voltage value and voltage withstand time are specified in the product standard. Through the voltage withstand test, the reliability of the product can be tested under the working voltage and serious defects in the insulation can be found. Some shortcomings of the production process can also be found, such as: the insulation has serious external damage, and the conductor has serious defects that make the electric field sharply distorted; Insulation in the production of penetration defects or large conductive impurities. Breakdown test is to measure the breakdown field strength or breakdown voltage by increasing the voltage until the test product breaks down under certain test conditions. The breakdown test can check the safety margin between the voltage bearing capacity of the cable and the operating voltage. Breakdown field strength is one of the important parameters in cable design. The cable is generally subjected to AC voltage in operation, but in the DC transmission system and some special occasions also have to withstand DC voltage, for high voltage cables may also be subjected to atmospheric voltage (lightning) and operating overvoltage attack. Therefore, according to the different experimental voltage waveform, it can be divided into 1. Ac (power frequency) voltage, 2. Dc voltage, 3 impulse voltage three kinds of insulation strength test.

5, partial discharge measurement:

There is basically no local power generation for oil-filled cables; Even if the oil paper cable has partial discharge, it is usually very weak such as a few PCS, so these cables can be unexpected partial discharge in the factory test. For extruded cable, not only the possibility of partial discharge, but also the damage of partial discharge to plastic and rubber is more serious, with the improvement of voltage level and the improvement of working field strength, this problem is more serious, so for high voltage extruded cable, partial discharge measurement should be done in the factory test. There are many methods for measuring partial discharge. The discharge pulse can be measured according to the instantaneous charge exchange generated by discharge (electrical measurement method). It can also measure its voltage according to the ultrasonic wave generated during discharge (acoustic measurement method); The intensity of the light can also be measured according to the light generated by the discharge (photometry). For cables are basically used electrical measurement method.

6. Aging and stability test:

Aging test is the stability test of whether the performance can be maintained under the action of stress (mechanical, electrical, thermal). Thermal aging test: simple thermal aging test is to test the characteristics of aging under the action of heat, put the test product in an environment higher than the rated operating temperature temperature of a certain value, after a specified time, measure some sensitive properties before and after aging changes to assess the aging characteristics. It can also be used to increase the temperature to accelerate the aging of the test product, coupled with thermal, mechanical, electrical and other stresses such as moisture, vibration, electric field to form an aging cycle, after each aging cycle, some selected sensitive performance parameters are determined. Until the performance declines to the value of the recognized life. In this way, at a higher temperature T, a shorter life L(the heating time of the sample) is obtained. Thermal stability test: Thermal stability test is the cable through the current heating at the same time also withstand a certain voltage, after a certain period of heating, determine some sensitive performance parameters to assess the stability of the insulation. Insulation stability test is divided into long-term stability test or short-term accelerated aging test. Responsible enterprises are thinking about how to improve the quality of the enterprise's products, in order to improve the market competitiveness of their own products, product quality is the production and development of the enterprise, especially in the wire and cable industry.

Qingdao Tianxing Cable Co., Ltd. is a technology enterprise in Shandong Province focusing on the production of wire and cable, with more than 150 sets of domestic excellent cable production equipment and testing equipment, excellent production technology, modern testing equipment, to ensure product quality and stability, timely delivery, products sell well all over the country. The company's main products are power cable, mineral cable, high life wire and cable, radiation crosslinked cable, control cable, computer cable, photovoltaic cable, communication cable, data cable, low smoke halogen free cable, flame retardant series wire and cable.