Views: 0 Author: Site Editor Publish Time: 2022-04-19 Origin: Site
The insulation strength of a wire and cable refers to the ability of the insulating structure and insulating material to withstand the action of an electric field without breakdown damage. In order to check the quality of wire and cable products and ensure the safe operation of the product, all insulation types of wires and cables are generally subject to insulation strength tests. . Dielectric strength test can be divided into withstand voltage test and breakdown test.
The withstand voltage test is to apply a certain voltage to the test sample under certain conditions, and after a certain period of time, whether the breakdown occurs is used as the criterion for judging whether the test product is qualified. The voltage of time is generally higher than the rated working voltage of the test product. The specific voltage value and withstand voltage time are stipulated in the product standard. Through the withstand voltage test, the reliability of the product running under the working voltage can be tested and the serious insulation problems can be found. Some defects in the production process can also be found, such as: the insulation has serious external damage, the conductor has serious defects that distort the electric field sharply; the insulation has penetrating defects or large conductive impurities in production.
The breakdown test is to measure the breakdown field strength or breakdown voltage under certain test conditions, increase the voltage until the breakdown of the sample occurs. Through the breakdown test, the safety margin between the ability of the cable to withstand the voltage and the working voltage can be assessed. The breakdown field strength is one of the important parameters in cable design.
Cables are generally subjected to AC voltage during operation, but they are also subjected to DC voltage in DC transmission systems and some special occasions. For high-voltage cables, they may also be attacked by atmospheric voltage (lightning) and operating overvoltage. Therefore, according to the different experimental voltage waveforms, it can be divided into three types of dielectric strength tests: 1. AC (power frequency) voltage, 2. DC voltage, and 3 impulse voltage.
Partial discharge measurement
There is basically no local power generation for oil-filled cables; even if there is partial discharge in oil-paper cables, it is usually very weak, such as a few PCs, so these cables can be exempted from partial discharge in the factory test. For extruded cables, not only the possibility of partial discharge is high, but also the damage of partial discharge to plastic and rubber is also serious. For extruded cables, partial discharge measurements are required in the factory test.
There are many measurement methods for partial discharge. The discharge pulse can be measured according to the instantaneous charge exchange generated by the discharge (electric measurement method); the voltage can also be measured according to the ultrasonic wave generated during the discharge (acoustic measurement method); it can also be measured according to the light generated by the discharge. , to measure the intensity of light (photometry). For cables, the electrical measurement method is basically used.
Aging and Stability Test
The aging test is a stability test that can maintain stable performance under the action of stress (mechanical, electrical, thermal).
Heat aging test
The simple thermal aging test is to test the aging characteristics of the sample under the action of heat. The sample is placed in an environment with a temperature higher than the rated working temperature. After a specified time, the sensitivity of some sensitive properties before and after aging is measured. change to assess aging characteristics. It is also possible to accelerate the aging of the test sample by increasing the temperature, and add thermal, mechanical, and electrical stresses such as moisture, vibration, and electric fields to form an aging cycle. After each aging cycle, certain selected sensitive performance parameters are determined. until the performance drops to the value of the indicated life. In this way, at a higher temperature T, a shorter lifetime L (the time for the sample to be heated) is obtained.
Thermal stability test
The thermal stability test is that the cable is heated by current and also bears a certain voltage. After a certain period of heating, some sensitive performance parameters are measured to evaluate the stability of the insulation.
Insulation stability test is divided into long-term stability test or short-term accelerated aging test.
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