Test method for insulation strength of insulated wire and cable


Release time:

2019-06-08

The insulation strength of wire and cable refers to the ability of insulation structure and insulation material to withstand electric field without breakdown damage. In order to check the quality of wire and cable products and ensure the safe operation of products, all insulation types of wire and cable are generally subject to insulation strength test.

Test method for insulation strength of insulated wire and cable

The insulation strength of wire and cable refers to the ability of insulation structure and insulation material to withstand electric field without breakdown damage. In order to check the quality of wire and cable products and ensure the safe operation of products, all insulation types of wire and cable are generally subject to insulation strength test. Insulation 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 article under certain conditions. After a certain period of time, whether the breakdown occurs is used as the standard to judge whether the test article is qualified. The time voltage is generally higher than the rated working voltage of the test article. The specific voltage value and withstand voltage time are stipulated in the product standard. The withstand voltage test can test the reliability of the product under the working voltage and find serious defects in the insulation. 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 cause sharp distortion of the electric field; insulation in the production of penetrating defects or large conductive impurities.

The breakdown test is to increase the voltage until the breakdown of the test product occurs under certain test conditions, and measure the breakdown field strength or breakdown voltage. Through the breakdown test, the safety margin between the ability of the cable to withstand voltage and the working voltage can be assessed. Breakdown field strength is one of the important parameters in cable design.

The cable in operation is generally subjected to AC voltage, but in the DC transmission system and some special occasions also have to withstand DC voltage, for high-voltage cables may also be subject to atmospheric voltage (lightning) and operating over-voltage attacks. Therefore, according to the different experimental voltage waveforms, can be divided into 1. AC (power frequency) voltage, 2. DC voltage, 3 impulse voltage three kinds of insulation strength test.

partial discharge measurement

For oil-filled cables, there is basically no local power generation; even if there is partial discharge in oil-paper cables, it is usually very weak, such as several PC, so these cables can not detect partial discharge in factory tests. For extruded cable, not only the possibility of partial discharge, and partial discharge of plastic, rubber damage is more serious, with the improvement of the voltage level, the working field strength, this problem is more serious, so the high voltage extrusion cable, in the factory test to do partial discharge measurement.

There are many methods for measuring partial discharge, which can be measured according to the instantaneous charge exchange generated by the discharge, and the discharge pulse (electrometric method); it can also be measured according to the ultrasonic wave generated by the discharge, and its voltage (acoustic method); it can also be measured according to the light generated by the discharge. The intensity of the light (optical method). For the cable is basically the use of electrical measurement method.

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).

Heat aging test

The simple thermal aging test is to test the aging characteristics of the test article under the action of heat. Place the test article in an environment with a certain value higher than the rated working temperature. After a specified time, measure the changes of some sensitive properties before and after aging to evaluate the aging characteristics. It is also possible to accelerate the aging of the test article by increasing the temperature, and to add thermal, mechanical and electrical stresses such as moisture, vibration and electric field to form an aging cycle. After each aging cycle, some selected sensitive performance parameters are determined. until the performance drops to the value of the apparent life. This results in a shorter life L (sample heating time) at a higher temperature T.

Thermal stability test

The thermal stability test is that the cable is heated by the current while it is also subjected to 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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