The insulation strength of wires and cables refers to the ability of insulating structures and insulating materials to withstand the action of electric field without breakdown damage. In order to check the product quality of wires and cables and ensure the safe operation of products, all insulation types of wires and cables generally need to undergo insulation strength test. Insulation strength test can be divided into withstand voltage test and breakdown test.

Withstand voltage test is to apply a certain voltage to the test object under certain conditions, and take whether breakdown occurs as the standard to judge whether the test object is qualified after a certain time. The time voltage is generally higher than the rated working voltage of the test object. The specific voltage value and withstand voltage time are specified 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, as well as some shortcomings of the production process, such as serious external damage to the insulation, There are serious defects on the conductor that cause sharp distortion of the electric field; 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 by increasing the voltage until the breakdown of the test object occurs. Through the breakdown test, the safety margin between the voltage bearing capacity of the cable and the working voltage can be assessed. Breakdown field strength is one of the important parameters in cable design.

Cables generally bear AC voltage in operation, but they also bear DC voltage in DC transmission system and some special occasions. For high-voltage cables, they may also be attacked by atmospheric voltage (lightning) and operating overvoltage. Therefore, according to different experimental voltage waveforms, it can be divided into three insulation strength tests: 1. AC (power frequency) voltage, 2. DC voltage and 3 impulse voltage.