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Leakage current setting

The leakage current here refers specifically to the leakage current generated in the withstand voltage test, which is the alarm threshold we set in the test. The human body's response to current is: perceptual current: male 1.1mA, female 0.7mA; get rid of current: male 9mA, female 6mA (probability 99.5%); lethal current (ventricular fibrillation current): 50mA (current duration exceeds heartbeat cycle) , 500mA (current duration is less than 0.1 seconds). When the current flowing through the human body exceeds 10 mA, there is a danger of electric shock. Therefore, in general, the leakage current standard of the type test is defined as 5 mA. In GB 7000.1, the type test part does not clearly specify the leakage current in the withstand voltage test, and the value of this value is clearly specified in the factory type test of the appendix.

Withstand voltage test and breakdown test

The standard specifies the specific voltage value at the time of the test. After the withstand voltage test, it can only indicate that the insulation structure of the product can withstand the test voltage, and it cannot indicate how much the insulation structure of the product can withstand. If the application of insulation materials and the design of electrical equipment are required, when it is necessary to measure the dielectric strength, a breakdown test is required. The breakdown test is to test the voltage at which the dielectric is broken down. When the electric field strength exceeds a certain limit, the relationship between the current passing through the medium and the voltage applied to the medium does not conform to Ohm's law, but increases abruptly. As shown in Figure 1, the insulating material is destroyed and the insulating properties are lost. For electrical products, if the insulation breaks down, it loses its operational function.

Some customers require a one-minute test according to the type test standard, which is “one harmless”: first, it may reduce the yield of the product; second, although it passes the test, it may damage part of the insulation structure, so that Product safety is reduced; third, some components may be damaged, so that the quality of the product is reduced and the life is shortened. Passing the withstand voltage test does not mean that the lamp is intact. In many cases, LED lamp beads can pass the pressure type test, but it will cause the lamp to be extinguished, but the actual life of the lamp will be greatly reduced due to the delay.

Test Methods

Typical withstand voltage test method:

1. Check to see if the main power switch of the withstand voltage tester is in the "off" position; 2. Unless the instrument is specially designed, all uncharged metal parts must be reliably grounded; 3. Connect the wires or terminals of all power input terminals of the device under test; 4. Close all power switches, relays, etc. of the device under test; 5. Adjust the test voltage of the withstand voltage tester to zero; 6. Connect the high voltage output line (usually red) of the withstand voltage tester to the power input of the device under test; 7. Connect the loop ground wire (usually black) of the withstand voltage tester to the accessible uncharged metal part of the device under test; 8. Close the main power switch of the withstand voltage tester and slowly raise the secondary voltage of the instrument to the required value. Generally, the boosting speed does not exceed 500 V/sec. 9. Maintain this test voltage for a specified period of time; 10. Slowly lower the test voltage; 11. Disconnect the main power switch of the withstand voltage tester. First disconnect the high voltage output line of the withstand voltage tester, and then disconnect the grounding wire of the withstand voltage tester circuit.

The following conditions indicate that the device under test does not pass the test:

1. When the test voltage does not rise to the specified voltage value or the voltage drops instead; 2. When the pressure tester has a warning signal. It should be noted that due to the high voltage that is dangerous to the human body in the withstand voltage test, special care must be taken when testing.

Things to pay special attention to:

1. It must be stipulated that only trained and authorized personnel can enter the test area to operate the instrument; 2. A fixed and obvious warning slogan must be placed around the test area to prevent other personnel from entering the danger zone; 3. When conducting the test, all personnel including the operator must be away from the test instrument and the device under test; 4. When the test instrument starts, do not touch its output line.

Common ways to improve voltage resistance

Adding an isolation transformer, and effectively reducing the withstand voltage value of the secondary line through the transformer; Increase the strength of the insulating medium, such as rubber, add insulating gaskets; Improve the voltage resistance of the circuit board: a, select the circuit board with high voltage resistance of the dielectric layer; b, increase the creepage distance of the circuit board. As the circuit board where the lamp bead is arranged, the creepage distance and the wiring space are contradictory. In order to increase the creepage distance, the wiring space can only be compressed as much as possible. Try to avoid sharp objects to reduce the scratching of the insulation or the breakdown of the voltage due to the tip discharge. If you try to reduce the use of self-tapping screws; when designing the circuit board, apply copper at right angles and do over-treatment.

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