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 during the test. The human body’s response to current is as follows: Sensing current: male 1.1mA, female 0.7mA; getting rid of current: male 9mA, female 6mA (probability 99.5%); lethal current (ventricular fibrillation current): 50mA (current duration exceeds the heartbeat cycle) , 500mA (current duration within 0.1 seconds). When the current flowing through the human body exceeds 10mA, there is a danger of electric shock. Therefore, under normal circumstances, the leakage current standard for type testing is defined as 5mA. In GB 7000.1, the type test part does not clearly specify the leakage current in the withstand voltage test, but in the factory type test in the appendix, the value of this value is clearly specified.
Withstand voltage test and breakdown test
The standard will specify the specific voltage value during the test. The withstand voltage test can only show that the insulation structure of the product can withstand the test voltage, but cannot explain how high the insulation structure of the product can withstand. If the application research of insulating materials and the design of electrical equipment need to be measured, the breakdown test must be carried out. The breakdown test is to test the voltage when the dielectric is broken down. When the electric field strength exceeds a certain limit, the relationship between the current through the medium and the voltage applied to the medium does not conform to Ohm's law, but increases suddenly. As shown in Figure 1, the insulating material is destroyed and loses its insulating properties. For electrical products, if the insulation breakdown occurs, it will lose its operational function.
Some customers require a one-minute test in accordance with the type test standard when inspecting goods. This is "no benefit" to the product: first, it may reduce the pass rate of the product; second, although it passes the test, it may damage part of the insulation structure and cause Product safety is reduced; third, some components may be damaged, reducing the quality of the product and shortening its life. Passing the withstand voltage test does not mean that the lamp is intact. In many cases, the LED lamp beads can pass the withstand voltage type test, but it will cause the extension of the lamp, but in fact, it will greatly reduce the life of the lamp because of the extension.
testing method
Typical withstand voltage test method:
1. Check whether the main power switch of the withstand voltage tester is in the "off" position;
2, unless the instrument is specially designed, all non-charged metal parts must be reliably grounded;
3. Connect the wires or terminals of all power input ends of the equipment 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 terminal of the device under test;
7. Connect the return ground wire (usually black) of the withstand voltage tester to the accessible non-charged metal part of the device under test;
8. Turn on the main power switch of the withstand voltage tester, and slowly increase the secondary voltage of the instrument to the required value. Generally, the boost speed does not exceed 500 V/sec;
9. Maintain this test voltage within the specified time;
10, slowly lower the test voltage;
11. Turn off the main power switch of the withstand voltage tester. Disconnect the high-voltage output wire of the withstand voltage tester first, and then disconnect the ground wire of the withstand voltage tester loop.
The following conditions indicate that the device under test failed the test:
1. When the test voltage cannot rise to the specified voltage value or the voltage drops instead;
2. When a warning signal appears on the withstand voltage tester.
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.
Matters needing special attention:
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 sign must be placed around the test area to prevent other people from entering the dangerous zone;
3. When testing, all personnel including the operator must stay away from the testing instrument and the equipment under test;
4. When the test instrument is started, never touch its output line.
Common ways to improve withstand voltage
·Add an isolation transformer to effectively reduce the withstand voltage of the secondary circuit through the transformer;
·Increase the strength of the insulating medium, such as glue, add insulating gaskets;
·Improve the circuit board withstand voltage: a. Choose a circuit board with a high dielectric layer withstand voltage; b. Increase the creepage distance of the circuit board.
As the circuit board where the lamp beads are 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 the use of sharp objects to reduce the damage to the insulating material or the voltage breakdown caused by the tip discharge. For example, reduce the use of self-tapping screws as much as possible; when designing the circuit board, apply copper at right angles and do excessive treatment.
