Setting of leakage current
The leakage current here refers to the leakage current generated in the withstand voltage test, which is the alarm threshold we set in the test. The response of human body to current is as follows: perceived current: male 1.1ma, female 0.7ma; escape current: male 9ma, female 6mA (probability 99.5%); fatal current (ventricular fibrillation current): 50mA (current duration exceeds heartbeat cycle), 500mA (current duration within 0.1s). When the current flowing through the human body exceeds 10 Ma, there is a risk of electric shock. Therefore, in general, the leakage current standard of type test is defined as 5mA. In GB 7000.1, the leakage current in the withstand voltage test is not specified in the type test, but the value is specified in the factory type test in the appendix.
Withstand voltage test and breakdown test
The standard specifies the specific voltage value at the time of the test. The withstand voltage test can only show that the insulation structure of the product can withstand the test voltage, but can not show how high the insulation structure of the product can withstand the voltage. If the insulation material application research and electrical equipment design, need to measure the insulation strength, it is necessary to carry out the breakdown test. 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 passing 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 damaged and loses its insulating property. For electrical products, if the insulation breaks down, it will lose its function.
Some customers require one minute test according to the type test standard, which is of no benefit to the product: first, it may reduce the qualified rate of the product; second, although it passes the test, it may damage part of the insulation structure, reducing the safety of the product; third, it may damage some components, reducing the quality and life of the product. Passing the withstand voltage test does not mean that the lamp is intact. In many cases, LED lamp beads can pass the voltage type test, but it will cause the lamp's delay extinction. In fact, the lamp's life will be greatly reduced because of the delay extinction.
test method
Typical withstand voltage test method:
1. Check whether the main power switch of the withstand voltage tester is in the "off" position;
2. Except for the special design of the instrument, all uncharged metal parts must be reliably grounded;
3. Connect the wires or terminals of all power input terminals of the equipment under test;
4. Turn on all power switches and relays of the equipment 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 tested equipment;
7. Connect the circuit grounding wire (usually black) of the withstand voltage tester to the accessible uncharged metal part of the equipment under test;
8. Close the main power switch of the withstand voltage tester, and slowly increase the secondary voltage of the tester to the required value. Generally, the boosting speed is not more than 500 V / sec;
9. Maintain the test voltage for a specified period of time;
10. Slow down the test voltage;
11. Disconnect the main power switch of withstand voltage tester. First disconnect the high voltage output line of the withstand voltage tester, and then disconnect the circuit ground wire of the withstand voltage tester.
The following conditions indicate that the tested equipment fails 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 dangerous high voltage in the withstand voltage test, special care must be taken during the test.
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. Fixed and obvious warning signs must be placed around the test area to prevent other personnel from entering the dangerous area;
3. When testing, all personnel, including operators, must stay away from testing instruments and equipment under test;
4. Do not touch the output line of the test instrument when it is started.
Common ways to improve withstand voltage capability
·By adding isolation transformer, the withstand voltage value of secondary line can be effectively reduced;
·Increase the strength of insulating medium, such as gluing, adding insulating gasket;
·Improve the circuit board withstand voltage capability: A. select the circuit board with high dielectric layer withstand voltage capability; 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, we can only compress the wiring space as much as possible. Avoid using sharp objects as far as possible, so as to reduce the voltage breakdown caused by the scratch of insulating materials or the tip discharge. Such as reducing the use of self tapping screws as far as possible; in the design of circuit board, copper should be properly laid at the right angle position, and over treatment should be done.